Near-field infrared microspectroscopy (NFIR) is a newly developed surface analysis method that is based on functional-group analysis and has a high spatial resolution. The objective of the present study is to perform nanoscale functional-group analysis of dialysis membrane surfaces by using NFIR. We focused on polyvinylpyrrolidone (PVP), which is employed as an additive to hydrophilize and create pores in synthetic polymer dialysis membranes, and evaluated the PVP distribution on the inner surface of the dialysis membranes. Dialysis membranes made from polysulfone (PSf) and polyester polymer alloy (PEPA) were first assessed by NFIR and then by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). The nanoscale NFIR analysis showed heterogeneous distribution of PVP on the PSf membrane even though the amount of PVP on the membrane surface was high. PVP was homogeneously distributed on the PEPA membrane even though the amount of PVP on the membrane surface was low. In contrast, the microscale ATR-FTIR results showed that PVP was homogeneously distributed on both PSf and PEPA membranes. PVP-rich and PVP-poor regions were distinguishable by NFIR and not by ATR-FTIR, because the spatial resolution of NFIR is higher than that of ATR-FTIR. This study demonstrates for the first time that NFIR can provide nanoscale chemical information on the structures of porous membranes. (C) 2010 Elsevier B.V. All rights reserved.

Reactive oxygen species (ROS) generated during hemodialysis treatment cause dialysis complications because of the high reactivity of ROS. To prevent dialysis complications caused by oxidative stress, it is important to evaluate the generation and dismutation of ROS during hemodialysis treatment. In this study, our aim was to develop a device to determine superoxide (O(2) (-)) generated inside a dialysis hollow fiber, and also to examine whether this device could detect O(2) (-) separated from plasma using hollow fibers. Experimental apparatus was set up so that hypoxanthine (HX) solution flowed inside the hollow fibers and 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) solution flowed outside the hollow fibers. Then, xanthine oxidase (XOD) solution was added to the HX solution to generate O(2) (-), and chemiluminescence resulting from the reaction of O(2) (-) with MPEC was measured with an optical fiber. Chemiluminescence intensity was measured at different HX concentrations, and the peak area of relative luminescence intensity yielded a first-order correlation with the HX concentration. Based on the relationship between HX and O(2) (-) concentrations determined by the cytochrome c reduction method, the relative luminescence intensity measured by this device was linearly dependent on the O(2) (-) concentration inside the hollow fibers. After modifications were made to the device, XOD solution injection into plasma including HX resulted in an increase in the relative luminescence intensity. We concluded that this novel device based on chemiluminescence is capable of determining aqueous O(2) (-) generated inside a hollow fiber and also of detecting O(2) (-) in plasma.

Reactive oxygen species (ROS) generated during hemodialysis treatment cause dialysis complications because of the high reactivity of ROS. To prevent dialysis complications caused by oxidative stress, it is important to evaluate the generation and dismutation of ROS during hemodialysis treatment. In this study, our aim was to develop a device to determine superoxide (O(2) (-)) generated inside a dialysis hollow fiber, and also to examine whether this device could detect O(2) (-) separated from plasma using hollow fibers. Experimental apparatus was set up so that hypoxanthine (HX) solution flowed inside the hollow fibers and 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) solution flowed outside the hollow fibers. Then, xanthine oxidase (XOD) solution was added to the HX solution to generate O(2) (-), and chemiluminescence resulting from the reaction of O(2) (-) with MPEC was measured with an optical fiber. Chemiluminescence intensity was measured at different HX concentrations, and the peak area of relative luminescence intensity yielded a first-order correlation with the HX concentration. Based on the relationship between HX and O(2) (-) concentrations determined by the cytochrome c reduction method, the relative luminescence intensity measured by this device was linearly dependent on the O(2) (-) concentration inside the hollow fibers. After modifications were made to the device, XOD solution injection into plasma including HX resulted in an increase in the relative luminescence intensity. We concluded that this novel device based on chemiluminescence is capable of determining aqueous O(2) (-) generated inside a hollow fiber and also of detecting O(2) (-) in plasma.

The instability of enzymatic glucose sensors has prevented the development of a practical artificial pancreas for diabetic patients. We therefore developed an enzyme-free glucose sensor using the gate effect of a molecularly imprinted polymer (MIP). This sensor has the advantages of improved stability and a simplified manufacturing procedure. An adduct of glucose and 4-vinylphenylboronic acid (VPBA) was synthesized by esterification and was then purified. The copolymer of the glucose/VPBA adduct and methylene bisacrylamide was grafted onto an indium tin oxide electrode surface. Glucose was washed out from the copolymer to obtain an MIP layer. Cyclic voltammetry of ferrocyanide in aqueous solution was performed using an MIP-grafted electrode, and the effect of glucose on the anodic current intensity was evaluated. The anodic current intensity was sensitive to the glucose concentration, and the dynamic range (0-900 mg/dl) covered the typical range of diabetic blood glucose levels. The response time of the MIP-grafted electrode to a stepwise change in the glucose concentration was approximately 3-5 min. Thus, we can conclude that, by taking advantage of its gate effect, it is feasible to use an MIP-grafted electrode as a glucose sensor for monitoring blood sugar in diabetic patients.

The instability of enzymatic glucose sensors has prevented the development of a practical artificial pancreas for diabetic patients. We therefore developed an enzyme-free glucose sensor using the gate effect of a molecularly imprinted polymer (MIP). This sensor has the advantages of improved stability and a simplified manufacturing procedure. An adduct of glucose and 4-vinylphenylboronic acid (VPBA) was synthesized by esterification and was then purified. The copolymer of the glucose/VPBA adduct and methylene bisacrylamide was grafted onto an indium tin oxide electrode surface. Glucose was washed out from the copolymer to obtain an MIP layer. Cyclic voltammetry of ferrocyanide in aqueous solution was performed using an MIP-grafted electrode, and the effect of glucose on the anodic current intensity was evaluated. The anodic current intensity was sensitive to the glucose concentration, and the dynamic range (0-900 mg/dl) covered the typical range of diabetic blood glucose levels. The response time of the MIP-grafted electrode to a stepwise change in the glucose concentration was approximately 3-5 min. Thus, we can conclude that, by taking advantage of its gate effect, it is feasible to use an MIP-grafted electrode as a glucose sensor for monitoring blood sugar in diabetic patients.

Fluorescence enhancement of fluorescein isothiocyanate-labeled protein A (FITC-protein A) caused by the binding with immunoglobulin G (IgG) in bovine plasma was studied. FITC-protein A was immobilized onto a glass surface by covalent bonds. An increase in fluorescence intensity was dependent on IgG concentration ranging from 20 to 78 mu g/mL in both phosphate buffer saline and bovine plasma. This method requires no separation procedure, and the reaction time is less than 15 min. A fluorescence enhancement assay by the affinity binding of fluorescence-labeled reagent is thus available for the rapid determination of biomolecules in plasma.

Fluorescence enhancement of fluorescein isothiocyanate-labeled protein A (FITC-protein A) caused by the binding with immunoglobulin G (IgG) in bovine plasma was studied. FITC-protein A was immobilized onto a glass surface by covalent bonds. An increase in fluorescence intensity was dependent on IgG concentration ranging from 20 to 78 mu g/mL in both phosphate buffer saline and bovine plasma. This method requires no separation procedure, and the reaction time is less than 15 min. A fluorescence enhancement assay by the affinity binding of fluorescence-labeled reagent is thus available for the rapid determination of biomolecules in plasma.

Well-defined diblock copolymers comprising thermoresponsive segments of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (P(IPAAm-co-DMAAm)) and hydrophobic segments of poly(D,L-lactide) were synthesized by combination of RAFT and ring-opening polymerization methods. Terminal conversion of thermoresponsive segments was achieved through reactions of maleimide or its Oregon Green 488 (OG) derivative with thiol groups exposed by cleavage of polymer terminal dithiobenzoate groups. Thermoresponsive micelles obtained from these polymers were approximately 25 nm when below the lower critical solution temperature (LCST) of 40 degrees C, and their sizes increased to an average of approximately 600 nm above the LCST due to aggregation of the micelles. Interestingly, the OG-labeled thermoresponsive micelles showed thermally regulated internalization to cultured endothelial cells, unlike linear thermoresponsive P(IPAAm-co-DMAAm) chains. While intracellular uptake of P(IPAAm-co-DMAAm) was extremely low at temperatures both below and above the micellar LCST, the thermoresponsive micelles showed time-dependent intracellular uptake above the LCST without exhibiting cytotoxicity. These results indicate that the new thermoresponsive micelle system may be a greatly promising intracellular drug delivery tool.

Dialyzer performance strongly depends on the flow of blood and dialysis fluid as well as membrane performance. It is necessary, particularly to optimize dialysis fluid flow, to develop a highly efficient dialyzer. The objective of the present study is to evaluate by computational analysis the effects of dialyzer jacket baffle structure, taper angle, and taper length on dialysis fluid flow. We modeled 10 dialyzers of varying baffle angles (0, 30, 120, 240, and 360 degrees) with and without tapers. We also modeled 30 dialyzers of varying taper lengths (0, 12.5, 25.0, and 50.0 mm) and angles (0, 2, 4, and 6 degrees) based on technical data of APS-SA dialyzers having varying surface areas of 0.8, 1.5, and 2.5 m(2) (Rexeed). Dialysis fluid flow velocity was calculated by the finite element method. The taper part was divided into 10 sections of varying fluid resistances. A pressure of 0 Pa was set at the dialysis fluid outlet, and a dialysis fluid flow rate of 500 mL/min at the dialysis fluid inlet. Water was used as the dialysis fluid in the computational analysis. Results for dialysis fluid flow velocity of the modeled dialyzers indicate that taper design and a fully surrounded baffle are important in making the dialysis fluid flow into a hollow-fiber bundle easily and uniformly. However, dialysis fluid flow channeling occurred particularly at the outflowing part with dialyzers having larger taper lengths and angles. Optimum design of dialysis jacket structure is essential to optimizing dialysis fluid flow and to increasing dialyzer performance.

Well-defined diblock copolymers comprising thermoresponsive segments of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (P(IPAAm-co-DMAAm)) and hydrophobic segments of poly(D,L-lactide) were synthesized by combination of RAFT and ring-opening polymerization methods. Terminal conversion of thermoresponsive segments was achieved through reactions of maleimide or its Oregon Green 488 (OG) derivative with thiol groups exposed by cleavage of polymer terminal dithiobenzoate groups. Thermoresponsive micelles obtained from these polymers were approximately 25 nm when below the lower critical solution temperature (LCST) of 40 degrees C, and their sizes increased to an average of approximately 600 nm above the LCST due to aggregation of the micelles. Interestingly, the OG-labeled thermoresponsive micelles showed thermally regulated internalization to cultured endothelial cells, unlike linear thermoresponsive P(IPAAm-co-DMAAm) chains. While intracellular uptake of P(IPAAm-co-DMAAm) was extremely low at temperatures both below and above the micellar LCST, the thermoresponsive micelles showed time-dependent intracellular uptake above the LCST without exhibiting cytotoxicity. These results indicate that the new thermoresponsive micelle system may be a greatly promising intracellular drug delivery tool.

Dialyzer performance strongly depends on the flow of blood and dialysis fluid as well as membrane performance. It is necessary, particularly to optimize dialysis fluid flow, to develop a highly efficient dialyzer. The objective of the present study is to evaluate by computational analysis the effects of dialyzer jacket baffle structure, taper angle, and taper length on dialysis fluid flow. We modeled 10 dialyzers of varying baffle angles (0, 30, 120, 240, and 360 degrees) with and without tapers. We also modeled 30 dialyzers of varying taper lengths (0, 12.5, 25.0, and 50.0 mm) and angles (0, 2, 4, and 6 degrees) based on technical data of APS-SA dialyzers having varying surface areas of 0.8, 1.5, and 2.5 m(2) (Rexeed). Dialysis fluid flow velocity was calculated by the finite element method. The taper part was divided into 10 sections of varying fluid resistances. A pressure of 0 Pa was set at the dialysis fluid outlet, and a dialysis fluid flow rate of 500 mL/min at the dialysis fluid inlet. Water was used as the dialysis fluid in the computational analysis. Results for dialysis fluid flow velocity of the modeled dialyzers indicate that taper design and a fully surrounded baffle are important in making the dialysis fluid flow into a hollow-fiber bundle easily and uniformly. However, dialysis fluid flow channeling occurred particularly at the outflowing part with dialyzers having larger taper lengths and angles. Optimum design of dialysis jacket structure is essential to optimizing dialysis fluid flow and to increasing dialyzer performance.

This study reports on evaluation of the optimum design of a blood outlet port structure for providing uniform flow by visualizing the blood flow in an extracapillary membrane oxygenator. We tested a cylindrical type extracapillary membrane oxygenator, HPO-20. The HPO-20 has a tangential blood outlet port and is thus referred to as "Tangential HPO20." We engineered "Vertical HPO-20" with a vertical blood outlet port by modifying the Tangential HPO-20. To visualize the blood-side flow, a total of 120 insulated copper-wire electrodes were placed in the "Tangential" and the Vertical HPO-20s. The test solution flow was visualized by the dimensionless fluid arrival time reaching each electrode. The test solution flow in the Tangential HPO-20 was not uniform, particularly at the outside blood channel. The flow was more uniform in the Vertical HPO-20. The blood flow in an extracapillary membrane oxygenator with a vertical blood outlet port is well distributed so that it produces more uniform blood flow than that with a tangential outlet port because of the small stagnation and reduced channeling. ASAIO Joumal 2009; 55:209-212.

Dialysis fluid flow and mass transfer rate of newly developed dialyzers were evaluated using mass transfer correlation equations of dialysis fluid-side film coefficient. Aqueous creatinine clearance and overall mass transfer coefficient for APS-15S (Asahi Kasei Kuraray) as a conventional dialyzer, and APS-15SA (Asahi Kasei Kuraray), PES-150S alpha (Nipro), FPX140 (Fresenius), and CS-1.61U (Toray) as newly developed dialyzers were obtained at a blood-side flow rate (Q,) of 200 ml/min, dialysis fluid-side flow rates (Q(D)) of 200-800 ml/min and a net filtration rate (Q,) of 0 ml/min. Mass transfer correlation equations between Sherwood number (Sh) containing dialysis fluid-side mass transfer film coefficient and Reynolds number (Re) were formed for each dialyzer. The exponents of Re were 0.62 for APS-15S whereas approximately 0.5 for the newly developed dialyzers. The dialysis fluid-side mass transfer film coefficients of the newly developed dialyzers were higher than those of the conventional dialyzer. Based on the mass transfer correlation equations, introduction of short taper, full baffle of dialyzer jacket and further wave-shaped hollow fiber improves the dialysis fluid flow of the newly developed dialyzers. ASAIO journal 2009; 55:231-235.

The objective of the present study was to evaluate the characteristics of protein adsorption on the inner surface of various dialysis membranes, to develop protein adsorption-resistant biocompatible dialysis membranes. The adsorption force of human serum albumin (HSA) on the inner surface of a dialysis membrane and the smoothness of the membrane were evaluated from a nanoscale perspective by atomic force microscopy. The content ratio of the hydrophilic polymer, polyvinylpyrrolidone (PVP), was determined by attenuated total reflection Fourier transform infrared spectroscopy. Nine synthetic-polymer dialysis membranes on the market made of polysulfone (PSF), polyethersulfone (PES), polyester polymer-alloy (PEPA), and ethylene vinylalcohol (EVAL) were used in the present study. The HSA adsorption force on the surface of the hydrophobic polymer PEPA membrane was higher than that on the hydrophilic polymer EVAL membrane surface. It has been considered beneficial, for decreasing the HSA adsorption force, to cover a hydrophobic polymer membrane surface with PVP. However, there were some areas on PVP-containing membrane surfaces at which much higher HSA adsorption forces were observed. The HSA adsorption force gave a nearly linear correlation with the surface roughness on the PSF membrane surface. However, the HSA adsorption force was uncorrelated with the PVP content ratio for any of the PSF membrane surfaces tested. in conclusion, protein adsorption can be minimized by the use of dialysis membranes made of hydrophobic polymers containing PVP with a smooth surface. ASAIO journal 2009; 55:236-242.

This study reports on evaluation of the optimum design of a blood outlet port structure for providing uniform flow by visualizing the blood flow in an extracapillary membrane oxygenator. We tested a cylindrical type extracapillary membrane oxygenator, HPO-20. The HPO-20 has a tangential blood outlet port and is thus referred to as "Tangential HPO20." We engineered "Vertical HPO-20" with a vertical blood outlet port by modifying the Tangential HPO-20. To visualize the blood-side flow, a total of 120 insulated copper-wire electrodes were placed in the "Tangential" and the Vertical HPO-20s. The test solution flow was visualized by the dimensionless fluid arrival time reaching each electrode. The test solution flow in the Tangential HPO-20 was not uniform, particularly at the outside blood channel. The flow was more uniform in the Vertical HPO-20. The blood flow in an extracapillary membrane oxygenator with a vertical blood outlet port is well distributed so that it produces more uniform blood flow than that with a tangential outlet port because of the small stagnation and reduced channeling. ASAIO Joumal 2009; 55:209-212.

Dialysis fluid flow and mass transfer rate of newly developed dialyzers were evaluated using mass transfer correlation equations of dialysis fluid-side film coefficient. Aqueous creatinine clearance and overall mass transfer coefficient for APS-15S (Asahi Kasei Kuraray) as a conventional dialyzer, and APS-15SA (Asahi Kasei Kuraray), PES-150S alpha (Nipro), FPX140 (Fresenius), and CS-1.61U (Toray) as newly developed dialyzers were obtained at a blood-side flow rate (Q,) of 200 ml/min, dialysis fluid-side flow rates (Q(D)) of 200-800 ml/min and a net filtration rate (Q,) of 0 ml/min. Mass transfer correlation equations between Sherwood number (Sh) containing dialysis fluid-side mass transfer film coefficient and Reynolds number (Re) were formed for each dialyzer. The exponents of Re were 0.62 for APS-15S whereas approximately 0.5 for the newly developed dialyzers. The dialysis fluid-side mass transfer film coefficients of the newly developed dialyzers were higher than those of the conventional dialyzer. Based on the mass transfer correlation equations, introduction of short taper, full baffle of dialyzer jacket and further wave-shaped hollow fiber improves the dialysis fluid flow of the newly developed dialyzers. ASAIO journal 2009; 55:231-235.

The objective of the present study was to evaluate the characteristics of protein adsorption on the inner surface of various dialysis membranes, to develop protein adsorption-resistant biocompatible dialysis membranes. The adsorption force of human serum albumin (HSA) on the inner surface of a dialysis membrane and the smoothness of the membrane were evaluated from a nanoscale perspective by atomic force microscopy. The content ratio of the hydrophilic polymer, polyvinylpyrrolidone (PVP), was determined by attenuated total reflection Fourier transform infrared spectroscopy. Nine synthetic-polymer dialysis membranes on the market made of polysulfone (PSF), polyethersulfone (PES), polyester polymer-alloy (PEPA), and ethylene vinylalcohol (EVAL) were used in the present study. The HSA adsorption force on the surface of the hydrophobic polymer PEPA membrane was higher than that on the hydrophilic polymer EVAL membrane surface. It has been considered beneficial, for decreasing the HSA adsorption force, to cover a hydrophobic polymer membrane surface with PVP. However, there were some areas on PVP-containing membrane surfaces at which much higher HSA adsorption forces were observed. The HSA adsorption force gave a nearly linear correlation with the surface roughness on the PSF membrane surface. However, the HSA adsorption force was uncorrelated with the PVP content ratio for any of the PSF membrane surfaces tested. in conclusion, protein adsorption can be minimized by the use of dialysis membranes made of hydrophobic polymers containing PVP with a smooth surface. ASAIO journal 2009; 55:236-242.

The control of protein adsorption on microchannel Surfaces is important for biosensors. In this Study, we demonstrated protein adsorption method that is controlled through temperature change, i.e., thermoresponsive protein adsorption, on polydimethylsiloxane (PDMS) microchannel surfaces using a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm). To provide general protein adsorption control method, we adopted biotin-streptavidin chemistry and synthesized streptavidin covalently modified with PNIPAAm (PNIPAAm-StAv). Modification of streptavidin, a hydrophilic protein, with PNIPAAm induced successful thermoresponsive adsorption on a PDMS microchannel Surfaces: PNIPAAm-StAv adsorbed at 37 degrees C and desorbed at 10 degrees C on the surfaces. We also demonstrated the thermoresponsive adsorption of biotinylated immunoglobulin G (IgG-b) using PNIPAAm-StAv. Conjugation of IgG-b with PNIPAAm-StAv induced successful thermoresponsive IgG-b adsorption on PDMS. Modification of PDMS surfaces with PNIPAAm reduced physical adsorption of the partially hydrophobic IgG-b on the surface and contributed to the high-contrast thermoresponsive adsorption of IgG-b: less than 1% of the IgG-b adsorbed at 37,C was detected after the PNIPAAm-PDMS surface was washed at 10 degrees C. The controllable adsorption of this system is expected to be applied to the regeneration of biosensor chips and to on-chip protein manipulation. (c) 2008 Elsevier B.V. All rights reserved.

The control of protein adsorption on microchannel Surfaces is important for biosensors. In this Study, we demonstrated protein adsorption method that is controlled through temperature change, i.e., thermoresponsive protein adsorption, on polydimethylsiloxane (PDMS) microchannel surfaces using a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm). To provide general protein adsorption control method, we adopted biotin-streptavidin chemistry and synthesized streptavidin covalently modified with PNIPAAm (PNIPAAm-StAv). Modification of streptavidin, a hydrophilic protein, with PNIPAAm induced successful thermoresponsive adsorption on a PDMS microchannel Surfaces: PNIPAAm-StAv adsorbed at 37 degrees C and desorbed at 10 degrees C on the surfaces. We also demonstrated the thermoresponsive adsorption of biotinylated immunoglobulin G (IgG-b) using PNIPAAm-StAv. Conjugation of IgG-b with PNIPAAm-StAv induced successful thermoresponsive IgG-b adsorption on PDMS. Modification of PDMS surfaces with PNIPAAm reduced physical adsorption of the partially hydrophobic IgG-b on the surface and contributed to the high-contrast thermoresponsive adsorption of IgG-b: less than 1% of the IgG-b adsorbed at 37,C was detected after the PNIPAAm-PDMS surface was washed at 10 degrees C. The controllable adsorption of this system is expected to be applied to the regeneration of biosensor chips and to on-chip protein manipulation. (c) 2008 Elsevier B.V. All rights reserved.

We prepared well-defined diblock copolymers of thermoresponsive poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) blocks and biodegradable poly(D,L-lactide) blocks by combination of reversible addition-fragmentation chain transfer radical (RAFT) polymerization and ring-opening polymerization. alpha-Hydroxyl, omega-dithiobenzoate thermoresponsive polymers were synthesized by RAFT polymerization using hydroxyl RAFT agents. Biodegradable blocks were prepared by ring-opening polymerization Of D,L-lactide initiated by a-hydroxyl groups of thermoresponsive polymers, which inhibit the thermal decomposition of omega-dithioester groups. Terminal dithiobenzoate (DTBz) groups of thermoresponsive blocks were easily reduced to thiol groups and reacted with maleimide (Mal). In aqueous media, diblock copolymer products formed surface-functionalized thermoresponsive micelles. These polymeric micelles had a low critical micelle concentration of 22 mu g/L. In thermoresponsive studies of the micelles, hydrophobic DTBz-surface micelles demonstrated a significant shift in lower critical solution temperature (LCST) to a lower temperature of 30.7 degrees C than that for Mal-surface micelles (40.0 degrees C). In addition, micellar LCST was controlled by changing bulk mixture ratios of respective heterogeneous end-functional diblock copolymers. Micellar disruption at acidic condition (pH 5.0) was completed within 5 days due to hydrolytic degradation of PLA cores, regardless of showing a slow disruption rate at physiological condition. Furthermore, we successfully improved water-solubility of hydrophobic drug, paclitaxel by incorporating into the micellar cores. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7127-7137, 2008

We prepared well-defined diblock copolymers of thermoresponsive poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) blocks and biodegradable poly(D,L-lactide) blocks by combination of reversible addition-fragmentation chain transfer radical (RAFT) polymerization and ring-opening polymerization. alpha-Hydroxyl, omega-dithiobenzoate thermoresponsive polymers were synthesized by RAFT polymerization using hydroxyl RAFT agents. Biodegradable blocks were prepared by ring-opening polymerization Of D,L-lactide initiated by a-hydroxyl groups of thermoresponsive polymers, which inhibit the thermal decomposition of omega-dithioester groups. Terminal dithiobenzoate (DTBz) groups of thermoresponsive blocks were easily reduced to thiol groups and reacted with maleimide (Mal). In aqueous media, diblock copolymer products formed surface-functionalized thermoresponsive micelles. These polymeric micelles had a low critical micelle concentration of 22 mu g/L. In thermoresponsive studies of the micelles, hydrophobic DTBz-surface micelles demonstrated a significant shift in lower critical solution temperature (LCST) to a lower temperature of 30.7 degrees C than that for Mal-surface micelles (40.0 degrees C). In addition, micellar LCST was controlled by changing bulk mixture ratios of respective heterogeneous end-functional diblock copolymers. Micellar disruption at acidic condition (pH 5.0) was completed within 5 days due to hydrolytic degradation of PLA cores, regardless of showing a slow disruption rate at physiological condition. Furthermore, we successfully improved water-solubility of hydrophobic drug, paclitaxel by incorporating into the micellar cores. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7127-7137, 2008

When uremic blood flows through dialyzers during hemodialysis, dialysis membrane surfaces are exposed to shear stress and internal filtration, which may affect the surface characteristics of the dialysis membranes. In the present study, we evaluated changes in the characteristics of membrane surfaces caused by shear stress and internal filtration using blood substitutes: water purified by reverse osmosis and 6.7 wt% dextran70 solution. We focused on the levels of a hydrophilic modifier, polyvinylpyrrolidone (PVP), on the membrane surface measured by attenuated total reflectance Fourier transform infrared spectroscopy. Experiments involving 4 h dialysis, 0-144 h shear-stress loading, and 4 h dead-end filtration were performed using polyester-polymer alloy (PEPA) and polysulfone (PS) membranes. After the dialysis experiments with accompanying internal filtration, average PVP retention on the PEPA membrane surface was 93.7% in all areas, whereas that on the PS membrane surface was 98.9% in all areas. After the shear-stress loading experiments, PVP retention on the PEPA membrane surface decreased as shear-stress loading time and the magnitude of shear stress increased. However, with the PS membrane, PVP retention scarcely changed. After the dead-end filtration experiments, PVP retention decreased in all areas for both PEPA and PS membranes, but PVP retention on the PEPA membrane surface was lower than that on the PS membrane surface. PVP on the PEPA membrane surface was eluted by both shear stress and internal filtration, while that on the PS membrane surface was eluted only by internal filtration.

The affinity control of integrin-RGD (Arg-Gly-Asp) binding by a thermal "on-off' switch has been achieved using newly designed surfaces presenting grafted temperature-responsive poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) copolymers functionalized with synthetic peptides. The prepared surface was designed to expose the tethered peptides available for cell binding at active "on" state above the lower critical solution temperature (LCST). The fully extended chains, on the other hand, masked the peptides completely and the cells started to detach from the surfaces at inactive "off' sate below the LCST. This paper elucidates the shielding effect of the grafted polymer chains on the dissociation of integrin-RGD binding below the LCST. To assess the ability of the polymer-shielding, extensible poly(ethylene glycol) (PEG) tethers were introduced between peptides and the grafted polymers. PEG chains allow peptides to be tethered to surfaces via functional PEG end-groups, leading to active "on" state even below the LCST. The time required to release cells from the surface was found to be longer when peptides were coupled to an extensible tether ends, suggesting that the surfaces can engender cell attachment through adhesive moieties covalently bound to the free ends of PEG chains. These results indicate that architectural changes on the nanometer length scale are crucial for controlling integrin-RGD binding and one of the main factors causing cell detachment is the shielding effect of the grafted polymer chains. (C) 2008 Elsevier Ltd. All rights reserved.

When uremic blood flows through dialyzers during hemodialysis, dialysis membrane surfaces are exposed to shear stress and internal filtration, which may affect the surface characteristics of the dialysis membranes. In the present study, we evaluated changes in the characteristics of membrane surfaces caused by shear stress and internal filtration using blood substitutes: water purified by reverse osmosis and 6.7 wt% dextran70 solution. We focused on the levels of a hydrophilic modifier, polyvinylpyrrolidone (PVP), on the membrane surface measured by attenuated total reflectance Fourier transform infrared spectroscopy. Experiments involving 4 h dialysis, 0-144 h shear-stress loading, and 4 h dead-end filtration were performed using polyester-polymer alloy (PEPA) and polysulfone (PS) membranes. After the dialysis experiments with accompanying internal filtration, average PVP retention on the PEPA membrane surface was 93.7% in all areas, whereas that on the PS membrane surface was 98.9% in all areas. After the shear-stress loading experiments, PVP retention on the PEPA membrane surface decreased as shear-stress loading time and the magnitude of shear stress increased. However, with the PS membrane, PVP retention scarcely changed. After the dead-end filtration experiments, PVP retention decreased in all areas for both PEPA and PS membranes, but PVP retention on the PEPA membrane surface was lower than that on the PS membrane surface. PVP on the PEPA membrane surface was eluted by both shear stress and internal filtration, while that on the PS membrane surface was eluted only by internal filtration.

The affinity control of integrin-RGD (Arg-Gly-Asp) binding by a thermal "on-off' switch has been achieved using newly designed surfaces presenting grafted temperature-responsive poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) copolymers functionalized with synthetic peptides. The prepared surface was designed to expose the tethered peptides available for cell binding at active "on" state above the lower critical solution temperature (LCST). The fully extended chains, on the other hand, masked the peptides completely and the cells started to detach from the surfaces at inactive "off' sate below the LCST. This paper elucidates the shielding effect of the grafted polymer chains on the dissociation of integrin-RGD binding below the LCST. To assess the ability of the polymer-shielding, extensible poly(ethylene glycol) (PEG) tethers were introduced between peptides and the grafted polymers. PEG chains allow peptides to be tethered to surfaces via functional PEG end-groups, leading to active "on" state even below the LCST. The time required to release cells from the surface was found to be longer when peptides were coupled to an extensible tether ends, suggesting that the surfaces can engender cell attachment through adhesive moieties covalently bound to the free ends of PEG chains. These results indicate that architectural changes on the nanometer length scale are crucial for controlling integrin-RGD binding and one of the main factors causing cell detachment is the shielding effect of the grafted polymer chains. (C) 2008 Elsevier Ltd. All rights reserved.

A novel assay for measuring time-dependant ligand-receptor affinity changes is developed based on a peptide-immobilized temperature-responsive surface, as schematically illustrated in the figure. The grafted thermoresponsive polymer acts as an "on-off" switch for mediating integrin-peptide bonding. At temperatures above and below the lower critical solution temperature (LCST), the peptides are accessible and shielded from integrin access, respectively.

A novel assay for measuring time-dependant ligand-receptor affinity changes is developed based on a peptide-immobilized temperature-responsive surface, as schematically illustrated in the figure. The grafted thermoresponsive polymer acts as an "on-off" switch for mediating integrin-peptide bonding. At temperatures above and below the lower critical solution temperature (LCST), the peptides are accessible and shielded from integrin access, respectively.

Hydrophilizing synthetic polymer dialysis membranes with polyvinylpyrrolidone (PVP) play an important role for inhibition of protein adsorption on membrane surface. In the present study, the effect of PVP on protein adsorption was evaluated from a nano-scale perspective. Swelling behavior of PVP present on wet polysulfone (PS)/PVP film surfaces was observed by atomic force microscopy (AFM). Fibrinogen and human serum albumin (HSA) were immobilized on the tip of AFM probes, with which a force-curve between protein and wet PS/PVP film surface was measured by AFM while scanning in order to visualize two-dimensional protein adsorbability on film surfaces. Furthermore, HSA adsorbability on non-PVP containing PEPA dialysis membrane (FLX-15GW) and PVP containing PEPA dialysis membrane (FDX-150GW) was evaluated by the AFM force-curve method. As a result, PS/PVP film surface was completely covered with hydrated and swollen PVP at 5 wt% or more PVP content. Protein adsorbability on PS/PVP film surfaces decreased greatly with increasing content of PVP. The adsorption of HSA was inhibited by the presence of PVP on film surfaces more significantly than that of more hydrophobic fibrinogen. HSA adsorbability on wet FLX-15GW dialysis membrane surface was 428+/-174 pN whereas that on wet FDX-150GW dialysis membrane surface was 42+/-29 pN. (C) 2007 Elsevier B.V. All rights reserved.

Hydrophilizing synthetic polymer dialysis membranes with polyvinylpyrrolidone (PVP) play an important role for inhibition of protein adsorption on membrane surface. In the present study, the effect of PVP on protein adsorption was evaluated from a nano-scale perspective. Swelling behavior of PVP present on wet polysulfone (PS)/PVP film surfaces was observed by atomic force microscopy (AFM). Fibrinogen and human serum albumin (HSA) were immobilized on the tip of AFM probes, with which a force-curve between protein and wet PS/PVP film surface was measured by AFM while scanning in order to visualize two-dimensional protein adsorbability on film surfaces. Furthermore, HSA adsorbability on non-PVP containing PEPA dialysis membrane (FLX-15GW) and PVP containing PEPA dialysis membrane (FDX-150GW) was evaluated by the AFM force-curve method. As a result, PS/PVP film surface was completely covered with hydrated and swollen PVP at 5 wt% or more PVP content. Protein adsorbability on PS/PVP film surfaces decreased greatly with increasing content of PVP. The adsorption of HSA was inhibited by the presence of PVP on film surfaces more significantly than that of more hydrophobic fibrinogen. HSA adsorbability on wet FLX-15GW dialysis membrane surface was 428+/-174 pN whereas that on wet FDX-150GW dialysis membrane surface was 42+/-29 pN. (C) 2007 Elsevier B.V. All rights reserved.

透析で用いられている合成高分子膜のうち、ポリスルホン(PS)とポリエステル系ポリマアロイ(PEPA)は、親水化剤であるポリビニルピロリドン(PVP)を添加することによって膜表面を親水化し、生体適合性の向上を図っている。しかし、透析により生じる中空糸膜表面のPVP分布の変化を定量的に検討した例はない。そこで、本研究では、透析器内の中空糸膜を軸方向および断面方向のいくつかのエリアに分け、各エリアにおける膜表面PVP残存率を測定し、PVPの溶出性を評価した。APS-15EX(試作品:PS膜、旭化成メディカル)およびFDX-15GW(PEPA膜、日機装)の透析器を用いて、血液側流量200mL/min、透析液側流量500mL/minで4時間透析を行った。このとき、血液側には血液と同粘度を有する6.7wt%デキストラン70水溶液、透析液側には逆浸透水を用いた。透析終了後に透析器ジャケットを取り外し、各エリア(透析器軸方向に3分割、断面方向に12分割、合計36エリア)から中空糸を取り出した。全反射減衰フーリエ変換赤外分光法(FTIR/ATR)で透析前後の中空糸膜内表面におけるPVP残存率を測定した。APS-15EXおよびFDX-15GWのいずれの透析器も、透析によって膜表面PVP残存率はすべてのエリアで減少しており、すべてのエリアでPVPが溶出したことがわかった。なお、APS-15EXとFDX-15GWの平均PVP残存率は、それぞれ94.1%、90.8%となり、APS-15EXの方が若干高いPVP残存率を示した。さらに、断面方向と軸方向で比較したところ、いずれの透析器も次のように同様の傾向を示した。断面方向では各断面にPVP残存率の偏りがみられた。軸方向では、中空糸束中央部に比較して、内部濾過量の多い中空糸束両端部においてPVP残存率が著しく低下した。特に、濾過が生じている血液出口部において、この傾向は顕著であった。(著者抄録)

This paper discusses the chiral discriminative gate effect of molecularly imprinted polymer (MIP) in organic solvents. We grafted L- (or D-) phenylalanine anilide (PAA) imprinted poly(ethylene glycol dimethacrylate-co-methacrylic acid) on an indium-tin oxide (ITO) in a number of organic solvents. Cyclic voltammetry of ferrocene with the grafted ITO electrode was carried out in several organic solvents and the effect Of L-(or D-) PAA on an electric current of ferrocene was evaluated. As the result, the faradic current at the electrode grafted in the non-polar solvent was remarkably sensitive to the template in the voltammetry carried out in the non-polar solvent. However, it was insensitive to the enantiomer of the template. The results indicate that the gate effect of MIP can discriminate between the template and its analogue by stereochemical structure even if the difference in the chemical or physical property is omitted. They also indicate that the gate effect could have limited applications with the enantio-selective amperometric sensors working in non-polar solvents where biosensors cannot work. (c) 2007 Elsevier B.V. All rights reserved.

Intracellular distribution of free doxorubicin (DOX) or DOX-loaded in polymeric micelles with thermoresponsive outer shells of poly(N-isopropylacrylamide) or its copolymers in cultured human breast cancer cells (MCF-7) were investigated by fluorescence and confocal laser scanning microscopy. Free DOX accumulated rapidly and selectively in cell nuclei, independent of temperature changes. In contrast to free drugs, the intracellular distribution of DOX-loaded in the thermoresponsive polymeric micelles was significantly affected by temperature changes across lower critical solution temperature (LCST) of the micelles. Above the micelle LCST, DOX delivered by the micelles was localized uniformly inside of MCF-7 cells. By contrast, the amount of DOX delivered to MCF-7 cells drastically decreased below the micelle LCST due to minimal interaction of the micelles with cell membrane surfaces. These results clearly showed that the mechanism of the intracellular drug localization was different between free drugs and DOX-loaded in the micelles. The thermoresponsive micelles aggressively interacted with the cells and carried DOX into the cells via triggered phase transition of the outer shells. In addition, much lower accumulation of free DOX was observed in the resistant cells compared to its parent sensitive MCF-7 due to the resistant mechanism. Of interest, DOX accumulation in the resistant cells was almost in the same level as with MCF-7 (sensitive) cells for the micelle system above the LCST. (c) 2007 Elsevier Ltd. All rights reserved.

This paper discusses the chiral discriminative gate effect of molecularly imprinted polymer (MIP) in organic solvents. We grafted L- (or D-) phenylalanine anilide (PAA) imprinted poly(ethylene glycol dimethacrylate-co-methacrylic acid) on an indium-tin oxide (ITO) in a number of organic solvents. Cyclic voltammetry of ferrocene with the grafted ITO electrode was carried out in several organic solvents and the effect Of L-(or D-) PAA on an electric current of ferrocene was evaluated. As the result, the faradic current at the electrode grafted in the non-polar solvent was remarkably sensitive to the template in the voltammetry carried out in the non-polar solvent. However, it was insensitive to the enantiomer of the template. The results indicate that the gate effect of MIP can discriminate between the template and its analogue by stereochemical structure even if the difference in the chemical or physical property is omitted. They also indicate that the gate effect could have limited applications with the enantio-selective amperometric sensors working in non-polar solvents where biosensors cannot work. (c) 2007 Elsevier B.V. All rights reserved.

Intracellular distribution of free doxorubicin (DOX) or DOX-loaded in polymeric micelles with thermoresponsive outer shells of poly(N-isopropylacrylamide) or its copolymers in cultured human breast cancer cells (MCF-7) were investigated by fluorescence and confocal laser scanning microscopy. Free DOX accumulated rapidly and selectively in cell nuclei, independent of temperature changes. In contrast to free drugs, the intracellular distribution of DOX-loaded in the thermoresponsive polymeric micelles was significantly affected by temperature changes across lower critical solution temperature (LCST) of the micelles. Above the micelle LCST, DOX delivered by the micelles was localized uniformly inside of MCF-7 cells. By contrast, the amount of DOX delivered to MCF-7 cells drastically decreased below the micelle LCST due to minimal interaction of the micelles with cell membrane surfaces. These results clearly showed that the mechanism of the intracellular drug localization was different between free drugs and DOX-loaded in the micelles. The thermoresponsive micelles aggressively interacted with the cells and carried DOX into the cells via triggered phase transition of the outer shells. In addition, much lower accumulation of free DOX was observed in the resistant cells compared to its parent sensitive MCF-7 due to the resistant mechanism. Of interest, DOX accumulation in the resistant cells was almost in the same level as with MCF-7 (sensitive) cells for the micelle system above the LCST. (c) 2007 Elsevier Ltd. All rights reserved.

The antioxidation property of vitamin E-coated dialysis membrane is effective for reduction of oxidative stress. Effect of amount of vitamin E coating on antioxidation property has been poorly understood yet. In the present study, we evaluated a relationship between amount of vitamin E coating and antioxidation property using a superoxide probe of 2-methyl-6-p-methoxyphenylethynylimidazopyrazinone (MPEC) by the optical fiber method to determine optimum amount of vitamin E coating and to improve antioxidation property of the vitamin E-coated dialysis membrane. Furthermore, from the viewpoint of reuse, we examined recovery of oxidized vitamin E by vitamin C treatment. In conclusion, it is necessary to coat polysulfone dialysis membranes with vitamin E at over 74 mg/m(2). The antioxidation property is recoverable by treating dialysis membrane containing oxidized vitamin E with vitamin C. By administrating vitamin C, higher antioxidation property may be realized with a small amount of vitamin E coating. (c) 2007 Elsevier B.V. All rights reserved.

The antioxidation property of vitamin E-coated dialysis membrane is effective for reduction of oxidative stress. Effect of amount of vitamin E coating on antioxidation property has been poorly understood yet. In the present study, we evaluated a relationship between amount of vitamin E coating and antioxidation property using a superoxide probe of 2-methyl-6-p-methoxyphenylethynylimidazopyrazinone (MPEC) by the optical fiber method to determine optimum amount of vitamin E coating and to improve antioxidation property of the vitamin E-coated dialysis membrane. Furthermore, from the viewpoint of reuse, we examined recovery of oxidized vitamin E by vitamin C treatment. In conclusion, it is necessary to coat polysulfone dialysis membranes with vitamin E at over 74 mg/m(2). The antioxidation property is recoverable by treating dialysis membrane containing oxidized vitamin E with vitamin C. By administrating vitamin C, higher antioxidation property may be realized with a small amount of vitamin E coating. (c) 2007 Elsevier B.V. All rights reserved.

The tortuous capillary pore diffusion model (TCPDM) has been used for estimating diffusive and pure water permeability from simple structure parameters such as pore diameter, surface porosity, wall thickness and tortuosity. The validity of this model for evaluation of homogeneous membrane has been already confirmed. Recently, there is a trend toward the use of asymmetrical dialysis membranes made of synthetic polymer such as poly(acrylonitrile) (PAN), polysulfone (PS) and a polyethersulfone polyarylate (PEPA) blend polymer. The purpose of the present study is to apply the TCPDM to evaluation of commercially available hollow-fiber dialysis membranes with asymmetrical structures by simplifying them to a double-layer membrane. The TCPDM is capable of estimating pore tortuosity of asymmetrical dialysis membranes having skin and supporting layers from data on membrane thickness, pore diameter, pure water permeability and water content. Values for diffusive permeability obtained by the TCPDM are in a good agreement with experimental data. This TCPDM model is useful for evaluation of not only homogeneous membrane but also asymmetrical membrane. (c) 2006 Elsevier B.V. All rights reserved.

The electrical potential oscillation at and the shape of the water/octanol interface were investigated using hydrophobic fluoroplastic containers. The interfacial potential between a water solution containing 1.5 mM sodium dodecyl sulfate (SDS) and an octanol solution containing 5 mM tetrabutylammonium chloride oscillated with an amplitude of 50-100 mV. The potential oscillation was also observed using a transparent fluoroplastic tube. The water/octanol interface shape was unchanged and no interfacial flow was observed during the oscillation. The interface shape was convex toward the octanol phase for 1.5 mM SDS, meaning that SDS adsorption to the wall was suppressed by the hydrophobic container. Therefore, the octanol system in a hydrophobic container enabled us to elucidate the electrical oscillation without any influence from the wall effect. (c) 2006 Elsevier Inc. All rights reserved.

Rexeed was developed by Asahi Kasei Medical using wave-shaped hollow fibers, a full baffle, and a short taper housing to improve dialysate flow. The present study is clarifies improvement in dialysate flow with Rexeed-15 compared with that of a conventional dialyzer. Dialysate flow was evaluated by the pulse-response method. Dialysate pressure and tracer concentration were measured at a blood-side flow rate (Q(B)) of 200 ml/min, a dialysate-side flow rate (Q(D)) of 500 ml/min, and a net filtration rate (Q(F)) of 0 ml/min using needles placed in the test dialyzer. Dialyzer performance was evaluated by measuring urea and vitamin B-12 clearance at Q(B) = 200 and 400 ml/min, Q(D) = 300-800 ml/min, and Q(F) = 0 ml/min. In the conventional dialyzer, dialysate channeling was observed. In contrast, Rexeed-15 had a uniform dialysate flow. Urea and vitamin B-12 clearance with Rexeed-15 was slightly sensitive to Q(D). The overall mass transfer coefficient for urea with Rexeed-15 was more than 50% higher than that of the conventional dialyzer, indicating the possibility of reduced dialysate usage with Rexeed. Rexeed has a highly optimal dialysate flow, due to the wave-shaped hollow fibers and the new housing, and gives increased clearance for lower-molecular-weight substances.

The tortuous capillary pore diffusion model (TCPDM) has been used for estimating diffusive and pure water permeability from simple structure parameters such as pore diameter, surface porosity, wall thickness and tortuosity. The validity of this model for evaluation of homogeneous membrane has been already confirmed. Recently, there is a trend toward the use of asymmetrical dialysis membranes made of synthetic polymer such as poly(acrylonitrile) (PAN), polysulfone (PS) and a polyethersulfone polyarylate (PEPA) blend polymer. The purpose of the present study is to apply the TCPDM to evaluation of commercially available hollow-fiber dialysis membranes with asymmetrical structures by simplifying them to a double-layer membrane. The TCPDM is capable of estimating pore tortuosity of asymmetrical dialysis membranes having skin and supporting layers from data on membrane thickness, pore diameter, pure water permeability and water content. Values for diffusive permeability obtained by the TCPDM are in a good agreement with experimental data. This TCPDM model is useful for evaluation of not only homogeneous membrane but also asymmetrical membrane. (c) 2006 Elsevier B.V. All rights reserved.

The electrical potential oscillation at and the shape of the water/octanol interface were investigated using hydrophobic fluoroplastic containers. The interfacial potential between a water solution containing 1.5 mM sodium dodecyl sulfate (SDS) and an octanol solution containing 5 mM tetrabutylammonium chloride oscillated with an amplitude of 50-100 mV. The potential oscillation was also observed using a transparent fluoroplastic tube. The water/octanol interface shape was unchanged and no interfacial flow was observed during the oscillation. The interface shape was convex toward the octanol phase for 1.5 mM SDS, meaning that SDS adsorption to the wall was suppressed by the hydrophobic container. Therefore, the octanol system in a hydrophobic container enabled us to elucidate the electrical oscillation without any influence from the wall effect. (c) 2006 Elsevier Inc. All rights reserved.

Rexeed was developed by Asahi Kasei Medical using wave-shaped hollow fibers, a full baffle, and a short taper housing to improve dialysate flow. The present study is clarifies improvement in dialysate flow with Rexeed-15 compared with that of a conventional dialyzer. Dialysate flow was evaluated by the pulse-response method. Dialysate pressure and tracer concentration were measured at a blood-side flow rate (Q(B)) of 200 ml/min, a dialysate-side flow rate (Q(D)) of 500 ml/min, and a net filtration rate (Q(F)) of 0 ml/min using needles placed in the test dialyzer. Dialyzer performance was evaluated by measuring urea and vitamin B-12 clearance at Q(B) = 200 and 400 ml/min, Q(D) = 300-800 ml/min, and Q(F) = 0 ml/min. In the conventional dialyzer, dialysate channeling was observed. In contrast, Rexeed-15 had a uniform dialysate flow. Urea and vitamin B-12 clearance with Rexeed-15 was slightly sensitive to Q(D). The overall mass transfer coefficient for urea with Rexeed-15 was more than 50% higher than that of the conventional dialyzer, indicating the possibility of reduced dialysate usage with Rexeed. Rexeed has a highly optimal dialysate flow, due to the wave-shaped hollow fibers and the new housing, and gives increased clearance for lower-molecular-weight substances.

An oscillating electrical potential across a liquid membrane is studied as a model of a biological system. The oscillating potential is caused by repeated surfactant adsorption and desorption at the interface. The surfactant desorption process was simulated using both Fick's diffusion equation and the Langmuir-Hinshelwood equation. A water/octanol/water liquid membrane containing sodium dodecyl sulfate (SDS) was used and the effect of NaCl was studied. Calculations agree closely with experimental results, supporting the validity of the model we propose. Adsorption rate constants were obtained by comparing the experimental and calculated results. The addition of NaCl increased adsorption rate constants and decreased desorption rate constants. Calculations suggest that surfactant desorbs mainly into the octanol phase and this desorption is not affected by the addition of NaCl. The disordering of potential oscillations by NaCl addition may be caused by decreased SDS accumulation in the octanol phase close to the interface. A lower adsorption rate of the surfactant from the octanol phase onto the water/octanol interface leads to an oscillating electrical potential across the liquid membrane. (c) 2006 Elsevier B.V. All rights reserved.

An oscillating electrical potential across a liquid membrane is studied as a model of a biological system. The oscillating potential is caused by repeated surfactant adsorption and desorption at the interface. The surfactant desorption process was simulated using both Fick's diffusion equation and the Langmuir-Hinshelwood equation. A water/octanol/water liquid membrane containing sodium dodecyl sulfate (SDS) was used and the effect of NaCl was studied. Calculations agree closely with experimental results, supporting the validity of the model we propose. Adsorption rate constants were obtained by comparing the experimental and calculated results. The addition of NaCl increased adsorption rate constants and decreased desorption rate constants. Calculations suggest that surfactant desorbs mainly into the octanol phase and this desorption is not affected by the addition of NaCl. The disordering of potential oscillations by NaCl addition may be caused by decreased SDS accumulation in the octanol phase close to the interface. A lower adsorption rate of the surfactant from the octanol phase onto the water/octanol interface leads to an oscillating electrical potential across the liquid membrane. (c) 2006 Elsevier B.V. All rights reserved.

We designed thenno-responsive and biodegradable polymeric micelles for an ideal drug delivery system whose target sites are where external stimuli selectively release drugs from the polymeric micelles. The thermo-responsive micelles formed from block copolymers that were composed both of a hydrophobic block and a thermo-responsive block. Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) showing a lower critical solution temperature (LCST) around 40 degrees C was synthesized for the thermo-responsive block, while biodegradable poly(D,L-lactide), poly(epsilon-caprolactone), or poly(D,L-lactide-co-epsilon-caprolactone) was used for the hydrophobic block. By changing both the block lengths of the poly(D,L-lactide)-containing block copolymers, physical parameters such as micelle diameter and critical micelle concentration were varied. On the other hand, the choice of the hydrophobic block was revealed to be critical in relation to both on the thermo-responsive release of the incorporated anticancer drug, doxorubicin, and the temperature-dependent change of the hydrophobicity of the micelles' inner core. One polymeric micelle composition successfully exhibited rapid and thermo-responsive drug release while possessing a biodegradable character. (c) 2006 Elsevier B.V. All rights reserved.

We designed thenno-responsive and biodegradable polymeric micelles for an ideal drug delivery system whose target sites are where external stimuli selectively release drugs from the polymeric micelles. The thermo-responsive micelles formed from block copolymers that were composed both of a hydrophobic block and a thermo-responsive block. Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) showing a lower critical solution temperature (LCST) around 40 degrees C was synthesized for the thermo-responsive block, while biodegradable poly(D,L-lactide), poly(epsilon-caprolactone), or poly(D,L-lactide-co-epsilon-caprolactone) was used for the hydrophobic block. By changing both the block lengths of the poly(D,L-lactide)-containing block copolymers, physical parameters such as micelle diameter and critical micelle concentration were varied. On the other hand, the choice of the hydrophobic block was revealed to be critical in relation to both on the thermo-responsive release of the incorporated anticancer drug, doxorubicin, and the temperature-dependent change of the hydrophobicity of the micelles' inner core. One polymeric micelle composition successfully exhibited rapid and thermo-responsive drug release while possessing a biodegradable character. (c) 2006 Elsevier B.V. All rights reserved.

The reactive oxygen species (ROS) have important physiological and protective roles in the maintenance of living systems. However, excessive production of ROS can impact cellular homeostasis and lead to oxidative stress. Superoxide has high reactivity acting as a reductant and an oxidant. Because of the pathophysiological roles of superoxide several methods for its detection have been developed. Spectrophotometric assay is nonspecific for superoxide, which limits its use. Chemiluminescent methods have been used frequently for vascular tissue samples because they are more sensitive than other conventional methods. Fluorescence-based assays have also been widely used in cultured cells and vascular tissues. Electron spin resonance (ESR) spectroscopy, also known as electron paramagnetic resonance (EPR), quantitatively measures superoxide concentration but is less suitable for its in vivo detection. Electrochemical sensors based on cytochrome c reduction or superoxide dismutase (SOD) enzymatic reaction have been developed for real-time monitoring, but lack adequate performance for in vivo superoxide measurement. Newly developed SOD-immobilized superoxide sensors reportedly have satisfactory performance, for in vitro measurement. In this paper, we review superoxide measurement methods from the early spectrophotometric assays to the third generation of electrochemical sensors.

The reactive oxygen species (ROS) have important physiological and protective roles in the maintenance of living systems. However, excessive production of ROS can impact cellular homeostasis and lead to oxidative stress. Superoxide has high reactivity acting as a reductant and an oxidant. Because of the pathophysiological roles of superoxide several methods for its detection have been developed. Spectrophotometric assay is nonspecific for superoxide, which limits its use. Chemiluminescent methods have been used frequently for vascular tissue samples because they are more sensitive than other conventional methods. Fluorescence-based assays have also been widely used in cultured cells and vascular tissues. Electron spin resonance (ESR) spectroscopy, also known as electron paramagnetic resonance (EPR), quantitatively measures superoxide concentration but is less suitable for its in vivo detection. Electrochemical sensors based on cytochrome c reduction or superoxide dismutase (SOD) enzymatic reaction have been developed for real-time monitoring, but lack adequate performance for in vivo superoxide measurement. Newly developed SOD-immobilized superoxide sensors reportedly have satisfactory performance, for in vitro measurement. In this paper, we review superoxide measurement methods from the early spectrophotometric assays to the third generation of electrochemical sensors.

dialysis patients are at risk of amyloidosis attributed to Et. This suggests that Et may affect the blood even if it does not mix with the blood. The objective of the present study is to evaluate the activity of Et trapped by membranes. We made mini modules out of hollow fibers using three different types of membranes and filtered Et solution. The lumen of the hollow fibers was then filled with limulus amebocyte lysate (LAL) for 15 min at 310 K. Et activity was then determined by measuring absorbance of the LAL reagent. The surfaces of test membranes were studied using an atomic force microscope. With polyester polyrner alloy (PEPA), no Et leakage or Et activity was detected in the hollow fibers under any conditions. With polysulfone (PS) and polyether sulfone (PES), no Et leakage was detected under clinical conditions, but Et activity was detected in the hollow fibers. These results show that Et trapped by the inner skin may affect the blood, even if Et does not mix with the blood. Therefore, Et should be trapped by an outer skin or the part somewhat far from the blood which does not contact with the blood directly. (c) 2005 Elsevier B.V. All rights reserved.

dialysis patients are at risk of amyloidosis attributed to Et. This suggests that Et may affect the blood even if it does not mix with the blood. The objective of the present study is to evaluate the activity of Et trapped by membranes. We made mini modules out of hollow fibers using three different types of membranes and filtered Et solution. The lumen of the hollow fibers was then filled with limulus amebocyte lysate (LAL) for 15 min at 310 K. Et activity was then determined by measuring absorbance of the LAL reagent. The surfaces of test membranes were studied using an atomic force microscope. With polyester polyrner alloy (PEPA), no Et leakage or Et activity was detected in the hollow fibers under any conditions. With polysulfone (PS) and polyether sulfone (PES), no Et leakage was detected under clinical conditions, but Et activity was detected in the hollow fibers. These results show that Et trapped by the inner skin may affect the blood, even if Et does not mix with the blood. Therefore, Et should be trapped by an outer skin or the part somewhat far from the blood which does not contact with the blood directly. (c) 2005 Elsevier B.V. All rights reserved.

Poly (N-isopropylacrylamide) (PIPAAm) of controlled molecular weight was densely grafted onto glass capillary lumenal surfaces using surface-initiated atom transfer radical polymerization (ATRP). Temperature-dependent changes of these thermoresponsive brush surfaces with hydrophobic steroids were investigated by exploiting thermoresponsive aqueous wettability changes of the polymer-modified surfaces in microfluidic systems. IPAAm was polymerized on ATRP initiator-immobilized glass surfaces using CuCl/CuCl2/tris(dimethylaminoethyl)amine (Me6TREN) as an ATRP catalyst in water at 25 C. PIPAAm graft layer thickness and its homogeneity on glass surfaces are controlled by changing ATRP reaction time. Aqueous wettability changes of PIPAAm-grafted surfaces responses drastically changed to both grafted polymer layer thickness and temperature, especially at lower temperatures. Temperature-responsive surface properties of these PIPAAm brushes within capillary inner wall surfaces were then investigated using capillary chromatography. Effective interaction of hydrophobic steroids with dehydrated, hydrophobized PIPAAm-grafted capillary surfaces was observed above 30 C without any column packing materials. Steroid elution behavior from PIPAAm-grafted capillaries contrasted sharply with that from PIPAAm hydrogel-grafted porous monolithic silica capillaries prepared by electron beam (EB) irradiation wherein significant peak broadening was observed at high-temperature regardless of sample hydrophobicity factors (log P values), indicating multistep separation modes in coated monolithic silica capillaries. In conclusion, thermoresponsive polymer-grafted capillary inner wall surfaces prepared by ATRP exhibit useful temperature-dependent surface property alterations effective to regulate interactions with biomolecules without requirements for separation bed packing materials within the capillary lumen.

Poly (N-isopropylacrylamide) (PIPAAm) of controlled molecular weight was densely grafted onto glass capillary lumenal surfaces using surface-initiated atom transfer radical polymerization (ATRP). Temperature-dependent changes of these thermoresponsive brush surfaces with hydrophobic steroids were investigated by exploiting thermoresponsive aqueous wettability changes of the polymer-modified surfaces in microfluidic systems. IPAAm was polymerized on ATRP initiator-immobilized glass surfaces using CuCl/CuCl2/tris(dimethylaminoethyl)amine (Me6TREN) as an ATRP catalyst in water at 25 C. PIPAAm graft layer thickness and its homogeneity on glass surfaces are controlled by changing ATRP reaction time. Aqueous wettability changes of PIPAAm-grafted surfaces responses drastically changed to both grafted polymer layer thickness and temperature, especially at lower temperatures. Temperature-responsive surface properties of these PIPAAm brushes within capillary inner wall surfaces were then investigated using capillary chromatography. Effective interaction of hydrophobic steroids with dehydrated, hydrophobized PIPAAm-grafted capillary surfaces was observed above 30 C without any column packing materials. Steroid elution behavior from PIPAAm-grafted capillaries contrasted sharply with that from PIPAAm hydrogel-grafted porous monolithic silica capillaries prepared by electron beam (EB) irradiation wherein significant peak broadening was observed at high-temperature regardless of sample hydrophobicity factors (log P values), indicating multistep separation modes in coated monolithic silica capillaries. In conclusion, thermoresponsive polymer-grafted capillary inner wall surfaces prepared by ATRP exhibit useful temperature-dependent surface property alterations effective to regulate interactions with biomolecules without requirements for separation bed packing materials within the capillary lumen.

The interaction of blood with a material surface results in activation of the body's humoral immune system and the generation of reactive oxygen species (ROS). It has recently become clear that ROS are central to the pathology of many diseases. In this study, we evaluated the superoxide generation, permeation, and dismutation in hollow-fiber dialysis membranes by using 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) as a superoxide-reactive chemiluminescence producer and an optical fiber probe to detect the resulting chemiluminescence in the hollow fiber lumen. We measured the superoxide generated when bovine blood leukocytes were brought into contact with dialysis membranes. Superoxide permeation was determined by measuring MPEC chemiluminescence in the hollow fiber lumen using an optical fiber probe. Additionally, superoxide dismutation was evaluated by examining the difference in superoxide permeability for membranes with and without vitamin E coating. Superoxide generation varies for different membrane materials, depending on the membrane's biocompatibility. Superoxide permeability depends on the diffusive permeability of membranes. No marked decrease in superoxide permeability was observed among membrane materials. The superoxide permeability of vitamin E-coated membrane was smaller than that of uncoated membrane. The antioxidant property of vitamin E-coated membranes is hence effective in causing superoxide dismutation. © The Japanese Society for Artificial Organs 2005.

The interaction of blood with a material surface results in activation of the body's humoral immune system and the generation of reactive oxygen species (ROS). It has recently become clear that ROS are central to the pathology of many diseases. In this study, we evaluated the superoxide generation, permeation, and dismutation in hollow-fiber dialysis membranes by using 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) as a superoxide-reactive chemiluminescence producer and an optical fiber probe to detect the resulting chemiluminescence in the hollow fiber lumen. We measured the superoxide generated when bovine blood leukocytes were brought into contact with dialysis membranes. Superoxide permeation was determined by measuring MPEC chemiluminescence in the hollow fiber lumen using an optical fiber probe. Additionally, superoxide dismutation was evaluated by examining the difference in superoxide permeability for membranes with and without vitamin E coating. Superoxide generation varies for different membrane materials, depending on the membrane's biocompatibility. Superoxide permeability depends on the diffusive permeability of membranes. No marked decrease in superoxide permeability was observed among membrane materials. The superoxide permeability of vitamin E-coated membrane was smaller than that of uncoated membrane. The antioxidant property of vitamin E-coated membranes is hence effective in causing superoxide dismutation. © The Japanese Society for Artificial Organs 2005.

The interaction of blood with a material surface results in activation of the body's humoral immune system and the generation of reactive oxygen species (ROS). It has recently become clear that ROS are central to the pathology of many diseases. In this study, we evaluated the superoxide generation, permeation, and dismutation in hollow-fiber dialysis membranes by using 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) as a superoxide-reactive chemiluminescence producer and an optical fiber probe to detect the resulting chemiluminescence in the hollow fiber lumen. We measured the superoxide generated when bovine blood leukocytes were brought into contact with dialysis membranes. Superoxide permeation was determined by measuring MPEC chemiluminescence in the hollow fiber lumen using an optical fiber probe. Additionally, superoxide dismutation was evaluated by examining the difference in superoxide permeability for membranes with and without vitamin E coating. Superoxide generation varies for different membrane materials, depending on the membrane's biocompatibility. Superoxide permeability depends on the diffusive permeability of membranes. No marked decrease in superoxide permeability was observed among membrane materials. The superoxide permeability of vitamin E-coated membrane was smaller than that of uncoated membrane. The antioxidant property of vitamin E-coated membranes is hence effective in causing superoxide dismutation. © The Japanese Society for Artificial Organs 2005.

Thermally regulated flow control using a thermoresponsive polymer grafted onto surfaces of capillary lumen facilitates rapid, reliable, and repeatable open-close cycles (see Figure). Hydration of the grafted polymer chains on the internal surfaces may increase the microviscosity of the hydration layers at the wall interfaces without physically occluding the lumen, producing complete and reversible on/off flow valving in microchannels under hydrostatic pressures relevant for microfluidics approaches.

Thermally regulated flow control using a thermoresponsive polymer grafted onto surfaces of capillary lumen facilitates rapid, reliable, and repeatable open-close cycles (see Figure). Hydration of the grafted polymer chains on the internal surfaces may increase the microviscosity of the hydration layers at the wall interfaces without physically occluding the lumen, producing complete and reversible on/off flow valving in microchannels under hydrostatic pressures relevant for microfluidics approaches.

For efficient removal of large molecular weight solutes by dialysis, several types of internal filtration-enhancing dialyzers (IFEDs) are commercially available. However, in a pressure-driven membrane separation process (i.e., filtration), membrane fouling caused by adhesion of plasma proteins is a severe problem. The objective of the present study is to investigate the effects of internal filtration on membrane fouling based on the membrane's pure-water permeability, diffusive permeability, and sieving coefficient. Hemodialysis experiments were performed with two different dialyzers, IFEDs and non-IFEDs. Local membrane fouling in each dialyzer was evaluated by measuring the pure-water permeability, the diffusive permeability, and the sieving coefficient of native membranes and membranes treated with bovine blood. The effects of packing ratio on dialysate flow pattern were also evaluated by measuring the time required for an ion tracer to reach electrodes placed in the dialyzers. In the IFED, membrane fouling caused by protein adhesion is increased because of enhanced internal filtration only at the early stage of dialysis, and this fouling tends to occur only near the dialysate outlet port. However, enhanced internal filtration has little effect on measured membrane transfer parameters. © The Japanese Society for Artificial Organs 2005.

Most of the surface patterning methods currently applied are based on lithography techniques and microfabrication onto silicon or glass substrates. Here we report a novel method to prepare patterned surfaces on polystyrene substrates by grafting ultrathin cell-repellent polymer layers utilising both electron beam (EB) polymerisation and local laser ablation techniques for microfabrication. Polyacrylamide was grafted onto tissue culture polystyrene (TCPS) dishes using EB irradiation. Water contact angles for these PAAm-grafted TCPS surfaces were less than 10 degrees (cos theta = 0.99) with PAAm grafted amounts of 1.6 mu g/cm(2) as determined by ATR/FT-IR. UV excimer laser (ArF: 193 nm) ablation resulted in the successful fabrication of micropatterned surfaces composed of hydrophilic PAAm and hydrophobic basal polystyrene layers. Bovine carotid artery endothelial cells adhered only to the ablated domains after pretreatment of the patterned surfaces with 15 mu g/mL fibronectin at 37 degrees C. The ablated domain sizes significantly influenced the number of cells occupying each domain. Cell patterning functionality of the patterned surfaces was maintained for more than 2 months without loss of pattern fidelity, indicating that more durable cell arrays can be obtained compared to those prepared by self-assembled monolayers of alkanethiols, as described in previous reports. The surface fabrication techniques presented here can be utilised for the preparation of cell-based biosensors as well as tissue engineering constructs. (c) 2005 Elsevier Ltd. All rights reserved.

For efficient removal of large molecular weight solutes by dialysis, several types of internal filtration-enhancing dialyzers (IFEDs) are commercially available. However, in a pressure-driven membrane separation process (i.e., filtration), membrane fouling caused by adhesion of plasma proteins is a severe problem. The objective of the present study is to investigate the effects of internal filtration on membrane fouling based on the membrane's pure-water permeability, diffusive permeability, and sieving coefficient. Hemodialysis experiments were performed with two different dialyzers, IFEDs and non-IFEDs. Local membrane fouling in each dialyzer was evaluated by measuring the pure-water permeability, the diffusive permeability, and the sieving coefficient of native membranes and membranes treated with bovine blood. The effects of packing ratio on dialysate flow pattern were also evaluated by measuring the time required for an ion tracer to reach electrodes placed in the dialyzers. In the IFED, membrane fouling caused by protein adhesion is increased because of enhanced internal filtration only at the early stage of dialysis, and this fouling tends to occur only near the dialysate outlet port. However, enhanced internal filtration has little effect on measured membrane transfer parameters. © The Japanese Society for Artificial Organs 2005.

Most of the surface patterning methods currently applied are based on lithography techniques and microfabrication onto silicon or glass substrates. Here we report a novel method to prepare patterned surfaces on polystyrene substrates by grafting ultrathin cell-repellent polymer layers utilising both electron beam (EB) polymerisation and local laser ablation techniques for microfabrication. Polyacrylamide was grafted onto tissue culture polystyrene (TCPS) dishes using EB irradiation. Water contact angles for these PAAm-grafted TCPS surfaces were less than 10 degrees (cos theta = 0.99) with PAAm grafted amounts of 1.6 mu g/cm(2) as determined by ATR/FT-IR. UV excimer laser (ArF: 193 nm) ablation resulted in the successful fabrication of micropatterned surfaces composed of hydrophilic PAAm and hydrophobic basal polystyrene layers. Bovine carotid artery endothelial cells adhered only to the ablated domains after pretreatment of the patterned surfaces with 15 mu g/mL fibronectin at 37 degrees C. The ablated domain sizes significantly influenced the number of cells occupying each domain. Cell patterning functionality of the patterned surfaces was maintained for more than 2 months without loss of pattern fidelity, indicating that more durable cell arrays can be obtained compared to those prepared by self-assembled monolayers of alkanethiols, as described in previous reports. The surface fabrication techniques presented here can be utilised for the preparation of cell-based biosensors as well as tissue engineering constructs. (c) 2005 Elsevier Ltd. All rights reserved.

Using the derived mass transfer correlations for hollow fibers, hollow fiber arrangements were optimized for an artificial gill that uses an oxygen carrier solution. FC-40, a perfluorocarbon (PFC), was used as the oxygen carrier solution. In the oxygen uptake module, a hollow fiber arrangement with parallel coiled hollow fibers is preferred. The optimum outside diameter of the hollow fibers and the transverse pitch between them are 300 and 500 μ m. respectively. In the oxygen release module, a hollow fiber arrangement of straight parallel hollow fibers is preferred. The optimum outside diameter of the hollow fibers and transverse pitch between them are 300 and 500 μ m, respectively. In the case of humans, the scaling up was estimated from the oxygen transfer rates using these optimum hollow fiber arrangements. The required total membrane surface area is 50.8 m(2), the total delivered pumping energy is 124 W, and the oxygen partial pressure in inspiration is 17.8 kPa. Importantly, the total membrane surface area required was significantly reduced using the modules with an optimum hollow fiber arrangement in comparison with that using connected membrane oxygenators as a gas exchanger. The optimization of hollow fiber arrangements in an artificial gill significantly enhances oxygen transfer from water to air. © 2005 Elsevier B.V. All rights reserved.

We have evaluated the mass transfer performance of four commercially available membrane oxygenators in which the blood path is external to and approximately perpendicular to the fiber bundle. Water flowed outside the hollow fibers as an oxygen carrier medium and substitution for blood, and nitrogen gas flowed inside the hollow fibers. The oxygen transfer rates in the membrane oxygenators were measured, and their mass transfer coefficients were obtained. When we analyzed the mass transfer performance using the theory of heat transfer across tube banks, the Sherwood numbers were obviously divided into two regions; one was the data for parallel hollow fibers, and the other was the data for crossed hollow fibers. This indicates that the mass transfer performance of the membrane oxygenator is attributable to the hollow fiber arrangement namely, parallel and crossed hollow fibers, in the same manner as that for heat transfer across tube banks (staggered and in-line bank). New mass transfer correlations have been developed for the membrane oxygenators composed of parallel hollow fibers and crossed hollow fibers. These mass transfer correlations may be used as a guide for the design of a new and efficient membrane oxygenator. (c) 2005 Elsevier B.V. All rights reserved.

Using the derived mass transfer correlations for hollow fibers, hollow fiber arrangements were optimized for an artificial gill that uses an oxygen carrier solution. FC-40, a perfluorocarbon (PFC), was used as the oxygen carrier solution. In the oxygen uptake module, a hollow fiber arrangement with parallel coiled hollow fibers is preferred. The optimum outside diameter of the hollow fibers and the transverse pitch between them are 300 and 500 μ m. respectively. In the oxygen release module, a hollow fiber arrangement of straight parallel hollow fibers is preferred. The optimum outside diameter of the hollow fibers and transverse pitch between them are 300 and 500 μ m, respectively. In the case of humans, the scaling up was estimated from the oxygen transfer rates using these optimum hollow fiber arrangements. The required total membrane surface area is 50.8 m(2), the total delivered pumping energy is 124 W, and the oxygen partial pressure in inspiration is 17.8 kPa. Importantly, the total membrane surface area required was significantly reduced using the modules with an optimum hollow fiber arrangement in comparison with that using connected membrane oxygenators as a gas exchanger. The optimization of hollow fiber arrangements in an artificial gill significantly enhances oxygen transfer from water to air. © 2005 Elsevier B.V. All rights reserved.

We have evaluated the mass transfer performance of four commercially available membrane oxygenators in which the blood path is external to and approximately perpendicular to the fiber bundle. Water flowed outside the hollow fibers as an oxygen carrier medium and substitution for blood, and nitrogen gas flowed inside the hollow fibers. The oxygen transfer rates in the membrane oxygenators were measured, and their mass transfer coefficients were obtained. When we analyzed the mass transfer performance using the theory of heat transfer across tube banks, the Sherwood numbers were obviously divided into two regions; one was the data for parallel hollow fibers, and the other was the data for crossed hollow fibers. This indicates that the mass transfer performance of the membrane oxygenator is attributable to the hollow fiber arrangement namely, parallel and crossed hollow fibers, in the same manner as that for heat transfer across tube banks (staggered and in-line bank). New mass transfer correlations have been developed for the membrane oxygenators composed of parallel hollow fibers and crossed hollow fibers. These mass transfer correlations may be used as a guide for the design of a new and efficient membrane oxygenator. (c) 2005 Elsevier B.V. All rights reserved.

An artificial gill has been developed that transfers oxygen from water to air, using oxo-molybdenum(IV)5,10,15,20-tetramesitylporphyrin ((MoO)-O-IV(tmp)) dissolved in o-xylene as an oxygen carrier solution and the energy of visible light. The oxygen partial pressure in the oxygen carrier solution is changed by photo-irradiation to enhance both the oxygen uptake from water and the oxygen release to air. The ratio of the oxygen mass transfer coefficient of the oxygen carrier solution to that of water is 0.746 for oxygen uptake and 0.654 for oxygen release. In designing a large-scale artificial gill for supplying oxygen to a closed space underwater such as submerged vessel, the required membrane surface area, the seawater flow rate and the reservoir tank volume were 123 m(2), 0.00533 m(3) s(-1), and 5.06 m(3), respectively. These values increased as the oxygen partial pressure of seawater decreased. However, the high partial pressure of oxygen required for human respiration (20.0 kPa) can be provided in a closed space even from seawater with an oxygen partial pressure as low as 10.0 kPa. This newly developed artificial gill may be useful for deep sea activities, such as underwater exploration, marine research and underwater habitation. (C) 2004 Elsevier B.V. All rights reserved.

An artificial gill has been developed that transfers oxygen from water to air, using oxo-molybdenum(IV)5,10,15,20-tetramesitylporphyrin ((MoO)-O-IV(tmp)) dissolved in o-xylene as an oxygen carrier solution and the energy of visible light. The oxygen partial pressure in the oxygen carrier solution is changed by photo-irradiation to enhance both the oxygen uptake from water and the oxygen release to air. The ratio of the oxygen mass transfer coefficient of the oxygen carrier solution to that of water is 0.746 for oxygen uptake and 0.654 for oxygen release. In designing a large-scale artificial gill for supplying oxygen to a closed space underwater such as submerged vessel, the required membrane surface area, the seawater flow rate and the reservoir tank volume were 123 m(2), 0.00533 m(3) s(-1), and 5.06 m(3), respectively. These values increased as the oxygen partial pressure of seawater decreased. However, the high partial pressure of oxygen required for human respiration (20.0 kPa) can be provided in a closed space even from seawater with an oxygen partial pressure as low as 10.0 kPa. This newly developed artificial gill may be useful for deep sea activities, such as underwater exploration, marine research and underwater habitation. (C) 2004 Elsevier B.V. All rights reserved.

Chemiluminescence (CL) of luminol with hydrogen peroxide is useful for the highly sensitive determination of biochemicals by conjugation with oxidase. However, the method has stability problems because reactant-mixing conditions influence the results. However, electrochemiluminescence (ECL) of luminol can be performed on well-mixed solutions of luminol and hydrogen peroxide. ECL has not yet been applied to the quantitative analysis of biochemicals due to low quantum yields at physiological pH. In this work, we evaluated the effect of modifying the electrode with cationic polymer on the ECL intensity of luminol. Transparent indium-tin oxide (ITO) electrode was treated with 1 wt% aqueous solution of polyethyleneimine (MW : 70,000) buffered by 0.1 M borate at pH 8.0. ECL intensity at the ITO electrode was measured in a mixed solution of 1.0 mM luminol and 10-30 muM hydrogen peroxide buffered by phosphate or Tris-HCI (pH 7.4). The electrode potential was applied in alternate pulses of 0.00 V versus Ag/AgCl for 3 s and 1.00 V for 3 s. The sensitivity of ECL to hydrogen peroxide concentration at the treated ITO increased remarkably. Results indicate that the cationic polymer adsorbed on the electrode enhances ECL by increasing pH in the vicinity of the electrode surface. However, the cationic polymer also enhanced inhibition of ECL by ascorbic acid, an anionic reducing reagent.

Chemiluminescence (CL) of luminol with hydrogen peroxide is useful for the highly sensitive determination of biochemicals by conjugation with oxidase. However, the method has stability problems because reactant-mixing conditions influence the results. However, electrochemiluminescence (ECL) of luminol can be performed on well-mixed solutions of luminol and hydrogen peroxide. ECL has not yet been applied to the quantitative analysis of biochemicals due to low quantum yields at physiological pH. In this work, we evaluated the effect of modifying the electrode with cationic polymer on the ECL intensity of luminol. Transparent indium-tin oxide (ITO) electrode was treated with 1 wt% aqueous solution of polyethyleneimine (MW : 70,000) buffered by 0.1 M borate at pH 8.0. ECL intensity at the ITO electrode was measured in a mixed solution of 1.0 mM luminol and 10-30 muM hydrogen peroxide buffered by phosphate or Tris-HCI (pH 7.4). The electrode potential was applied in alternate pulses of 0.00 V versus Ag/AgCl for 3 s and 1.00 V for 3 s. The sensitivity of ECL to hydrogen peroxide concentration at the treated ITO increased remarkably. Results indicate that the cationic polymer adsorbed on the electrode enhances ECL by increasing pH in the vicinity of the electrode surface. However, the cationic polymer also enhanced inhibition of ECL by ascorbic acid, an anionic reducing reagent.

Several cultured cell types are easily detached from poly(N-isopropylacrylamide) (PIPAAm)-grafted surfaces only by reducing culture temperature without traditional proteolytic treatments that might damage certain cell functions. We have exploited these novel surfaces for tissue engineering applications where harvested intact cell sheets are useful for fabricating tissue-like constructs. We now extend the polymer chemistry of such grafted surfaces with new charged co-monomers. Functional carboxylate groups are incorporated into temperature-responsive surfaces with newly designed analogous carboxylate co-monomers, 2-carboxyisopropylacrylamide (CIPAAm) and 3-carboxy-n-propylacrylamide (CNPAAm), which have a small structural difference in the placement of the carboxylate group (iso or normal to the monomer propyl group). P(IPAAm-co-CIPAAm) demonstrates a similar phase transition behavior to that of pure PIPAAm, and the ionic dissociation of carboxyl groups is suppressed (elevated pK'a) even under physiological conditions. By contrast, P(IPAAm-co-CNPAAm) exhibits a higher charge density (lower pK'a), higher hydration, and reduced temperature-sensitivity under identical conditions. Introduction of 5 mol% CNPAAm into PIPAAm grafted surfaces produces no cell attachment under typical cell culture conditions, while identical introductions of CIPAAm into grafted copolymers functions well for cell attachment. Cultured cell spreading efficiency was essentially similar on PIPAAm-grafted surfaces as on copolymer-grafted surfaces with I mol% introduction of either carboxylate co-monomer. Accelerated cell detachment upon reducing culture temperature was observed for the 1 mol% these copolymer-grafted surfaces since polymer hydration and swelling kinetics are enhanced by the increased ionizable moiety in these grafted surfaces. (C) 2004 Elsevier B.V. All rights reserved.

Several cultured cell types are easily detached from poly(N-isopropylacrylamide) (PIPAAm)-grafted surfaces only by reducing culture temperature without traditional proteolytic treatments that might damage certain cell functions. We have exploited these novel surfaces for tissue engineering applications where harvested intact cell sheets are useful for fabricating tissue-like constructs. We now extend the polymer chemistry of such grafted surfaces with new charged co-monomers. Functional carboxylate groups are incorporated into temperature-responsive surfaces with newly designed analogous carboxylate co-monomers, 2-carboxyisopropylacrylamide (CIPAAm) and 3-carboxy-n-propylacrylamide (CNPAAm), which have a small structural difference in the placement of the carboxylate group (iso or normal to the monomer propyl group). P(IPAAm-co-CIPAAm) demonstrates a similar phase transition behavior to that of pure PIPAAm, and the ionic dissociation of carboxyl groups is suppressed (elevated pK'a) even under physiological conditions. By contrast, P(IPAAm-co-CNPAAm) exhibits a higher charge density (lower pK'a), higher hydration, and reduced temperature-sensitivity under identical conditions. Introduction of 5 mol% CNPAAm into PIPAAm grafted surfaces produces no cell attachment under typical cell culture conditions, while identical introductions of CIPAAm into grafted copolymers functions well for cell attachment. Cultured cell spreading efficiency was essentially similar on PIPAAm-grafted surfaces as on copolymer-grafted surfaces with I mol% introduction of either carboxylate co-monomer. Accelerated cell detachment upon reducing culture temperature was observed for the 1 mol% these copolymer-grafted surfaces since polymer hydration and swelling kinetics are enhanced by the increased ionizable moiety in these grafted surfaces. (C) 2004 Elsevier B.V. All rights reserved.

We have developed temperature-responsive cell culture surfaces to harvest intact cell sheets for tissue-engineering applications. Both cost and safety issues (e.g., prions, bovine spongiform encephalopathy) are compelling reasons to avoid use of animal-derived materials, including serum, in such culture. In the present study, synthetic cell-adhesive peptides are immobilized onto temperature-responsive polymer-grafted surfaces, and cell adhesion and detachment under serum-free conditions were examined. The temperature-responsive polymer poly(N-isopropylacrylamide) (PI-PAAm) was functionalized by copolymerization with a reactive comonomer having both a carboxyl group and an isopropylacrylamide group. These copolymers were covalently grafted onto tissue culture-grade polystyrene dishes. Synthetic cell-adhesive peptides were then immobilized onto these surfaces via carboxyl groups. Bovine aortic endothelial cells both adhered and spread on these surfaces even under serum-free conditions at 37degreesC, similar to those in 10% serum-supplemented culture. Spread cells promptly detached from the surfaces on lowering culture temperatures below the lower critical solution temperature of the polymer, 32degreesC. These surfaces would be useful for serum-free culture for tissue-engineering applications.

The mechanism of the change in diffusive permeability of nanometer-ordered thin layers of molecularly imprinted polymer (MIP) in the presence of its template is examined and discussed based on electrostatic interactions. In this work, the theophylline-imprinted copolymer of ethyleneglycol dimethacrylate and methacrylic acid (Theo-MIP) is grafted onto indium-tin oxide (ITO) as an electrode for cyclic voltammetry of ferrocyanide with the grafted ITO, and the permeability of the Theo-MIP is estimated from the faradic current. The permeability is found to decrease with increasing pH, and the change in permeability due to the presence of the template is found to decrease with increasing concentration of the supporting electrolyte. These results indicate that the layer of grafted copolymer swells due to electric repulsion between carboxyl groups, representing a major factor in the gate effect of the Theo-MIP. If the grafted layer is considered to be porous, the porosity of Theo-MIP should increase as the polymer shrinks, and decrease as it swells. The increase in the permeability of the MIP in the presence of the template is therefore due to the increase in porosity due to shrinking.

We have developed temperature-responsive cell culture surfaces to harvest intact cell sheets for tissue-engineering applications. Both cost and safety issues (e.g., prions, bovine spongiform encephalopathy) are compelling reasons to avoid use of animal-derived materials, including serum, in such culture. In the present study, synthetic cell-adhesive peptides are immobilized onto temperature-responsive polymer-grafted surfaces, and cell adhesion and detachment under serum-free conditions were examined. The temperature-responsive polymer poly(N-isopropylacrylamide) (PI-PAAm) was functionalized by copolymerization with a reactive comonomer having both a carboxyl group and an isopropylacrylamide group. These copolymers were covalently grafted onto tissue culture-grade polystyrene dishes. Synthetic cell-adhesive peptides were then immobilized onto these surfaces via carboxyl groups. Bovine aortic endothelial cells both adhered and spread on these surfaces even under serum-free conditions at 37degreesC, similar to those in 10% serum-supplemented culture. Spread cells promptly detached from the surfaces on lowering culture temperatures below the lower critical solution temperature of the polymer, 32degreesC. These surfaces would be useful for serum-free culture for tissue-engineering applications.

The mechanism of the change in diffusive permeability of nanometer-ordered thin layers of molecularly imprinted polymer (MIP) in the presence of its template is examined and discussed based on electrostatic interactions. In this work, the theophylline-imprinted copolymer of ethyleneglycol dimethacrylate and methacrylic acid (Theo-MIP) is grafted onto indium-tin oxide (ITO) as an electrode for cyclic voltammetry of ferrocyanide with the grafted ITO, and the permeability of the Theo-MIP is estimated from the faradic current. The permeability is found to decrease with increasing pH, and the change in permeability due to the presence of the template is found to decrease with increasing concentration of the supporting electrolyte. These results indicate that the layer of grafted copolymer swells due to electric repulsion between carboxyl groups, representing a major factor in the gate effect of the Theo-MIP. If the grafted layer is considered to be porous, the porosity of Theo-MIP should increase as the polymer shrinks, and decrease as it swells. The increase in the permeability of the MIP in the presence of the template is therefore due to the increase in porosity due to shrinking.

Protein adsorption on dialysis membrane was studied by time-of-flight secondary ion mass spectrometry (TOF-SIMS), which is expected to be capable of chemical imaging of insulated samples, such as hollow-fiber dialysis membranes. Three commercially available hollow-fiber dialysis membranes having different pore sizes and structures, were tested in the present study. Bovine serum albumin (BSA) solutions were used to adsorb the protein on the samples. TOF-SIMS images and spectra of native membranes and membranes treated with BSA were compared in order to identify secondary ions related to BSA and membranes. Mutual information, one of applications of information theory, was employed to select fragment ions related to BSA. TOF-SIMS images show distribution of adsorbed BSA on the dialysis membranes and indicate that BSA permeability and interaction between the membranes and BSA definitely depend on pore size, structure and material. (C) 2004 Elsevier B.V. All rights reserved.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is capable of chemical imaging of proteins on insulated samples such as hollow-fiber dialysis membranes. Albumin loss and a lowering of diffusive permeability caused by protein adsorption on dialysis membranes should be reduced in order to enhance dialysis adequacy of the patients. Bovine serum albumin (BSA)adsorbed hollow-fiber dialysis membranes were tested in the present study. TOF-SIMS images and spectra of both native membranes and BSA-adsorbed membranes were compared in order to identify secondary ions related to BSA and membranes. Peaks of secondary ions related to BSA and each membrane were selected by means of information theory, and they are characterized by principal component analysis (PCA). Chemical images of BSA adsorption on both native and treated membranes were obtained to find that BSA permeability and interaction between the membranes and BSA definitely depend on the properties of a membrane. TOF-SIMS imaging obtained with information theory is a powerful tool to estimate protein adsorption on the dialysis membranes. (C) 2004 Elsevier B.V. All rights reserved.

Protein adsorption on dialysis membrane was studied by time-of-flight secondary ion mass spectrometry (TOF-SIMS), which is expected to be capable of chemical imaging of insulated samples, such as hollow-fiber dialysis membranes. Three commercially available hollow-fiber dialysis membranes having different pore sizes and structures, were tested in the present study. Bovine serum albumin (BSA) solutions were used to adsorb the protein on the samples. TOF-SIMS images and spectra of native membranes and membranes treated with BSA were compared in order to identify secondary ions related to BSA and membranes. Mutual information, one of applications of information theory, was employed to select fragment ions related to BSA. TOF-SIMS images show distribution of adsorbed BSA on the dialysis membranes and indicate that BSA permeability and interaction between the membranes and BSA definitely depend on pore size, structure and material. (C) 2004 Elsevier B.V. All rights reserved.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is capable of chemical imaging of proteins on insulated samples such as hollow-fiber dialysis membranes. Albumin loss and a lowering of diffusive permeability caused by protein adsorption on dialysis membranes should be reduced in order to enhance dialysis adequacy of the patients. Bovine serum albumin (BSA)adsorbed hollow-fiber dialysis membranes were tested in the present study. TOF-SIMS images and spectra of both native membranes and BSA-adsorbed membranes were compared in order to identify secondary ions related to BSA and membranes. Peaks of secondary ions related to BSA and each membrane were selected by means of information theory, and they are characterized by principal component analysis (PCA). Chemical images of BSA adsorption on both native and treated membranes were obtained to find that BSA permeability and interaction between the membranes and BSA definitely depend on the properties of a membrane. TOF-SIMS imaging obtained with information theory is a powerful tool to estimate protein adsorption on the dialysis membranes. (C) 2004 Elsevier B.V. All rights reserved.

Polysulfone (PS) dialysis membranes hydrophilized by blending poly vinylpyrrolidone (PVP) are well known to have excellent biocompatibility in clinical use. The objective of the present study is thus to clarify how PVP improves biocompatibility of PS membranes and furthermore to develop a patient-friendly PS dialysis membrane with higher biocompatibility. Biocompatibility based on both lactate dehydrogenase (LDH) activity and amount of protein adsorption was greatly different among four commercially available PS hollow-fiber dialysis membranes. PVP present on the inner surface of the hollow fiber was quantitatively determined by X-ray photoelectron spectroscopy (XPS), demonstrating the amount of PVP to be varying for each membrane. Structure parameters such as surface roughness, three-dimensional surface area and polymer particle diameter, indications of the physicochemical properties of the membranes, were measured on the observed inner surface images in both wet and dry conditions by atomic force microscopy (AFM) to account for dependence of biocompatibility on these structure parameters. The higher regularity polymer particle structure has in the wet condition, the lower wet/dry ratio surface roughness has and the larger wet/dry ratio polymer particle diameter has, that is, the more greatly the polymer particles swell by wetting, the higher biocompatibility is achieved by "cushion effect". (C) 2004 Elsevier B.V. All rights reserved.

Polysulfone (PS) dialysis membranes hydrophilized by blending poly vinylpyrrolidone (PVP) are well known to have excellent biocompatibility in clinical use. The objective of the present study is thus to clarify how PVP improves biocompatibility of PS membranes and furthermore to develop a patient-friendly PS dialysis membrane with higher biocompatibility. Biocompatibility based on both lactate dehydrogenase (LDH) activity and amount of protein adsorption was greatly different among four commercially available PS hollow-fiber dialysis membranes. PVP present on the inner surface of the hollow fiber was quantitatively determined by X-ray photoelectron spectroscopy (XPS), demonstrating the amount of PVP to be varying for each membrane. Structure parameters such as surface roughness, three-dimensional surface area and polymer particle diameter, indications of the physicochemical properties of the membranes, were measured on the observed inner surface images in both wet and dry conditions by atomic force microscopy (AFM) to account for dependence of biocompatibility on these structure parameters. The higher regularity polymer particle structure has in the wet condition, the lower wet/dry ratio surface roughness has and the larger wet/dry ratio polymer particle diameter has, that is, the more greatly the polymer particles swell by wetting, the higher biocompatibility is achieved by "cushion effect". (C) 2004 Elsevier B.V. All rights reserved.

Morphology and solute diffusive permeability of thin layer of molecularly imprinted polymer (MIP) change in the presence of templates, which is termed as "gate effect". To optimize morphological changes induced by the gate effect, the flexibility, density, and the amount of specific binding sites for templates of the MIP-grafted layer must be tightly controlled during radical polymerization. Living radical polymerization with "iniferter" (initiator-transfer agent-terminator) is useful tool for controlling degree of polymerization by reaction time. In this work, photoactive iniferter (benzyl dietyldithiocarbamate) was immobilized on a cellulose membrane via a silane coupler. This treated membrane was grafted with theophylline-imprinted copolymer of methacrylic acid and ethylene glycol dimethacrylate by ultraviolet irradiation. The relationship between the amount of graft copolymer, the degree of the gate effect and the time of UV irradiation was studied. The amount of grafted copolymer increase by repeating polymerization cycle. In addition, the variation of the diffusive permeability by template clearly differs to that by analogue. Therefore, these MIP membranes can discriminate two alkaloids by difference of diffusive permeability. The variation by the template or the analogue and the selectivity of the permeability depended on irradiation time. Those results indicate that synthesized MIP has a "living nature" and the gate effect is feasible to control by irradiation time. Living radical polymerization is a promising method to build sophisticated architecture of MIP membranes possessing self-controllable permeability by gate effect. (C) 2004 Elsevier B.V. All rights reserved.

Morphology and solute diffusive permeability of thin layer of molecularly imprinted polymer (MIP) change in the presence of templates, which is termed as "gate effect". To optimize morphological changes induced by the gate effect, the flexibility, density, and the amount of specific binding sites for templates of the MIP-grafted layer must be tightly controlled during radical polymerization. Living radical polymerization with "iniferter" (initiator-transfer agent-terminator) is useful tool for controlling degree of polymerization by reaction time. In this work, photoactive iniferter (benzyl dietyldithiocarbamate) was immobilized on a cellulose membrane via a silane coupler. This treated membrane was grafted with theophylline-imprinted copolymer of methacrylic acid and ethylene glycol dimethacrylate by ultraviolet irradiation. The relationship between the amount of graft copolymer, the degree of the gate effect and the time of UV irradiation was studied. The amount of grafted copolymer increase by repeating polymerization cycle. In addition, the variation of the diffusive permeability by template clearly differs to that by analogue. Therefore, these MIP membranes can discriminate two alkaloids by difference of diffusive permeability. The variation by the template or the analogue and the selectivity of the permeability depended on irradiation time. Those results indicate that synthesized MIP has a "living nature" and the gate effect is feasible to control by irradiation time. Living radical polymerization is a promising method to build sophisticated architecture of MIP membranes possessing self-controllable permeability by gate effect. (C) 2004 Elsevier B.V. All rights reserved.

We revealed morphology and physicochemical behavior of a widely used powerful hydrophilizing agent, polyvinylpyrrolidone (PVP), present on polysulfone (PS)/PVP films by atomic force microscopy (AFM). This is the first time such clear PS/PVP phase-separated morphology was observed by nanoscopic technique. The film surfaces were observed by the identical observation mode, probe and scanning conditions to reveal the change of PVP morphology and behavior between dry and wet conditions. Morphology was related to biocompatibility by combining AFM data with results of surface element composition, contact angle, adhesion amount of rabbit platelet and relative amount of adsorbed fibrinogen. PVP nano-particles of one or several molecules were formed on the dry PS/PVP film surfaces. Amount of PVP present on the surfaces increased with the molecular weight of PVP. At a mixed amount of 1-5 wt%, PVP K90 formed crowded particles on the dry surface. When wet, they swelled, followed by their union to produce a smooth surface leading to improved biocompatibility. The highest biocompatibility with excellent mechanical strength is achieved by blending the highest molecular weight PVP K90 at 1-5 wt%. (C) 2003 Elsevier Ltd. All rights reserved.

In this study, specific interactions between immobilized RGDS (Arg-Gly-Asp-Ser) cell adhesion peptides and cell integrin receptors located on cell membranes are controlled in vitro using stimuli-responsive polymer surface chemistry. Temperature-responsive poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) (P(IPAAm-co-CIPAAm)) copolymer grafted onto tissue culture grade polystyrene (TCPS) dishes permits RGDS immobilization. These surfaces facilitate the spreading of human umbilical vein endothelial cells (HUVECs) without serum depending on RGDS surface content at 37degreesC (above the lower critical solution temperature, LCST, of the copolymer). Moreover, cells spread on RGDS-immobilized surfaces at 37degreesC detach spontaneously by lowering culture temperature below the LCST as hydrated grafted copolymer chains dissociate immobilized RGDS from cell integrins. These cell lifting behaviors upon hydration are similar to results using soluble RGDS in culture as a competitive substitution for immobilized ligands. Binding of cell integrins to immobilized RGDS on cell culture substrates can be reversed spontaneously using mild environmental stimulation, such as temperature, without enzymatic or chemical treatment. These findings are important for control of specific interactions between proteins and cells, and subsequent "on-off" regulation of their function. Furthermore, the method allows serum-free cell culture and trypsin-free cell harvest, essentially removing mammalian-sourced components from the culture process.

We revealed morphology and physicochemical behavior of a widely used powerful hydrophilizing agent, polyvinylpyrrolidone (PVP), present on polysulfone (PS)/PVP films by atomic force microscopy (AFM). This is the first time such clear PS/PVP phase-separated morphology was observed by nanoscopic technique. The film surfaces were observed by the identical observation mode, probe and scanning conditions to reveal the change of PVP morphology and behavior between dry and wet conditions. Morphology was related to biocompatibility by combining AFM data with results of surface element composition, contact angle, adhesion amount of rabbit platelet and relative amount of adsorbed fibrinogen. PVP nano-particles of one or several molecules were formed on the dry PS/PVP film surfaces. Amount of PVP present on the surfaces increased with the molecular weight of PVP. At a mixed amount of 1-5 wt%, PVP K90 formed crowded particles on the dry surface. When wet, they swelled, followed by their union to produce a smooth surface leading to improved biocompatibility. The highest biocompatibility with excellent mechanical strength is achieved by blending the highest molecular weight PVP K90 at 1-5 wt%. (C) 2003 Elsevier Ltd. All rights reserved.

In this study, specific interactions between immobilized RGDS (Arg-Gly-Asp-Ser) cell adhesion peptides and cell integrin receptors located on cell membranes are controlled in vitro using stimuli-responsive polymer surface chemistry. Temperature-responsive poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) (P(IPAAm-co-CIPAAm)) copolymer grafted onto tissue culture grade polystyrene (TCPS) dishes permits RGDS immobilization. These surfaces facilitate the spreading of human umbilical vein endothelial cells (HUVECs) without serum depending on RGDS surface content at 37degreesC (above the lower critical solution temperature, LCST, of the copolymer). Moreover, cells spread on RGDS-immobilized surfaces at 37degreesC detach spontaneously by lowering culture temperature below the LCST as hydrated grafted copolymer chains dissociate immobilized RGDS from cell integrins. These cell lifting behaviors upon hydration are similar to results using soluble RGDS in culture as a competitive substitution for immobilized ligands. Binding of cell integrins to immobilized RGDS on cell culture substrates can be reversed spontaneously using mild environmental stimulation, such as temperature, without enzymatic or chemical treatment. These findings are important for control of specific interactions between proteins and cells, and subsequent "on-off" regulation of their function. Furthermore, the method allows serum-free cell culture and trypsin-free cell harvest, essentially removing mammalian-sourced components from the culture process.

We have reported a novel method of visualizing endotoxin (Et) distribution inside an Et-blocking filtration membrane using both fluorescence-labeled Et and a confocal laser scanning fluorescence microscope (CLSFM) in our previous paper [J. Membr. Sci. 210 (2002) 45]. The objective of the present study is to clarify Et-blocking mechanism of dialysis membranes. Six kinds of dialysis membranes with varying materials (hydrophilic and hydrophobic) and varying structures (pore diameter, skin layer location and thickness, and water content) were evaluated by CLSFM together with other techniques such as atomic force microscopy (AFM). Physicochemical property of a membrane material affects Et-adsorbing efficiency, and further membrane structure affects Et-plugging efficiency. Rejected Et distribution in the membranes with varying materials and structures is successfully visualized using fluorescence-labeled Et by CLSFM. Et adsorption on the membranes occurs first, followed by the narrowing of their pores, and afterward pore plugging is continued. Adsorption plays a vital role in Et-blocking. Double skin layer structure is valid for preventing of Et contamination than only inner skin layer structure because the double skin layer structure blocks Et more farther from blood-side surfaces than the only inner skin layer structure. (C) 2003 Elsevier Science B.V. All rights reserved.

Cross-linked, thermoresponsive poly(N-isopropylactylamide-co-acrylic acid-co-N-tert-butylacrylamide) [poly(IPAAm-co-AAc-co-tBAAm)] thin hydrogel layers on silica beads were used as new column matrix modifiers for LC separation of basic bioactive peptides, angiotensin subtypes I, II, and III. Terpolymer poly(IPAAm-co-AAc-co-tBAAm) showed both phase transition and apparent carboxylate pK(a) shifts in water, depending on temperature. Polymer-grafted silica bead surfaces exhibited simultaneous thermally modulated changes in hydrophilic/hydrophobic properties and charge densities. More effective separation of angiotensin peptide subtypes was achieved on columns of these terpolymer thin hydrogel grafted surfaces, as compared to an uncharged control binary copolymer of IPAAm and tBAAm. Although hydrophobic interactions effect separation of angiotensin subtypes, combined electrostatic and hydrophobic interaction resulted in more pronounced retention. At temperature below the terpolymer phase transition, hydrophobic interactions predominated, and minimal changes in electrostatic interactions were supported by little shift in the apparent AAc carboxylate pK(a) values. Above the phase transition temperature, electrostatic interactions were dramatically reduced as a result of the decreased charge densities of the polymer grafted surfaces. Therefore, peptide retention times were also reduced, exhibiting a maximum at near 30-35 degreesC. Interestingly, column retention behavior of angiotensins is dramatically modulated by applied step temperature gradients. Thermoresponsive surface property alteration is a very rapid, reversible phenomenon, allowing step temperature gradients on thermoresponsive columns to enable the analogous performance advantages as gradient elution in reversed-phase HPLC. More importantly, injected peptides were recovered completely from the columns from calculation of peak area. In conclusion, these anionic thermoresponsive polymer-modified surfaces are good candidates for improved separation of bioactive peptides under exclusively aqueous conditions.

We have reported a novel method of visualizing endotoxin (Et) distribution inside an Et-blocking filtration membrane using both fluorescence-labeled Et and a confocal laser scanning fluorescence microscope (CLSFM) in our previous paper [J. Membr. Sci. 210 (2002) 45]. The objective of the present study is to clarify Et-blocking mechanism of dialysis membranes. Six kinds of dialysis membranes with varying materials (hydrophilic and hydrophobic) and varying structures (pore diameter, skin layer location and thickness, and water content) were evaluated by CLSFM together with other techniques such as atomic force microscopy (AFM). Physicochemical property of a membrane material affects Et-adsorbing efficiency, and further membrane structure affects Et-plugging efficiency. Rejected Et distribution in the membranes with varying materials and structures is successfully visualized using fluorescence-labeled Et by CLSFM. Et adsorption on the membranes occurs first, followed by the narrowing of their pores, and afterward pore plugging is continued. Adsorption plays a vital role in Et-blocking. Double skin layer structure is valid for preventing of Et contamination than only inner skin layer structure because the double skin layer structure blocks Et more farther from blood-side surfaces than the only inner skin layer structure. (C) 2003 Elsevier Science B.V. All rights reserved.

Cross-linked, thermoresponsive poly(N-isopropylactylamide-co-acrylic acid-co-N-tert-butylacrylamide) [poly(IPAAm-co-AAc-co-tBAAm)] thin hydrogel layers on silica beads were used as new column matrix modifiers for LC separation of basic bioactive peptides, angiotensin subtypes I, II, and III. Terpolymer poly(IPAAm-co-AAc-co-tBAAm) showed both phase transition and apparent carboxylate pK(a) shifts in water, depending on temperature. Polymer-grafted silica bead surfaces exhibited simultaneous thermally modulated changes in hydrophilic/hydrophobic properties and charge densities. More effective separation of angiotensin peptide subtypes was achieved on columns of these terpolymer thin hydrogel grafted surfaces, as compared to an uncharged control binary copolymer of IPAAm and tBAAm. Although hydrophobic interactions effect separation of angiotensin subtypes, combined electrostatic and hydrophobic interaction resulted in more pronounced retention. At temperature below the terpolymer phase transition, hydrophobic interactions predominated, and minimal changes in electrostatic interactions were supported by little shift in the apparent AAc carboxylate pK(a) values. Above the phase transition temperature, electrostatic interactions were dramatically reduced as a result of the decreased charge densities of the polymer grafted surfaces. Therefore, peptide retention times were also reduced, exhibiting a maximum at near 30-35 degreesC. Interestingly, column retention behavior of angiotensins is dramatically modulated by applied step temperature gradients. Thermoresponsive surface property alteration is a very rapid, reversible phenomenon, allowing step temperature gradients on thermoresponsive columns to enable the analogous performance advantages as gradient elution in reversed-phase HPLC. More importantly, injected peptides were recovered completely from the columns from calculation of peak area. In conclusion, these anionic thermoresponsive polymer-modified surfaces are good candidates for improved separation of bioactive peptides under exclusively aqueous conditions.

Based on the enhancement of fluorescein isothiocyanate (FITC) fluorescence caused by reactions between proteins, we developed a reagentless, regenerable and rapid immunosensing system to determine immunoglobulin G (IgG). Fluorescence intensity of the immobilized FITC depends on IgG concentration, ranging from 10 to 50 mug/ml, specifically, even with co-existing proteins. The response time is 30 min during steady-state measurement and is less than a minute during transient measurement. When the FITC-labeled protein A binds to IgG, the surrounding atmosphere of FITC becomes hydrophobic. Since the fluorescence intensity of fluorescent substances generally increases at a hydrophobic environment, FITC fluorescence intensity increases with the concentration of protein A bonding to IgG. This system is regenerable because the fluorescence enhancement repeatedly occurs every time the immobilized fluorescent reagent is immersed in sample solutions. (C) 2003 Elsevier Science B.V. All rights reserved.

An artificial gill was developed using a concentrated hemoglobin solution containing inositol hexaphosphate (IHP), as the oxygen carrier solution, with the oxygen affinity controlled by temperature. Oxygen dissolved in sea water is first taken up from water to the oxygen carrier solution at 293 K. The oxygen carrier solution is then heated and the oxygen is released from the oxygen carrier solution to expired air at 310 K. The enhancement factors of the oxygen carrier solution that indicate its performance were obtained from the oxygen uptake rate and oxygen release rate. The values were approximately 3 at oxygen uptake and 16 at oxygen release. The scale-up for a human being at rest was estimated using these values, and the optimal operating condition was determined. The required membrane surface area for a human being is 63.8 m(2). The oxygen partial pressure of inspiration is 20.7 kPa, adequate for the respiration. These indicate the feasibility of a compact and portable artificial gill device. (C) 2003 Elsevier Science B.V. All rights reserved.

An artificial gill was developed using a concentrated hemoglobin solution containing inositol hexaphosphate (IHP), as the oxygen carrier solution, with the oxygen affinity controlled by temperature. Oxygen dissolved in sea water is first taken up from water to the oxygen carrier solution at 293 K. The oxygen carrier solution is then heated and the oxygen is released from the oxygen carrier solution to expired air at 310 K. The enhancement factors of the oxygen carrier solution that indicate its performance were obtained from the oxygen uptake rate and oxygen release rate. The values were approximately 3 at oxygen uptake and 16 at oxygen release. The scale-up for a human being at rest was estimated using these values, and the optimal operating condition was determined. The required membrane surface area for a human being is 63.8 m(2). The oxygen partial pressure of inspiration is 20.7 kPa, adequate for the respiration. These indicate the feasibility of a compact and portable artificial gill device. (C) 2003 Elsevier Science B.V. All rights reserved.

Acrylic acid (AAc) has been utilized to introduce reactive carboxyl groups to a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm). However, AAc introduction shifts the copolymer phase transition temperatures higher and dampens the steep homopolymer phase transition with increasing AAc content. We previously synthesized 2-carboxyisopropylacrylamide (CIPAAm) having both a similar side chain structure to IPAAm and a functional carboxylate group in order to overcome these shortcomings. In the present study, these copolymers, grafted onto cell culture plastic, were assessed for cell adhesion control using their phase transition. AAc introduction to PIPAAm-grafted surfaces resulted in excessive surface hydration and hindered cell spreading in culture at 37 degreesC. In contrast, CIPAAm-containing copolymer-grafted surfaces exhibited relatively weak hydrophobicity similar to both homopolymer PIPAAm-grafted surfaces as well as commercial ungrafted tissue culture polystyrene dish surfaces. Cells adhered and spread well on these surfaces at 37 degreesC in culture. As observed previously on PIPAAm-grafted surfaces, cells were spontaneously detached from the copolymer-grafted surfaces by reducing culture temperature. Cell detachment was accelerated on the CIPAAm copolymer-grafted surfaces compared to pure IPAAm surfaces, suggesting that hydrophilic carboxyl group microenvironment in the monomer and polymer is important to accelerate grafted surface hydration below the lower critical solution temperature, detaching cells.

Acrylic acid (AAc) has been utilized to introduce reactive carboxyl groups to a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm). However, AAc introduction shifts the copolymer phase transition temperatures higher and dampens the steep homopolymer phase transition with increasing AAc content. We previously synthesized 2-carboxyisopropylacrylamide (CIPAAm) having both a similar side chain structure to IPAAm and a functional carboxylate group in order to overcome these shortcomings. In the present study, these copolymers, grafted onto cell culture plastic, were assessed for cell adhesion control using their phase transition. AAc introduction to PIPAAm-grafted surfaces resulted in excessive surface hydration and hindered cell spreading in culture at 37 degreesC. In contrast, CIPAAm-containing copolymer-grafted surfaces exhibited relatively weak hydrophobicity similar to both homopolymer PIPAAm-grafted surfaces as well as commercial ungrafted tissue culture polystyrene dish surfaces. Cells adhered and spread well on these surfaces at 37 degreesC in culture. As observed previously on PIPAAm-grafted surfaces, cells were spontaneously detached from the copolymer-grafted surfaces by reducing culture temperature. Cell detachment was accelerated on the CIPAAm copolymer-grafted surfaces compared to pure IPAAm surfaces, suggesting that hydrophilic carboxyl group microenvironment in the monomer and polymer is important to accelerate grafted surface hydration below the lower critical solution temperature, detaching cells.

Since the finding Of beta(2)-microglobulin as a causal substance in the carpal tunnel syndrome of chronic hemodialysis patients, removal Of beta(2)-microglobulin has been performed using highly permeable dialysis membranes with larger pores. Such large-pore membranes tend to allow endotoxins (Et), harmful substances contained in dialysate, to enter blood. At present, as a countermeasure, Et-blocking filtration membranes are used to remove Et from dialysate. However, Et removal mechanism by these membranes has not been clarified yet. The objective of this study is thus to visualize distribution of fluorescence-labeled Et trapped inside the polyester-polymer alloy (PEPA) membrane, a widely used Et-blocking filtration membrane using a confocal laser scanning fluorescence microscope (CLSFM). Et were observed mainly in the outer skin layer of the hollow fiber, while some in the void and inner skin layers. No Et were present inside the hollow fiber. In conclusion, we succeeded in visualization of Et distribution inside the Et-blocking filtration membrane using CLSFM. This novel visualization technique may allow evaluation of distribution of Et trapped inside various kinds of Et-blocking filtration membranes. (C) 2002 Elsevier Science B.V. All rights reserved.

Since the finding Of beta(2)-microglobulin as a causal substance in the carpal tunnel syndrome of chronic hemodialysis patients, removal Of beta(2)-microglobulin has been performed using highly permeable dialysis membranes with larger pores. Such large-pore membranes tend to allow endotoxins (Et), harmful substances contained in dialysate, to enter blood. At present, as a countermeasure, Et-blocking filtration membranes are used to remove Et from dialysate. However, Et removal mechanism by these membranes has not been clarified yet. The objective of this study is thus to visualize distribution of fluorescence-labeled Et trapped inside the polyester-polymer alloy (PEPA) membrane, a widely used Et-blocking filtration membrane using a confocal laser scanning fluorescence microscope (CLSFM). Et were observed mainly in the outer skin layer of the hollow fiber, while some in the void and inner skin layers. No Et were present inside the hollow fiber. In conclusion, we succeeded in visualization of Et distribution inside the Et-blocking filtration membrane using CLSFM. This novel visualization technique may allow evaluation of distribution of Et trapped inside various kinds of Et-blocking filtration membranes. (C) 2002 Elsevier Science B.V. All rights reserved.

A new pH-/temperature-responsive poly(N-isopropylacr-ylarnide-co-acrylicacid-co-N-tert-butylacrylamide) (poly(IPAAmco-AAc-co-tBAAm)) hydrogel grafted on silica beads was evaluated as colunm matrix for a cation-exchange thermoresponsive chromatography. The stationary phase showed simultaneous changes in temperature-responsive surface charge density and hydrophobicity by incorporation of anionic AAc and hydrophobic tBAAm into IPAAm sequences, Thermoresponsive polymer property alterations were confirmed by temperature-responsive phase transition and shift in apparent pK(a) values. Catecholamine derivatives were retained on poly (IPAAm-co-AAc-co-tBAAm)-modified column at pH 7.0. Analyte retention was primarily due to the electrostatic interaction. It was noted that the temperature-induced phase transition of poly(IPAAmco-AAc-co-tBAAm) hydrogel layer on the stationary phases was evidenced by the apparent inflection point in van't Hoff plots around 36 degreesC. This suggests that solute interactions should be changed below and above the stationary phase transition temperature, reducing electrostatic interaction above the transition temperature, (C) 2002 Elsevier Science B.V. All rights reserved.

A new pH-/temperature-responsive poly(N-isopropylacr-ylarnide-co-acrylicacid-co-N-tert-butylacrylamide) (poly(IPAAmco-AAc-co-tBAAm)) hydrogel grafted on silica beads was evaluated as colunm matrix for a cation-exchange thermoresponsive chromatography. The stationary phase showed simultaneous changes in temperature-responsive surface charge density and hydrophobicity by incorporation of anionic AAc and hydrophobic tBAAm into IPAAm sequences, Thermoresponsive polymer property alterations were confirmed by temperature-responsive phase transition and shift in apparent pK(a) values. Catecholamine derivatives were retained on poly (IPAAm-co-AAc-co-tBAAm)-modified column at pH 7.0. Analyte retention was primarily due to the electrostatic interaction. It was noted that the temperature-induced phase transition of poly(IPAAmco-AAc-co-tBAAm) hydrogel layer on the stationary phases was evidenced by the apparent inflection point in van't Hoff plots around 36 degreesC. This suggests that solute interactions should be changed below and above the stationary phase transition temperature, reducing electrostatic interaction above the transition temperature, (C) 2002 Elsevier Science B.V. All rights reserved.

Determining pore size distribution is important for characterization of a dialysis membrane. However, conventional microscopic techniques cannot present a sufficient image for determining pore size distribution. In the present study, tapping mode atomic force microscopy (TMAFM) has been shown to be a powerful tool for observing and evaluating the small surface pores of a hollow-fiber dialysis membrane. Sample fixing technique described below and a highly sharpened probe have made it possible to observe small pores on a soft and undulant surface of a dialysis membrane. This is the first time that clear TMAFM images of surface pores of a hollow-fiber dialysis membrane at such high resolution have been presented. Pore diameter was determined by image analysis. Average pore diameter of APS-150 (Asahi-kasei, Japan) determined by TMAFM was compared with those by field emission scanning electron microscopy (FESEM) and by the Hagen-Poiseuille equation. The average pore diameter of APS-150 determined by TMAFM was slightly higher than that by FESEM. The average pore diameter determined by the Hagen-Poiseuille equation was intermediate between values for that of inside and outside surfaces determined by TMAFM. (C) 2002 Elsevier Science B.V. All rights reserved.

Superoxide (O-2(-), one of the reactive oxygen species (ROS)) produced in vivo plays various pathphysiological and physiological roles, and thus it is of great importance and value to evaluate quantitatively dynamic changes in superoxide concentration. We thus aimed at developing a superoxide dismutase (SOD)-immobilized sensor. Using a batch cell, the amount of superoxide produced via oxidation of hypoxanthine by xanthine oxidase (XOD) was quantitatively determined based on the measured electrical current. The peak current increased linearly with hypoxanthine concentration (0-100 muM, r(2) = 0.99). Using a flow cell, the concentration of superoxide produced from the isolated heart of an endotoxin-administered rat was successfully measured. Overall, the new superoxide sensor demonstrated satisfying performance and reproducibility for the tissue-derived superoxide. (C) 2002 Elsevier Science B.V. All rights reserved.

Determining pore size distribution is important for characterization of a dialysis membrane. However, conventional microscopic techniques cannot present a sufficient image for determining pore size distribution. In the present study, tapping mode atomic force microscopy (TMAFM) has been shown to be a powerful tool for observing and evaluating the small surface pores of a hollow-fiber dialysis membrane. Sample fixing technique described below and a highly sharpened probe have made it possible to observe small pores on a soft and undulant surface of a dialysis membrane. This is the first time that clear TMAFM images of surface pores of a hollow-fiber dialysis membrane at such high resolution have been presented. Pore diameter was determined by image analysis. Average pore diameter of APS-150 (Asahi-kasei, Japan) determined by TMAFM was compared with those by field emission scanning electron microscopy (FESEM) and by the Hagen-Poiseuille equation. The average pore diameter of APS-150 determined by TMAFM was slightly higher than that by FESEM. The average pore diameter determined by the Hagen-Poiseuille equation was intermediate between values for that of inside and outside surfaces determined by TMAFM. (C) 2002 Elsevier Science B.V. All rights reserved.

Superoxide (O-2(-), one of the reactive oxygen species (ROS)) produced in vivo plays various pathphysiological and physiological roles, and thus it is of great importance and value to evaluate quantitatively dynamic changes in superoxide concentration. We thus aimed at developing a superoxide dismutase (SOD)-immobilized sensor. Using a batch cell, the amount of superoxide produced via oxidation of hypoxanthine by xanthine oxidase (XOD) was quantitatively determined based on the measured electrical current. The peak current increased linearly with hypoxanthine concentration (0-100 muM, r(2) = 0.99). Using a flow cell, the concentration of superoxide produced from the isolated heart of an endotoxin-administered rat was successfully measured. Overall, the new superoxide sensor demonstrated satisfying performance and reproducibility for the tissue-derived superoxide. (C) 2002 Elsevier Science B.V. All rights reserved.

In a hollow-fiber dialyzer, uremic toxins are removed by diffusion and convection, which are influenced by the dialysate flow patterns in the dialyzer. Recently available high-performance dialyzers have complicated dialysate flow patterns, because both positive filtration and negative filtration occur. The objective of the present study was to evaluate dialysate flow in high-performance dialyzers experimentally. Glass-coated 0.1 mmφ platinum electrodes were used for the electrode counter and the working electrode. A counter electrode was placed at the inlet of the dialyzer, and working electrodes were placed at 20 different positions. A voltage of 0.5V was applied between the counter and the working electrodes with a potentiostat, and after the dialyzer was filled with water purified by reverse osmosis, 0.9% NaCl solution was caused to flow. The time at which the 0.9% NaCl solution reached each working electrode from the counter electrode was then measured at a dialysate-side flow rate of 300ml/min and blood-side flow rates of 0 and 200 ml/min. It was found that in dialyzers with high permeability to pure water, dialysate flow was affected by both positive and negative filtration. A comparison was then made between the experimental results and the results of simulation by the finite element method
at positions at which positive and negative filtration occurred, good agreement was obtained. This method makes possible the experimental evaluation of dialysate flow in a high-performance dialyzer in which positive and negative filtration occur.

In the purification process of hemoglobin (Hb) from red blood cells, we stabilized Hb as carbonylhemoglobin (HbCO) against pasteurization at 60°C. In this study, the process of carbonylation (HBO2 → HbCO) was tested with a membrane oxygenator (CX-II08
membrane area, 0.8m2
maximum circulation rate, 1.21/min) under the conditions of a solution flow rate of 100-1000 ml/min and a CO gas flow rate of 30-100 ml/min. Comparing the overall O2 transfer coefficient of carbonylation with that of deoxygenation (N2 flow) revealed that the resistance to O2 transfer of carbonylation was about 35 times smaller, indicating that carbonylation hindered O2 rebinding (deoxyHb → HbO2). On the other hand, the O2 released in the course of carbonylation hindered carbonylation at the beginning, because rebinding of O2 is competitive with carbonylation. The time required for carbonylation was significantly shortened from 1000 to 150s when the solution flow rate was increased from 50 to 400 ml/min
however, the CO gas flow rate did not affect it very much. Increasing the Hb concentration from 7.5 to 15 g/dl accelerated carbonylation by 1.3 times. Even though further study is necessary to select a suitable polymer membrane to avoid protein adsorption, a membrane oxygenator will be effective for the large-scale carbonylation of Hb as a starting material of HbV in the production process.

In a hollow-fiber dialyzer, uremic toxins are removed by diffusion and convection, which are influenced by the dialysate flow patterns in the dialyzer. Recently available high-performance dialyzers have complicated dialysate flow patterns, because both positive filtration and negative filtration occur. The objective of the present study was to evaluate dialysate flow in high-performance dialyzers experimentally. Glass-coated 0.1 mmφ platinum electrodes were used for the electrode counter and the working electrode. A counter electrode was placed at the inlet of the dialyzer, and working electrodes were placed at 20 different positions. A voltage of 0.5V was applied between the counter and the working electrodes with a potentiostat, and after the dialyzer was filled with water purified by reverse osmosis, 0.9% NaCl solution was caused to flow. The time at which the 0.9% NaCl solution reached each working electrode from the counter electrode was then measured at a dialysate-side flow rate of 300ml/min and blood-side flow rates of 0 and 200 ml/min. It was found that in dialyzers with high permeability to pure water, dialysate flow was affected by both positive and negative filtration. A comparison was then made between the experimental results and the results of simulation by the finite element method
at positions at which positive and negative filtration occurred, good agreement was obtained. This method makes possible the experimental evaluation of dialysate flow in a high-performance dialyzer in which positive and negative filtration occur.

In the purification process of hemoglobin (Hb) from red blood cells, we stabilized Hb as carbonylhemoglobin (HbCO) against pasteurization at 60°C. In this study, the process of carbonylation (HBO2 → HbCO) was tested with a membrane oxygenator (CX-II08
membrane area, 0.8m2
maximum circulation rate, 1.21/min) under the conditions of a solution flow rate of 100-1000 ml/min and a CO gas flow rate of 30-100 ml/min. Comparing the overall O2 transfer coefficient of carbonylation with that of deoxygenation (N2 flow) revealed that the resistance to O2 transfer of carbonylation was about 35 times smaller, indicating that carbonylation hindered O2 rebinding (deoxyHb → HbO2). On the other hand, the O2 released in the course of carbonylation hindered carbonylation at the beginning, because rebinding of O2 is competitive with carbonylation. The time required for carbonylation was significantly shortened from 1000 to 150s when the solution flow rate was increased from 50 to 400 ml/min
however, the CO gas flow rate did not affect it very much. Increasing the Hb concentration from 7.5 to 15 g/dl accelerated carbonylation by 1.3 times. Even though further study is necessary to select a suitable polymer membrane to avoid protein adsorption, a membrane oxygenator will be effective for the large-scale carbonylation of Hb as a starting material of HbV in the production process.

Graft copolymerization of ethyleneglycol dimethacrylate and merthacrylic acid onto cellulosic membrane was performed in the presence and absence of theophylline as the template for imprinting the copolymer molecularly. The effect of the presence of the template on the diffusive permeability of the grafted membrane was estimated by batch-wise dialysis of creatinine. The permeability of the theophylline-imprinted membrane was increased by the presence of theophylline, but was virtually unaffected by caffeine, which is an analogue of theophylline. The permeability of the non-imprinted grafted membrane decreased in the presence of theophylline or caffeine without discrimination. These results indicate that the diffusive permeability of the cellulosic membrane grafted with molecularly imprinted copolymer discriminates between the template and its analogue.

Graft copolymerization of ethyleneglycol dimethacrylate and merthacrylic acid onto cellulosic membrane was performed in the presence and absence of theophylline as the template for imprinting the copolymer molecularly. The effect of the presence of the template on the diffusive permeability of the grafted membrane was estimated by batch-wise dialysis of creatinine. The permeability of the theophylline-imprinted membrane was increased by the presence of theophylline, but was virtually unaffected by caffeine, which is an analogue of theophylline. The permeability of the non-imprinted grafted membrane decreased in the presence of theophylline or caffeine without discrimination. These results indicate that the diffusive permeability of the cellulosic membrane grafted with molecularly imprinted copolymer discriminates between the template and its analogue.

Enhanced hydroxyl radical production in the Fenton reaction with ATP or ADP based on luminol chemiluminescence was clarified. Luminol chemiluminescence intensity increases with the concentration of ATP or ADP due to their influence on the Fenton reagents which produce hydroxyl radicals. Fenton reagents containing hydrogen peroxide and ferrous ion produce hydroxyl radicals which attack luminol and this emits light. The effect of ATP and ADP on the Fenton reaction is detected as luminol CL intensity with a photon counting system. This method allows measurement of ATP or ADP concentration ranging from 0 to 15 mM, which covers the physiological concentration range.

Enhanced hydroxyl radical production in the Fenton reaction with ATP or ADP based on luminol chemiluminescence was clarified. Luminol chemiluminescence intensity increases with the concentration of ATP or ADP due to their influence on the Fenton reagents which produce hydroxyl radicals. Fenton reagents containing hydrogen peroxide and ferrous ion produce hydroxyl radicals which attack luminol and this emits light. The effect of ATP and ADP on the Fenton reaction is detected as luminol CL intensity with a photon counting system. This method allows measurement of ATP or ADP concentration ranging from 0 to 15 mM, which covers the physiological concentration range.

Phosphate ion, which is a cause of metabolic bone disease, is excessively accumulated in the blood of chronic dialysis patients, because many of dialysis membranes have negative charge, which inhibit removal of phosphate ion from their blood. The ability to remove phosphate ion can be evaluated by membrane charge. The electrical charge of the membrane affects the rate of ion permeability, and the phosphate ion is no exception. The membrane charge of sheet dialysis membranes can be readily evaluated by measuring the membrane potential and calculating the effective charge density. Accordingly a study was made of the influence on the phosphate ion permeability exerted by the membrane charge of sheet membranes composed of the same material as the hollow-fiber membranes used in hemodialysis. The diffusive permeability of phosphate ion was greater due to the result that the higher the ionic strength in the solution, the higher the absolute ion mobility. On the other hand, because of their shape, it is impossible to measure the membrane potential of hollow-fiber membranes using conventional techniques, making it difficult to determine the effective charge density. The authors therefore, have proposed a novel technique to enable the measurement of membrane potential in hollow-fiber membranes, and have studied the influence exerted on the phosphate ion permeability by the effective charge density calculated by this technique. The phosphate ion permeability increases when the following situations occur: (1) the smaller the absolute value of effective charge density, (2) the greater the ionic strength of the solution, and (3) the greater the concentration of plasma proteins. This agrees with the theoretical results. By calculating the effective charge density from the membrane potential of the hollow-fiber membranes, as measured by the technique proposed here, it is possible to evaluate the rate of phosphate ion permeability in such membranes. (C) 2001 Elsevier Science B.V. All rights reserved.

A new technique for analysis by means of chemiluminescence (CL) is reported. Conventional CL methods for analysis using a homogeneous catalyst can be unsuitable for stable analysis, because the conditions of mixing of the reactant solutions greatly affects the results. Though, electrochemiluminescence (ECL) is capable of solving this problem, it requires more complicated equipment than CL. A platinum plate-immobilized flow-cell is capable of stably controlling the CL from luminol as in ECL and has the advantage of requiring no electrical equipment. Human serum albumin (HSA) concentrations ranging from 0 to 100 mug ml(-1) in water and in dialysate are measured by means of the CL intensity enhancement of luminol-labeled anti-HSA antibody caused by an antigen-antibody reaction in the presence of hydrogen peroxide using the Pt-immobilized flow-cell. (C) 2001 Elsevier Science B.V. All rights reserved.

Phosphate ion, which is a cause of metabolic bone disease, is excessively accumulated in the blood of chronic dialysis patients, because many of dialysis membranes have negative charge, which inhibit removal of phosphate ion from their blood. The ability to remove phosphate ion can be evaluated by membrane charge. The electrical charge of the membrane affects the rate of ion permeability, and the phosphate ion is no exception. The membrane charge of sheet dialysis membranes can be readily evaluated by measuring the membrane potential and calculating the effective charge density. Accordingly a study was made of the influence on the phosphate ion permeability exerted by the membrane charge of sheet membranes composed of the same material as the hollow-fiber membranes used in hemodialysis. The diffusive permeability of phosphate ion was greater due to the result that the higher the ionic strength in the solution, the higher the absolute ion mobility. On the other hand, because of their shape, it is impossible to measure the membrane potential of hollow-fiber membranes using conventional techniques, making it difficult to determine the effective charge density. The authors therefore, have proposed a novel technique to enable the measurement of membrane potential in hollow-fiber membranes, and have studied the influence exerted on the phosphate ion permeability by the effective charge density calculated by this technique. The phosphate ion permeability increases when the following situations occur: (1) the smaller the absolute value of effective charge density, (2) the greater the ionic strength of the solution, and (3) the greater the concentration of plasma proteins. This agrees with the theoretical results. By calculating the effective charge density from the membrane potential of the hollow-fiber membranes, as measured by the technique proposed here, it is possible to evaluate the rate of phosphate ion permeability in such membranes. (C) 2001 Elsevier Science B.V. All rights reserved.

A new technique for analysis by means of chemiluminescence (CL) is reported. Conventional CL methods for analysis using a homogeneous catalyst can be unsuitable for stable analysis, because the conditions of mixing of the reactant solutions greatly affects the results. Though, electrochemiluminescence (ECL) is capable of solving this problem, it requires more complicated equipment than CL. A platinum plate-immobilized flow-cell is capable of stably controlling the CL from luminol as in ECL and has the advantage of requiring no electrical equipment. Human serum albumin (HSA) concentrations ranging from 0 to 100 mug ml(-1) in water and in dialysate are measured by means of the CL intensity enhancement of luminol-labeled anti-HSA antibody caused by an antigen-antibody reaction in the presence of hydrogen peroxide using the Pt-immobilized flow-cell. (C) 2001 Elsevier Science B.V. All rights reserved.

Cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (poly(IPAAm-co-AAc))-grafted silica bead surfaces mere prepared and applied as new column matric; materials that exploit temperature-responsive anionic chromatography to separate basic bioactive compounds,specifically catecholamine derivatives,in aqueous mobile phases. Since poly(IPAAm-co-AAc); has a well-known temperature-responsive phase transition and apparent pK(a) shift, polymer-grafted silica bead surfaces are expected to exhibit simultaneous hydrophilic/hydrophobic and charge density alterations under thermal stimuli. Elution behavior of catecholamine derivatives from a copolymer-modified head packed column was monitored using aqueous mobile-phase HPLC under varying temperature and pH, Catecholamine derivatives had higher retention times on poly(IPAAm-co-AAc) columns at higher pH in comparison with those or, noncharged PIPAAm reference columns, suggesting an electrostatic interaction as a separation mode. Temperature also affected the retention behavior of catecholamine derivatives. Optimal separation of four catecholamine derivatives aas achieved at elevated temperature, 50 degreesC, and at pH 7.0. This is due to the increased hydrophobicity of the stationary phase as evidenced by the elution of a nonionic hydrophobic steroid. From these results, mutual influences of both electrostatic and hydrophobic interactions between basic catecholamine derivatives and pH-/temperature-responsive surfaces are noted. Consequently, elution of weakly charged bioactive compounds is readily regulated through the modulation of stationary-phase thermoresponsive hydrophilic/hydrophobic and charge density changes.

Cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (poly(IPAAm-co-AAc))-grafted silica bead surfaces mere prepared and applied as new column matric; materials that exploit temperature-responsive anionic chromatography to separate basic bioactive compounds,specifically catecholamine derivatives,in aqueous mobile phases. Since poly(IPAAm-co-AAc); has a well-known temperature-responsive phase transition and apparent pK(a) shift, polymer-grafted silica bead surfaces are expected to exhibit simultaneous hydrophilic/hydrophobic and charge density alterations under thermal stimuli. Elution behavior of catecholamine derivatives from a copolymer-modified head packed column was monitored using aqueous mobile-phase HPLC under varying temperature and pH, Catecholamine derivatives had higher retention times on poly(IPAAm-co-AAc) columns at higher pH in comparison with those or, noncharged PIPAAm reference columns, suggesting an electrostatic interaction as a separation mode. Temperature also affected the retention behavior of catecholamine derivatives. Optimal separation of four catecholamine derivatives aas achieved at elevated temperature, 50 degreesC, and at pH 7.0. This is due to the increased hydrophobicity of the stationary phase as evidenced by the elution of a nonionic hydrophobic steroid. From these results, mutual influences of both electrostatic and hydrophobic interactions between basic catecholamine derivatives and pH-/temperature-responsive surfaces are noted. Consequently, elution of weakly charged bioactive compounds is readily regulated through the modulation of stationary-phase thermoresponsive hydrophilic/hydrophobic and charge density changes.

A measurement without the influence of protein adsorption on the sensor surface has been developed using transient current of an enzyme-immobilized electrode. Response current decreases due to protein adsorption on the sensor surface and the enzyme-immobilized membrane causing glucose concentration gradient. By measuring glucose concentration in the transient state while controlling GOD activity, it is possible to prevent the influence of protein adsorption. A needle-type electrode glucose sensor on which enzyme is immobilized with a polyurethane membrane, with electrochemical on-off control of enzyme activity, is capable of accurate measurement of glucose concentration in bovine serum at least for 24 hrs.

A measurement without the influence of protein adsorption on the sensor surface has been developed using transient current of an enzyme-immobilized electrode. Response current decreases due to protein adsorption on the sensor surface and the enzyme-immobilized membrane causing glucose concentration gradient. By measuring glucose concentration in the transient state while controlling GOD activity, it is possible to prevent the influence of protein adsorption. A needle-type electrode glucose sensor on which enzyme is immobilized with a polyurethane membrane, with electrochemical on-off control of enzyme activity, is capable of accurate measurement of glucose concentration in bovine serum at least for 24 hrs.

Development of an artificial gill, for the uptake of oxygen from water to air, requires an increase in oxygen transfer rate. In the present study, oxygen transfer rate was enhanced using a washed red blood cell suspension as a thermo-responsive oxygen carrier solution, which changes oxygen affinity with temperature. Oxygen dissolved in water first combined with the oxygen carrier solution at a low temperature using a membrane module. The oxygen carrier solution was then heated to release oxygen into the air using a second membrane module. The water flow rate required to sustain a human being at rest was greatly reduced by heating the oxygen carrier solution due to increase in the limit of the oxygen partial pressure of water of which can be transferred, compared with when oxygen was transferred directly from water. The required membrane surface area is 225 m(2), sufficient for the development of a compact artificial gill. (C) 2001 Elsevier Science B.V. All rights reserved.

Development of an artificial gill, for the uptake of oxygen from water to air, requires an increase in oxygen transfer rate. In the present study, oxygen transfer rate was enhanced using a washed red blood cell suspension as a thermo-responsive oxygen carrier solution, which changes oxygen affinity with temperature. Oxygen dissolved in water first combined with the oxygen carrier solution at a low temperature using a membrane module. The oxygen carrier solution was then heated to release oxygen into the air using a second membrane module. The water flow rate required to sustain a human being at rest was greatly reduced by heating the oxygen carrier solution due to increase in the limit of the oxygen partial pressure of water of which can be transferred, compared with when oxygen was transferred directly from water. The required membrane surface area is 225 m(2), sufficient for the development of a compact artificial gill. (C) 2001 Elsevier Science B.V. All rights reserved.

Molecular imprinting is a new technology for the synthesis of polymers with antibody-like specificity, which art: potentially useful in sensing or separation devices. Here, we report that a thin layer of molecularly-imprinted copolymer exhibits an increase in its diffusive permeability in the presence of its template. A thin layer of molecularly-imprinted poly(methacrylic acid-co-ethyleneglycol dimethacrylate) of theophylline was observed to form on the surface of electrically conductive indium-tin oxide (ITO) him. Cyclic voltammetry of ferrocyanide was performed using the copolymer-grafted ITO as a working electrode in the presence and absence of the template. The presence of the template was found to enhance the anodic current remarkably, which suggests that the diffusive permeability of the thin layer of the molecularly-imprinted polymer (MIP) is sensitive to the presence of its template molecule. This idea is supported by atomic force microscopy (AFM) in which the surface porosity of the layer of the MIP was observed to increased in the presence of its template. We conclude that the structure and diffusive permeability of a thin layer of molecularly-imprinted poly(methacrylic acid-co-ethyleneglycol dimethacrylate) enables this system to be used as a sensor for a given template, (C) 2001 Elsevier Science B.V. All rights reserved.

Aqueous gel deswelling rates for copolymer hydrogels comprising N-isopro-pylacrylamide (IPAAm) and 2-carboxyisopropylacrylamide (CIPAAm) in response to increasing temperatures were investigated. Compared with pure IPAAm-based gels, IPAAm-CIPAAm gels shrink very rapidly in response to small temperature increases across their lower critical solution temperature (their volume is reduced by five-sixths within 60 s). Shrinking rates for these hydrogels increase with increasing CIPAAm content. In contrast, structurally analogous IPAAm-acrylic acid (AAc) copolymer gels lose their temperature sensitivity with the introduction of only a few mole percent of AAc. Additionally, deswelling rates of IPAAm-AAc gels decrease with increasing AAc content. These results indicate that IPAAm-CIPAAm copolymer gels behave distinctly from IPAAm-AAc systems even if both comonomers, CIPAAm and AAc, possess carboxylic acid groups. Thus, we propose that the sensitive deswelling behavior for lPAAm-CIPAAm gels results from strong hydrophobic chain aggregation maintained between network polymer chains due to the similar chemical structures of CIPAAm and IPAAm. This structural homology facilitates aggregation of chain isopropylamide groups for both IPAAm and CIPAAm sequences with increasing temperature. The incorporation of AAc, however, shows no structural homology to IPAAm, inhibiting chain aggregation and limiting collapse. A functionalized temperature-sensitive poly(N-isopropylacrylamide) hydrogel containing carboxylic acid groups is possible with CIPAAm, producing rapid and large volume changes in response to smaller temperature changes. (C) 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 335-342, 2001.

Molecular imprinting is a new technology for the synthesis of polymers with antibody-like specificity, which art: potentially useful in sensing or separation devices. Here, we report that a thin layer of molecularly-imprinted copolymer exhibits an increase in its diffusive permeability in the presence of its template. A thin layer of molecularly-imprinted poly(methacrylic acid-co-ethyleneglycol dimethacrylate) of theophylline was observed to form on the surface of electrically conductive indium-tin oxide (ITO) him. Cyclic voltammetry of ferrocyanide was performed using the copolymer-grafted ITO as a working electrode in the presence and absence of the template. The presence of the template was found to enhance the anodic current remarkably, which suggests that the diffusive permeability of the thin layer of the molecularly-imprinted polymer (MIP) is sensitive to the presence of its template molecule. This idea is supported by atomic force microscopy (AFM) in which the surface porosity of the layer of the MIP was observed to increased in the presence of its template. We conclude that the structure and diffusive permeability of a thin layer of molecularly-imprinted poly(methacrylic acid-co-ethyleneglycol dimethacrylate) enables this system to be used as a sensor for a given template, (C) 2001 Elsevier Science B.V. All rights reserved.

Aqueous gel deswelling rates for copolymer hydrogels comprising N-isopro-pylacrylamide (IPAAm) and 2-carboxyisopropylacrylamide (CIPAAm) in response to increasing temperatures were investigated. Compared with pure IPAAm-based gels, IPAAm-CIPAAm gels shrink very rapidly in response to small temperature increases across their lower critical solution temperature (their volume is reduced by five-sixths within 60 s). Shrinking rates for these hydrogels increase with increasing CIPAAm content. In contrast, structurally analogous IPAAm-acrylic acid (AAc) copolymer gels lose their temperature sensitivity with the introduction of only a few mole percent of AAc. Additionally, deswelling rates of IPAAm-AAc gels decrease with increasing AAc content. These results indicate that IPAAm-CIPAAm copolymer gels behave distinctly from IPAAm-AAc systems even if both comonomers, CIPAAm and AAc, possess carboxylic acid groups. Thus, we propose that the sensitive deswelling behavior for lPAAm-CIPAAm gels results from strong hydrophobic chain aggregation maintained between network polymer chains due to the similar chemical structures of CIPAAm and IPAAm. This structural homology facilitates aggregation of chain isopropylamide groups for both IPAAm and CIPAAm sequences with increasing temperature. The incorporation of AAc, however, shows no structural homology to IPAAm, inhibiting chain aggregation and limiting collapse. A functionalized temperature-sensitive poly(N-isopropylacrylamide) hydrogel containing carboxylic acid groups is possible with CIPAAm, producing rapid and large volume changes in response to smaller temperature changes. (C) 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 335-342, 2001.

Blood and dialysate flow patterns in hollow-fiber dialyzers are complicated, and hence the flow patterns and mass transfer are difficult to analyze theoretically. Consequently, dialyzers are usually developed by a trial-and-error method. We attempt to design dialyzers by computer simulation analysis in this work. Blood-side and dialysate-side flows were modeled using the Hagen-Poiseuille equation and the Blake-Kozeny equation, respectively. These flow patterns were evaluated as pressure drop and velocity distribution. The mass transfer rate was evaluated as solute clearance. Computed values of the pressure drops and clearance for urea and vitamin B12 were found to agree closely with those obtained experimentally. We evaluated the influences of the inner diameter of hollow fibers, module geometry, and void fraction on the pressure drop and clearance, and computer-aided design was performed.

Blood and dialysate flow patterns in hollow-fiber dialyzers are complicated, and hence the flow patterns and mass transfer are difficult to analyze theoretically. Consequently, dialyzers are usually developed by a trial-and-error method. We attempt to design dialyzers by computer simulation analysis in this work. Blood-side and dialysate-side flows were modeled using the Hagen-Poiseuille equation and the Blake-Kozeny equation, respectively. These flow patterns were evaluated as pressure drop and velocity distribution. The mass transfer rate was evaluated as solute clearance. Computed values of the pressure drops and clearance for urea and vitamin B12 were found to agree closely with those obtained experimentally. We evaluated the influences of the inner diameter of hollow fibers, module geometry, and void fraction on the pressure drop and clearance, and computer-aided design was performed.

Effects of hollow fiber packing fraction on gas transfer rate, blood pressure drop and blood flow characteristics of an intravascular oxygenator (IVOX) were evaluated by in vitro experiments. An IVOX module was prepared by packing hollow fiber membranes, of which packing fraction ranged from 0.056 to 0.338, in a pipe corresponding to vena cava. Overall mass transfer coefficients for oxygen and carbon dioxide were evaluated using water, and gas transfer rates through blood were estimated. Blood flow in the IVOX was evaluated by both pulse response method and electrode method. Blood flow was not uniform and depended on the hollow fiber packing fraction. Easy-flow channels between vascular wall and bundle of the hollow fibers were produced and stagnation of blood flow occurred in the bundle of the hollow fibers at the blood inlet. More uniform blood flow was obtained by optimizing the hollow fiber packing fraction. With respect to gas transfer rate, blood pressure drop and uniformity of the blood how the optimum hollow fiber packing fraction was approximately 0.28 when the outside diameter of the hollow fiber was 300 mum. Effect of inner diameter of the hollow fibers was also evaluated, demonstrating that reduction in the inner;diameter was an effective way to increase oxygen transfer rate. (C) 2000 Elsevier Science B.V. All rights reserved.

Effects of hollow fiber packing fraction on gas transfer rate, blood pressure drop and blood flow characteristics of an intravascular oxygenator (IVOX) were evaluated by in vitro experiments. An IVOX module was prepared by packing hollow fiber membranes, of which packing fraction ranged from 0.056 to 0.338, in a pipe corresponding to vena cava. Overall mass transfer coefficients for oxygen and carbon dioxide were evaluated using water, and gas transfer rates through blood were estimated. Blood flow in the IVOX was evaluated by both pulse response method and electrode method. Blood flow was not uniform and depended on the hollow fiber packing fraction. Easy-flow channels between vascular wall and bundle of the hollow fibers were produced and stagnation of blood flow occurred in the bundle of the hollow fibers at the blood inlet. More uniform blood flow was obtained by optimizing the hollow fiber packing fraction. With respect to gas transfer rate, blood pressure drop and uniformity of the blood how the optimum hollow fiber packing fraction was approximately 0.28 when the outside diameter of the hollow fiber was 300 mum. Effect of inner diameter of the hollow fibers was also evaluated, demonstrating that reduction in the inner;diameter was an effective way to increase oxygen transfer rate. (C) 2000 Elsevier Science B.V. All rights reserved.

Introduction of significant quantities of functional carboxyl groups into temperature-responsive poly(N-isopropylacrylamide) (PIPAAm) hydrogels without compromising their intrinsic temperature sensitivity has proven difficult. We have overcome this problem by incorporating the newly synthesized 2-carboxyisopropylacrylamide (CIPAAm) monomer, with a side chain structure similar to N-isopropylacrylamide (IPAAm). Hydrogels containing more than 10 mol % CIPAAm exhibit large and sensitive volume phase transitions in response to temperature changes. These volume phase transition temperatures were nearly identical to that seen for IPAAm homopolymer gels. This is in contrast to IPAAm-acrylic acid (AAc) copolymer gels whose phase transition temperatures increase with reduced magnitudes of phase transitions with increasing AAc content. Moreover, volume phase transition temperatures and transition magnitudes for IPAAm-CIPAAm gels were not influenced by solution pH, which significantly influences the IPAAm-AAc gel. These results indicate that IPAAm-CIPAAm gels maintain their hydrophobic aggregation forces without disruption by ionized or hydrogen-bonded carboxyl groups. Because of the common carboxyl functionality and the noted apparent differences between the structures of CIPAAm and AAc monomers, differences in respective gel behaviors were rationalized to result from the structural analogy of CIPAAm's isopropylamide side chain groups with those of IPAAm. We therefore propose that maintaining alignment of isopropylamide side chains within the copolymer facilitates introduction of large amounts of functional groups into IPAAm copolymer gels without loss of phase transition behavior. The new monomer, CIPAAm, should prove useful to introduce functional carboxyl groups into temperature-responsive IPAAm hydrogels while maintaining their intrinsic temperature-sensitive behavior.

Introduction of significant quantities of functional carboxyl groups into temperature-responsive poly(N-isopropylacrylamide) (PIPAAm) hydrogels without compromising their intrinsic temperature sensitivity has proven difficult. We have overcome this problem by incorporating the newly synthesized 2-carboxyisopropylacrylamide (CIPAAm) monomer, with a side chain structure similar to N-isopropylacrylamide (IPAAm). Hydrogels containing more than 10 mol % CIPAAm exhibit large and sensitive volume phase transitions in response to temperature changes. These volume phase transition temperatures were nearly identical to that seen for IPAAm homopolymer gels. This is in contrast to IPAAm-acrylic acid (AAc) copolymer gels whose phase transition temperatures increase with reduced magnitudes of phase transitions with increasing AAc content. Moreover, volume phase transition temperatures and transition magnitudes for IPAAm-CIPAAm gels were not influenced by solution pH, which significantly influences the IPAAm-AAc gel. These results indicate that IPAAm-CIPAAm gels maintain their hydrophobic aggregation forces without disruption by ionized or hydrogen-bonded carboxyl groups. Because of the common carboxyl functionality and the noted apparent differences between the structures of CIPAAm and AAc monomers, differences in respective gel behaviors were rationalized to result from the structural analogy of CIPAAm's isopropylamide side chain groups with those of IPAAm. We therefore propose that maintaining alignment of isopropylamide side chains within the copolymer facilitates introduction of large amounts of functional groups into IPAAm copolymer gels without loss of phase transition behavior. The new monomer, CIPAAm, should prove useful to introduce functional carboxyl groups into temperature-responsive IPAAm hydrogels while maintaining their intrinsic temperature-sensitive behavior.

Collagen gel was prepared by an ordinary method as that used for preparing a cell-culture medium from an aqueous type-1 atelocollagen solution through crosslinking with glutaraldehyde (GA). Solute diffusivity in the gels prepared in the different conditions was discussed, being related to their water content. The water content of the gel decreased with increasing GA concentration at crosslinking but the solute diffusivity in the gel hardly changed. On the other hand, collagen concentration, at crosslinking of the collagen solution, dramatically affected the solute diffusivity of the obtained gel, although the water content of the gel was not changed and maintained at higher value around 0.9. The inconsistency suggested that the gel had a heterogeneous microstructure although the content of the gel was almost water. This result suggests that the process to prepare collagen medium for cell culture affects cell growth in the case that mass transfer is dominant. (C) 2000 Elsevier Science S.A. All rights reserved.

Collagen gel was prepared by an ordinary method as that used for preparing a cell-culture medium from an aqueous type-1 atelocollagen solution through crosslinking with glutaraldehyde (GA). Solute diffusivity in the gels prepared in the different conditions was discussed, being related to their water content. The water content of the gel decreased with increasing GA concentration at crosslinking but the solute diffusivity in the gel hardly changed. On the other hand, collagen concentration, at crosslinking of the collagen solution, dramatically affected the solute diffusivity of the obtained gel, although the water content of the gel was not changed and maintained at higher value around 0.9. The inconsistency suggested that the gel had a heterogeneous microstructure although the content of the gel was almost water. This result suggests that the process to prepare collagen medium for cell culture affects cell growth in the case that mass transfer is dominant. (C) 2000 Elsevier Science S.A. All rights reserved.

Poly(ethylene glycol) (PEG) and a hydrophobic-hydrophilic microdomain structured block copolymer comprising poly(2-hydroxyethyl methacrylate) and polystyrene (HEMA-St) have been reported to show good blood compatibility owing to inhibition of platelet activation. By using a computer-assisted novel technique to analyze platelet behavior on the surfaces, we found two different mechanisms to prevent platelet adhesion. Platelets were prevented from adhesion and spreading on the microdomain surface and retained cell movement for a long time. The platelet movement velocity was not significantly different between PEG-grafted surfaces and HEMA-SI block copolymer-cast surfaces. However, platelet motion was qualitatively different. Platelets on HEMA-St block copolymer-cast surfaces moved with rolling, spinning, and vibrating, whereas platelet movement was limited to oscillatory vibration on PEG-grafted surfaces. When platelets were treated with NaN3, an adenosine triphosphate (ATP) synthesis inhibitor, before contacting the surfaces, platelets movement velocity was decreased only on HEMA-St block copolymer-cast surfaces. Such an inhibitory effect was hardly observed with platelets on PEG-grafted surfaces. We propose two different mechanisms to prevent platelet adhesion onto surfaces. One is ATP-independent as observed with PEG, and the other is ATP-dependent for HEMA-St block copolymer, where platelets consume ATP to prevent adhesion. (C) 2000 John Wiley & Sons, Inc.

Poly(ethylene glycol) (PEG) and a hydrophobic-hydrophilic microdomain structured block copolymer comprising poly(2-hydroxyethyl methacrylate) and polystyrene (HEMA-St) have been reported to show good blood compatibility owing to inhibition of platelet activation. By using a computer-assisted novel technique to analyze platelet behavior on the surfaces, we found two different mechanisms to prevent platelet adhesion. Platelets were prevented from adhesion and spreading on the microdomain surface and retained cell movement for a long time. The platelet movement velocity was not significantly different between PEG-grafted surfaces and HEMA-SI block copolymer-cast surfaces. However, platelet motion was qualitatively different. Platelets on HEMA-St block copolymer-cast surfaces moved with rolling, spinning, and vibrating, whereas platelet movement was limited to oscillatory vibration on PEG-grafted surfaces. When platelets were treated with NaN3, an adenosine triphosphate (ATP) synthesis inhibitor, before contacting the surfaces, platelets movement velocity was decreased only on HEMA-St block copolymer-cast surfaces. Such an inhibitory effect was hardly observed with platelets on PEG-grafted surfaces. We propose two different mechanisms to prevent platelet adhesion onto surfaces. One is ATP-independent as observed with PEG, and the other is ATP-dependent for HEMA-St block copolymer, where platelets consume ATP to prevent adhesion. (C) 2000 John Wiley & Sons, Inc.

We evaluated effects of the number of tied hollow fibers of an outside blood flow membrane oxygenator with cross-wound hollow fibers on the blood flow pattern and oxygen transfer rate. The number of tied hollow fibers in a bundle was varied from one to six, and the blood flow pattern was observed by X-ray computed tomography. The oxygen transfer rate and blood pressure drop were measured by in vitro experiments using bovine blood. Uniform blood flow patterns were obtained for each number of tied hollow fibers. A decrease in the number of tied hollow fibers caused more effective contact of blood with the tied hollow fibers and oxygen transfer rate was enhanced, demonstrating that single hollow fiber was the most effective. Empirical equations were obtained based on these results and optimum structure parameters of the membrane oxygenator were determined by simulation analysis. Optimum membrane surface area and axial jacket length of the oxygenator were 3.0 m(2) and 320 mm, respectively, at a hollow fiber outside diameter of 250 mu m. (C) 2000 Elsevier Science B.V. All rights reserved.

We evaluated effects of the number of tied hollow fibers of an outside blood flow membrane oxygenator with cross-wound hollow fibers on the blood flow pattern and oxygen transfer rate. The number of tied hollow fibers in a bundle was varied from one to six, and the blood flow pattern was observed by X-ray computed tomography. The oxygen transfer rate and blood pressure drop were measured by in vitro experiments using bovine blood. Uniform blood flow patterns were obtained for each number of tied hollow fibers. A decrease in the number of tied hollow fibers caused more effective contact of blood with the tied hollow fibers and oxygen transfer rate was enhanced, demonstrating that single hollow fiber was the most effective. Empirical equations were obtained based on these results and optimum structure parameters of the membrane oxygenator were determined by simulation analysis. Optimum membrane surface area and axial jacket length of the oxygenator were 3.0 m(2) and 320 mm, respectively, at a hollow fiber outside diameter of 250 mu m. (C) 2000 Elsevier Science B.V. All rights reserved.

Interactions between a temperature-responsive poly(N-isopropylacrylamide)-grafted surface and blood platelets have been analyzed with computerized image analysis. Platelet behavior on this surface is dramatically dependent upon temperature in contrast to that on poly(ethylene glycol) (PEG)-grafted surfaces or polystyrene. The poly(N-isopropylacrylamide)-grafted surface interacts with platelets similarly as the poly(ethylene glycol)-rafted surface at 18 degrees C at 37 degrees C, platelets readily adhere onto the poly(N-isopropylacrylamide)-grafted surface similarly as to that of polystyrene.

Interactions between a temperature-responsive poly(N-isopropylacrylamide)-grafted surface and blood platelets have been analyzed with computerized image analysis. Platelet behavior on this surface is dramatically dependent upon temperature in contrast to that on poly(ethylene glycol) (PEG)-grafted surfaces or polystyrene. The poly(N-isopropylacrylamide)-grafted surface interacts with platelets similarly as the poly(ethylene glycol)-rafted surface at 18 degrees C at 37 degrees C, platelets readily adhere onto the poly(N-isopropylacrylamide)-grafted surface similarly as to that of polystyrene.

To introduce reactive groups into temperature-responsive polymeric chains of poly(N-isopropylacrylamide) (PIPAAm), IPAAm is copolymerized with other monomer such as acrylic acid (AAc). IPAAm homopolymer exhibited temperature-responsive properties and phase transition at 32 degrees C, however, the lower critical solution temperature (LCST) of the IPAAm-AAc copolymer shifts to a higher temperature and the phase transition becomes insensitive with increasing,AAc content. To achieve a useful bifunctional copolymer containing both reactivity and temperature-sensitivity, we assumed that the homopolymer-like structure in the polymer chain would be required to maintain a sensitive temperature response with functional groups. Therefore, we designed a reactive monomer, 2-carboxyisopropylacrylamide (CIPAAm), and investigated its copolymerization with IPAAm. The important characteristic of the poly(IPAAm-co-CIPAAm) structure is that it was composed of the same polymer backbone and isopropylamide groups and some additional carboxyl groups. The transmittance measurement of the polymer aqueous solution revealed that phase transition of IPAAm-co-CIPAAm random copolymer occurred within a very narrow temperature range in pH 6.4, 7.4, and also even 9.0 phosphate buffered solution. These profiles were almost same as that of IPAAm homopolymer. While, under the same conditions, phase transition properties of poly(IPAAm-co-AAc)s solution were considerably influenced by small AAc content. We succeeded with the preparation of bifunctional polymer that possessed reactive functional groups and very sensitive response to temperature change.

To introduce reactive groups into temperature-responsive polymeric chains of poly(N-isopropylacrylamide) (PIPAAm), IPAAm is copolymerized with other monomer such as acrylic acid (AAc). IPAAm homopolymer exhibited temperature-responsive properties and phase transition at 32 degrees C, however, the lower critical solution temperature (LCST) of the IPAAm-AAc copolymer shifts to a higher temperature and the phase transition becomes insensitive with increasing,AAc content. To achieve a useful bifunctional copolymer containing both reactivity and temperature-sensitivity, we assumed that the homopolymer-like structure in the polymer chain would be required to maintain a sensitive temperature response with functional groups. Therefore, we designed a reactive monomer, 2-carboxyisopropylacrylamide (CIPAAm), and investigated its copolymerization with IPAAm. The important characteristic of the poly(IPAAm-co-CIPAAm) structure is that it was composed of the same polymer backbone and isopropylamide groups and some additional carboxyl groups. The transmittance measurement of the polymer aqueous solution revealed that phase transition of IPAAm-co-CIPAAm random copolymer occurred within a very narrow temperature range in pH 6.4, 7.4, and also even 9.0 phosphate buffered solution. These profiles were almost same as that of IPAAm homopolymer. While, under the same conditions, phase transition properties of poly(IPAAm-co-AAc)s solution were considerably influenced by small AAc content. We succeeded with the preparation of bifunctional polymer that possessed reactive functional groups and very sensitive response to temperature change.

Adriamycin (ADR)-loaded thermally responsive polymeric micelles composed of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)-b-poly(D,L-lactide were prepared by dialysis from its dimethylacetamide solution against water. Microfiltration was successfully applied to removal of block copolymer associates, which were smaller than micellar structures. By this microfiltration polymeric micelles showing a lower critical solution temperature (LCST) at 40 degrees C in phosphate buffered saline was obtained with a monodispersed size distribution of 69.2 nm in cumulant average diameter. ADR-loaded micelles released more ADR at 42.5 degrees C (above the LCST) than at 37 degrees C (below the LCST). ADR-loaded micelles did not show much cytotoxic activity against bovine aorta endothelial cells at 37 degrees C, in contrast to high cytotoxicity at 42.5 degrees C. On the other hand, free ADR expressed high cytotoxicity at both the incubation temperatures. Thus, thermally responsive polymeric micelles showed distinct control of ADR cytotoxic activity by temperature, while free ADR did not. From these results, an effective target therapy against solid tumors is feasible for these polymeric micelles by a combination of selective delivery to tumor sites based on stable micellar structures at 37 degrees C and enhanced cytotoxic activity of these drug-loaded micelles at 42.5 degrees C by local heating at tumor sites. (C) 1999 Elsevier Science B.V. All rights reserved.

Adriamycin (ADR)-loaded thermally responsive polymeric micelles composed of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)-b-poly(D,L-lactide were prepared by dialysis from its dimethylacetamide solution against water. Microfiltration was successfully applied to removal of block copolymer associates, which were smaller than micellar structures. By this microfiltration polymeric micelles showing a lower critical solution temperature (LCST) at 40 degrees C in phosphate buffered saline was obtained with a monodispersed size distribution of 69.2 nm in cumulant average diameter. ADR-loaded micelles released more ADR at 42.5 degrees C (above the LCST) than at 37 degrees C (below the LCST). ADR-loaded micelles did not show much cytotoxic activity against bovine aorta endothelial cells at 37 degrees C, in contrast to high cytotoxicity at 42.5 degrees C. On the other hand, free ADR expressed high cytotoxicity at both the incubation temperatures. Thus, thermally responsive polymeric micelles showed distinct control of ADR cytotoxic activity by temperature, while free ADR did not. From these results, an effective target therapy against solid tumors is feasible for these polymeric micelles by a combination of selective delivery to tumor sites based on stable micellar structures at 37 degrees C and enhanced cytotoxic activity of these drug-loaded micelles at 42.5 degrees C by local heating at tumor sites. (C) 1999 Elsevier Science B.V. All rights reserved.

A great deal of research has been conducted focusing on membrane materials with reference to their blood compatibility, but blood compatibility is influenced both by the material used in membranes and their structure, and by the flow conditions at the membrane surface. Accordingly, the relationship between membrane surface roughness and hemocompatibility has been evaluated using five types of membranes of differing surface roughness by evaluating the inner surfaces of the hollow fibers by atomic force microscopy (AFM) and by measuring platelet adhesion ratios using bovine blood. The yield stress, which equates to flow characteristics, was also evaluated using a glycerol suspension of polymethylmethacrylate (PMMA), a Bingham fluid. It was found that membranes having rough surfaces had high platelet adhesion ratios and poor hemocompatibility, whereas those with smoother surfaces had lower platelet adhesion ratios and better hemocompatibility. Measurement of the yield stresses for these membranes revealed higher values far those with rough surfaces, and lower values for those with smoother polyethylene glycol (PEG) grafted surfaces. This suggests that flow conditions at the membrane surface differ according to its surface roughness, and that this difference in flow conditions also influences hemocompatibility.

A great deal of research has been conducted focusing on membrane materials with reference to their blood compatibility, but blood compatibility is influenced both by the material used in membranes and their structure, and by the flow conditions at the membrane surface. Accordingly, the relationship between membrane surface roughness and hemocompatibility has been evaluated using five types of membranes of differing surface roughness by evaluating the inner surfaces of the hollow fibers by atomic force microscopy (AFM) and by measuring platelet adhesion ratios using bovine blood. The yield stress, which equates to flow characteristics, was also evaluated using a glycerol suspension of polymethylmethacrylate (PMMA), a Bingham fluid. It was found that membranes having rough surfaces had high platelet adhesion ratios and poor hemocompatibility, whereas those with smoother surfaces had lower platelet adhesion ratios and better hemocompatibility. Measurement of the yield stresses for these membranes revealed higher values far those with rough surfaces, and lower values for those with smoother polyethylene glycol (PEG) grafted surfaces. This suggests that flow conditions at the membrane surface differ according to its surface roughness, and that this difference in flow conditions also influences hemocompatibility.

An artificial gill, which takes oxygen from water, would enhance the ability of people to function under water for extended periods. Increasing oxygen transfer rate, however, would be essential to the realization of compact, commercially viable equipment. Fish have evolved a variety of techniques to enable them to breathe under water, and their mechanisms must be clarified before compact, high-performance artificial gills can be developed. A model of the secondary lamellae of fish gills, through which oxygen is taken up from water to the blood, was devised, and its structure and oxygen transfer rate were evaluated by computer simulation analysis for carp and dogfish. Oxygen transfer rates were also found for an outside-water-flow artificial gill using a hollow fiber membrane at various fiber packing ratios. The biologic membrane is rate-determining for oxygen transfer through the secondary lamellae. Blood and water side boundary film resistances are small for fish because the blood and water channels are very narrow and numerous. When the fiber packing ratio of the artificial gill is raised, the oxygen transfer rate increases because of lower water side boundary film resistance. An optimum fiber packing ratio should be selected so that there is no major increase in pressure drop and no channeling occurs.

An artificial gill, which takes oxygen from water, would enhance the ability of people to function under water for extended periods. Increasing oxygen transfer rate, however, would be essential to the realization of compact, commercially viable equipment. Fish have evolved a variety of techniques to enable them to breathe under water, and their mechanisms must be clarified before compact, high-performance artificial gills can be developed. A model of the secondary lamellae of fish gills, through which oxygen is taken up from water to the blood, was devised, and its structure and oxygen transfer rate were evaluated by computer simulation analysis for carp and dogfish. Oxygen transfer rates were also found for an outside-water-flow artificial gill using a hollow fiber membrane at various fiber packing ratios. The biologic membrane is rate-determining for oxygen transfer through the secondary lamellae. Blood and water side boundary film resistances are small for fish because the blood and water channels are very narrow and numerous. When the fiber packing ratio of the artificial gill is raised, the oxygen transfer rate increases because of lower water side boundary film resistance. An optimum fiber packing ratio should be selected so that there is no major increase in pressure drop and no channeling occurs.

Cross-linked poly(N-isopropylacrylamide) (PIPAAm) hydrogel-modified surfaces were prepared to investigate the effects of a three-dimensionally cross-linked structure of PIPAAm layers on both wettability changes and hydrophobic interactions with hydrophobic solutes in response to temperature changes. The temperature-responsive surface was prepared by polymerization of IPAAm in the presence of cross-linker on the substrates on which an azo polymerization initiator was covalently bonded. The PIPAAm hydrogel-modified surface showed temperature-responsive hydrophilic/hydrophobic surface property alterations as demonstrated by a large and discontinuous wettability changes in a range of 27-32 degrees C, a slightly lower temperature range than the phase transition temperature for soluble PIPAAm in aqueous media. This implies that the dynamic motion in response to temperature for PIPAAm segments in the modified hydrogel is restricted due to the cross-linked structure. The effect of the three-dimensional PIPAAm structure on the separation of hydrophobic steroids was investigated by high-performance liquid chromatography with an aqueous mobile phase. The retention times for steroids with different hydrophobicities were increased as the temperature was raised. Cortisone and prednisolone, those showing close hydrophobicity, were successfully separated at an elevated temperature above 25 degrees C owing to the amplified hydrophobic interaction of prednisolone compared to that of cortisone with the hydrophobic gel surfaces. The separation of relatively hydrophobic steroids was achieved even at lower temperature. The expanded network of the highly hydrated gel layer allowed the penetration of steroid molecules within the hydrogel layer which resulted in the changes in peak width. The cross-linked structure of PIPAAm hydrogels on substrates strongly influences both surface wettability changes and interaction with hydrophobic steroids in response to temperature due to the restricted dynamic motion of PIPAAm segments in the gel.

Cross-linked poly(N-isopropylacrylamide) (PIPAAm) hydrogel-modified surfaces were prepared to investigate the effects of a three-dimensionally cross-linked structure of PIPAAm layers on both wettability changes and hydrophobic interactions with hydrophobic solutes in response to temperature changes. The temperature-responsive surface was prepared by polymerization of IPAAm in the presence of cross-linker on the substrates on which an azo polymerization initiator was covalently bonded. The PIPAAm hydrogel-modified surface showed temperature-responsive hydrophilic/hydrophobic surface property alterations as demonstrated by a large and discontinuous wettability changes in a range of 27-32 degrees C, a slightly lower temperature range than the phase transition temperature for soluble PIPAAm in aqueous media. This implies that the dynamic motion in response to temperature for PIPAAm segments in the modified hydrogel is restricted due to the cross-linked structure. The effect of the three-dimensional PIPAAm structure on the separation of hydrophobic steroids was investigated by high-performance liquid chromatography with an aqueous mobile phase. The retention times for steroids with different hydrophobicities were increased as the temperature was raised. Cortisone and prednisolone, those showing close hydrophobicity, were successfully separated at an elevated temperature above 25 degrees C owing to the amplified hydrophobic interaction of prednisolone compared to that of cortisone with the hydrophobic gel surfaces. The separation of relatively hydrophobic steroids was achieved even at lower temperature. The expanded network of the highly hydrated gel layer allowed the penetration of steroid molecules within the hydrogel layer which resulted in the changes in peak width. The cross-linked structure of PIPAAm hydrogels on substrates strongly influences both surface wettability changes and interaction with hydrophobic steroids in response to temperature due to the restricted dynamic motion of PIPAAm segments in the gel.

Improvement in filtration performance of artificial membranes will be possible if their structure mimics the renal glomerulus. Blood filtration with glomerular capillary and artificial membranes was, therefore, modeled to clarify the effects of their structure on filtration rates. Filtration rates were obtained by dividing membrane modules axially into a number of sections and using a calculus of finite differences. The modules were assumed to be composed of straight hollow fibers arranged in parallel, with a membrane surface area of 1.5 m(2). The mean transmembrane pressure (TMP) was assumed to be too low for a protein gel layer to form on the membrane surface. A decrease in the inner diameter of membrane hollow fibers led to an increase in filtration rate because of an increased film mass transfer coefficient. A decrease in hollow fiber length also produced an increase in filtration rate because of decreased axial TMP drop. The glomerular capillary has a higher filtration rate than artificial membranes because of the low TMP drop and the low osmotic pressure at the membrane surface. Decreasing both the inner diameter and the length of the hollow fibers is effective in increasing the filtration rate at constant TMP.

Continuous measurement of endotoxin concentration in dialysate, using a separated endotoxin-specific limulus reagent, promises rapid measurement without the complex operating procedures of the limulus reagent. To achieve high sensitivity measurements in a short period of time, an improved system featuring stopped-flow operation was developed. To prevent dispersion of the limulus reagent and residence of reacting solution containing the limulus reagent in the system reactor, the circuit in the reactor was changed from a coil configuration to a straight line, and its length was reduced. An endotoxin test solution was supplied at 760 mu l/min, into which 40 mu l of limulus reagent was pulse-injected. Flow was stopped at the point where the test solution entered the reactor. After the completion of the reaction, the solution was passed through a spectrophotometer and the relationship between reaction time and absorbance was determined. Peak tailing was less than that obtained by the conventional technique, good correlation was obtained from the peak height, and a decrease in sensitivity caused by broadening of the peak was suppressed. The lower detection limit of dialysate was 100 endotoxin units (EU)/L at a reaction time of 20 minutes, and 60 EU/L at 30 minutes. Change from the monitoring system to stop-flow operation made high sensitivity monitoring of endotoxin concentration with a short reaction time possible.

Two types of thermo-responsive hydrogels are synthesized to obtain comb-type grafted gels with different lower critical solution temperatures (LCSTs) between graft chains and crosslinked backbone networks: these are poly(N-isopropylacrylamide) (PIPAAm) cross-linked hydrogels grafted with poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (poly(IPAAm-co-DMAAm)) maintaining a freely mobile end and poly(IPAAm-co-DMAAm) cross-linked hydrogels grafted with PIPAAm chains. The effect of graft chain hydrophilic/hydrophobic balance as well as its mobility on deswelling kinetics of these grafted gels are investigated through the polymer LCST modulation and external temperature changes. The deswelling rate of poly(IPAAm-co-DMAAm)-grafted PIPAAm gel increases with increasing in temperature. This gel shows a discontinuous increase of the deswelling rate when the temperature is applied from below to above the graft chain LCST (37 degrees C). The deswelling rate of PIPAAm-grafted poly(IPAAm-co-DMAAm) gel increases continuously when the temperature is applied from below to above the graft chain LCST (31 degrees C). Due to the strong hydrophilicity of backbone network, the hydrophobic aggregation force weak. In contrast to the graft-type gels, normal-type poly(IPAAm-co-DMAAm) cross-linked gel without graft chains demonstrates the discontinuous decrease for the deswelling rate when the temperature is applied from below to above the polymer LCST (36 degrees C), entrapping water inside the gel due to the formation of an impermeable dense skin layer at the gel surface. These gel deswelling mechanisms are discussed in terms of gel structures.

Improvement in filtration performance of artificial membranes will be possible if their structure mimics the renal glomerulus. Blood filtration with glomerular capillary and artificial membranes was, therefore, modeled to clarify the effects of their structure on filtration rates. Filtration rates were obtained by dividing membrane modules axially into a number of sections and using a calculus of finite differences. The modules were assumed to be composed of straight hollow fibers arranged in parallel, with a membrane surface area of 1.5 m(2). The mean transmembrane pressure (TMP) was assumed to be too low for a protein gel layer to form on the membrane surface. A decrease in the inner diameter of membrane hollow fibers led to an increase in filtration rate because of an increased film mass transfer coefficient. A decrease in hollow fiber length also produced an increase in filtration rate because of decreased axial TMP drop. The glomerular capillary has a higher filtration rate than artificial membranes because of the low TMP drop and the low osmotic pressure at the membrane surface. Decreasing both the inner diameter and the length of the hollow fibers is effective in increasing the filtration rate at constant TMP.

Continuous measurement of endotoxin concentration in dialysate, using a separated endotoxin-specific limulus reagent, promises rapid measurement without the complex operating procedures of the limulus reagent. To achieve high sensitivity measurements in a short period of time, an improved system featuring stopped-flow operation was developed. To prevent dispersion of the limulus reagent and residence of reacting solution containing the limulus reagent in the system reactor, the circuit in the reactor was changed from a coil configuration to a straight line, and its length was reduced. An endotoxin test solution was supplied at 760 mu l/min, into which 40 mu l of limulus reagent was pulse-injected. Flow was stopped at the point where the test solution entered the reactor. After the completion of the reaction, the solution was passed through a spectrophotometer and the relationship between reaction time and absorbance was determined. Peak tailing was less than that obtained by the conventional technique, good correlation was obtained from the peak height, and a decrease in sensitivity caused by broadening of the peak was suppressed. The lower detection limit of dialysate was 100 endotoxin units (EU)/L at a reaction time of 20 minutes, and 60 EU/L at 30 minutes. Change from the monitoring system to stop-flow operation made high sensitivity monitoring of endotoxin concentration with a short reaction time possible.

Two types of thermo-responsive hydrogels are synthesized to obtain comb-type grafted gels with different lower critical solution temperatures (LCSTs) between graft chains and crosslinked backbone networks: these are poly(N-isopropylacrylamide) (PIPAAm) cross-linked hydrogels grafted with poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (poly(IPAAm-co-DMAAm)) maintaining a freely mobile end and poly(IPAAm-co-DMAAm) cross-linked hydrogels grafted with PIPAAm chains. The effect of graft chain hydrophilic/hydrophobic balance as well as its mobility on deswelling kinetics of these grafted gels are investigated through the polymer LCST modulation and external temperature changes. The deswelling rate of poly(IPAAm-co-DMAAm)-grafted PIPAAm gel increases with increasing in temperature. This gel shows a discontinuous increase of the deswelling rate when the temperature is applied from below to above the graft chain LCST (37 degrees C). The deswelling rate of PIPAAm-grafted poly(IPAAm-co-DMAAm) gel increases continuously when the temperature is applied from below to above the graft chain LCST (31 degrees C). Due to the strong hydrophilicity of backbone network, the hydrophobic aggregation force weak. In contrast to the graft-type gels, normal-type poly(IPAAm-co-DMAAm) cross-linked gel without graft chains demonstrates the discontinuous decrease for the deswelling rate when the temperature is applied from below to above the polymer LCST (36 degrees C), entrapping water inside the gel due to the formation of an impermeable dense skin layer at the gel surface. These gel deswelling mechanisms are discussed in terms of gel structures.

The pore-size distribution and diffusive permeability of homogeneous cellulosic dialysis membranes were measured by thermoporometry and by radioisotope and photoabsorption techniques, respectively. A tortuous pore model incorporating membrane pore-size distribution in which tortuosity differs with pore size, can predict diffusive permeability for a wide range of solute molecular weights. The tortuosity obtained using the tortuous pore model by fitting the experimentally obtained diffusive permeability varied with molecular weight (Stokes radius). To evaluate the physical meaning of the tortuosity varied with solute Stokes radius, the tortuosity of the tortuous pore model was correlated to permeability parameters of the friction model. Tortuosity is represented by a ratio of intramembrane friction coefficients for solute and water between actual and hypothetical membrane having isodiametric pores for which the straight pore model is valid. The change in the ratio with the solute is attributable to the pore-size distribution.

The pore-size distribution and diffusive permeability of homogeneous cellulosic dialysis membranes were measured by thermoporometry and by radioisotope and photoabsorption techniques, respectively. A tortuous pore model incorporating membrane pore-size distribution in which tortuosity differs with pore size, can predict diffusive permeability for a wide range of solute molecular weights. The tortuosity obtained using the tortuous pore model by fitting the experimentally obtained diffusive permeability varied with molecular weight (Stokes radius). To evaluate the physical meaning of the tortuosity varied with solute Stokes radius, the tortuosity of the tortuous pore model was correlated to permeability parameters of the friction model. Tortuosity is represented by a ratio of intramembrane friction coefficients for solute and water between actual and hypothetical membrane having isodiametric pores for which the straight pore model is valid. The change in the ratio with the solute is attributable to the pore-size distribution.

The objectives of the present study are to clarify the phenomenon of solute transfer occurring inside dialyzers made from asymmetric membranes, to examine the structure of asymmetric membranes capable of suppressing the inflow of endotoxins from the dialysate, and thereby to contribute to the design of a more effective dialysis membrane. Using membranes that have tight layers on both sides (drum-shaped membrane) with the outer one tighter, solutes are more easily transferred from the inside out than from the outside in, leading to effective removal of pathogenic substances from the blood and a significant lowering of endotoxin inflow from the dialysate. The anisotropy of solute permeability of asymmetric dialysis membranes is caused by the difference in the amount of solute transfer due to filtration from the inside out and from the outside in. (C) 1998 Elsevier Science S.A. All rights reserved.

The objectives of the present study are to clarify the phenomenon of solute transfer occurring inside dialyzers made from asymmetric membranes, to examine the structure of asymmetric membranes capable of suppressing the inflow of endotoxins from the dialysate, and thereby to contribute to the design of a more effective dialysis membrane. Using membranes that have tight layers on both sides (drum-shaped membrane) with the outer one tighter, solutes are more easily transferred from the inside out than from the outside in, leading to effective removal of pathogenic substances from the blood and a significant lowering of endotoxin inflow from the dialysate. The anisotropy of solute permeability of asymmetric dialysis membranes is caused by the difference in the amount of solute transfer due to filtration from the inside out and from the outside in. (C) 1998 Elsevier Science S.A. All rights reserved.

The thermally sensitive block copolymer, poly(N-isopropylacrylamide-b-DL-lactide) (PIPAAm-PLA), was synthesized by ring-opening polymerization of DL-lactide initiated from hydroxy-terminated poly (N-isopropylacrylamide) (PIPAAm). A PIPAAm bearing a single terminal hydroxyl group was prepared by telomerization using 2-hydroxyethanethiol as a chain-transfer agent. Successful preparation of PIPAAm and the PIPAAm-PLA block copolymer was verified by gel permeation chromatography (GPC) and H-1-NMR spectroscopy. Polymeric micelles were prepared from block copolymers using a dialysis method. Their solutions showed reversible changes in optical properties: transparent below a lower critical solution temperature (LCST) and opaque above the LCST. Dynamic light scattering measurements were used to observe the formation of micellar structures approximately 40 nm in diameter, which do not change between 20 degrees C and 30 degrees C, Above the LCST, polymer micelles aggregated, a phenomenon found to be reversible since the aggregates dissociated again by cooling below the LCST. Further observations using atomic force microscopy (AFM) confirmed this behaviour. The properties of this block copolymer system are interesting from both applied and fundamental perspectives, particularly for active targeting as drug carriers. (C) 1998 Elsevier Science B.V.

The thermally sensitive block copolymer, poly(N-isopropylacrylamide-b-DL-lactide) (PIPAAm-PLA), was synthesized by ring-opening polymerization of DL-lactide initiated from hydroxy-terminated poly (N-isopropylacrylamide) (PIPAAm). A PIPAAm bearing a single terminal hydroxyl group was prepared by telomerization using 2-hydroxyethanethiol as a chain-transfer agent. Successful preparation of PIPAAm and the PIPAAm-PLA block copolymer was verified by gel permeation chromatography (GPC) and H-1-NMR spectroscopy. Polymeric micelles were prepared from block copolymers using a dialysis method. Their solutions showed reversible changes in optical properties: transparent below a lower critical solution temperature (LCST) and opaque above the LCST. Dynamic light scattering measurements were used to observe the formation of micellar structures approximately 40 nm in diameter, which do not change between 20 degrees C and 30 degrees C, Above the LCST, polymer micelles aggregated, a phenomenon found to be reversible since the aggregates dissociated again by cooling below the LCST. Further observations using atomic force microscopy (AFM) confirmed this behaviour. The properties of this block copolymer system are interesting from both applied and fundamental perspectives, particularly for active targeting as drug carriers. (C) 1998 Elsevier Science B.V.

To develop high performance dialysis membranes, the asymmetric structure should be positively accepted and the relationship between asymmetric structure and diffusive permeability should be further clarified. A little information on the asymmetric structure can be obtained from SEM observation. The objective of the present study is to propose a new method for evaluating asymmetric hollow-fiber dialysis membranes by dye adsorption. Adsorption experiments were carried out using mini-modules composed of test membranes (AM-SD-M, PS-UW, PEPA, PAN-DX, PAN-CX2) of which the inside was packed with paraffin to make solutes diffuse only from the outside inward, or of which the outside was packed with paraffin to make solutes diffuse only from the inside outward. The amount of solutes (cytochrome C, Evans blue, Congo red, ethidium bromide) transferred into the membranes was plotted as a function of time. In membranes of asymmetric structure the shape of the transfer rate curves differed with the direction of transfer, and a difference in the rate of solute transfer was produced which is due to the asymmetric structure of the membrane. Further, depending on the solute size and on the membrane, the directional difference in the transfer rate curves appeared either in the middle portion or the initial portion of the curves. It is concluded that the adsorption technique can be used to evaluate the asymmetric structure and diffusive permeability. (C) 1998 Elsevier Science S.A. All rights reserved.

To develop high performance dialysis membranes, the asymmetric structure should be positively accepted and the relationship between asymmetric structure and diffusive permeability should be further clarified. A little information on the asymmetric structure can be obtained from SEM observation. The objective of the present study is to propose a new method for evaluating asymmetric hollow-fiber dialysis membranes by dye adsorption. Adsorption experiments were carried out using mini-modules composed of test membranes (AM-SD-M, PS-UW, PEPA, PAN-DX, PAN-CX2) of which the inside was packed with paraffin to make solutes diffuse only from the outside inward, or of which the outside was packed with paraffin to make solutes diffuse only from the inside outward. The amount of solutes (cytochrome C, Evans blue, Congo red, ethidium bromide) transferred into the membranes was plotted as a function of time. In membranes of asymmetric structure the shape of the transfer rate curves differed with the direction of transfer, and a difference in the rate of solute transfer was produced which is due to the asymmetric structure of the membrane. Further, depending on the solute size and on the membrane, the directional difference in the transfer rate curves appeared either in the middle portion or the initial portion of the curves. It is concluded that the adsorption technique can be used to evaluate the asymmetric structure and diffusive permeability. (C) 1998 Elsevier Science S.A. All rights reserved.

Glucose reacts with glucose oxidase to form gluconolactone and hydrogen peroxide (H2O2) and the glucose concentration may be determined indirectly from the amount of hydrogen peroxide produced. The authors have developed a method of H2O2 assay that uses the electroluminescence (EL) of indium-tin oxide (ITO). Since this method depends on a reversible reaction of the ITO itself, it does not require the addition of an emitting substance, allowing convenient continuous monitoring of the anylates. In the present work the triangular-wave potential was set at 0 - +1.4 - 0V against the Ag/AgCl reference electrode, and swept at a rate of 200 mV s(-1). The integrated number of photons was taken as the electroluminescence intensity, and its response to changes in H2O2 concentration was investigated. As a result a value that was dependent on H2O2 concentration was obtained. Electroluminescence intensity was measured varying the pH of the test solution from 7 to 13 with a Britton-Robinson buffer solution, and it was found that electroluminescence intensity was constant at pH 9 and above. When glucose and glucose oxidase were mixed in the test solution, measurements of electroluminescence intensity showed a good correlation with glucose concentration.

Glucose reacts with glucose oxidase to form gluconolactone and hydrogen peroxide (H2O2) and the glucose concentration may be determined indirectly from the amount of hydrogen peroxide produced. The authors have developed a method of H2O2 assay that uses the electroluminescence (EL) of indium-tin oxide (ITO). Since this method depends on a reversible reaction of the ITO itself, it does not require the addition of an emitting substance, allowing convenient continuous monitoring of the anylates. In the present work the triangular-wave potential was set at 0 - +1.4 - 0V against the Ag/AgCl reference electrode, and swept at a rate of 200 mV s(-1). The integrated number of photons was taken as the electroluminescence intensity, and its response to changes in H2O2 concentration was investigated. As a result a value that was dependent on H2O2 concentration was obtained. Electroluminescence intensity was measured varying the pH of the test solution from 7 to 13 with a Britton-Robinson buffer solution, and it was found that electroluminescence intensity was constant at pH 9 and above. When glucose and glucose oxidase were mixed in the test solution, measurements of electroluminescence intensity showed a good correlation with glucose concentration.

A glucose sensor, using glucose oxidase immobilized in an electrically conductive polymer membrane, is developed for transient-mode measurement by on-off reaction control in the present work. An implantable glucose sensor loses its stability under the skin by fouling resulting from fibroblast adhesion on the glucose oxidase-immobilized membrane. Change in glucose distribution inside the membrane and in the vicinity of the surface of the membrane resulting from the fouling makes the measurement of the glucose concentration unstable. A technique of measuring transient current of the glucose sensor after activation of glucose oxidase may hardly be affected by the fouling as oxidation of coenzyme of glucose oxidase is rapid and the transient current is sensitive to glucose concentration. A glucose sensor with glucose oxidase immobilized in an electrically conductive polypyrrole membrane was fabricated. The activity of the glucose oxidase is switched on and off by a stepwise change of potential of the polypyrrole membrane from 0.15 V to 0.45 V versus a saturated calomel electrode. The two conditions described above can be confirmed by measuring transient current. Current increased momentarily after activation of glucose oxidase and decreased moderately after that. The oxidation and reduction of glucose oxidase is sufficiently rapid, and current intensity depends on glucose concentration in the test solution.

Regarding hemodialysis membranes as layers packed with uniform polymeric particles, the size of the particles is determined using the Kozeny-Carman equation. Diameter of the spheres forming cellulosic membranes is the same order as the size of primary polymeric particles determined by electron microscopy in a previous article. Pore radii of the membranes calculated by the Kozeny-Carman equation are in agreement with those determined by the tortuous capillary pore model. The result suggests that an estimate of a pore radius of a membrane is feasible by the Kozeny-Carman equation only with water permeability of the membrane. Intramembrane diffusion coefficients of vitamin B(12) calculated from an equation derived from the analogy of heat conduction in heterogeneous media consisting of a continuous phase and particles are larger than the experimental values. The result suggests the failure of the analogy between heat conduction and diffusion of vitamin B(12) in a heterogeneous medium. (C) 1998 John Wiley & Sons, Inc.

Deswelling mechanism for comb-type grafted poly(N-isopropylacrylamide) (PIPAAm) hydrogel was investigated to make clear the effect of gel architecture on the gel deswelling kinetics. Deswelling rate and mechanism were compared with those for conventional crosslinked PIPAAm gel and poly(ethylene oxide) (PEO)-grafted PIPAAm gel in response to temperature increase from below to above the gel-phase transition temperatures. The deswelling rate for the conventional PIPAAm gel are reciprocal to the gel size square, indicative of collective diffusion mediated manner for crosslinked network into water. Although PEO graft chains formed water release channels within the network to produce fast gel deswelling changes, deswelling change of PEG-grafted gel also demonstrated collective diffusion mediated manner of crosslinked backbone chains. On the other hand, one order faster rate of deswelling change of PIPAAm-grafted gel was observed than that of PEG-grafted gel with identical gel dimension. The deswelling change of PIPAAm grafted gel did not obey collective diffusion mediated manner, demonstrating reciprocal to the gel size to 1.58th power. This deswelling mechanism was explained in terms of rapid hydrophobic aggregation of freely mobile PIPAAm graft chains and an operation of intrinsic elastic forces of polymer network. The operation of both elastic force and strong hydrophobic aggregation force between the dehydrated PIPAAm graft chains released water inside the gel, causing more rapid deswelling changes of the PIPAAM-grafted gels. (C) 1999 Elsevier Science Ltd. All rights reserved.

Regarding hemodialysis membranes as layers packed with uniform polymeric particles, the size of the particles is determined using the Kozeny-Carman equation. Diameter of the spheres forming cellulosic membranes is the same order as the size of primary polymeric particles determined by electron microscopy in a previous article. Pore radii of the membranes calculated by the Kozeny-Carman equation are in agreement with those determined by the tortuous capillary pore model. The result suggests that an estimate of a pore radius of a membrane is feasible by the Kozeny-Carman equation only with water permeability of the membrane. Intramembrane diffusion coefficients of vitamin B(12) calculated from an equation derived from the analogy of heat conduction in heterogeneous media consisting of a continuous phase and particles are larger than the experimental values. The result suggests the failure of the analogy between heat conduction and diffusion of vitamin B(12) in a heterogeneous medium. (C) 1998 John Wiley & Sons, Inc.

Deswelling mechanism for comb-type grafted poly(N-isopropylacrylamide) (PIPAAm) hydrogel was investigated to make clear the effect of gel architecture on the gel deswelling kinetics. Deswelling rate and mechanism were compared with those for conventional crosslinked PIPAAm gel and poly(ethylene oxide) (PEO)-grafted PIPAAm gel in response to temperature increase from below to above the gel-phase transition temperatures. The deswelling rate for the conventional PIPAAm gel are reciprocal to the gel size square, indicative of collective diffusion mediated manner for crosslinked network into water. Although PEO graft chains formed water release channels within the network to produce fast gel deswelling changes, deswelling change of PEG-grafted gel also demonstrated collective diffusion mediated manner of crosslinked backbone chains. On the other hand, one order faster rate of deswelling change of PIPAAm-grafted gel was observed than that of PEG-grafted gel with identical gel dimension. The deswelling change of PIPAAm grafted gel did not obey collective diffusion mediated manner, demonstrating reciprocal to the gel size to 1.58th power. This deswelling mechanism was explained in terms of rapid hydrophobic aggregation of freely mobile PIPAAm graft chains and an operation of intrinsic elastic forces of polymer network. The operation of both elastic force and strong hydrophobic aggregation force between the dehydrated PIPAAm graft chains released water inside the gel, causing more rapid deswelling changes of the PIPAAM-grafted gels. (C) 1999 Elsevier Science Ltd. All rights reserved.

On the assumption that continuous treatment is effective in preventing β2-microglobulin deposition in a patient without kidney function, a wearable artificial kidney device was theoretically designed on the basis of using presently commercially available hollow-fiber membrane for hemodialysis. The device was assumed to be connected between an arteriole and a large vein. The device, with an optimal dimension consisting of the membrane with an appropriate filtration permeability, was capable of carrying out continuous hemofiltration using the blood pressure of the patient only and of preventing β2-microglobulin deposition. If dialysate was fed into the device for an appropriate time every day, concentrations of urea nitrogen and creatinine were also maintained at a lower level than that of conventional intermittent hemodialysis. Because the dimension and technical data of the device giving these results are comparable to those of commercially available hemodialyzers, we should reconsider whether the wearable artificial kidney can be put into clinical use. © The Japanese Society for Artificial Organs 1998.

Virtually all of the artificial membranes such as reverse-osmosis membrane, dialysis membrane, ultrafiltration membrane, microfiltration membrane and gas separation membrane in use industrially also have therapeutic applications. Dialysis membranes used clinically in the treatment of patients with renal failure account for by far the largest volume of membranes and, worldwide, their consumption has reached some 70 million square meters a year. Almost all dialyzers now in use are of the hollow-fiber type.
A hollow-fiber dialyzer contains a bundle of approximately 10,000 hollow fibers having an inner diameter of about 200 mu m when wet, a membrane thickness of 20-45 mu m when wet, and a length of 160-250 mm. The walls of the hollow fibers function as the dialysis membrane and the materials used for dialysis membranes are many and varied, and include cellulose-based materials and synthetic polymers.
This paper reviews blood purification and dialysis membranes and also discusses differences in performance between the natural kidney and filters to clarify separation mechanism of glomerular basement membranes and filtration membranes. An intelligent membrane is proposed of temperature-responsive dialysis membrane with pores the size of which varies with temperature.

Since artificial organs are intended to replicate chemical processes, knowledge of chemical engineering is essential in their design so that they will function with the maximum efficiency. The most commonly used artificial organ is the artificial kidney, a machine that performs a treatment known as hemodialysis. This process cleanses the bodies of renal failure patients by dialysis and filtration which are simple physicochemical processes. Hemodialysis membranes act to remove accumulated uremic toxins, excess ions and water from the patient via the dialysate, and to supply from the dialysate those ions that are insufficient.
This paper describes dialysis membranes and dialyzers for blood purification, the solute transport mechanism of the membrane, and a technical evaluation of the dialysis membrane. Lastly, the next generation of artificial kidney is reviewed.

In the present study, cyclic voltammograms obtained with an indium-tin oxide (ITO) anode were compared with those obtained with a platinum anode. The peak currents generated by luminol oxidation at the platinum anode showed convex curves facing upwards with increasing luminol concentration, as the result of the prevention of the oxidation of the platinum electrode by the presence of Luminol. With the ITO anode, no current due to electrode oxidation or reduction was detected. The peak current intensity of luminol oxidation was proportional to the luminol concentration, but the peak current was also in a linear relationship with the square root of the scan rate. However, the intercept current was largely deviated from zero. The deviation suggests radial diffusion of luminol at the ITO anode which has a small active point density. In conclusion, the ITO anode is useful for accurate measurement of the rate of luminol oxidation, but radial diffusion of luminol in the vicinity of the ITO surface should be taken into consideration in analysis of luminol oxidation.

In the present study, cyclic voltammograms obtained with an indium-tin oxide (ITO) anode were compared with those obtained with a platinum anode. The peak currents generated by luminol oxidation at the platinum anode showed convex curves facing upwards with increasing luminol concentration, as the result of the prevention of the oxidation of the platinum electrode by the presence of Luminol. With the ITO anode, no current due to electrode oxidation or reduction was detected. The peak current intensity of luminol oxidation was proportional to the luminol concentration, but the peak current was also in a linear relationship with the square root of the scan rate. However, the intercept current was largely deviated from zero. The deviation suggests radial diffusion of luminol at the ITO anode which has a small active point density. In conclusion, the ITO anode is useful for accurate measurement of the rate of luminol oxidation, but radial diffusion of luminol in the vicinity of the ITO surface should be taken into consideration in analysis of luminol oxidation.

Urea removal by continuous ambulatory peritoneal dialysis (CAPD) was compared with that by hemodialysis (HD) using a mathematical kinetic model. The time-averaged urea-nitrogen concentration (TAG) in the blood of a patient on maintenance HD was calculated by the model. Clearance with HD giving a TAC value equal to the constant urea-nitrogen concentration in the blood of a patient on CAPD was obtained, leading to the relation of equivalent clearances between HD and CAPD on the assumption that the urea-generation rate of the patient on CARD was equal to that of the patient on HD.

Urea removal by continuous ambulatory peritoneal dialysis (CAPD) was compared with that by hemodialysis (HD) using a mathematical kinetic model. The time-averaged urea-nitrogen concentration (TAG) in the blood of a patient on maintenance HD was calculated by the model. Clearance with HD giving a TAC value equal to the constant urea-nitrogen concentration in the blood of a patient on CAPD was obtained, leading to the relation of equivalent clearances between HD and CAPD on the assumption that the urea-generation rate of the patient on CARD was equal to that of the patient on HD.

Since artificial organs are intended to replicate chemical processes, knowledge of chemical engineering is essential in their design so that they will function with the maximum efficiency. The most commonly used artificial organ is the artificial kidney, a machine that performs a treatment known as hemodialysis. This process cleanses the bodies of renal failure patients by dialysis and filtration which are simple physicochemical processes. Hemodialysis membranes act to remove accumulated uremic toxins, excess ions and water from the patient via the dialysate, and to supply from the dialysate those ions that are insufficient. This paper describes dialysis membranes and dialyzers for blood purification, the solute transport mechanism of the membrane, and a technical evaluation of the dialysis membrane. Lastly, the next generation of artificial kidney is reviewed.

The purpose of the present work is to characterize the cathodic electrochemiluminescence of luminol with a view to its application in continuous immunoassay. The authors designed a method for continuous antibody determination from the change in electrochemiluminescent intensity of luminol resulted from antigen-antibody reactions. The cathodic electrochemiluminescences of luminol-labeled antigens in hydrogen peroxide solution were enhanced by the presence of the respective antibodies. Cathodic electrochemiluminescence Of a luminol-labeled antibody was also enhanced by the presence of antigen. The enhancement of electrochemiluminescence may be useful in homogeneous immunoassay of antibodies or antigens. Analysis of a batchwise reaction suggested that the presence of antibody increases the quantum yield of electrochemiluminescence of luminol-labeled antigen. And analysis of the electrolytic current of luminol and hydrogen peroxide at indium-tin oxide (ITO) cathode revealed that hydrogen peroxide was electrochemically active at the cathode, while luminol was inert. These results suggest that cathodic electrochemiluminescence of luminol or luminol-labeled proteins is triggered by hydroxide radical produced from hydrogen peroxide at the ITO cathode.

The purpose of the present work is to characterize the cathodic electrochemiluminescence of luminol with a view to its application in continuous immunoassay. The authors designed a method for continuous antibody determination from the change in electrochemiluminescent intensity of luminol resulted from antigen-antibody reactions. The cathodic electrochemiluminescences of luminol-labeled antigens in hydrogen peroxide solution were enhanced by the presence of the respective antibodies. Cathodic electrochemiluminescence Of a luminol-labeled antibody was also enhanced by the presence of antigen. The enhancement of electrochemiluminescence may be useful in homogeneous immunoassay of antibodies or antigens. Analysis of a batchwise reaction suggested that the presence of antibody increases the quantum yield of electrochemiluminescence of luminol-labeled antigen. And analysis of the electrolytic current of luminol and hydrogen peroxide at indium-tin oxide (ITO) cathode revealed that hydrogen peroxide was electrochemically active at the cathode, while luminol was inert. These results suggest that cathodic electrochemiluminescence of luminol or luminol-labeled proteins is triggered by hydroxide radical produced from hydrogen peroxide at the ITO cathode.

The synthesis and characterization of comb-type grafted thermo-sensitive hydrogels is presented. These hydrogels were synthesized by polymerization of N-isopropylacrylamide (IPAAm) with a PlPAAm macromonomer. This process leads to a crosslinked IPAAm backbone polymer, copolymerized with highly mobile comb-type PIPAAm chains. These new thermo-responsive copolymers displayed higher equilibrium swellings at lower temperatures and rapid deswelling kinetics at elevated temperatures. The swelling/deswelling for comb-type gels is dependent on the graft chain lengths, in contrast to normal PIPAAm gel lacking the graft chains. As the temperature is increased above the critical temperature, the dehydrated graft chains aggregated due to hydrophobic attraction. Rapid and reversible kinetics of the graft-type gel were observed in response to stepwise temperature changes within short time cycles: phenomena not observed in normal crosslinked thermo-sensitive gels. The influence of freely mobile graft chains on both the equilibrium and dynamic properties of comb-type PIPAAm gel is demonstrated. Possible application of graft-type gel is discussed for actuator systems.

The synthesis and characterization of comb-type grafted thermo-sensitive hydrogels is presented. These hydrogels were synthesized by polymerization of N-isopropylacrylamide (IPAAm) with a PlPAAm macromonomer. This process leads to a crosslinked IPAAm backbone polymer, copolymerized with highly mobile comb-type PIPAAm chains. These new thermo-responsive copolymers displayed higher equilibrium swellings at lower temperatures and rapid deswelling kinetics at elevated temperatures. The swelling/deswelling for comb-type gels is dependent on the graft chain lengths, in contrast to normal PIPAAm gel lacking the graft chains. As the temperature is increased above the critical temperature, the dehydrated graft chains aggregated due to hydrophobic attraction. Rapid and reversible kinetics of the graft-type gel were observed in response to stepwise temperature changes within short time cycles: phenomena not observed in normal crosslinked thermo-sensitive gels. The influence of freely mobile graft chains on both the equilibrium and dynamic properties of comb-type PIPAAm gel is demonstrated. Possible application of graft-type gel is discussed for actuator systems.

Some patients on long-term dialysis may suffer from metabolic bone disease owing to abnormal metabolizing of phosphorus and calcium. It is possible to prevent these conditions by controlling serum ion concentrations to an appropriate level, and to do this the rate of ion permeability through the dialysis membrane must be clarified. The rate of ion permeability is influenced by membrane structure and membrane charge. The changes in membrane charge occurring when protein was adsorbed on a polyacrylonitrile dialysis membrane were evaluated for cytochrome C, which is positively charged in an aqueous solution at pH 7.4 and for alpha-lactalbumin, which is negatively charged at pH 7.4, by means of changes in zeta potential, and these were compared with changes in rates of ion permeability. Changes brought about in membrane structure were also evaluated from changes in the diffusive permeability coefficient of urea, which is a non-electrolyte. After cytochrome C adsorption, the absolute zeta potential of the membrane decreased, and the charge on the membrane became electrically closer to neutral than before the adsorption. In membranes on which alpha-lactalbumin was adsorbed, on the contrary, absolute zeta potential increased and the negative charge on the membrane increased. The diffusive permeability coefficient of urea decreased no matter which protein was adsorbed, but the amount of decrease was slight and there was little change in membrane structure. The diffusive permeability coefficients of sodium hydrogen phosphate and NaCl increased after cytochrome C adsorption and decreased after alpha-lactalbumin adsorption. The changes in electric charge evaluated by zeta potential and changes in the rate of ion permeability due to protein adsorption are in qualitative agreement with ion permeability theory. It is therefore suggested that the zeta potential can be used as an index of membrane charge when evaluating the membrane permeability of ions.

Some patients on long-term dialysis may suffer from metabolic bone disease owing to abnormal metabolizing of phosphorus and calcium. It is possible to prevent these conditions by controlling serum ion concentrations to an appropriate level, and to do this the rate of ion permeability through the dialysis membrane must be clarified. The rate of ion permeability is influenced by membrane structure and membrane charge. The changes in membrane charge occurring when protein was adsorbed on a polyacrylonitrile dialysis membrane were evaluated for cytochrome C, which is positively charged in an aqueous solution at pH 7.4 and for alpha-lactalbumin, which is negatively charged at pH 7.4, by means of changes in zeta potential, and these were compared with changes in rates of ion permeability. Changes brought about in membrane structure were also evaluated from changes in the diffusive permeability coefficient of urea, which is a non-electrolyte. After cytochrome C adsorption, the absolute zeta potential of the membrane decreased, and the charge on the membrane became electrically closer to neutral than before the adsorption. In membranes on which alpha-lactalbumin was adsorbed, on the contrary, absolute zeta potential increased and the negative charge on the membrane increased. The diffusive permeability coefficient of urea decreased no matter which protein was adsorbed, but the amount of decrease was slight and there was little change in membrane structure. The diffusive permeability coefficients of sodium hydrogen phosphate and NaCl increased after cytochrome C adsorption and decreased after alpha-lactalbumin adsorption. The changes in electric charge evaluated by zeta potential and changes in the rate of ion permeability due to protein adsorption are in qualitative agreement with ion permeability theory. It is therefore suggested that the zeta potential can be used as an index of membrane charge when evaluating the membrane permeability of ions.

Temperature-responsive poly(N-isopropylacrylamide) and its copolymer gels with the hydrophilic comonomer, acrylamide and the hydrophobic comonomer, butyl methacrylate, all exhibit swelling-deswelling changes in response to external temperature changes. These hydrogels show negative swelling thermosensitivities, particularly swelling at lower temperature and complete deswelling over specific phase transition temperatures (T-p). Shrinking kinetics of these gels from swollen to deswollen states at several different temperature changes have been investigated. When temperature changes are performed entirely below T-p, the shrinking process is dominated by polymer network diffusion. On the other hand, shrinking kinetics for temperature changes from below to above T-p are dramatically influenced by gel surface structural changes and formation of a collapsed polymer skin layer. This surface skin formation prompts the accumulation of internal hydrodynamic pressure inside the gels upon shrinking by blocking the outflux of entrapped water. Both rate and magnitude of internal hydrodynamic pressure are modulated by the gel volume, the hydrophobicity of the gel polymer chains and the degree of external temperature changes. This internal pressure eventually causes convective outflow of water from the gel interior. Hydrodynamic internal pressure affects the drug release on-off pattern during gel shrinking.

The distribution volume of water contained in 31 hemodialysis membranes made from seven polymers was measured by three different methods, Water contained in the membranes was classified into three groups according to thermal mobility of the molecules, Structural analysis of the membranes was feasible through determining proportion of nonfreezing water to total water contained in the membranes. (C) 1995 Academic Press, Inc.

Temperature-responsive poly(N-isopropylacrylamide) and its copolymer gels with the hydrophilic comonomer, acrylamide and the hydrophobic comonomer, butyl methacrylate, all exhibit swelling-deswelling changes in response to external temperature changes. These hydrogels show negative swelling thermosensitivities, particularly swelling at lower temperature and complete deswelling over specific phase transition temperatures (T-p). Shrinking kinetics of these gels from swollen to deswollen states at several different temperature changes have been investigated. When temperature changes are performed entirely below T-p, the shrinking process is dominated by polymer network diffusion. On the other hand, shrinking kinetics for temperature changes from below to above T-p are dramatically influenced by gel surface structural changes and formation of a collapsed polymer skin layer. This surface skin formation prompts the accumulation of internal hydrodynamic pressure inside the gels upon shrinking by blocking the outflux of entrapped water. Both rate and magnitude of internal hydrodynamic pressure are modulated by the gel volume, the hydrophobicity of the gel polymer chains and the degree of external temperature changes. This internal pressure eventually causes convective outflow of water from the gel interior. Hydrodynamic internal pressure affects the drug release on-off pattern during gel shrinking.

The distribution volume of water contained in 31 hemodialysis membranes made from seven polymers was measured by three different methods, Water contained in the membranes was classified into three groups according to thermal mobility of the molecules, Structural analysis of the membranes was feasible through determining proportion of nonfreezing water to total water contained in the membranes. (C) 1995 Academic Press, Inc.

Swelling layers formed by poly(ethylene glycol) (PEG) chains grafted onto surfaces of a cellulosic membrane are known to improve hemocompatibility of the membrane. Three types of hemodialysis membranes were derived from the same regenerated-cellulose hollow-fiber membrane by grafting PEG with different formulas onto the surfaces to clarify the influence of the grafted PEG chains on solute permeability of the membranes. Determination of volume fractions of nonfreezing water contained in the membranes by differential scanning calorimetry revealed that most of the PEG chains were grafted onto the external surfaces and less into the pores in the membranes. Permeability of vitamin B-12 for the PEG-grafted membranes except for the one with the shortest PEG chains was reduced as compared with the original membrane, while that of tritium-labeled water for all the PEG-grafted membranes was the same as that of the original membrane. Structural parameters only of the PEG-grafted membrane with the largest alkyl groups at the terminal of the PEG chains were different from those of the other PEG grafted and original membranes. The shorter PEG chains with the larger terminal alkyl groups are suitable for grafting onto a cellulosic membrane to increase hemocompatibility of the membrane without significant reduction in the solute permeability of the membrane. (C) 1995 John Wiley & Sons, Inc.

Swelling layers formed by poly(ethylene glycol) (PEG) chains grafted onto surfaces of a cellulosic membrane are known to improve hemocompatibility of the membrane. Three types of hemodialysis membranes were derived from the same regenerated-cellulose hollow-fiber membrane by grafting PEG with different formulas onto the surfaces to clarify the influence of the grafted PEG chains on solute permeability of the membranes. Determination of volume fractions of nonfreezing water contained in the membranes by differential scanning calorimetry revealed that most of the PEG chains were grafted onto the external surfaces and less into the pores in the membranes. Permeability of vitamin B-12 for the PEG-grafted membranes except for the one with the shortest PEG chains was reduced as compared with the original membrane, while that of tritium-labeled water for all the PEG-grafted membranes was the same as that of the original membrane. Structural parameters only of the PEG-grafted membrane with the largest alkyl groups at the terminal of the PEG chains were different from those of the other PEG grafted and original membranes. The shorter PEG chains with the larger terminal alkyl groups are suitable for grafting onto a cellulosic membrane to increase hemocompatibility of the membrane without significant reduction in the solute permeability of the membrane. (C) 1995 John Wiley & Sons, Inc.

In porous media such as adsorbents, catalysts or sandy soil, the porosity - the size and distribution and specific surface area of the capillary pores - is an important factor providing such media with their respective functions of adsorbency, catalysis and permeability.
Largely, the synthetic membranes used in separation may also be thought of as porous media. In dialysis membranes, the area in which water is present when the membrane is wet acts as a channel for the solute. Thus, the proportion of water present in the membrane (that is, the prove volume), the width of the layer of water acting as the solute channel (that is, the pore size) and the pore size distribution are the main factors governing the function of dialysis membranes.
Therefore, it is the purpose of this review to provide a general description of the concept and determination of pore size; the size of pores in dialysis membranes in the broad sense and pore size distribution, pore volume, etc.

Poly(N-isopropylacrylamide) gel has negative temperature dependency of swelling behavior in aqueous solution. In this study, IPAAm copolymer gel was utilized to design positive thermosensitive pulsatile drug release system to induce drug release with increasing temperature and stop the release with decreasing temperature. Skin structure of the shrunken gel at higher temperature was controlled by introduction of hydrophilic acrylamide to allow drug release. Using an impermeable capsule equipped with a release orifice, positive thermosensitive pulsatile release was achieved by diffusion area-regulating mechanism, which was different from surface-regulating mechanism to achieve conventional negative thermosensitive pulsatile release. A new concept to convert negative thermosensitivity of IPAAm gels to positive thermosensitive pulsatile release has been demonstrated.

Poly(N-isopropylacrylamide) gel has negative temperature dependency of swelling behavior in aqueous solution. In this study, IPAAm copolymer gel was utilized to design positive thermosensitive pulsatile drug release system to induce drug release with increasing temperature and stop the release with decreasing temperature. Skin structure of the shrunken gel at higher temperature was controlled by introduction of hydrophilic acrylamide to allow drug release. Using an impermeable capsule equipped with a release orifice, positive thermosensitive pulsatile release was achieved by diffusion area-regulating mechanism, which was different from surface-regulating mechanism to achieve conventional negative thermosensitive pulsatile release. A new concept to convert negative thermosensitivity of IPAAm gels to positive thermosensitive pulsatile release has been demonstrated.

Suitable evaluation systems are critical for ranking various biomaterials in order to develop a method to design and synthesize nonthrombogenic biomaterials. We have recently developed an in vitro test system to evaluate platelet/biomaterial interactions in whole blood. The system consists of a parallel plate flow cell and epifluorescent video microscopy (EVM). A glass coverslip coated with a polymer was incorporated into the flow cell, and blood was perfused using a syringe pump via a polymer-coated PVC tubing connected to the flow cell. Whole human blood was anticoagulated with heparin (2 U/ml), and the platelets were labeled with the fluorescent dye mepacrine (5 mu M). This system permitted real-time and dynamic observations of platelet/biomaterial interactions in whole blood under a defined flow condition. In order to evaluate the feasibility of this system, two different segmented polyether-poryurethanes (SPEUs), PU-PTMG(650) and PU-PTMG(2000), were chosen as test polymers. Surface characteristics verified with electron spectroscopy for chemical analysis (ESCA) and contact angle measurements showed similar results in both SPEUs. Blood was perfused at a wall shear rate of 200 s(-1) for 20 min. Excitation light was applied for 2 s at 1 min intervals. The real-time image was then analyzed at each time point for the percentage of surface area of platelet coverage. Plasma beta-thromboglobulin (beta-TG) levels were also measured before and after each run. PU-PTMG(650) showed a significantly higher number of adhered platelets than PU-PTMG(2000) at each time point. beta-TG levels of PU-PTMG(650) were also higher than those of PU-PTMG(2000), which is comparable to the results of EVM. Thus, this EVM system has been proven to be an excellent and highly sensitive in vitro analytical method for evaluating platelet/biomaterial interactions.

Suitable evaluation systems are critical for ranking various biomaterials in order to develop a method to design and synthesize nonthrombogenic biomaterials. We have recently developed an in vitro test system to evaluate platelet/biomaterial interactions in whole blood. The system consists of a parallel plate flow cell and epifluorescent video microscopy (EVM). A glass coverslip coated with a polymer was incorporated into the flow cell, and blood was perfused using a syringe pump via a polymer-coated PVC tubing connected to the flow cell. Whole human blood was anticoagulated with heparin (2 U/ml), and the platelets were labeled with the fluorescent dye mepacrine (5 mu M). This system permitted real-time and dynamic observations of platelet/biomaterial interactions in whole blood under a defined flow condition. In order to evaluate the feasibility of this system, two different segmented polyether-poryurethanes (SPEUs), PU-PTMG(650) and PU-PTMG(2000), were chosen as test polymers. Surface characteristics verified with electron spectroscopy for chemical analysis (ESCA) and contact angle measurements showed similar results in both SPEUs. Blood was perfused at a wall shear rate of 200 s(-1) for 20 min. Excitation light was applied for 2 s at 1 min intervals. The real-time image was then analyzed at each time point for the percentage of surface area of platelet coverage. Plasma beta-thromboglobulin (beta-TG) levels were also measured before and after each run. PU-PTMG(650) showed a significantly higher number of adhered platelets than PU-PTMG(2000) at each time point. beta-TG levels of PU-PTMG(650) were also higher than those of PU-PTMG(2000), which is comparable to the results of EVM. Thus, this EVM system has been proven to be an excellent and highly sensitive in vitro analytical method for evaluating platelet/biomaterial interactions.

Temperature-responsive poly(N-isopropylacrylamide-co-butyl methacrylate) gels exhibit ''on-off'' regulation of drug release in response to temperature. In a previous study, swelling kinetics of these gels from deswollen to swollen states at several temperatures were investigated. It was demonstrated that the swelling behavior of the gel changed at various temperatures, yielding several patterns of drug release profiles. At 20-degrees-C, gel swelling increased with time, which was explained using a Case-II transport mechanism. In this mechanism, the glassy polymer matrix core acts to suppress the swelling of the outer region when swelling forces dominate. By reducing the experimental temperature to 10-degrees-C and utilizing the greatly enhanced hydration of polymer chains after disappearance of the glassy core, a sigmoidal swelling pattern gives rise to novel drug release profiles. In this study, these swelling mechanisms have been verified in detail by theoretical analysis. The existence of a swelling front was confirmed by observation of the colored gel using a dye. When the thickness of gel was changed. the acceleration of swelling was delayed with increasing thickness, and the acceleration times agreed with theoretical values predicted from the model. The observed changes in diameter and thickness of the gel also supported the model. These results demonstrate the validity of the model presented in the previous paper.

Temperature-responsive poly(N-isopropylacrylamide-co-butyl methacrylate) gels exhibit ''on-off'' regulation of drug release in response to temperature. In a previous study, swelling kinetics of these gels from deswollen to swollen states at several temperatures were investigated. It was demonstrated that the swelling behavior of the gel changed at various temperatures, yielding several patterns of drug release profiles. At 20-degrees-C, gel swelling increased with time, which was explained using a Case-II transport mechanism. In this mechanism, the glassy polymer matrix core acts to suppress the swelling of the outer region when swelling forces dominate. By reducing the experimental temperature to 10-degrees-C and utilizing the greatly enhanced hydration of polymer chains after disappearance of the glassy core, a sigmoidal swelling pattern gives rise to novel drug release profiles. In this study, these swelling mechanisms have been verified in detail by theoretical analysis. The existence of a swelling front was confirmed by observation of the colored gel using a dye. When the thickness of gel was changed. the acceleration of swelling was delayed with increasing thickness, and the acceleration times agreed with theoretical values predicted from the model. The observed changes in diameter and thickness of the gel also supported the model. These results demonstrate the validity of the model presented in the previous paper.

Absorbancy of a solution in the narrow lumen of a tubular membrane under dialysis is continuously measurable with a newly-developed apparatus using quartz optical fibers. The solute permeability of the membrane was determined by calculating time-dependent changes in the absorbancy measured with the apparatus by the mathematical solution derived for unsteady-state concentration profiles in an infinitely long composite cylinder. This method was independent of convective mass transport and osmotic flow through membranes, leading to superiority to ordinary techniques with respect to accuracy.

Absorbancy of a solution in the narrow lumen of a tubular membrane under dialysis is continuously measurable with a newly-developed apparatus using quartz optical fibers. The solute permeability of the membrane was determined by calculating time-dependent changes in the absorbancy measured with the apparatus by the mathematical solution derived for unsteady-state concentration profiles in an infinitely long composite cylinder. This method was independent of convective mass transport and osmotic flow through membranes, leading to superiority to ordinary techniques with respect to accuracy.

In recent years, temporal control of drug delivery has been of interest to achieve improved drug therapies. Intelligent drug delivery systems (DDS) are one expected result, demonstrating an ability to sense external environmental changes, judge the degree of external signal, and release appropriate amounts of drug. Intelligent DDS may be achieved using stimuli-responsive polymeric hydrogels which alter their structure and physical properties in response to external stimuli. Pulsatile drug release has the advantages of avoiding drug tolerance or matching the body's release of specific peptides or hormones. In this review, recent studies for pulsatile drug delivery in response to stimuli such as chemical agents, pH, electric fields, and temperature are discussed. Achievement of pulsatile drug release from stimuli-responsive polymeric hydrogels as on-off switches and its mechanism are reviewed in terms of control for stimuli-responsive swelling.

In recent years, temporal control of drug delivery has been of interest to achieve improved drug therapies. Intelligent drug delivery systems (DDS) are one expected result, demonstrating an ability to sense external environmental changes, judge the degree of external signal, and release appropriate amounts of drug. Intelligent DDS may be achieved using stimuli-responsive polymeric hydrogels which alter their structure and physical properties in response to external stimuli. Pulsatile drug release has the advantages of avoiding drug tolerance or matching the body's release of specific peptides or hormones. In this review, recent studies for pulsatile drug delivery in response to stimuli such as chemical agents, pH, electric fields, and temperature are discussed. Achievement of pulsatile drug release from stimuli-responsive polymeric hydrogels as on-off switches and its mechanism are reviewed in terms of control for stimuli-responsive swelling.

Thermo-responsive hydrogels of poly(N-isopropylacrylamide-co-butyl methacrylate) (poly-(IPAAm-co-BMA)) are capable of swelling-deswelling changes in response to external temperature. As poly(IPAAm-co-BMA) gels swell larger at a lower temperature, the degree and rate of the swelling could be controlled by temperature without altering the chemical structure. Therefore, drug release profiles were remarkably changed by alternation of temperature. The release profiles of indomethacin from poly(IPAAm-co-BMA) were observed to be zero-order at 20-degrees-C. This release profile was explained in terms of a Case-II diffusion mechanism; which indicates relaxation of polymer chains with swelling was rate-determining. In the case of 10-degrees-C, release demonstrated a sigmoidal profile. The acceleration of drug release was due to a rapid increase in swelling with disappearance of the glassy core which had constrained swelling. The regulation of the water-uptake process by changing external temperature remarkably affected drug release and resulted in several different release profiles.

The authors have demonstrated that an amphiphilic block co-polymer composed of 2-hydroxyethyl methacrylate (HEMA) and styrene (HEMA-st) showed excellent blood compatibility in in vitro, ex vivo, and in vivo experiments. The poor elastomeric properties of HEMA-st, however, have been an obstacle to its wider application in medical devices. To improve the mechanical properties of HEMA-st, the authors have developed a new amphiphilic block co- polymer composed of HEMA and octylstyrene (HEMA-oct). The size and morphology of the microdomain structures of HEMA-oct observed by transmission electron microscopy were similar to those of HEMA-st. Kink resistance tests showed improved elastomeric properties of HEMA-oct over HEMA-st. The blood compatibility of HEMA-oct was evaluated using an in vitro flow cell system combined with an epifluorescent video microscope, in which real time platelet adhesion and activation in whole blood can be observed and quantified, and ex vivo rabbit A-A shunt experiments. HEMA-st and a polyurethane (Pellethane(TM)2363-80AE) were used for comparison. In a flow cell system, both HEMA-st and HEMA-oct showed minimal platelet coverage on the surfaces and less platelet activation as measured by β-thromboglobulin (β-TG), whereas Pellethane showed a considerable amount of platelet coverage with high β-TG production. A-A shunt occlusion times were 309 ± 31.2 min for HEMA-st, 251 ± 47.7 min for HEMA-oct, and 30 ± 3.4 min for Pellethane. Thus, HEMA-oct has improved elastomeric properties while still preserving excellent blood compatibility, comparable to HEMA-st, and has a significant potential to be widely applied as a coating to the blood contacting surfaces of various medical devices.

To clarify ion transport, dialysis membranes are evaluated in terms of zeta potential calculated by the Helmholtz-Smoluchowski equation from data on streaming potential ΔE and pressure drop ΔP, depending upon the operating conditions at which the values are measured. The objective of the current study is to design an improved method for measurement of ΔE and ΔP of hollow fiber dialysis membranes and to clarify the diffusive permeability of hydrogen phosphate ion. A polytetrafluoroethylene cylindrical cell with an inside diameter of 14 mm and a height of 10 mm was packed with 2,000-3,000 pieces of hollow fibers, and glass filters were set on either side of the cell. Deaerated water purified by ion exchange and reverse osmosis with an electric conductivity of approximately 150 μS/m was caused to flow in the hollows at 293 K to determine ΔE and ΔP. A good linear relationship between ΔE and ΔP and the reproducibility of the data was obtained and is shown in Figures 5 and 6, demonstrating the utility of the improved method to measure ΔE and ΔP, and the validity of the Helmholtz-Smoluchowski equation to calculate zeta potential from data on ΔE and ΔP. Hydrogen phosphate ion permeability increased with zeta potential for the membranes at about the same rate as pure water permeability. This indicates that hydrogen phosphate ion permeability depends upon the charge and internal structure of dialysis membranes.

Thermo-responsive hydrogels of poly(N-isopropylacrylamide-co-butyl methacrylate) (poly-(IPAAm-co-BMA)) are capable of swelling-deswelling changes in response to external temperature. As poly(IPAAm-co-BMA) gels swell larger at a lower temperature, the degree and rate of the swelling could be controlled by temperature without altering the chemical structure. Therefore, drug release profiles were remarkably changed by alternation of temperature. The release profiles of indomethacin from poly(IPAAm-co-BMA) were observed to be zero-order at 20-degrees-C. This release profile was explained in terms of a Case-II diffusion mechanism; which indicates relaxation of polymer chains with swelling was rate-determining. In the case of 10-degrees-C, release demonstrated a sigmoidal profile. The acceleration of drug release was due to a rapid increase in swelling with disappearance of the glassy core which had constrained swelling. The regulation of the water-uptake process by changing external temperature remarkably affected drug release and resulted in several different release profiles.

The authors have demonstrated that an amphiphilic block co-polymer composed of 2-hydroxyethyl methacrylate (HEMA) and styrene (HEMA-st) showed excellent blood compatibility in in vitro, ex vivo, and in vivo experiments. The poor elastomeric properties of HEMA-st, however, have been an obstacle to its wider application in medical devices. To improve the mechanical properties of HEMA-st, the authors have developed a new amphiphilic block co- polymer composed of HEMA and octylstyrene (HEMA-oct). The size and morphology of the microdomain structures of HEMA-oct observed by transmission electron microscopy were similar to those of HEMA-st. Kink resistance tests showed improved elastomeric properties of HEMA-oct over HEMA-st. The blood compatibility of HEMA-oct was evaluated using an in vitro flow cell system combined with an epifluorescent video microscope, in which real time platelet adhesion and activation in whole blood can be observed and quantified, and ex vivo rabbit A-A shunt experiments. HEMA-st and a polyurethane (Pellethane(TM)2363-80AE) were used for comparison. In a flow cell system, both HEMA-st and HEMA-oct showed minimal platelet coverage on the surfaces and less platelet activation as measured by β-thromboglobulin (β-TG), whereas Pellethane showed a considerable amount of platelet coverage with high β-TG production. A-A shunt occlusion times were 309 ± 31.2 min for HEMA-st, 251 ± 47.7 min for HEMA-oct, and 30 ± 3.4 min for Pellethane. Thus, HEMA-oct has improved elastomeric properties while still preserving excellent blood compatibility, comparable to HEMA-st, and has a significant potential to be widely applied as a coating to the blood contacting surfaces of various medical devices.

To clarify ion transport, dialysis membranes are evaluated in terms of zeta potential calculated by the Helmholtz-Smoluchowski equation from data on streaming potential ΔE and pressure drop ΔP, depending upon the operating conditions at which the values are measured. The objective of the current study is to design an improved method for measurement of ΔE and ΔP of hollow fiber dialysis membranes and to clarify the diffusive permeability of hydrogen phosphate ion. A polytetrafluoroethylene cylindrical cell with an inside diameter of 14 mm and a height of 10 mm was packed with 2,000-3,000 pieces of hollow fibers, and glass filters were set on either side of the cell. Deaerated water purified by ion exchange and reverse osmosis with an electric conductivity of approximately 150 μS/m was caused to flow in the hollows at 293 K to determine ΔE and ΔP. A good linear relationship between ΔE and ΔP and the reproducibility of the data was obtained and is shown in Figures 5 and 6, demonstrating the utility of the improved method to measure ΔE and ΔP, and the validity of the Helmholtz-Smoluchowski equation to calculate zeta potential from data on ΔE and ΔP. Hydrogen phosphate ion permeability increased with zeta potential for the membranes at about the same rate as pure water permeability. This indicates that hydrogen phosphate ion permeability depends upon the charge and internal structure of dialysis membranes.

Exposure of platelets to shear stress leads to aggregation in the absence of exogenous agonists. We have now found that different adhesive proteins and platelet membrane glycoproteins are involved in aggregation depending on the shear stress conditions and the concentration of divalent cations in the medium. When blood is collected with trisodium citrate as anticoagulant, which causes a decrease in the levels of external ionized calcium ([Ca2+]0), platelet aggregation can be induced under low shear force (12 dyn/cm2) and is mediated by fibrinogen binding to the glycoprotein IIb-IIIa complex. Aggregates formed under these conditions are not stable, and when shear force is increased to 68 dyn/cm2, disaggregation results. By contrast, platelets from blood collected with hirudin as anticoagulant, wherein [Ca2+]0 is within normal plasma levels, do not undergo low shear-induced aggregation; however, after exposure to a shear force above 80 dyn/cm2, aggregation is observed but only when von Willebrand factor is present and can interact with both its platelet binding sites, glycoprotein Ib-IX and glycoprotein IIb-IIIa. Fibrinogen is not involved in high shear-induced aggregation which, in fact, occurs normally in patients with severe afibrinogenemia. Thus, von Willebrand factor in the absence of exogenous agonists can mediate platelet aggregation in experimental conditions that may mimic the hemorheological situation of partially occluded arteries. This pathway of platelet aggregation involving only one adhesive ligand and two membrane adhesion receptors may play a relevant role in thrombogenesis.

Exposure of platelets to shear stress leads to aggregation in the absence of exogenous agonists. We have now found that different adhesive proteins and platelet membrane glycoproteins are involved in aggregation depending on the shear stress conditions and the concentration of divalent cations in the medium. When blood is collected with trisodium citrate as anticoagulant, which causes a decrease in the levels of external ionized calcium ([Ca2+]0), platelet aggregation can be induced under low shear force (12 dyn/cm2) and is mediated by fibrinogen binding to the glycoprotein IIb-IIIa complex. Aggregates formed under these conditions are not stable, and when shear force is increased to 68 dyn/cm2, disaggregation results. By contrast, platelets from blood collected with hirudin as anticoagulant, wherein [Ca2+]0 is within normal plasma levels, do not undergo low shear-induced aggregation; however, after exposure to a shear force above 80 dyn/cm2, aggregation is observed but only when von Willebrand factor is present and can interact with both its platelet binding sites, glycoprotein Ib-IX and glycoprotein IIb-IIIa. Fibrinogen is not involved in high shear-induced aggregation which, in fact, occurs normally in patients with severe afibrinogenemia. Thus, von Willebrand factor in the absence of exogenous agonists can mediate platelet aggregation in experimental conditions that may mimic the hemorheological situation of partially occluded arteries. This pathway of platelet aggregation involving only one adhesive ligand and two membrane adhesion receptors may play a relevant role in thrombogenesis.

Appropriate design of dialysis membranes requires correct values of structural parameters such as pore radius, surface porosity, water content and tortuosity. It is impossible, however, to find the pore radius of dialy sis membranes using a mercury porosimeter or an electron microscope because the pores are only several tens of angstroms in radius. Consequently, diffu sional and convectional procedures such as the Lw method that uses both pure water permeability and water content, the Lw and Pm method which uses both solute and pure water permeability, and the σ method which uses the reflection coefficient, have been employed extensively to determine the pore radius of dialysis membranes. The structural parameters of symmetric membranes are determined from water content, solute and pure water permeability data based on the Lw and Pm method combined with the tortuous pore model we have pro posed. Determination of the structural parameters of microfiltration mem branes for plasma separation having huge pores by various methods is required to verify the method of characterizing dialysis membranes based on the tor tuous pore model. A dyeing method is also suitable for characterizing dialysis membranes of regenerated cellulose. Pore model studies using permeability and water content data for sterilized and treated membranes facilitate optimal design of dialysis membranes for clinical applications. © 1989, Sage Publications. All rights reserved.

This study elucidates changes in membrane structure and permeability due to the methods of sterilisation and the conditions under which they are carried out. Tubular dialysis membranes of regenerated cellulose having various values for porosity were sterilised by ethylene oxide gas, autoclave or gamma irradiation under varying conditions. Non-sterilised membranes were included as controls. The solute permeability of the membranes was determined using14C-urea. The membranes tested showed no difference in clearance of urea or creatinine. Gamma-ray sterilisation under dry conditions greatly reduced the vitamin B12 clearance and hydraulic permeability of membranes with a water content of below 60%. Hydraulic permeability increased with gamma irradiation for membranes sterilised under wet conditions. A reduction in vitamin B12 clearance for membranes with a water content of above 60% resulted after autoclave sterilisation. Pore model calculation reveals that membrane shrinkage resulted from sterilisation both by gamma-rays under dry conditions, and by autoclave. Thus, the structure of dialysis membranes varies with the method of sterilisation and the conditions under which the sterilisation is carried out. © 1987 European Dialysis and Transplant Association-European Renal Association.