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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The purification of dialysate has been widely discussed. It is necessary to reduce endotoxin concentration first, and essential to measure endotoxin concentration continuously in order to prevent endotoxin contamination. We have developed a system for inline monitoring of endotoxin. In the previous study, it was possible to measure endotoxin concentrations above 40EU/l at a reaction time of 30min. However, the sensitivity was insufficient for purposes of endotoxin monitoring. In the present study, we developed a inline measuring system based on flow injection and using a 6-position rotary valve to control dispersion and prevent contamination. The absorbance of the reaction product was linearly related to endotoxin concentrations ranging from 0 to 125EU/l at a reaction time of 20min. These results demonstrate that it is possible to control endotoxin concentration using this new system, which could make a vital contribution to safe and comfortable dialysis treatments.

«BIOREX AM-BC-X» is a new cellulosic membrane whose pore size is distributed asymmetrically in the membrane wall. 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 the asymmetric membrane capable of suppressing the inflow of endotoxins from dialysate, and thereby to contribute to the design of a more effective dialysis mem-brane. Using membranes that have tight layers on both sides (drum-shaped membrane), «(BIOREX AM-BC-X») 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 blood and a significant lowering of endotoxin inflow from the dialysate. In asymmetric dialysis membranes, the anisotropy of solute permeability is caused by the difference in the amount of solute transfer due to filtration from the inside out and from the outside in.

Molecular imprinting is a new technology used for synthe-sis of polymers potentially useful in sensing or separating devices with antibody-like specificity. Here we report that a thin layer of molecularly imprinted copolymer has the property of increasing its diffusive permeability in the presence of its template. A thin layer of molecularly imprinted poly (methacrylic acid -co- ethyleneglycol dimethacrylate) against theophylline was formed on the surface of indium-tin oxide (ITO). Cyclic voltammetry was performed with ferrocyanide using the copolymer-grafted ITO as a working electrode in the presence or absence of the template. The presence of the template remarkably enhanced the anodic current. This result suggests that the diffusive permeability of the thin layer of molecularly imprinted polymer is sensitive to the presence of its template molecule. This hypothesis is supported by atomic force micrography, in which the surface porosity of the layer of molecularly imprinted polymer is increased by 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) is sensitive to the presence of its template.

We have developed a new system to evaluate platelet adhesion on the surface of biomaterials under a defined flow condition. This system could be applied to the evaluation of blood compatibility of opaque materials such as metal, ceramics, etc., none of which could be examined in our previous system. In this study, we have evaluated pure-Titanium, SUS-316L, Heparin-immobilized pure-Titanium, Heparin-immobilized SUS316L with this EVM system. Heparin-immobilized metal surfaces showed significantly lower platelet adhesional behavior than did the non-treated metal surfaces (<0.05). In contrast, no significant differences were observed between the other metals. These results showed that heparin immobilization was effective in improving the blood compatibility of metal. Further, it was found that this EVM system was reliable as an in vitro screening method for the evaluation of blood compatibility of opaque biomaterials.

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.

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.

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.

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 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.

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.

We tried to control mass transport and microstructure in collagen gel applied to cell culture medium. An aqueous solution of type I atelocollagen of pigskin was cast into a glass Petn-dish and dried to control collagen concentration. Then, the semi-dried film of collagen was crosslnked with glutaraldehyde aqueous solution saturated by sodium chloride. Finally, a collagen-gel flat membrane was obtained after washing the crosslinked thin film with excess pure water. Analysis of intramembrane diffusivity of the membranes using the tortuous pore diffusion model represented that glutaraldehyde concentration at crosslinkng had no effect on microstructure of the membranes. On the other hand, intramembrane diffusivity of the membranes was depend on collagen concentration at crosslinking in the range of 77-96 wt%. The collagen concentration was also correlated with structural parameters of the membranes. In conclusion, we could obtain various collagen-gel flat membranes with different solute permeabilities and microstructures.

The segmented polyether urethanes (PEUs) have been used in implantable medical devices because of excellent mechanical properties, acceptable blood compatibility, and good biostability. However, recent studies demonstrated that polyether soft segment of PEU was susceptible to oxidative degradation in vivo due to the scission of the polyether group. Recently, polycarbonate urethanes (PCUs) having no ether linkage in the soft segment have been developed, and showed improved stability against oxidative degradation over PEUs. The present study evaluated blood compatibility of these PCUs in comparison to PEUs using our epifluorescent video microscopy (EVM) combined with a parallel plate flow chamber. We selected five PCUs: PCU(1090), PCU(1140), PCU(1150), PCU(1560) and Corethane 80A, and two PEUs: Pellethene2363-80AE and Tecoflex EG80A, all of which have similar hard segment compositions(MDI or HMDI: BD). The EVM measured the amount of platelet coverage on the surfaces using human whole blood perfused at a wall shear rate of 100s^-1 for 20 min. PCUs surfaces showed lower platelet adhesion comparable to PEUs. The amount of platelet adhesion depended on molecular weight of soft segment. Based on these results, it is recommenced that PEUs should be replaced by ether free PCUs for the application to implantable blood contacting devices such as artificial hearts and pacemaker leads insulations.

One of the factors to reduce the performance of a hemodialyzer during clinical treatment is membrane fouling caused by protein adsorption. Highly permeable dialysis membranes recently developed are of asymmetrical structure and the reduction in permeability after protein adsorption may vary with their asymmetrical structure. Intramembrane diffusion coefficients and rejection factor for several solutes of polysulfone membranes having asymmetrical structure were measured before and after plasma protein adsorption. Ratio of intramembrane diffusion coefficient to diffusion coefficient in water for higher molecular weight solutes is reduced after plasma protein adsorption, but that for lower molecular weight solutes is slightly reduced. Rejection factor after plasma protein adsorption increases at lower filtration flux especially for smaller molecules, but that at higher filtration flux hardly changes.

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. In evaluating dialysis membranes, the most important factors are diffusive and hydraulic permeability. It is primarily through diffusion, resulting from the difference in concentration between the blood and the dialysate, that the toxins and ions pass through the dialysis membrane. Thus if diffusive and hydraulic permeability can be measured, it becomes possible to evaluate dialysis membranes.<br>Basically, the diffusive permeability can be found from data on differences in concentration and on the solute flux obtained when filtration flux is set to zero. Techniques for the measurement of the diffusive and hydraulic permeability of flat dialysis membranes are already well established and measurement is comparatively simple, but this is not the case for hollow-fiber dialysis membranes.<br>To find the hydraulic permeability of a dialysis membrane, the filtrate volume obtained at a certain trnsmembrane pressure is measured over a given period of time. If a dialyzer is used, the (static) pressure of the fluid along the length of the flow channel changes, so that it is technically difficult to determine transmembrane pressure accurately while the blood and dialyste are flowing. Thus in measuring the filtration coefficient available method include the dead-end or complete filtration method.<br>This paper describes dialysis membrane and dialyzer for blood purification, solute transport mechanism of membrane and technical evaluation of dialysis membrane. The next generation of artificial kidney is lastly viewed.

An outside blood flow membrane oxygenator (OFMO) currently available in clinical treatments was developed by the try-and-error method where much time and cost were spent. The objective of the present study is to simulate the blood flow and oxygen transfer rate of the OFMO. The Darcy's law for fluid flow through porous media and the enhancement factor for the mass transfer with chemical reaction were used for evaluation of the blood flow and oxygen transfer rate of the OFMO, respectively. The governing differential equations were numerically solved by the finite element method. Simulation analysis of the blood flow found that channeling occurred depending on fiber arrangement. These results agree well with visual observations previously obtained in our laboratory by X-ray computed tomography. Simulation analysis of the oxygen transfer rate of the OFMO, where the liquid side mass transfer coefficient for blood k_LB, estimated using the dimensionless equations of mass transfer coefficient in fluid flow outside a tube, was used, is capable of theoretically predicting the oxygen transfer performance of the OFMO. We conclude that the simulation analysis using both Darcy's law and enhancement factor is useful for evaluation of the blood flow and oxygen transfer rate of the OFMO.

A stopped flow type system consisting of a single tube for monitoring endotoxin by the limulus test was developed. In this system sample solution reacted with limulus reagent without contact with outer atmosphere. The objective of the present study is to obtain a sensitive system for monitoring endotoxin concentration ranging under 100 EU/l in a short time. Peak area of absorbance observed as a function of reaction time at 405 nm was similar to absorbance observed with batch reaction. Short time monitoring of endotoxin concentration ranging above 40 EU/l at a reaction time of 20 min and 80 EU/l at 10min was possible.

Biocompatibility of dialysis membrane has been studied directing our attention to difference in membrane material. To clarify a membrane of thrombus formation, it should be evaluated with respect to not only membrane material but also flow characteristics on membrane surface depending on surface roughness. Platelet adhesion on the membrane surface was measured using 5 dialysis membranes of different surface roughneses. Bovine blood (500ml) added with trisodium citrate dihydrate (approximately 2g) as an anticoagulant was circulated in a test dialyzer at a flow rate of 200ml/min. Pressure drop and flow rate of PMMA (particle diameter: 1μm) suspension in glycerol(Bingham fluid)(glycerol: PMMA=2: 1 by weight ratio) were measured to determine yield stress. The yield stress of the membranes and increased with surface roughness. The amount of platelet adhesion increased with yield stress, indicating that the platelet adhesion depends on surface roughness.

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.

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.

Conventional drug release regulation using hydragels was depended on drug diffusive transport in the gels. In contrast, we investigated a novel thermo-responsive drug release regulation synchronized with convectional water outflow induced by aggregation of network containing comb-type graft chains. Deswelling kinetics of conventional gel without graft chains becomes slow: size-upended kinetics is obtained. This is because swelling to deswelling changes of the conventional gel is governed by collective diffusion of network. In contrast, poly (N-isopropylacrylamide) (PIPAAm) network containing combtype PIPAAm grafts with freely mobile ends shows rapid deswelling changes in response to stepwise temperature changes above 32°C. The graft chains undergo rapid dehydration with temperature changes, accelerating the deswelling changes, of the grafttype gel due to strong hydrophobic interaction between dehydrated graft chains. Difference is apparent in drug release pattern from the conventional gel and the graft-type gel. Upon increasing temperature, the conventional gel stops the drug diffusion due to formation of skin layers at the gel surface. In contrast, pulsed drug release is achieved synchronized with the convectional water release during the rapid deswelling of the graft-type gel. Details are studied for a new function of thermoresponsive graft-type gel as a micro-pumping matrix.

A commercially available flat membrane of type I atelocollagen was crosslinked by 1% gultalaldehyde aqueous solution without reduction in the high water content. Diffusivity of the solutes with molecular weight under 45, 000 for the collagen-gel membrane was much higher than those for hemodialysis membranes, while that of albumin for thee collagen-gel membrane was nearly equal to those for the hemodialysis membranes. A novel hollow fiber membrane was prepared by filling collagen gel into the pores of a membrane for plasmapheresis using filtration of 3g/l collagen solution to make the thickness of collagen gel thinner without reduction in mechanical strength. Observation by scanning electron microscopy and analysis of the time-coursed changes in filtration flux of the collagen solution by the filtration laws of Hermans and Bredee suggested the thickness of collagen-gel layer filled in the pores was about 1 micrometer. Diffusivity of solutes in the collagen-gel layer in the pores calculated from the solute permeability of the collagen-gel-filling membrane was almost equal to that of the collagen-gel flat membrane.

We have evaluated four surface modification techniques for polymeric materials used in the blood contacting artificial organs. Proposed approaches to design nonthrombogenic polymer surfaces include 1) phase separated microdomain surfaces, 2) hydrophilic surfaces, 3) bioactive molecule incorporated surfaces, 4) biomembranelike surfaces. We have developed several in situ surface modification techniques according to these approaches to improve the blood compatibility of blood contacting surfaces of medical devices, including 1) HEMA-styrene block copolymer coating (HEMA/st), 2) poly ethylene glycol grafting (EG), 3) human thrombomodulin immobilization (hTM), 4) 2-methacryloyl oxyethyl phosphorylcholin (MPC) copolymer coating onto segmented polyurethane (PU) surfaces. These surface-modified PUs were evaluated using an epifluorescent video microscope combined with a parallel plate flow cell (EVM system) for assessing in vitro platelet adhesion and complement activation. All surfaces showed significantly lower platelet adhesion than nontreated PU, and showed the ranking of the amount of adhered platelet as follows: PU>EG>hTM>MPCs>HEMA/st. As for complement activation, hTM showed the least C3a production, which attributed to its inherent inhibitory effects on complement activation. Ever known characteristics of each material were confirmed in this experiment. Thus, this EVM system has been proven to be an excellent in vitro analytical method for relative evaluations of nonthrombogenicity of biomaterials.

Highly permeable dialysis membranes of asymmetrical structure were developed to mitigate amyloidosis which patients undergoing long-term dialysis treatment caught. Filtration and backfiltration through the membranes play an important part in solute transport. The rejections of the asymmetrical membranes are different between transport directions. To design high performance membranes, it is important to clarify the effects of the difference in rejection between directions of solute transport. Rejection and overall mass transfer coefficient of dextran were determined by filtration and counter-current dialysis experiments to compare transport characteristics of gradient structure membranes having a skin layer inside the wall of hollow fibers with those of the reverse gradient structure membranes having a skin layer outside. Overall mass transfer resistance and rejection of the gradient structure membranes are lower for transport from outside to inside than for that from inside to outside, indicating that solutes are easy to move from outside to inside. On the other hand, those of the reverse gradient structure membranes are lower for transport from inside to outside than for that from outside to inside, indicating that solutes are easy to move from inside to outside. The solute transport characteristics of the reverse gradient structure membranes are suitable for dialysis treatment. We conclude that thee overall mass transfer coefficient of the asymmetrical dialysis membrane increases by providing them with differences in rejection between transport directions.

A response current may be changed by fouling caused by protein or fibrobrast adsorption when a glucose sensor is implanted. By making the slope of glucose concentration in an enzyme layer flat, the influence of the fouling layer can be disregarded. In the present study, ferrocene binding with bovine serum albumin was used as a mediator of the glucose sensor. The proportionality between transient current after activation of glucose oxidase controlled by pulse potential and glucose concentration was examined. As a result, reaction right after the activation was not controlled by glucose diffusion, and transient current was dependent on glucose concentration. In conclusion, glucose concentration is determinable by measurement of transient current after the activation of glucose oxidase in the enzyme layer, and this method is applicable to long-term monitoring of glucose concentration.

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 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.

Solute permeability reduction of dialysis membrane caused by protein adsorption is one of the factors to reduce its performance during clinical hemodialysis. Many highly permeable dialysis membranes recently developed have asymmetrical structure and may vary the performance and the performance reduction after protein adsorption depending on their asymmetrical structure. To determine the diffusive permiability for Thiourea, Tryptophan, Riboflavin, VitaminB₁₂, Cytochrome C of polysulfone dialysis membrane (PS-400, PS-UW, PS-NW, APS), dialysis experiments were made at 310K before and after bovine plasma protein adsorption using a single hollow fiber dialysis membrane at both ends of which optical fibers were inserted into the hollow. Dependence of ratio of intramembrane diffusion coefficient to diffusion coefficient in water, Dm/Dw on stokes radius and reduction of Dm/DW after the plasma protein adsorption were reflected with their asymmetrical structure. Dm/Dw for higher molecular weight solutes after the plasma protein adsorption reduced and that for lower molecular weight solutes slightly reduced. The ratio of membrane resistance to overall mass transfer resistance of higher permeable membranes (PS-UW, PS-NW, APS) was lower than that of conventional membrane (PS-400). Clearance reduction for larger solutes after the plasma protein adsorption attribute to the increase in membrane resistance and largeness of membrane resistance ratio to overall mass transfer resistance.

To improve the performance of dialysis membranes, it is important to relate diffusive and convective permeabilities with asymmetrical structure of the membranes. We evaluated the asymmetrical structure of three polysulfone dialysis membranes (PS-400, PS-UW, APS) by observation with SEM, comparison of sorption rates, BET method and DSC method. The membranes were found to consist of the skin layer near the inner surface and the supporting layer at interior region and the outer surface of the membranes by the observation with SEM. The sorption rate curves of inside to outside and outside to inside were different for PS-400 and PS-UW, and were the same for APS, suggesting that the differences in the sorption rate curve were attributed to the difference in the structure of the skin layer and the supporting layer. The pore size distributions of the membranes determined by BET method could not be evaluated for larger pore that almost comprise the supporting layer. The pore size distributions of the membranes determined by DSC method, representing those of the supporting layer, were similar. In conclusions, the polysulfone dialysis membranes consist of the skin layer and the supporting layer, and have the difference in structure of skin layer.

Highly permeable dialysis membranes with asymmetrical structure are developed to mitigate the amyloidosis of the patients on long-term dialysis treatment. The information on the convective solute transport of the dialysis membranes has increased its importance. We measured rejections of asymmetrical polysulfone dialysis membranes (PS-UW, PS-NW, APS) for dextrans with various molecular weights (10, 000-70, 000) before and after bovine plasma protein adsorption, and related the rejection of the membranes to their asymmetrical structure. Solute rejection of the membrane decreased in order of PS-UW, PS-NW, APS and pure water permeability increased in the same order. Rejection for higher molecular weight solutes at higher filtration flux decreased with increasing filtration flux, whereas that for lower molecular weight solutes increased. The tendency appeares in asymmetrical membrane in which the solute rejection of outside surface was larger than that of interior region of the membrane. Increase in rejection coefficient after the plasma protein adsorption was larger at lower filtration flux for lower molecular weight solutes. We conclude that molecular weights of solutes and the asymmetrical structure of the membranes affect the solute rejection of the membranes and the dependence of the rejection on the filtration flux.

The authors have evaluated blood compatibility of in situ heparin immobilized and sulfonated polyurethane (PU) using our epifluorescent video microscopy (EVM) combined with parallel plate flow chamber. EVM system measured the amount of adhered platelet on the surface under the flow of human whole blood containing mepacrine labelled platelets perfused at a wall shear rate of 100/sec every one minute intervals for 20min. Platelet activation (β-TG) and complement activation (C3a) were also measured. Both heparin immobilized and sulfonatedPUs showed significantly lower levels of platelet adhesion than the control PU.The β-TG levels of these modified PUs also correspond to the results of the platelet adhesion. As for the complement activation, while sulfonated PU and the control PIP showed a higher levels of complement activation. In situ surface modification techniques, which utilize either ozone oxidation or photo reaction are useful in a variety of medical devices even of a complex design, such as a membrane oxygenator or artificial heart.

Endotoxin concentration in dialysate fluid should be frequently monitored. But conventional limulus test needs complicated operation to prevent the contamination by atmospheric endotoxin. We have developed the flow type measurement system using single tube in which sample solution reacted to limulus reagent without contact with atmosphere. The objective of the present study is to gain a sensitivity of the system to measure the endotoxin concentration ranging under 100EU/1 accurately. Batch reaction experiments and flow type measurements were performed to determine the optimal wavelength and the reaction time for optimal operation of the continuous system. The highest sensitivity is obtained at a wavelength of 381nm for measuring the endotoxin concentration by limulus reagent. Proper reaction time differed depending on concentration range of samples. The sensitivity of measuring the endotoxin concentration ranging under 100EU/1 increased with reaction time. But longer reaction time in the flow type measurement system produces dispersion of the limulus reagent and lower sensitivity. Optimal reaction time of the flow type measurement system is then 45min. Handy and exact measurements of the endotoxin concentration ranging above 50EU/1 were able by the condition of a wavelength of 381nm and a reaction time of 45 min.

We designed a technique of continuous and simple immunoassay using an electrochemiluminescence flow cell for monitoring antibody or antigen concentration as an indication of optimal amount of immunosupressors, and attempted to clarify enhanced ECL intensity produced by the binding of antigen and antibody. Luminol-labeled antigens were used to measure the concentration of these antibodies. Luminol-labeled anti-human serum albumin (HSA) antibody was used to measure HSA concentration. Both anti-HSA antibody and anti-immunogloblin G antibody ranging from 0 to 2.2mg/ml, 0 to 200μg/ml, respectively, increased the ECL intensity of aqueous luminol-labeled antigens. HSA ranging from 0 to 3.8μM also increased the ECL of luminol-labeled anti-HSA antibody. The ECL intensity of luminol-labeled antigen also increased with antibody concentration in bovine plasma. These results demonstrate that this system is promising for the homogeneous immunoassay of antibodies or antigens and the principal reason of ECL intensity enhancement is an increase in quantum yield of luminol caused by the binding of antigen and antibody.

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.

Intramembrane diffusivity and water permeability are essential for characterization of dialysis membranes. The physical state of water present in the membrane may affect the solute diffusivity because solutes diffuse into only a fraction of water in the membrane and water inside the membrane changes places with that outside the membrane. Water content was measured in 31 dialysis membranes made of 7 polymers. The physical state of water was determined from data on water content by the conventional method and the differential scanning calorimetry and on partition coefficient measured by the use of tritium-labeled water. Three kinds of water state of varying molecular mobilities were found in the membranes and their volume ratio was dependent on the membrane material. The mechanism of solute transport through hydrophilic dialysis membranes of regenerated cellulose that strongly put restrictions on the movement of water in the membrane was different from that through hydrophobic dialysis membranes. Analysis of the intramembrane diffusivity of the regenerated cellulose membrane based on the free volume theory revealed that the solute diffusivity was dependent on water content.

We have evaluated blood compatibility of six different segmented polyurethanes (PUs) including five polyether-PUs and one polyurethane-urea (PUU) having PTMG as a soft segment, using our epifluorescent video microscopy (EVM) combined with a parallel plate flow cell. HEMA/Styrene block copolymer (HEMA/St), which we have already proven to be an excellent nonthrombogen is polymer over existing PUs, was used as a control. EVM system measured the amount of adhered platelet on the surfaces under the flow of human whole blood containing mepacrine labelled platelets perfused at a wall shear rate of 200/sec every one minute intervals for 20min. Platelet activation (β-TG) and complement activation (C3a) were also measured. PUU showed significantly higher platelet adhesional behavior than the other PUs. On the other hand, PU-PTMG (MW 1500) showed lowest platelet adhesional behavior among six PUs, which was comparable to HEMA/St. β-TG level of each polymer was somewhat related to platelet adhesional tendency. Complement activation was inversely correlated with the results of platelet adhesion and activation potentials except HEMA/St, which showed least platelet activation and complement activation. From the chemical compositions, we could divide these PUs into three categories: 1) PUU, 2) PU with lower MW of PTMG, 3) PU with higher MW of PTMG. From our experimental results, we could confirm that these PUs were divided into three categories above mentioned, i. e., 1) PU with higher MW of PTMG showed lesser platelet adhesion and higher complement activation than PU with lower MW of PTMG, 2) PUU showed the highest platelet adhesion. Thus, blood compatibility of PUs were much influenced by their chemical compositions.

To clarify ion transport, it is important to evaluate changes in effective charge density and internal structure of the membrane after protein adsorption, because protein adsorption on the membrane may change both their charge and internal structure. Dialysis experiments at 310K were made with cocurrently-operated dialyzers (700 hollow fibers of 25cm long) composed of polysulfone membranes (PS-600, PS-620) to determine the permeability for hydrogenphosphate ion, CuSO₄, NaCl and urea before and after cytochrome C and α-lactalbumin adsorption by the Wilson plot. Urea permeabilities of the membranes decreased after cytochrome C and α-lactalbumin adsorption, indicating the change in the internal structure of the membranes. Ion permeabilities of the membranes adsorbing cytochrome C was larger than that calculated from the change in the internal structure of the membranes that cause a decrease of the effective charge densities of the membranes and that adsorbing α-lactalbumin was close to that calculated from the change in internal structure of the membranes. In conclusion, ion permeability changes after protein adsorption because of altered effective charge density and internal structure of the polysulfone dialysis membranes, and the protein adsorption is an important factor to evaluate the performance of dialysis membrane for medical application.

Many dialysis membranes of varying hydraulic and diffusive permeabilities have been developed to produce high permeability and better biocompatibility, and have been clinically applied to hemodialysis. Diffusive permeability related with membrane structure especially its asymmetric internal structure is important data to prepare high performance membrane. Asymmetric structure of the membrane affects solute transfer rate into the asymmetric membrane by diffusion accompanied with adsorption because equilibrium amount of sorption and diffusion coefficient vary in the membrane. Sorption experiments were made with mini-modules composed of the hollow fibers of which inside was occupied with paraffin to diffuse from only outside to inside and of which outside was occupied with paraffin to diffuse only from inside to outside for protein and dyes of various molecular weights. The differences of adsorption rate curve and shapes of the curve are found to depend on the difference of internal asymmetric structure and the molecular weight of the solute. In conclusion, comparing sorption rate from inside to outside with that from outside to inside of hollow fiber dialysis membrane is capable of estimating the asymmetric structure of the membrane.

Reported herein are solute removal characteristics of P/P HDF with a single bag examined using aqueous solutions. From the results of single pass dialysis experiments at various filtration flow rates, myoglobin clearance significantly increased with filtration flow rate (QPull) and slightly, decreased with increasing backfiltration (QPush). Urea clearance slightly increased with QPull and significantly decreased with QPush. From the results of circulation-dialysis experiments, P/P HDF has a higher efficiency of myoglobin removal and a lower for urea in comparison with HD. From a theoretical analysis using an unsteady state mass transfer model for a hemodiafilter, P/P HDF had negative myoglobin clearance in the push phase. Optimum operating conditions in P/P HDF was determined as a higher QPull, QPush and/or bag volume.

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.

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.

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.

When a membrane oxygenator is used in a liquid-liquid system, entrainment of oxygen bubbles and cell damage caused by the direct contact with the bubbles are eliminated. Enhancement of oxygen transfer rate may give high performance to the membrane oxygenator with high safety. Oxygen transfer experiments were made to determine the oxygen transfer rate of a dialyzer (S. SP-1.5H:Senko Medical Instrument Mfg.) composed of Cuprophan membrane used as a membrane oxygenator. Water, stroma free hemoglobin (SFH) and perfluorooctyl-bromide (PFOB) for gas carriers were used to transfer enough oxygen to water and bovine blood. When PFOB was caused to flow inside the hollow and then the blood outside, oxygen transfer rate was ade-quate. No leak of hydrophobic PFOB to the blood was further observed using hydrophilic membranes.

Development of continuous recirculating peritoneal dialysis(CRPD) as a new dialysis therapy. CRPD was newly introduced in order to improve solute removal efficiency in conventional dialysis therapies such as HD and CAPD. In CRPD, a part of the dialysate in the peritoneal cavity was circulated through a double-lumen catheter and purified by an out-side dialyzer. Safety and solute removal characteristics in CRPD were examined during a canine study. Peritoneal dialysance was obtained by a compartment model for CRPD. From this result, time-averaged concentration of BUN for an 8 hr/day CRPD combined with three exchanges/day CAPD is estimated to be 34.3mn/dl, which is much lower than 45.2mn/dl for a 12 hr/week HD. The optimum design of the out-side dialyzer for CRPD was examined during a study using an aqueous solution. A smaller type of hollow-fiber dialyzer having 87 μm for inner diameter and 112 mm for effective length can be determined as an optimal for CRPD.

Intramembrane diffusivity and water permeability are essential for characterization of dialysis membranes. The physical state of water present in the membrane may affect the solute diffusivity because solutes diffuse into only a fraction of water in the membrane and water inside the membrane changes places with that outside the membrane. Water content was measured in 31 dialysis membranes made of 7 polymers. The physical state of water was determined from data on water content by the conventional method and the differential scanning calorimetry and on partition coefficient measured by the use of tritium-labeled water. Three kinds of water state of varying molecular mobilities were found in the membranes and their volume ratio was dependent on the membrane material. The mechanism of solute transport through hydrophilic dialysis membranes of regenerated cellulose that strongly put restrictions on the movement of water in the membrane was different from that through hydrophobic dialysis membranes. Analysis of the intramembrane diffusivity of the regenerated cellulose membrane based on the free volume theory revealed that the solute diffusivity was dependent on water content.

To monitor the changes in the concentration of antibody produced in body fluids due to infection, we developed a new method for continuous measuring of the antibody concentration. Conventional immunoassay is applicable to heterogeneous reaction between antigen and antibody, and is unavailable for continuous measurement. We used the technique of electrochemiluminescence(ECL) to measure antibody concentration continuouslyin a homogeneous reaction system. We used human serum albumin(HSA) as antigen and luminol as luminous substance, ECL reaction occurred on electrically conductive glass electrode the electric potential of which was kept constant at -0.70V vs saturated calomel electrode(SCE), In conclusion, antibody concentration can be measured continuously by the ECL reaction which is a promising technique of measurement of antibody specifically reacting with antigen.

An optimum designed dialyzer requires an advanced explication of a mechanism of solute transfer through a hollow fiber membrane. As a measurement of dialysate flow condition in the dialyzer is usually difficult to carry out, an explanation of the transfer mechanism has many problems. The overall mass transfer resistance is calculated as a sum of membrane, blood and dialysate side mass transfer resistances. The dialysate side mass transfer resistance influences on the solute clearance. Therefore, this paper describes effect of fins on a dialysis membrane. These fins could decrease the degree of contact of membranes each other in a dialyzer, for increase of the effective surface area, and for improvement on the dialysate flow conditions. Hand made modules of single hollow fiber with and without fins showed no difference in dialysate side mass transfer coefficient. It suggested that the fns have no effects on increasing the dialysate side resistance. A dimensionless calculation with solute clearances showed an increase of effective surface area in a dialyzer having fin type hollow fiber membrane. An observation of dialysate flow pattern with X-ray CT suggested that the fins decrease the channeling in a dialyzer.

Individualized therapy is capable of the quality control of dialysis treatments. In clinical situations, blood chemistries are taken only twice a month. Predicting blood concentrations from dialysate concentrations using mass balance equations is possible with real time evaluation of dialysis treatments at each hemodialysis. We measured the concentrations of urea, creatinine, phosphoric acid and uric acid in dialysate as well as in blood to confirm accuracy of the estimation during hemodialysis with high performance dialyzers for 8 patients. Estimation results for uric acid and phosphoric acid were not very accurate in treatments with high performance dialyzers compared with in those with conventional ones. Then an apparent distribution volume for each solute was determined for better estimation. The apparent distribution volume of uric acid was lower than that of urea, and that of phosphoric acid varied for each patient. These results demonstrate that the individualized therapy using a high performance dialyzer is feasible by collecting dialysate concentration data of the patients on hemodialysis.

To clarify ion transport, it is important to evaluate changes in membrane charge and structure after protein adsorption. Dialysis experiments at 310K were carried out in a parallel flow operation to determine the permeabilityfor hydrogenphosphate ion and urea of polyacrylonitrile membrane (PAN-DX) at varying dialysate flow rates using a test dialyzer of original design composed of 10cm long, 200 hollow fibers before and after cytochrome C and α-lactalbumin adsorption at concentrations of 0.1g/l.<br>Hydrogenphosphate ion permeability of the membrane increased and urea permeability decreased after cytochrome C adsorption that caused an increase in membrane charge. Hydrogenphosphate ion and urea permeabilities decreased after α-lactalbumin adsorption that caused a decrease in membrane charge, and the hydrogenphosphate ion permeability highly decreased compared with the permeability, In conclusion, ion permeability changes after protein adsorption because of altered membrane charge and structure and the protein adsorption is one of the important factor to evaluate the performance of dialysis membrane for medical applications.

Suitable evaluation systems are critical to design antithrombogenic biomaterials. We developed an in vitro real-time observation test system to evaluate platelet/biomaterial interactions in whole blood under a defined flow condition. The system consists of a parallel plate flow chamber and epifluorescent video microscope (EVM). A glass coverslip coated with a polymer was incorporated into a flow chamber, and human whole blood containing platelets labeled with flourescent dye mepacrin was perfused at a wall shear rate of 200 sec^-1 for 20 min. In order to evaluate the feasibility of this system, two different segmented polyether-polyurethanes (SPEUs), PU-PTMG(650) and PU-PTMG(2000), were used. The results of surface characterizations by electron spectroscopy for chemical analysis (ESCA) and contact angle measurements were similar in both SPEUs. The percentage of the surface area of platelet coverage was measured at 1 min intervals. Plasma β-thromboglobulin (β-TG) and complement activation levels were also measured before and after each run. PU-PTMG(650) showed significantly higher adhered platelets than PU-PTMG(2000) at each time point. β-TG levels of PU-PTMG(650) were also higher than those of PU-PTMG(2000). Complement activation levels of PU-PTMG(650) were lower than those of PU-PTMG(2000). Thus, this EVM system has been proven to be an excellent and highly sensitive in vitro analytical method for evaluation of platelet /biomaterial interactions.

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.

Protein adsorption on materials for medical applications may change their thrombus formation and biocompatibility Zeta potential was determined from data on streaming potential measured on a streaming potential analyzer for three kinds of polymer alloy (polyarylate/polyethersulfone) (PEPA) membranes of varying polymer blend ratios and polacrylonitrile (PAN) membrane before and after cytochrome-C adsorption. Adsorption experiments were also made to determine the time-dependent amount of cytochrome-C adsorbed on the membranes. Intramembrane diffusion coefficient of the PEPA membranes for cytochrome-C was greatly lower than that of the PAN membrane, demonstrating that the PEPA membranes were controlled by adsorption and the PAN membrane by diffusion. The zeta potential of negatively charged membranes such as the PEPA and PAN membranes increased after adsorption of cytochrome-C that behaved like a cation in an aqueous solution of a pH of 6.4. The PAN membrane of higher negative charge gave great changes in zeta potential after cytochrome-C adsorption. In conclusion, adsorption of serum proteins that are ampholytes changes the zeta potential of dialysis membranes and may improve thrombus formation and biocompatibility.

The dependence of diffusive clearance of a high performance dialyzer (SSP-1.5L) for vitamin B₁₂ on dialysate flow rate was larger than that of a conventional dialyzer (SSP-1.5H) with the same dimension as SSP-1.5L. Diffusive resistance of highly permeable membranes is no longer the sole factor governing removal rate of dialyzers for middle molecule substances. We determined optimal dimensions of high performance dialyzers, using empirical equations for dialysate- and blood-side mass transfer and the tortuous pore model combined with equations for estimating pressure drop and priming blood volume. The fraction of membrane diffusive resistance of SSP-1.5L for vitamin B₁₂ calculated from the theory was 0.73 times that of SSP-1.5H. The decrease in inner diameter of the membrane highly increased blood-side pressure drop in spite of slight improvement in diffusive clearance for vitamin B₁₂, leading to optimal inner diameter of approximately 200μm. The decrease in inner diameter of the shell also increased diffusive clearance for vitamin B₁₂. However, the fiber density of 75% with decreasing inner diameter of the shell was calculated to be the upper limit that would maximize the solute removal performance. Dimension of SSP-1.5L was nearly equal to the optimal one calculated from the theory.

As a new dialysis system, continuous recirculating peritoneal dialysis (CRPD) was introduced in order to improve solute removal efficiency. In CRPD, because peritoneal dialysate in patient peritoneal cavity is recirculated in an extracoporeal system with a newly developed doublelumen catheter and it is purified by an out-side dialyzer continuously, therapeutic efficiency of CRPD strongly depends on performance of the dialyzer. In this study, the optimum design of the out-side dialyzer for CRPD was examined. In CRPD, peritoneal dialysate flows inner side of the hollow-fibers and commercially available dialysate for HD flows outer side of them. If an aimed clearance of the dialyzer was set to 95% of the maximum under 50mmHg of allowable pressure drop, a design specification of 87μm of inner diameter and 11.2cm of length for the hollow-fiber was determined to be optimal. Time averaged concentration of urea (TAC) was calculated tobe 32.2mg/dl in 8hr/day CRPD, using the optimum dialyzer, which would be superior to 45.3mg/dl of conventional HD.

Complement activation is reduced by grafting polyethylene glycol (PEG) on the surface of conventional regenerated cellulose (RC) membranes. However, the solute permeability of PEG-grafted RC membranes may be lower than that of conventional RC membranes because of the presence of swollen-layers formed with PEG chains on the PEG-grafted RC membranes. The objective of the present study is to clarify the difference in membrane structure between conventional RC (AM-SD) and PEG-grafted RC (AM-PC) membranes, and to characterize three PEG-grafted cellulosic membranes (AM-PC(l), PC(m), PC(s)) with varying PEG chain lengths based on the tortuous capillary pore model using data on tritium-labeled water (HTO) permeability and filtration coefficient.<br>The pore radius and surface porosity of the AM-SD, PC (m) and PC (s) membranes were calculated to be 2.8nm and 35%, respectively. On the other hand, the pore radius and surface porosity of the PC(l) membrane grafted with the longest PEG chains were lower than those of the conventional RC membrane (SD). This indicates that the pores of the PC (l) membrane are partially covered with the PEG chains.

<br>In case of treating blood, the filtrate flux of a plasma separator decreases with time and is several orders of magnitude lower than that of pure water and plasma. This phenomenon is explained by the enhanced filtration resistance resulted from formation of red blood cell polarization layer, accumulation of RBCs on the membrane and further pore blocking with RBCs. Since the filtrate flux depends on blood-side flow rate, the plasma separation model concerns the red blood cell polarization layer alone. The authors proposed a new model for estimating of the filtrate flux of a plasma separator by considering the variation of diffusion coefficient of RBCs in the blood with hematocrit and pore blocking with RBCs. Constant-pressure filtration experiments with the suspension of washed RBCs were done to clarify the new plasma separation model. In conclusion, the model we have proposed fully accounts for hematocrit dependence of the filtrate flux of a plasma separator at varying hematocrits ranging from 0.5 to 80%.

Zeta potential identifies the electric charge of hollow-fiber dialysis membranes; however, there is no well established method to measure it. The objective of the present study is to improve the method of measuring streaming potential necessary for determination of the zeta potential. Both streaming potential and pressure drop were dependent on the packing of hollow fibers in a test cell, its assembled form and aqueous electrolyte concentration. Time-dependent streaming potentials were observed using commonly used aqueous 0.01N KCl. Much time was then required to attain equilibrium. An aqueous electrolyte, the concentration of which is 1/1000 of the aqueous 0.01N KCl was suited for stable and exact determination of streaming potential with the improved cell. Using the improved method, the zeta potential of seven different hollow-fiber dialysis membranes was determined, with a good relationship between the zeta potential and HPO₄^2- permeability. We conclude that performance of charged hollow-fiber dialysis membranes can be evaluated by the zeta potential calculated from the streaming potential measured by the improved method.

Endotoxin concentration in the diallysate can be continuously monitored with the medical sensor by the Limulus test we have proposed. The objective of the present study is to change TOXICOLOR to ENDOSPECY as a suitable color-producing reagent, and to improve the washing of reaction tube and the mixing of reagent and sample for endotoxin measurements of greater precision. Batchwise reaction experiments were first performed to obtain reaction time, producing a miniunm reaction time of 12min required for appropriate measurements of endotoxin concentration that was the same as that obtained with TOXICOLOR. The time to attain equilibrium after stepwise injection of the sample into the device was 15min at a reaction time of 12min. Measurement precision was greatly enhanced when impurities contaminating the reaction tube were removed by fully washing it with sodium ethoxide, hydrochloric acid and pure water for injection. In conclusion, the improved method is capable of contiunous and exact measurements of endotoxin concentration ranging from 0 to 20pg/ml.

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.

Most of blood purification methods are grouped among separation process according to chemical engineering. This paper describes separation principles used for blood purification methods on the basis of chemical engineering. Separation process consists of three basic operations, mechanical separation, transport separation and diffusion separation. Mechanical separation suited for immiscible phases is used for plasma separation and blood cell separation. Transport separation and diffusion separation are well suited for homogeneous phases. Hemofiltration and hemodialysis are typical of transfer separation and of diffusion separation respectively. Solute transport through dialysis membranes is not caused only by diffusion, but also by filtration. So it is impossible to distinguish between three different modalities of hemodialysis, hemodiafiltration and hemofiltration. Adsorption operation is one of diffusion separation and also a typical modality of blood purifications. Adsorption operation had little been used for blood purifications because of several reasons. Recently, excellent selectivity of adsorption, especially immunoadsorption, is noted again. Toxin removal characteristics by blood purification methods depend on combination of three basic phenomena, diffusion, filtration and adsorption. To elucidate specifications of blood purification, to enable selectivity separation through affinities like immunoadsorption and to increase biocompatibility of separation media are very indispensable for further development of blood purifications.

Thermo-responsive copolymers of N-isopropyl acrylamide with alkyl methacrylate are capable of "on-off" regulation of drug release in response to external temperature change. To search the minimum temperature change achieving "on-off" regulation, dynamic process of "on-off" switching has been investigated by changing the chemical structure of polymer and the degree of temperature changes. In the switching process of drug release from the "on" state to the "off" state, large temperature changes lead to large volume changes at the gel surface and resulted in remarkable squeezing of drug from the gel surface. Squeezing was suppressed by small temperature changes, but in this case, sharp peaks appeared with a lag time due to the accumulation of internal pressure in the shrunken gel. Effects of the length of the copolymer alkyl side chain and the degree of temperature changes are discussed to achieve controlled pulsatile drug release pattern.

An artificial organ is a great boon to medical cares produced by the collaboration of medicine and engineering. Practical use of artificial organs actually contributes to variety of medical cares and prolongation of the life of patients, and further introduction of new concepts of medical cares to medicine. The switchover of idea often causes a great discovery. Medicine is no exception to this rule. Medicine is deeply indebted to medical technology for remarkable progress in modern medical cares. Collaboration of medicine and engineering surely develops the medical technology, but unfortunately does not necessarily meet our ideal to date. It is an urgent necessity for further development of artificial organs to establish fresh collaboration of medicine and engineering.

In recent years, temporal control of drug delivery has been of interest in basic and applied fields as a new approach to achieve improved drug therapies. This new drug delivery may be achieved by utilization of "intelligent" polymeric materials having auto-feedback functions. Stimuli-responsive polymers have been investigated as potential molecular devices to achieve intelligent drug delivery systems such as self-regulating and externally modulated drug delivery systems. A stimuli-responsive polymer (sensing) can change its structure and physical properties (responding) in response to appropriate external stimuli (signals), which changes can subsequently affect drug release (acting) from a drug reservoir. In this paper, this new concept of intelligent drug delivery system is described in detail and related studies are reviewed and discussed.

The authors intend to develop rapid and convenient method for plasma extraction. This method is able to progress treatment speed and inspection accuracy in biochemical analysis. Plasma extraction was tried with small sized hollow-fiber plasma separator. Saline was added to membrane to avoid hemolysis. Pump and syringe were used to feed blood. Filtrate was evaluated by sieving coefficient for Total Protein and degree of hernolysis. Maximum filtrate flux was obtained from polyethylene membrane's plasma separator at a transmembrane pressure of 100 mmHg and a wall shear rate of 5000s^-1.2 ml of plasma was obtained from 11ml of blood in 14 seconds with pump, and in 75 seconds with syringe. Hemolysis was not confirmed. Real sieving coefficient were calculated from volumes of added saline and obtained plasma.

Safe and stable long-term uses of artificial pancreas require noninvasive and continuous monitoring of the glucose concentration(GC) of plasma(P). A highly sensitive sensor is capable of noninvasively determining the glucose of P from data on the GC of either sweat or diluted solution of tissue fluid(TF) sampled by skin suction. The authors made a column packed with microporous glass beads that were immobilized with glucose oxidase to produce H₂O₂ and an ECL flow cell to measure luminescence intensity(LI) corresponding to the concentration of H₂O₂ through an optically transparent electrode at constant potential. A good linear relationship was obtained between GC ranging from 0, 05 to 1.00mg/dl and LI. Contindous measurements of LI for 8hr produced extremely stable data within a variation of ±5% since the ECL reaction was caused to occur after sufficient agitation of luminol and test solutions to overcome the instability of the conventional methods of determination of glucose by chemiluminescence. In conclusion, the highly sensitive and stable glucose sensor by ECL with luminol is a promising device for noninvasive determination of glucose of P from data on the GC of of either sweat or diluted TF.

The superstructure of polymer alloys responsible for their functions is most readily controllable at varying polymers, polymer blend ratios, solvents and temperatures. Dialysis membranes made of polymer alloys may have various pure water and solute permeabilities, pore sizes and pore size distributions. Commercially available FLX-12GW dialyzers and three kinds of test dialyzers of varying coagulation rate of forming PEPA membranes were prepared. Filtration experiments were made with a mixed solution of dextrans ranging in their molecular weights from 3, 000 to 60, 000. Reflection coefficient of dextrans was determined by Spiegler-Kedem equation from real rejection data calculated from rejection data by the velocity variation method. Reflection coefficient of FLX-12GW increased with molecular weights ranging from 10, 000 to 50, 000 of substances. Coagulation rate of forming PEPA membrane decreases with reflection coefficient.

Highly permeable (HP) membranes have higher solute permeabilities than conventional ones. Contribution of blood- and dialysate-side mass transfer resistances to solute removal performance is more increased in HP dialyzers than conventional ones. To reduce blood- and dialysate-side mass transfer resistances effectively increases solute removal performance especially of HP dialyzers. This paper describes the technical design of dialyzers with being reduced blood-side mass transfer resistance. Dialyzers consisting of hollow-fiber membranes of 19.4cm in length was superior in solute removal perormance to dialyzers consisting of hollow-fiber membranes of 23.5cm in length. Overall mass transfer coefficient and blood-side mass transfer coefficient were independent of blood-side flow rate. Overall mass transfer coefficient was independent of inner diameter of hollow fibers.

Electrolyte transport depends on the effective charge density of charged dialysis membranes, and hence determination of effective charge density i s needed to determine inorganic phosphate permeability. However, great difficulty i n measurement of membrane potential of hollow-fiber dialysis membranes makes it impossible to quantitatively compare effective charge density with diffusive permeability for inorganic phosphate. We prepared sheet membranes (16μm thick) of the same material as that of hollog-fiber RC (Regenerated Cellulose) and Hemophan membranes to measure membrane potential from which effective charge density was calculated. Zeta potential of each hollow-fiber membrane was determi nened by the streaming potential method. Diffusive permeability of hollow-fiber RC and Hemophan membranes was also measured with inorganic phosphate in purified water and in saline. Hemophan membrane has higher diffusive permeability than Regenerated Cellulose (RC) membrane, and its value i n saline i s higher than that i n purified water when the absolute value of effective charge density of positively charged Hemophan membrane i s comparable to that of negatively charged RC membrane. Zeta potential of each membrane is negative, and the absolute value of zeta potential of Hemophan membrane is smaller than that of RC membrane. Hemophan membrane has the same internal structure as RC membrane. This indicates that electrostatic resistance may control inorganic phosphate permeability. In conclusion, charge density affects inorganic phosphate transport through charged dialysis membranes that is enhanced by positively charged Hemophan membrane. Inorganic phosphate transport through dialysis membranes may be evaluated by the measurement of zeta potential of hollow-fiber membranes.

The amount of dialysis membrane charge affects electrolyte transport through membrane. But its exact charge has not been measured directly. The authors tried to use fluorescence method which is used for biomembrane potential measurement in order to measure hollow-fiber dialysis membrane charge. An intensity of anionic fluorescent dye;1-anilinonaphthalene-8-solfonic acid(ANS);increases when it binds to charged parts of hydrophobic substances. Measurement of fluorescent intensity was made with two kinds of hollow-fiber dialysis membranes of regenerated cellulose;negative charged RC and positive charged Hemophan. Little fluorescence detected with RC indicates no ionic bond between ANS and negative charged membrane. In case of Hemophan, extremely intensive fluorescent was observed, but fluorescent intensity was decreasing with a decrease of membrane charge. A fluorescent intensity of ANS is considered to reflect hollow-fiber membrane charge. Moreover, fluorescent intensity corresponds to the quantity of bound ANS in dialysis membrane. This may also make it possible to analyze dialysis membrane structure.

Relationship between mass transfer and flow patttern in dialyzers is very important for optimal design of dialyzers. Mass transfer in dialysate-side is extremely complex to understand due to complexity of flow pattern. In this work, the basic analysis about mass transfer of dialysate was performed with single follow fiber membrane, which is considered as a simplest laminar flow condition. The experiment was carried out by the new method with optical fibers. The unsteady mass transfer model in a capillary membrane was applied to the new calculation method for the mass transfer coefficient of outside film of the hollow fiber membrane. AM-SD-10M which is conventional membrane and AM-FP-15 which is highly permeaole membrane were used in the experiment. No matter which membrane was concerned, mass transfer resistances of outside film were equal. Sherwood number measured experimentally fitted in with the Leveque's equation which was led by the theoretical analysis of heat transfer in laminar flow.

Binding of drugs to serum protein is an adsorption phenomena. Adsorption equilibrium and velocity of drugs influence their dialysance. We measured adsorption equilibrium and velocity with four cephem antibiotics and human serum albumin. CAZ, CDZM and CTRX had the adsorption isotherms that were obedient to Langmuir equation, but CTX did not. The difference of adsorption mechanism caused this difference. Protein-binding ratio changed with whole concentration of antibiotics, and they depended on antibiotics. The order of adsorption velocity was CDZM or CTRX, CTX and CAZ. Desorption amount of CAZ can be ignored while blood runs in a dialyzer, that of CTX cannot. Adsorption equilibrium of CDZM and CTRX forms anywhere in a dialyzer. It is important to examine the effect of adsorption equilibrium and velocity of drugs on their dialysance. We designed a mass transfer model of protein-binding drugs in a dialyzer. Based on this model, we calculated distribution of antibiotics concentration in a dialyzer. Distribution of free drug concentration and adsorption amount was dependent on their adsorption velocity, that of the whole concentration in blood side were not.

Solute permeability is available using Wilson-Plot Method, Klein's Method, RI Method with radioisotope-labeled solute and a new method with optical fibers. Each method gives different values for solute permeability of same membranes, and little is known real values for solute permeability. This paper describes characteristics of methods of measuring solute permeability, and effects of membrane structure on solute permeability of highly permeable (HP) dialysis membranes.<br>Real values for solute permeability of hollow-fiber dialysis membranes can be measured by a new method with optical fibers. Structural parameters of pore radius, surface porosity and tortuosity were determined for HP membranes from pure water permeability, solute permeability and water content data using the tortuous pore model. PAN-DX membrane has higher solute permeability than AM-EP membrane for substances of molecular weight ranging from 6, 000 to 20, 000, because PAN-DX membrane has huge pores.

The object of present study is the development of a continuously monitoring sensor for ET concentration in dialysate. ET is readily capable of penetrating from dialysate into blood through highly permeable membranes. Dialysate should be kept ET free and should be observed absence of ET by continuous measurement. Limulus test is generally used for the measurement of ET concentration in clinical settings. Conventional operation of Limulus test needs complicated operation because of its sensitivity to contamination from atmosphere. Therefore conventional Limulus test is unsuitable for continuous ET measurement. The authors designed a new ET sensor operating the continuous reaction of Limulus test in single tube. This sensor enabled sample solution to react without contact with atmosphere and simplified continuous ET concentration measurement. The sensor showed faster response than conventional Limulus test and had measurable ET concentration range concluding allowable ET concentration limit. The developed ET sensor is promising for monitoring of ET in dialysate lines.

As a new dialysis system, continuous recirculation peritoneal dialysis(CRPD) was introduced in order to improve solute removal efficiency. In CRPD, patient's dialysate in peritoneal cavity was extracorporated through a double-lumen catheter and purified by an out-side dialyzer. From an canine ex vivo study, urea peritoneal and dialyzer dialy-sances were 3.05 and 33.3 ml/min under 100 and 200 ml/min of recirculation and dialysate flow rates using FB-50H(0.5 m²). From these results, weekly urea clearance was estimated as 115.51/week in 12 hr/day CRPD superior to 70.01/week of conven-tional CAPD and 99.81/week of 12 hr/week HD.

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.

The quantitative research of hemolysis using the experimental circuit was performed in order to study the effect of screen filter for bovine blood. Experimental conditions were chosen referring to surgical operations, and the effect of a screen filter on bovine red cells was evaluated. The amount of hemolysis was determined by measuring concentration of plasma hemoglobin. Experiments were performed to confirm damages of red blood cells caused by the screen filter with variations in hematocrit, flow rate, materials of the filters and pressures. The degree of damage of red blood cells was evaluated by the osmotic fragility test. Subtle damages of red blood cells became apparent with the osmotic fragility test particularly with a 0.6 g/dl NaCl solution.

Silicone membrane emits a yellow fluorescence of wavelength 518nm with a use of ultraviolet light of wavelength 416nm. The fluorescence is quenched in the presence of oxygen, the concentration of which can be calculated by an extended Stern-Volmer relation. However, oxygen sensors currently used do not have rapid response to oxygen in liquid because membranes used in the sensor depress oxygen transport rate. The authors prepared oxygen sensors in which silicone membranes containing alkylated decacyclene was used. The membrane were 46.36 to 2057μm in thickness. The alkylated decacyclene concentration in organic solvent was changed from 0.167 to 33.3mol/m³. Using our sensor, partial pressures of oxygen in the air and/or in water were obtained, in spite of variations in temperature or flow patterns. The half life periods of the fluorescence was 70.3ms at the membrane thickness of 46.36 U m. These data support that a thinner silicone membrane makes it possible to develop a more rapidly sensible oxygen sensor.

Determination of cardiac output(CO) measured with Swan-Ganz catheter(SGC) depends on the time constant for heat transfer. Clinically used SGC's have thermistors with variable time constant. As a result, currently employed CO monitoring system is not accurate and use of the Stewart-Hamilton equation may cause marked errors The authors propose a new method of determining CO using SGC's with variable time constants using the Newton's law of cooling for analyzing the thermal dilution data. Blood flow rate calculated by the new method for a bovine blood with a perfectly mixtured tank mimicking a natural heart were insensitive to the time constants under the pulsatile and non-pulsatile flow conditions. Results were consistent regardless volume and temperature of the infused saline even after several tests hadd been performed.

Oxygen transfer rate of oxygenators composed of bundles of 1 to 6 and 24 hollow-fibers was compared in O₂-water experiments. The parts where hollow-fibers are in contact with each other do not work for gas exchange. A single hollow-fiber oxygenator had the best oxygen transfer rate, because the hollow-fibers in the single hollow-fiber oxygenator do not contact with each other. By X-ray computed tomography showing blood flow patterns of the 1, 3 and 6 hollow-fiber oxygenators, higher flow rates at the center of oxygenators causing lowering of oxygen transfer rate are observable for the 3 and 6 hollow-fiber oxygenators than that for the single hollow-fiber one. By pulse-response experiments made for flow pattern observation, the single hollow-fiber oxygenator had only one peak in the flow velocity distribution curve, showing no channeling flow exists.

Microporous glassy membranes have high resistances to chemicals and heating and can be regenerated repeatedly by rinsing with chemicals. They also have a limited pore diameter distribution. Both filtration fluxes and protein sievings of those glassy membranes for bovine blood are adequate at pore diameters ranging from 1 to 1.5μm, a transmembrane pressure of 25mmHg an a wall shear rate of 2000s^-1 in the clinical point of view. The filtrate flux is proportional to the -1/3 power of the tube length for variable shear rates. The ultrafiltration theory is not appropriate for explaining the dependence of filtrate flux on hematocrit of the bovine blood. Low temperature plasmapheresis is feasible at transmembrane pressure ranging from 25 to 50mmHg and a wall shear rate of 2000s^-1.

According to the improvement of hemodialysis membrane limitation of solute permeability, the dialyzer is able to eliminate low molecular weight proteins not only by convection, but also by diffusion. The permeation of low molecular weight proteins means diffusion of same molecular weight materials from dialysate to the blood compartment when these exist in the dialysate. Blood contamination with antigen proteins will cause various immunoreactions, which may lead to unknown uremic complications. Therefore, to eliminate these proteins in the dialysate line between the dialysis machine and the dialyzer, adsorptive removal with ceramic powder was devised. The diameter of this ceramic powder is from 100 to 200um and average pore diameter is 1, 500Å. Batchwise operation which had 1g of ceramic powder and 100ml solution of a marker protein in acetic acid dialysate showed the decrease of concentration. The order of adsorption capacity is as follows; lysozyme, cytochrome C, ribonuclease A and α-lactalbumin. It is same as the descending order of isoelectric point. Another experiment with a column of 10mm diameter, containing 1g ceramic powder, showed the elimination of 1, 000ng/ml lysozyme in dialysate which flowed into the column as single pass. The removal ratio is around 80% at from 3 to 11 sec residence time. This result shows the rapid adsorption of protein onto the ceramic surface. Low isoelectric point proteins are not so well adsorped as high isoelectric point proteins, the modification of the ceramic powder, such as pore radius variation and/or surface reactant modulation, makes an effective removal of all kinds of proteins and toxic substances which will exist in dialysate.

Determination of solute permeabilities of hollow-fiber membranes is crucial for designing dialyzers. Previously reported method of evaluating solute permeabilities was modified in this paper. The new method was found to be effective for determining a solute permeability for vitamin B12 in bovine blood and in plasma. A hollow fiber soaked in an isotonic saline solution was placed in bovine blood or plasma containing vitamin B12. The vitamin B12 permeated through the membrane to the inside of hollow fiber which had been originally filled with an isotonic saline so that no bulk flow across the membrane would occur. Assuming the Lambert-Beer's law, the concentration of vitamin B12 inside of the hollow-fiber was continuously monitored by measuring the light intensity traveling axially over the inside solution from one end to the other. No differences were found in vitamin B12 permeabilities for isotonic saline, bovine blood and bovine plasma solutions. This demonstrated that large molecules such as proteins and erythrocytes did not interfere with the transport of vitamin B12 in bovine blood or bovine plasma.

The mechanism of electrolyte transport through a dialysis membrane should be clarified to improve inorganic phosphate removal from patients on long-term hemodialysis. Dialysis experiments were made with aqueous radioisotope (32P)-labeled disodium hydrogenphosphate mixed with sodium chloride or potassium chloride of varying ionic strengths. Inorganic phosphate ion permeabilities were obtained for regenerated cellulose (RC) and polymethylmethacrylate (PMMA) membranes. Aqueous sodium chloride or potassium chloride whose ionic strength equals that of an inner solution of the hollow fiber was used as dialysate. Permeability for inorganic phosphate ion of each membrane increased with the ionic strength of cations. On the same ionic strength, presence of cations of higher ionic mobility was advantageous to the permeability for inorganic phosphate. From the analysis based on the electrolyte diffusion theory, membrane structures would also affect on the membrane permeabilities. It is necessary to establish a new electrolyte diffusion theory, considering charge densities, membrane structures and membrane properties.

Highly permeable (HP) membranes have higher solute permeabilities than conventional ones. As a result, the contribution of dialysate film mass transfer resistance increased on HP dialyzers. It should be reduced to improve the mass transfer performance of HP dialyzers. Little is known concerning the technical design of dialyzers, considering dialysate film mass transfer resistance. This paper describes the technical design of dialyzers to reduce the dialysate film mass transfer resistance. The dialysate film mass transfer coefficient increased with the fiber density. The increase in fiber density increased the mass transfer rate of HP dialyzers more effectively than that of conventional dialyzers. Keller's equation, commonly used for the technical design of dialyzers, should be modified because the dialysate film mass transfer coefficient calculated from the equation did not agree with those determined by a dialysis experiment.

Adosorption isotherms of dialysis membranes were determined by the BET method, calculating the amount of adsorbed nitrogen and equilibrium pressure. From those isotherms the membrane pore diameter distribution was calculated by the Inkley method, The pore diameter distribution of vacuum-dried membranes and freeze-dried membranes were obtained by the BET method, Pore volume of freeze-dried membranes was higher than that of vacuum-dried membranes. Freeze-drying is well suited to obtain the same pore volume as wet membranes that are used clinically, A contraction in fiber length and wall thickness may occur on drying, and the rate of the contraction depends on material, water content and surface porosities. Pore diameter distributions of dialysis membranes were also determined by the DSC method, Results were nearly the same as those by the BET method, The DSC method also allows determination of the pore diameter distribution. Permeabilities for Beta-2-microglobulin and pure water were found to increase with the pore volume.

Backfiltration in HP dialyzers, which are used for removing a larger amount of beta-2-microglobulin, could cause an inflow of endotoxins from contaminated dialysate. Change of dialyzer specifications makes it possible to reduce Backfiltration rate or to prevent endotoxins from getting into blood stream. The authors propose a theoretical design method for HP dialyzers to reduce backfiltration. Under countercurrent operations, simulation results showed that the backfiltration could be prevented for dialyzers with FB-190UGA and PAN-12CX2 membranes of a length of 5cm and housing diameters of 7.7 and 8.8cm, respectively. Under cocurrent operations, however, dialyzers had the minimal backfiltration rates, which could be zero, at a given hollow fiber density. No backfiltration would occur under cocurrent operations in dialyzers with above two membranes of a length of 25cm and a fiber density of 0.52 and 0.62, respectively. Results can be generalized that enlarging housing diameters and shortening fiber length for countercurrent operations prevent backfiltration to occur and choosing an appropriate fiber density for cocurrent operations reduces backfiltration rate.

"On-off" regulation of drug permeation through membranes in response to external temperature change has already been achieved using thermosensitive copolymers of N-isopropyl acrylamide (IPAAm) with butyl methacrylate (BMA). It was clarified that increasing temperature induced formation of a dehydrated polymeric surface skin layer that stopped drug permeation. In this study, to control "on-off" permeability of a drug, the polymer surface shrinking process was regulated by changing the length of alkyl side chain of the copolymer methacrylate component. Permeation experiments with indomethacin were performed in response to step-wise temperature change between 20°C and 30°C with copolymers of IPAAm with BMA, hexyl methacrylate (HMA), and lauryl methacrylate (LMA). Burst permeation was found at the initial stage of the second "on" period for IPAAm-co-HMA or IPAAm-co-LMA. These results suggest that drug diffuses to change the concentration profile in the polymer gel during "off" periods. Polymer surface skin formation maintains a localized high water content inside the polymer gel even if drug permeation stops. The length of the alkyl side chain is an important parameter to control "on-off" permeability of drug.

To clarify the effects of deformability of particles on cross-flow microfiltration rate, constant transmembrane pressure filtration experiments were performed with rotating cylindric filters composed of polycarbonate membrane at varying rotational speeds. We used two kinds of suspensions in which red blood cells as a deformable particle and red blood cells treated with gultaraldehyde as a rigid particle were suspended. Filtrate flux reaches the maximum value and then declines to the normal value with increasing transmembrane pressure. Deformability of particles promotes the lift force which moves particles against convective flow. At higher rotational speeds, values for polarization resistance for deformable and rigid particles at a transmembrane pressure of 6.5kPa have no difference. On the other hands, at lower rotational speeds, polarization resistance for the rigid particles are larger than that for the deformable particles. These results suggest that deformability of particles affects formation and characteristic of concentration polarization layer.

Pore size distribution was determined from solute permeability data for urea, glucose and sucrose as a function of Stokes radius. Regenerated cellulose membranes have more limited pore size distribution than polymethylmethacrylate membrane. The solute permeability of glucose oligomers (monomer to octomer) was calculated from clearance data obtained by dialysis experiments.

Poly(N-isopropyl acrylamide)(IPAAm) shows a remarkable change in aqueous swelling with a change in temperature. Random copolymers of IPAAm and butyl methacrylate(BMA), hexylmethacrylate(HMA), or lauryl methacrylate(LMA) were systhesized and indomethacin was loaded into these polymers. Drug release experiment was performed at each temperature. At constant temperature, release pattern was observed as zero order release pattern when temperature was low. This can be explained in terms of permeability increase in polymer matrix and agree with release pattern derived from model. Pulsate release patternrn was found to be regulated by temperature flactuation between 20°C and 30°C due to surface shrinking layer with an increase in temperature. In the case of 20hr for 3°C, release rate remained constant. The results suggested that loaded drug in polymer migrates to the syrface at 30°C even if release was completely stopped.

Techniques of membrane distillation have been developed in the field of the desalination of seawater and the dehydration of alcohol.We have tried for the removal of solute-free water from bovine blood by membrane distillation which have the advantages of high flux and outstanding selectivity at lower temperatures. In membrane distillation of which driving force is vapor pressure difference across hydrophobic membrane, the development of temperature and concentration polarization layers on either side of microporous hydrophobic membranes leads to the decline of permeation flux because of the reduction of vapor pressure difference across the membrane. Conventional theory of heat and mass transfer was applied to transport processes in membrane distillation to clarify effects of temperature and concentration polarization on water vapor permeability for ethylene glycol solution and bovine blood. In membrane distillation with bovine blood, the resistance of temperature polarization layer accounted for 61% of total permeation resistance at a stirring speed of 200r pm. At a stirring speed of 1000rpm the permeation resistance of membrane accounted for 52% of total permeation resistance. Destruction of temperature polarization layer and thinning of the membrane are essential for practical use.

The mechanism of electrolyte transport through dialysis membranes should be clarified to improve inorganic phosphate removal from patients on long-term hemodialysis. Permeability to inorganic phosphate of regenerated cellulose(RC) and polymethyimethacrylate (PMMA) membranes was determined with aqueous radioisotope (³²P)-labeled disodium hydrogenphosphate at varying inorganic phosphate concentrations. We measured permeability to inorganic phosphate in bovine serum and compared with the permeability in aqueous disodium hydrogenphosphate. Zeta potential of RC and PMMA membranes was measured by the streaming potential method. Inorganic phosphate concentrations ranging from 3.33 to 66.6mEq/l don't affect the permeability to inorganic phosphate which increases significantly with inorganic phosphate concentration at concentraions from 66.6 to 100mEq/l and is insensitive to the inorganic phosphate concentration at a concentration of >100mEq/l. Permeability to inorganic phosphate in bovine serum is higher than that in aqueous solution.

Clearances of small molecular substances such as urea are very sensitive to the membrane permeability, also to the flow dynamics of dialysate and blood. Especially, the dialysate flow pattern is widely changed by the fiber packing condition. The results with X-rays CT photographs present the channeling and/or dead spaces in the dialysate flow pass. Hand made dialyzers which have different fiber packing density show the effect of flow dynamics on the solute mass transfer coefficient. Poor packing density dialyzer has small mass transfer rate. Blended dialyzers with PS and EVAL-D5 have higher mass transfer rate because of its good flow distribution and adsorption.

The present study elucidates diffusion characteristics for B2MG of newly-developed RCM. Dialysis experiments were made with 1251-labeled B2MG to obtain solute permeability. The solute permeability for B2MG of AM-EP-19 nearly equals that of FB-190UGA which are capable of removing B2MG by diffusion alone. This support satisfactory removal of B2MG by diffusion also using highly permeable dialysis membranes prepared from regenerated cellulose. Through analysis of data on the tritium-labeled water permeability and hydraulic permeability based on the tortuous pore model, we obtain 10nm, 48% and 1.7 as pore radius, surface porosity and tortuosity, respectively.

Determination of solute permeability is essential for improving hollow fiber membranes for clinical dialysis. To develop a new method of determining such permeability more simply and accurately, the authors employed light traveling along quartz optic fibers, which is well suited for spectroscopic and continuous measurements of solute concentration in narrow hollows. The resent paper describes the novel method of determination of the diffusional permeability of hollow fiber membranes from time-dependent absorbance data. We confirmed that the Lambert-Beer's law was applicable to dilute solutions. Values for solute permeability obtained by this novel method are almost agreement with those by radioisotope method and overall mass transfer coefficients fran clearance data. This study suggests the possibility of simulaneous determination of solute permeability for mixed solutes at various wavelengths giving maximal absorbance to each solute.

Low molecular proteins which should be eliminated from long term hemodialysis patients such as beta-2-microglobulin are difficult to remove through the dialysis membrane only by diffusion. Some membrans adsorp the proteins, though, there are no good methods to meaure its adsorption capacity. Therefore, we tried one of an easy way to measure and to compaire the membrane adsorption capacity. This method shows that polysulfon and PMMA-BK have high adsorption capacity to beta-2-microglobulin which pK is around 5. Although polysulfon also adsorps 1 ysozi me of pK 11, only few is adsorped on the PMMA-BK membrane. It is neccessary to measure the capacity with low and high pK proteins.

With various highly permeable dialysis membranes which were developed to remove Beta-2-microglobulin, pore size was obtained by both differential scanning calorimetry (DSC) and tortuous pore model studies, and pore diameter distribution was measured by the BET method. The pore size of dry membranes is lower than that of wet membranes. Both pore diameter and pore volume of highly permeable dialysis membranes are higher than those of conventional dialysis membranes. Pore diameter distribution of regenerated cellulose membranes is somewhat different from that of synthetic polymer membranes.

Outside blood flow membrane oxygenators we have developed are composed of tied bundle of 6 hollow-fibers. However it has not been examined how many hollow-fibers are the best in oxygen transfer rate. Oxygen transfer rate of oxygenators composed of bundles of 1, 2, 3, 4, 5, 6 and 24 hollow-fibers was compared in O₂-water and O₂-blood experiments. The single hollow-fiber oxygenator had the best oxygen transfer rate, because the hollow-fibers in the single hollow-fiber oxygenator do not contact with each other while the hollow-fibers in the 6 hollow-fiber oxygenator partly do. The parts where hollow-fibers are in contact with each other do not work for gas exchange. The oxygen transfer rate of the single hollow-fiber oxygenator is 1.5 times of that of the 6 hollow-fiber oxygenator in an O₂-water system and 2 times in an O₂-blood system. The pressure drop of gas flow in the single hollow-fier oxygenator is 60% of that in the 6 hollow-fiber oxygenator. Microphotographs by X-ray computed tomography show blood flow patterns of the 1, 3 and 6 hollow-fiber oxygenators. Higher flow rates at the center of oxygenators are observable for the 3 and 6 hollow-fiber oxygenators, causing a lowering of oxygen transfer rate.

Various materials are presently available for hollow fiber dialysis membranes which satisfy technical and medical requirements such as high permeability to uremic toxins and water, biocompatibility, resistance to sterilization, and high mechanical strength. New dialysis membranes with high permeability to β₂-microglobulin and with biocompatibility leading to low complement activation have been developed for more optimal hemodialysis. Data on structure and permeability are then required to prepare the new dialysis membranes. Much attention should be paid also to the geometry of hollow fiber dialysis membranes available for chronic renal failure patients with elevated hematocrits caused by the administration of erythropoietin.

Constant transmembrane pressure experiments were made to clarify sieving characteristics of inorganic and organic membranes for plasma fractionation. The inorganic membranes were found to be suitable for plasma fractionation because they have not only limited pore size distribution with minimal tortuosity but also resistance to chemicals and heat. Microporous inorganic membranes have high filtrate flux and high selectivity.

This study elucidates permeability characteristics for beta-2-microgl obulin (abbreviated to BMG) of newly-developed cellul osic and synthetic polymer membranes to determine diffusive clearance for BMG. Dialysis experiments were made with ¹²⁵I labeled BMG to obtain the solute permeability. The cellulose tri acetate membranes CT-190GA had a high solute permeability for BMG. This demonstrates that BMG can be markedly remove by diffusion alone with highly permeable dialysis membranes. Back filtration has been reported to occur during hemodialysis treatment with high flux dialysis membranes. Since value for myoglobin clearance of cocurrently operated equals that of countercurrently operated, back filtration does not affect mass transport of large molecular weight substances.

We clarified gas tansport in inside and outside blood flow oxygenators with and without pulsatile flow pump from the standpoint of boundary layer resistance. Pulsatile flow is of Beat 60 cycle/min and Duratlon 60%. Blood flow rate of inside blood flow oxygenator ranged from 1.0 to 4.0l/mln, while that of outside blood flow oxygenator ranged from 1.5 to 6.7l/min. Pulsatile flow is superior to nonpulsatile flow in gas exchange efficfency because of marked differences in the destruction of boundary layer resistance. We examined differences in gas exchange efficiency at the inner position of the module. The outer position of the module is superior to the inner position in gas exchange efficiency.

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.

The present study elucidates gas transport in outside and inside blood flow oxygenators from the standpoint of boundary layer resistance. Overall gas transfer resistance was calculated, and the rate-determining step was determined by a Wilson plot. This may be attributed to the obliquely wound hollow fibers and complicated flow patterns on membrane surfaces in outside blood flow oxygenators. It is concluded that outside blood flow oxygenators are superior to the inside blood flow type because of significant differences in liquid-side boundary layer resistance.

Plasmapheresis experiments were made to determine filtration characteristics of tubular microporous glass membranes. The present study deals with effects of pore size and membrane length on filtration characteristics at transmembrane pressures of 25mmHg and 50mmHg. Filtrate flux increased with pore diameter, and was kept constant at a pore diameter of above 1 μm. Filtrate flux was proportional to (membrane length)-1/3 and wall shear rate. Resistance of polarization layer was most dominant. Filtrate flux decreased nonlinearly with an increase in logarithms of hematocrit.

Constant transmembrane pressure experiments were made to clarify sieving characteristics of 3 type inorganic membranes for plasma fractionation. It is suitable for plasma fractionation because of the distribution of pore diameter i s more limited in the inorganic membranes than in currently-utilized synthetic polymer membranes. The resistance of concentration polarization layer i s the dominant factor i n plasma fractionation using membranes. It i s suggested that the suitable determination of pore diameter enable for mi croporous membranes and aluminum oxide films to remove selectively desirable plasma protein.

To solve the mecahnism of plasmapheresis with rotating cylinder membrane, we made in-vitro experiment changing inlet pressure, rotation speed and hematocrit. As inlet pressure overcame the pressure of centrifugal force, filtration started. As inlet pressure was higher, filtration flux increased rapidly and approached the steady state. As rotation speed was higher, filtration flux increased, then approached plateau. This rotating cylinder membrane system was more than ten times as efficient as cross flow filtration. This fact resulted from high wall shear rate and reduction of RBC polarization layer resistance caused by Taylor vortex. We proposed mass transfer model which was function of axial length and this model explained satisfactoly the filtration property of this system.

The objective of the present study elucidates changes in pure water permeability after plasma contact and adsorption capacity of serum albumin on dialysis membranes. Both reduction percentage (RP) of pure water permeability and adsorbed amount of bovine serum albumin (BSA) were determined for nine dialysis membranes including high flux membrane. The amount of BSA adsorbed on high flux membrane (BK-1.0) is three order of magnitude higher than that on the other membranes. Pore plugging causes a lowering of pure water permeability of treated membranes. Values for BSA adsorption capacity of PMMA, EVAL, CA and RC membranes decrease in that order.

Permeability for inorganic phosphate and sodium ion using regenerated cellulose (RC) membrane and pol ymethyi methacryl ate (PMMA) membrane was studied by zeta potential measurement. Zeta potential was determined by the streaming potential method. A newly-improved method using radioisotope labeled disodium hydrogenphosphate has been employed to determined the solute permeability of RC membranes and PMMA membranes. Zeta potential of RC membrane is not contributed to over-all mass transfer coefficient and solute permeability for inorganic phosphate. That of PMMA membrane, however, affects these for it and over-all mass transfer coefficient for sodium ion.

The objective of the present study is to clarify beta-2-microglobulin (B2-m) behavior at intra- and interdialysis periods by kinetic modelling. Pools of B2-m are composed of intracellular, interstitial and plasma spaces. Values for generation rate of B2-m for patients on long-term hemodialysis are less than 100mg/day, which are lower than those of healthy subjects. Cell membrane clearance data indicate that B2-m is released easily from cell membrane surface.

We studied to elucidate adsorption characteristic for beta-2-microglobulin (beta-2-mg) on several adsorbents. Beta-2-mg is much adsorbed by collagen beads, DHP-1 active carbon, XAD-7 and 8. The amount of adsorbed beta-2-mg is fully equilibrayted 5 to 10 hrs for collagen beads, XAD-7 and XAD-8, over 60 hrs for DHP-1 and over 24 hrs for microporous glass beads. XAD-7 with mild hydrophobic property was the most amount of adsorption beta-2-mg. Adsorbent with mild hydrophobic properties and pore diameter of over 40 angstrom is required for adsorption of beta-2-mg.