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.

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.

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.

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.

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.

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.

To develop a high-performance artificial gill, the mechanism of a biological gill should be elucidated in terms of variables such as the required oxygen flux, the Reynolds number of water, and the difference in oxygen partial pressure, between water and blood (or oxygen carrier solution), which is the driving force for oxygen transfer and oxygen uptake. The oxygen flux of both biological and artificial gills increases with the water flow rate. The oxygen flux of a biological gill is approximately double that of an artificial gill. The Reynolds number of water flow in the biological gill is lower than that in the artificial gill. Hence the higher oxygen transfer flux is independent of the flow velocity of water in the biological gill. The oxygen partial pressure difference between water and blood in the biological gill is double that in the artificial gill. This larger partial pressure difference leads to a higher rate of oxygen transfer. Thus decreasing the oxygen partial pressure in the oxygen carrier solution is essential to effective oxygen uptake from water in an artificial gill.

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.

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.

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.

For the efficient and well-controlled incorporation of the anti cancer drug adriamycin (ADR) into the inner core of a thermo-responsive polymeric micelle carrier system, we have analyzed and optimized the incorporation procedure in this paper. A dialysis method was used for preparing the micelle solution and ADR incorporation simultaneously. Quantities of ADR and triethylamine (TEA) were varied and the effects of their quantities were analyzed. Solvent composition at the starting time of dialysis was also varied. The initial dialysis condition, solvent with 40% water, brought about the largest amount and yield of ADR incorporation. With the initial 40% water content, it was considered that the block polymers formed a micelle-like association with a swollen hydrophobic core. This swollen core may be suitable for a large amount of ADR incorporation, since this core, swollen by an organic solvent-water mixture, is expected to show a liquid-state character to allow ADR molecules entry into the cores. By starting the dialysis procedure at this 40% water content, this swollen core suitable for the ADR incorporation is considered to be maintained for a much longer period than a case starting with a polyrner-ADR solution in a solvent with a water content of less than 40%, and, therefore, ADR is expected to be incorporated efficiently. Preparation temperature of 20-25degreesC was found to provide the most effective ADR incorporation in this thermo-responsive polymeric micelle system. These results indicate that the efficient incorporation of ADR can be achieved in consideration of the dynamic micelle formation and drug incorporation processes. (C) 2002 Elsevier Science B.V. All rights reserved.

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

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.

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.

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.