Ethylene Vinyl Alcohol Membrane Research Articles

Simultaneously enhanced separation and antifouling properties by synergistic effect of pore-formation and surface segregation through incorporating bowl-like amphiphiles

Herein, we propose a new strategy to improve the separation and antifouling properties of ethylene vinyl alcohol (EVAL) membranes by a dual pore formation mechanism modified with natural macrocyclic amphiphiles cyclodextrin (CDs). The amphiphilic bowl-like geometry of CDs, consisting of a hydrophobic cavity and hydrophilic rim, induces spontaneous surface segregation during the non-solvent induced phase separation to form a CD-enriched layer. Here, CDs play multiple roles, including pore-forming and antifouling enhancement agents, by modifying the morphological, physical, permeation, and separation properties of the membranes. The three-dimensional honeycomb sponge-like structure was determined by SEM analysis, and the elemental composition was examined by SEM-EDX analysis. The O element indicated a gradient decrease distribution from the top to the bottom layer of the cross-section, concomitant with the combination of pore-forming and surface segregation functions. The introduction of amphiphilic CDs increases the roughness, hydrophilicity, and porosity of the membranes. Furthermore, the CDs-modified EVAL (d-M) membranes have excellent mechanical properties, a high water flux (148 L/m2h) with superior rejection to BSA (98%), and can be used for dye separation (Congo Red: 99.7%, Coomassie brilliant blue: 97.5%, Trypan blue: 92.4%). Moreover, the modified EVAL with the best performance has excellent antifouling capacity and long-term stability. This work demonstrates the effect of the addition of CDs and octanol as dual pore formers on the fabrication of hydrophilic antifouling membranes for efficient separation.

Photocatalytic self-cleaning EVAL membrane by incorporating bio-inspired functionalized MIL-101(Fe) for dye/salt separation

This work was expected to develop a new loose NF membrane with facile materials to conduct dye/salt separation and endow it with versatile capacities to offer an applicable solution to treat textile wastewater. Ethylene vinyl alcohol (EVAL) was first chosen to fabricate loose nanofiltration (NF) membrane through non-solvent induced phase separation (NIPS) method. Besides, MIL-101(Fe) showed outstanding photocatalytic capacity in degrading organic molecules while a low-cost bio-inspired coating, catechol, was utilized to modify MIL-101(Fe). A combination of modified MIL-101(Fe) and EVAL could have a high water permeability (43.2 L·m−2·h−1·bar−1) with superior rejection to small molecule negative charged dyes (Chlorazol black T: 99.8%, Congo Red: 99.7%, Eriochrome black T: 98.4%) and low rejection to various salts (Na2SO4: 4.8 %, NaCl: 2.1 %, MgCl2: 2.9%, MgSO4: 4.9% and CaCl2: 3.3%). Meanwhile, the EVAL loose NF membrane with the best performance had excellent antifouling capacity and long-term stability in EBT/Na2SO4 separation. Moreover, the membrane could degrade dyes to self-clean the membrane surface through photocatalytic process, which originated from the Fe-O clusters in MIL-101(Fe).

Bioartificial pulsatile cuffs fabricated from human induced pluripotent stem cell-derived cardiomyocytes using a pre-vascularization technique

There is great interest in the development of techniques to bioengineer pulsatile myocardial tissue as a next-generation regenerative therapy for severe heart failure. However, creation of thick myocardial grafts for regenerative medicine requires the incorporation of blood vessels. In this study, we describe a new method of constructing a vascular network in vivo that allows the construction of thick human myocardial tissue from multi-layered cell sheets. A gelatin sheet pre-loaded with growth factors was transplanted onto the superficial femoral artery and vein of the rat. These structures were encapsulated together within an ethylene vinyl alcohol membrane and incubated in vivo for 3 weeks (with distal superficial femoral artery ligation after 2 weeks to promote blood flow to the vascular bed). Subsequently, six cardiomyocyte sheets were transplanted onto the vascular bed in two stages (three sheets, two times). Incubation of this construct for a further week generated vascularized human myocardial tissue with an independent circulation supplied by an artery and vein suitable for anastomosis to host vessels. Notably, laminating six cell sheets on the vascular bed in two stages rather than one allowed the creation of thicker myocardial tissue while suppressing tissue remodeling and fibrosis. Finally, the pulsatile myocardial tissue was shown to generate auxiliary pressure when wrapped around the common iliac artery of a rat. Further development of this technique might facilitate the generation of circulatory assist devices for patients with heart failure.

Increasing lithium extraction performance by adding sulfonated poly (ether ether ketone) into block‐copolymer ethylene vinyl alcohol membrane

AbstractBACKGROUNDHigh efficiency membrane extraction (ME) of lithium from brine has been constrained by membrane mass transfer resistance. We report here a new solvent‐resistant membrane produced from ethylene vinyl alcohol (EVAL) and sulfonated polyether ether ketone (SPEEK).RESULTSThe effect of the SPEEK on the thermodynamics and kinetics of demixing to the membrane morphology was investigated systematically. Addition SPEEK created extra resistance to the movement of the polymer chains in solution which was reflected in the reduced gelation diffusion coefficient. About 0.5 wt% of SPEEK was sufficient to reduce the mass transfer resistance of lithium ions (Li+). Membrane thickness showed linear correlation with Li+ flux, but was limited by its weak mechanical strength. Finally, a composite EVAL/SPEEK membrane supported by a thin loose nonwoven fabric showed a stress of 12.5 MPa, nearly 10‐fold greater than the unsupported membrane, and the highest lithium extraction flux of 4.80 × 10−8 mol cm−2 s−1.CONCLUSIONThe work provides a rationale for developing mechanically stable, high extraction flux membranes for ME. © 2020 Society of Chemical Industry

A new strategy to simultaneously improve the permeability and antifouling properties of EVAL membranes via surface segregation of macrocyclic supra-amphiphiles

Herein, we propose a new strategy to improve the flux and antifouling properties of ethylene vinyl alcohol (EVAL) membranes by blending with macrocyclic supra-amphiphiles (cyclodextrin; CD). The amphiphilic ‘molecular cage’ geometry of CD, consisting of a hydrophobic cavity segment and hydrophilic rim segment, induces spontaneous surface segregation of CD to form a CD-enriched layer on the membrane surface. The membrane matrix structure was observed by SEM-EDX, wherein elemental composition indicated a gradient distribution of elemental O content from the top to the bottom layer of the cross-section. The layer segregation was governed by the synergistic interactions with hydrophobic and hydrophilic segments of amphiphilic CD polymer during the phase inversion process. When clickable azide-β-CD was fixed into the clickable alkyne-EVAL matrix as a comparative experiment, no surface segregation was observed. The aggregation of hydrophilic CD on the membrane surface increased the surface roughness, hydrophilicity, and water flux (200 L/m2h) of the membrane. Furthermore, the macrocyclic supra-amphiphile-blended membrane showed better antifouling performance than raw EVAL membrane, with a lower water flux decline (21%) and higher water flux recovery (89%). The proposed 3D strategy based on macrocyclic supra-amphiphiles shed lights on the formation of hydrophilic membrane surface with potential applications in membrane technology.

Bioinspired EVAL membrane modified with cilia-like structures showing simultaneously enhanced permeability and antifouling properties

A simple and effective strategy to simultaneously enhance the permeability and antifouling properties of ethylene vinyl alcohol (EVAL) membrane was developed based on the bioinspired natural cleaner, cilia. Taking clue from the self-cleaning effect of cilia, supramolecular polyrotaxanes (PRs) with sliding and rotating cyclic molecules along linear chains were synthesized using azide-alkyne click chemistry. Cilia-like PRs were incorporated into EVAL matrix in the fabrication of modified EVAL membranes. Cilia-like structures protruding from the membrane surface have been observed by SEM, TEM and AFM. By imitating natural ciliary movements, these structures provided a proactive self-cleaning system to remove the foulants. The introduction of cilia-like PRs enhanced the surface roughness and hydrophilicity, and significantly enhanced permeability by 55.3% compared to raw EVAL membrane. Moreover, the membrane modified with cilia-like PRs showed an excellent antifouling property with a lower water flux decline (12.6%) and higher water flux recovery (94%) in dynamic fouling tests. Furthermore, this modified membrane develops the scope of bioinspired membranes, inspiring more attractive potential applications in self-cleaning materials, dynamic membranes and supramolecular machines.

Low-adhesive ethylene vinyl alcohol-based packaging to xenogeneic islet encapsulation for type 1 diabetes treatment.

Transplantation of encapsulated porcine islets is proposed to treat type 1 diabetes. However, the envelopment of fibrous tissue and the infiltration of immune cells impair islet function and eventually cause implant failure. It is known that hemodialysis using an ethylene vinyl alcohol (EVOH) membrane results in minor tissue responses. Therefore, we hypothesized that using a low-adhesive EVOH membrane for encapsulation may prevent host cell accumulation and fibrous capsule formation. In this study, rat islets suspended in chitosan gel were encapsulated in bags made from highly porous EVOH membranes, and their in vitro insulin secretion function as well as in vivo performance was evaluated. The results showed that the EVOH bag did not affect islet survival or glucose-stimulated insulin secretion. Whereas naked islets were dysfunctional after 7 days of culture in vitro, islets within the EVOH bag produced insulin continuously for 30 days. Streptozotocin-induced diabetic mice were given islets-chitosan gel-EVOH implants intraperitoneally (650-800 islets equivalent) and exhibited lower blood glucose levels and regained body weight during a 4-week observation period. The transplanted mice had higher levels of serum insulin and C-peptide, with an improved blood glucose disappearance rate. Retrieved implants had minor tissue adhesion, and histology showed a limited number of mononuclear cells and fibroblasts surrounding the implants. No invasion of host cells into the EVOH bags was noticed, and the encapsulated islets were intact and positive for insulin-glucagon immunostaining. In conclusion, an EVOH bag can protect encapsulated islets, limit fibrous capsule formation, and extend graft function.

Novel affinity membranes with macrocyclic spacer arms synthesized via click chemistry for lysozyme binding

Affinity membrane has great potential for applications in bioseparation and purification. Disclosed herein is the design of a novel affinity membrane with macrocyclic spacer arms for lysozyme binding. The clickable azide-cyclodextrin (CD) arms and clickable alkyne ethylene-vinyl alcohol (EVAL) chains are designed and prepared. By the azide-alkyne click reaction, the EVAL-CD-ligands affinity membranes with CD spacer arms in three-dimensional micro channels have been successfully fabricated. The FT-IR, XPS, NMR, SEM and SEM-EDS results give detailed information of structure evolution. The abundant pores in membrane matrix provide efficient working channels, and the introduced CD arms with ligands (affinity sites) provide supramolecular atmosphere. Compared with that of raw EVAL membrane, the adsorption capacity of EVAL-CD-ligands membrane (26.24mg/g) show a triple increase. The study indicates that three effects (inducing effect, arm effect, site effect) from CD arms render the enhanced performance. The click reaction happened in membrane matrix in bulk. The effective lysozyme binding and higher adsorption performance of affinity membranes described herein compared with other reported membranes are markedly related with the proposed strategy involving macrocyclic spacer arms and supramolecular working channels.

The Role of Dialysis Membranes on Intradialytic Selenium Removal and on Selenium Status in Patients Receiving Renal Replacement Therapy

Background/Aims: Dialysis membrane has been implicated in selenium (Se) deficiency in hemodialysis (HD). Intradialytic Se removal into dialysate through different membranes was investigated. Methods: We studied 19 patients on standard HD with low-flux polysulfone membrane (group A), 10 patients on standard HD with ethylene vinyl alcohol membrane (group B), 12 patients on hemodiafiltration (HDF; group C) and 16 healthy subjects (control group D). Se was measured in blood before and after dialysis session and in effluent dialysate every hour during session. Results: In all patients together, pre-dialysis serum Se levels were lower than those in control group, but, in a separate analysis, only in standard HD. In all patient groups, there was a net Se removal into dialysate but it was greater in HDF patients who, however, had similar pre-dialysis serum Se levels to those in healthy controls. Conclusion: An intradialytic Se loss was found with all 3 membrane types, but it is not the principal factor for Se depletion in HD.

Water and oxygen permeation through transparent ethylene vinyl alcohol/(graphene oxide) membranes

We prepared ethylene vinyl alcohol (EVOH)/graphene oxide (GO) membranes by solution casting method. X-ray diffraction analysis showed that GOs were fully exfoliated in the EVOH/GO membrane. The glass transition temperatures of EVOH were increased by adding GOs into EVOH. The melting temperatures of EVOH/GO composites were decreased by adding GOs into EVOH, indicating that GOs may inhibit the crystallization of EVOH during non-isothermal crystallization. However, the equilibrium melting temperatures of EVOH were not changed by adding GOs into EVOH. The oxygen permeability of the EVOH/GO (0.3 wt%) film was reduced to 63% of that of pure EVOH film, with 84% light transmittance at 550 nm. The EVOH/GO membranes exhibited 100 times better (water vapor)/(oxygen) selectivity performance than pure EVOH membrane.

A metal ion charged mixed matrix membrane for selective adsorption of hemoglobin

In this work, we developed a mixed matrix membrane by incorporating 20–40μm size iminodiacetic acid modified immobeads within porous Ethylene vinyl alcohol (EVAL) polymer matrix. The MMM were charged with copper ions for selective adsorption of bovine hemoglobin in presence of bovine serum albumin. EVAL membrane without immobead and immobead alone showed low non-specific adsorption towards bovine hemoglobin and bovine serum albumin. Use of buffers with pH ⩽6.8 i.e. pI of bovine hemoglobin resulted in high bovine hemoglobin adsorption. The developed mixed matrix membrane has a maximum static adsorption capacity of 219.5mg bovine hemoglobin per g bead and the adsorption isotherm curve is of a Langmuir type. Under similar flow rates, the mixed matrix membrane showed significant low pressure drop compared to a packed bed column containing equal amount of beads. Maximum and faster (6h) adsorption of bovine hemoglobin can be achieved through dynamic mode only using mixed matrix membrane and not by packed bed column and static mode of mixed matrix membrane. The mixed matrix membrane has three times selective adsorption of bovine hemoglobin than bovine serum albumin, from a binary mixture containing equivalent amounts of both proteins.

Coagulation Activation Is Associated with Nicotinamide Adenine Dinucleotide Phosphate Oxidase-Dependent Reactive Oxygen Species Generation in Hemodialysis Patients

This study investigated on (i) the role of gp91(phox)/NOX2 in reactive oxygen species (ROS) generation in hemodialysis (HD) patients, and (ii) the link between clotting activation and ROS production in this setting. The study was performed on peripheral blood mononuclear cells (PBMCs) isolated from HD patients randomized to polysulphon/polyamide (S-group, n=30) or ethylene-vinyl-alcohol (EVAL) membrane (E-group, n=30) treatment and from healthy subjects (control group, n=15). ROS generation was increased in PBMCs of HD patients compared with healthy subjects. S-group showed higher levels of intracellular ROS generation than control, whereas E-group did not. In addition, S-group displayed an increase in nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity compared with E-group and healthy subjects. A further increase in NADPH activity shortly after HD treatment was observed only in S-group. The plasma levels of the prothrombin fragment F1+2, a marker of in vivo clotting activation, were significantly higher in S-group than in E-group. Moreover, a heightened thrombin generation was recorded in the plasma of S-group. Intracellular ROS production correlated with NADPH oxidase activity and coagulation priming in HD patients. The in vitro validation study demonstrated that incubation of PBMCs with activated FX induced a significant increase in intracellular ROS production, superoxide generation, and gp91(phox)/NOX2 expression. The pivotal role of NADPH oxidase in the upregulation of ROS in HD patients makes this enzyme a potential target for therapeutic intervention in the treatment of HD-related oxidative stress. The EVAL membrane, by reducing clotting activation, inhibits gp91(phox)/NOX2-related ROS production in HD patients.

The development of novel micro-capillary film membranes

This paper reports the experimental results for the processing of micro-capillary film (MCF) membranes. MCFs are films with embedded multiple hollow capillaries and can be considered as a hybrid geometry between flat sheet and hollow fibres. Compared to the conventional membrane geometries, MCFs potentially provide a higher surface area per unit volume, better mechanical strength, ease of handling and more efficient module fabrication. MCF membranes were fabricated out of ethylene vinyl alcohol (EVOH) copolymer through a solution extrusion followed by a nonsolvent induced phase separation process (NIPS). Single capillary EVOH membranes were also fabricated prior to the fabrication of MCFs to establish a base process. Fluid flow observations were carried out at different regions in the process in order to better understand the dynamics of extrusion and phase inversion. It was observed that polymer solution and bore fluid rheology as well as processing conditions including air-gap distance and take up rate have significant effects on the flow dynamics and consequently the macrostructure of the membranes. Furthermore, the flow observations led to the identification of an extrudate expansion phenomenon in the external coagulation bath which strongly influenced the membrane formation process. The micro-structure characterization of the fabricated membranes showed the formation of a highly porous, interconnected and macrovoid-free microstructure in the membranes. MCF membranes can be applied with a potentially promising performance in a variety of membrane applications such as micro and ultrafiltration, membrane bioreactors (MBR), porous microfluidic devices as well as membrane contactors for process intensifications.

Nanotechnological Characterization of Human Serum Albumin Adsorption on Wet Synthetic Polymer Dialysis Membrane Surfaces

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.

Oxidative Stress Potentials of Different Synthetic Hemodialysis Membranes

AbstractBACKGROUNDOxidative stress resulting from membranes is dependent on the increase in production of toxic‐free oxygen radicals occurring through the mediation of complement and leukocyte activation. Increased oxidative stress causes morbid results such as erythropoietin resistance, accelerated aging, and atherosclerosis. This study aimed to determine the stress potentials of 2 distinct synthetic membranes different than used in previous studies. In our study, the effects of using polysulfone (PSU) and ethylene vinyl alcohol (EVAL) for 3‐month periods in the same patient group on malondialdehyde (MDA) levels, biomarker for oxidative stress, and proinflammatory cytokine production were compared.METHODSPSU and EVAL membranes with the same surface area were used in 21 chronic hemodialysis patients (12 men and 9 women, mean age 66.66 ± 12.47 years) during successive 3‐month periods. Treatments and dialysate contents administered during this period were not changed. At the end of each period, interleukin (IL)‐1, IL‐6, tumor necrosis factor a (TNF‐α), and MDA levels in patients' sera were determined before dialysis, and the data obtained from the study were compared using the paired‐sample t test.RESULTSA significant decrease in C‐reactive protein levels was seen after EVAL usage compared with PSU usage (p < 0.05). Although an increase was seen in hemoglobin levels, it was not considered statistically significant. It was determined that there was not a statistically significant difference in the change in TNF‐α, IL‐1, and IL‐6 levels (0.002 ± 0.0009 ng/mL, 1.33 ± 0.84 ng/mL, and 0.05 ± 0.05 ng/mL, respectively) measured after PSU usage with that in the TNF‐α, IL‐1, and IL‐6 levels (0.003 ± 0.001 ng/mL, 1.44 ± 1.37 ng/mL, and 0.05 ± 0.05 ng/mL, respectively) measured after EVAL usage (p > 0.05). MDA levels were determined to be 15.08 ± 5.28 mM after PSU usage and 5.96 ± 2.24 mM after EVAL usage. Lower MDA levels obtained after EVAL usage were considered to be highly statistically significant (p = 0.001).CONCLUSIONSStudies and searches are continuing toward determining and controlling oxidative stress potentials of dialysates used in addition to determining their high efficacy. This study, which investigated oxidative stress levels produced by 2 synthetic membranes in the same patient group, demonstrated that widely used PSU membranes cause more oxidative stress than EVAL membranes. Studies to decrease oxidative stress potentials of PSU membranes that have high diffusion and convection ability and also high‐flow forms in production compared with EVAL membranes are focusing on vitamin E–coated forms.

Current topics on cryofiltration technologies.

In the last 40 years, therapeutic plasmapheresis techniques have been improving considerably. These include cryofiltration technologies providing novel ways of removing large amounts of cryoproteins from plasma. The concept of cryofiltration involves exposure of plasma to below core (37 degrees C) and room temperatures (25 degrees C) without freezing. It was initially used to treat diseases such as cryoglobulinemia with systemic vasculitis, rheumatoid arthritis, systemic lupus erythematosus, and ABO-incompatible transplants. There are 2 basic types of cryofiltration. The first method removes cryoproteins, namely cryoglobulins that precipitate at 4 degrees C. Several filters have been used for this procedure like the AP06M (Asahi Medical, Tokyo, Japan) with a 0.2 microm pore size, a 0.65 m2 surface area, and a cellulose diacetate (CDA) membrane. It has been used in the United States and Japan for treatment of rheumatoid arthritis and cryoglobulinemia. A major disadvantage was frequent filter plugging, which was cumbersome and it is no longer used in the United States. The G3 cryofilter (Gelman Sciences, Ann Arbor, MI, U.S.A.) with a 3 microm pore size was tried in vitro but proved inadequate by design. Currently in our institution, the cryoglobulin filter (Pall Medical, Ann Arbor, MI, U.S.A.) is used with a 4.3 microm pore size, a 0.135 m2 surface area, and an acrylic co-polymer pleat membrane. We performed over 1,200 procedures in 40 patients in the last 8 years. The second type of cryofiltration removes cryogel, which is an agglutination complex of fibrinogen, fibronectin, fibrin split products, and cold insoluble proteins with a heparin core, at temperatures between 2 and 10 degrees C. The AP06M, the AC1740 (Asahi Medical) with a 0.02 microm pore size, a 1.70 m2 surface area, and a CDA membrane, and the Evaflux-4A (Kuraray Company, Osaka, Japan) with a 0.03 microm pore size, a 2 m2 surface area, and an ethylene vinyl alcohol membrane are used to remove cryogel to treat ABO-incompatible transplants as well as rheumatoid arthritis and other previously mentioned diseases. This article will discuss each cryofiltration treatment modality.

The effect of surface properties of EVAL membranes on the inflammatory response

The purpose of this study was to examine the relationship between tissue response and the membrane surface structure. A series of ethylene vinyl alcohol (EVAL) membranes provide an ideal system for a study of the relative contributions to biocompatibility derived from the surface morphology. This is different from other reports using different kinds of polymers, which may thus result in considerable variation since polymer implants are both chemically and physically heterogeneous. This study demonstrated that the tissue response to three different membrane structures were quite different. Flat and dense EVAL surfaces induced a mild foreign body reaction indicating that EVAL copolymer does not provide a stimulus for a continued inflammatory response. The inflammatory response was strong using a porous surface and a surface with a particulate morphology. In addition, particulate surfaces provoked a more intense inflammatory response than porous surfaces, indicating that a material in particulate form, suitable for phagocytosis, may provoke a different degree of inflammatory response than the same material in a nonphagocytosable form. Therefore, although a material may be considered to be biocompatible, however, its surface properties may alter the observed tissue reaction and inflammatory response. Consequently, the surface properties should be suitably selected according to the purpose for which the material is to be used.

Measurement of somatostatin release in rat brain by microdialysis

We determined the most suitable conditions for measuring the somatostatin (SRIF) level by brain microdialysis and investigated its release from the hypothalamus. The relative recovery rate of SRIF was 8.4 ± 0.5%(mean ± SE) using a polycarbonate (PC) membrane with the push-pull method at a flow rate of 2 μl/min. Using tubes with an internal diameter of 0.28 mm and lengths of 5, 25, 50 and 100 cm, the relative recovery rates using a PC membrane with the push method were 8.2 ± 0.5%, 7.3 ± 0.6%, 6.2 ± 0.5% and 4.1 ± 0.6%, respectively. When using tubes with an internal diameter of 0.1 mm and lengths of 5, 25, 50 and 100 cm, the relative recovery rates were 7.3 ± 0.7%, 5.6 ± 1.0%, 3.5 ± 1.1% and 1.4 ± 0.7%, respectively. The relative recovery rate was 5.2 ± 0.5% with a polysulfone (PS-F, Fresenius) membrane, 4.5 ± 0.4% with a PS-H (Hospal) membrane, 2.6 ± 0.2% with an ethylenevinyl alcohol membrane (EVAL), 5.1 ± 0.8% with a polyvinyl alcohol (PVA) membrane and 10.4 ± 0.8% with a PS-K (Kaneka) membrane. With the push method, the extracellular SRIF level in rat pituitary was 42.8 ± 1.8 pg/ml with a PC membrane, 23.1 ± 2.9 pg/ml with an EVAL membrane at a flow rate of 2 μl/min. With the push-pull method, it was 52.7 ± 5.2 pg/ml using a PC membrane, 33.5 ± 2.8 pg/ml using a PVA membrane and 54.4 ± 3.2 pg/ml using a PS-K membrane. Intraperitoneal injection of urethane significantly increased SRIF from a basal level of 36.8 ± 10.6 pg/ml to 66.6 ± 12.5 pg/ml ( P < 0.05) after 1 h; however, pentobarbital decreased it from 44.7 ± 4.1 pg/ml to 16.0 ± 4.6 pg/ml after 1 h. These data, which give optimum microdialysis conditions for measuring SRIF release in the rat, were useful for measuring the physiological release of SRIF from the hypothalamus.

Dialysis treatment using an ethylene vinyl alcohol membrane and no anticoagulation for chronic uremic patients.

Anticoagulation used in hemodialysis treatment brings with it the risk of hemorrhagic complications and the possible consequences associated with chronic heparin administration. These problems have not been satisfactorily addressed to date. This study examined a new dialysis method that does not require the administration of anticoagulants. Dialysis is performed for 3 h with a continuous infusion of 750 ml of physiological saline solution in predilution mode and using filters made of ethylene vinyl alcohol copolymer membranes. Eleven patients with chronic uremia underwent more than 2,000 dialysis treatments performed with 9 episodes of coagulation of the dialyzer or blood tubings (0.43%). An evaluation of individual treatments revealed a high degree of biocompatibility and only a scanty activation of coagulation. Blood depuration efficacy was very good as evaluated from pretreatment and posttreatment routine blood chemistries. The technique described here represents a simple and effective method for performing regular dialysis treatment and does not require anticoagulant therapy.

Study of Glomerular Permselectivity for Proteins of the Glomerular Basement Membrane Using a Dialyzer Model

The glomerular basement membrane (GBM) is considered to regulate glomerular permselectivity for proteins by acting as both size barrier and charge barrier. Since heparan sulfate-proteoglycan (HS-PG), which forms the charge barrier of GBM, contains a sulfonic acid, we made membranes with various degrees of negative charge models of GBM by addition of sulfonic acid to ethylene vinyl alcohol (EVAL) membranes. A high-resolution scanning electron-microscopic study revealed no ultrastructural alterations after adding sulfonic acid to EVAL membranes. Both neutrally and negatively charged membranes had porous structures in the inner surface of the membranes. The interrelation between the two actions of size and charge of GBM was studied using special dialyzers with various degrees of negative charge and different pore sizes. The negatively charged membranes adsorbed proteins with positive charge and repulsed proteins with negative charge. The degrees of adsorption and repulsion were weaker in membranes with larger pores and were stronger for proteins with larger molecular weights. The permselectivity for proteins of a charged membrane depends largely upon the interrelation between the pore size of the membrane and the size of the proteins. It is, therefore, suggested that the presence of a size barrier in GBM is necessary for the charge barrier to effectively exert glomerular permselectivity for proteins. Our study may lead to the development of a dialyzer with higher permselectivity by adding sulfonic acid rather than conventional dialyzers.