Nanotechnological evaluation of protein adsorption on dialysis membrane surface hydrophilized with polyvinylpyrrolidone

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.     

Intrinsic Surface‐Drying Properties of Bioadhesive Proteins

Sessile marine mussels must “dry” underwater surfaces before adhering to them. Synthetic adhesives have yet to overcome this fundamental challenge. Previous studies of bioinspired adhesion have largely been performed under applied compressive forces, but such studies are poor predictors of the ability of an adhesive to spontaneously penetrate surface hydration layers. In a force‐free approach to measuring molecular‐level interaction through surface‐water diffusivity, different mussel foot proteins were found to have different abilities to evict hydration layers from surfaces—a necessary step for adsorption and adhesion. It was anticipated that DOPA would mediate dehydration owing to its efficacy in bioinspired wet adhesion. Instead, hydrophobic side chains were found to be a critical component for protein–surface intimacy. This direct measurement of interfacial water dynamics during force‐free adsorptive interactions at solid surfaces offers guidance for the engineering of wet adhesives and coatings.     

Online SAXS investigations of polymeric hollow fibre membranes

Polymeric membranes are used in industrial and analytical separation techniques. In this study small-angle X-ray scattering (SAXS) with synchrotron radiation has been applied for in-situ characterisation during formation of polymeric membranes. The spinning of a polyetherimide (PEI) hollow fibre membrane was chosen for investigation of dynamic aggregation processes during membrane formation, because it allows the measurement of the dynamic equilibrium at different distances from the spinning nozzle. With this system it is possible to resolve structural changes in the nm-size range which occur during membrane formation on the time-scale of milliseconds. Integral structural parameters, like radius of gyration and pair-distance distribution, were determined. Depending on the chosen spinning parameters, e.g. the flow ratio between polymer solution and coagulant water, significant changes in the scattering curves have been observed. The data are correlated with the distance from the spinning nozzle in order to get information about the kinetics of membrane formation which has fundamental influence on structure and properties of the membrane.     

Novel Methods for Obtaining High Modulus Aliphatic Polyamide Fibers

Super high modulus polyethylene fibers can be created by converting high molecular weight flexible PE chains into highly oriented and extended chain conformations. However, unlike polyethylene, aliphatic polyamides have very high cohesive energy and therefore cannot be easily drawn and highly oriented. This review addresses this fundamental problem by analyzing various novel approaches that can be used to suppress hydrogen bonding in these types of polyamides. Plasticization of such polymers with ammonia, iodine, salts, and Lewis acids, as well as dry spinning, wet spinning, and gel spinning, are discussed. Specialized techniques that involve vibrational zone drawing and annealing as well as laser heating zone drawing and annealing are also reviewed. Some of these methods definitely lead to remarkable improvements in initial modulus and other mechanical properties. The development of recombinant spider silk proteins as well progress in spinning these materials is also reported. The advantages and disadvantages of all of these processes are then summarized.     

Preparation and characterization of polyvinylidene fluoride (PVDF) hollow fiber membranes

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared by dry/wet and wet phase inversion methods. In spinning these PVDF hollow fibers, dimethylacetamide (DMAc) and polyvinyl pyrrolidone (PVP) were used as a solvent and an additive, respectively. Water was used as the external coagulant. Water or ethanol was used as the internal coagulants. The membranes were characterized in terms of water flux, molecular weight cut-off for the wet membranes. Gas permeation fluxes and effective surface porosity were determined by a gas permeation method for the dried membranes. The cross-sectional structures were examined by scanning electron microscopy. The effects of polymer concentration, air-gap, PVP molecular weight, PVP content in the polymer dope, and the internal coagulant on the permeation properties and membrane structures were examined. Highly permeable PVDF hollow fiber membranes could be prepared from a polymer dope containing low molecular weight PVP and using ethanol as the internal coagulant.     

Evolution of the precipitation kinetics,morphologies, permeation performances,and crystallization behaviors of polyvinylidenefluoride (PVDF) hollow fiber membrane by adding different molecular weight polyvinylpyrrolidone (PVP)

Polyvinylidenefluoride (PVDF) hollow fiber membranes were fabricated by wet spinning (wet/wet) and dry‐jet wet spinning (dry/wet; 3 cm air gap) processes with four types of polyvinylpyrrolidone (PVP) of different molecular weight as additives. Evolution of the precipitation kinetics, morphologies, permeation performances, and crystallization behaviors of the as‐spun PVDF membranes were investigated. The PVDF membranes were well characterized by numerous state‐of‐the‐art analytical techniques: scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and attenuated total reflectance fourier Transform Infrared (FTIR‐ATR) and elucidated accompanying with its precipitation kinetics obtained by light transmittance measurements. The precipitation kinetics results confirm that four PVDF/PVP/NMP dopes experience instantaneous demixing mechanism and the precipitation rate decreases as PVP molecular weight increases. Little peaks are found in the precipitation curves of the PVDF dopes containing PVP of low molecular weight. The SEM images indicate that the middle sponge‐like layer sandwiched by double finger‐like layers becomes thinner for the special precipitation behaviors. Visible large pores exist in the internal surfaces of the PVDF membranes spun by both wet/wet and dry/wet spinning processes. The increase in PVP molecular weight restricts the formation of large pores in the internal surfaces of the PVDF membranes for the increase in dope viscosity. The pure water permeability (PWP) of the as‐spun PVDF membranes increases initially and then decreases as PVP molecular weight increases. The largest PWP flux of 316.7 L m^?2 h^?1 bar^?1 is obtained for the PVDF membrane containing PVP K25 by wet/wet spinning process. The rejections for bovine serum albumin (BSA) by the as‐spun PVDF membranes range from 35.4 to 82.9%. It illustrates that typical PVDF ultrafiltration membranes were obtained in this research. The melting temperature(T_m) of the PVDF hollow fiber membranes decreases with the increase in the PVP molecular weight as a whole. IR spectra and XRD patterns verify the exclusive formation of β crystalline phase structure in the as‐spun PVDF membranes. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of solution extrusion rate on morphology and performance of polyvinylidene fluoride hollow fiber membranes using polyvinyl pyrrolidone as an additive

<正>Polyvinylidene fluoride(PVDF) hollow fiber membranes prepared from spinning solutions with different polyvinyl pyrrolidone(PVP) contents(1%and 5%) at different extrusion rates were obtained by wet/dry phase process keeping all other spinning parameters constant.In spinning these PVDF hollow fibers,dimethylacetamide(DMAc) and PVP were used as a solvent and an additive,respectively.Water was used as the inner coagulant.Dimethylformamide(DMF) and water(30/70) were used as the external coagulant.The performances of membranes were characterized in terms of water flux,solute rejection for the wet membranes.The structure and morphology of PVDF hollow fiber were examined by BET adsorption,dry/wet weight method and scanning electron microscopy(SEM).It is found that the increase in PVP content and extrusion rate of spinning solution can result in the increase of water flux and decrease of solute rejection.The improvements of interconnected porous structure and pore size are induced by shear-thinning behavior of spinning solution at high extrusion rates,which could result in the increase of water flux of hollow fiber membranes.The increase of extrusion rate also leads to the increase of membrane thickness due to the recovery effect of elastic property of polymer chains.     

Microscopic behavior of polyvinylpyrrolidone hydrophilizing agents on phase inversion polyethersulfone hollow fiber membranes for hemofiltration

In some biomedical applications, hollow fiber membranes are highly demanded with desirably asymmetric structures, characterized by a dense selective inner skin with which the blood is in contact and supported by porous outer-layer. In this work, such membranes have been successfully prepared by appropriately adjusting membrane manufacturing parameters. Different molecular weights of polyvinylpyrrolidones (PVPs) were used as the hydrophilizing additives for membrane spinning in order to examine their underlying effects on membrane physicochemical properties, morphological structure, solute rejection behavior and hemofiltration performance. Numerous state-of-the-art characterizations on the resultant membranes showed that the hollow fiber membranes spun with the PVP having a molecular weight of 360K as the additive have the most hydrophilic, smooth and highly net negative charged inner surfaces. These membranes also exhibit the best hemofiltration performance in terms of the characteristically least fouling behavior with a normalized flux above 90%, the highest retention of serum albumin for more than 90%, and the best clearance for the simulated β₂-microglobulin toxin in blood waste.     

Preparation of composite hollow fiber membranes: co-extrusion of hydrophilic coatings onto porous hydrophobic support structures

Coating a layer onto a support membrane can serve as a means of surface functionalization of membranes. Frequently, this procedure is a two-step process. In this paper, we describe a concept of membrane preparation in which a coating layer forms in situ onto a support membrane in one step by a co-extrusion process. Our aim is to apply a thin ion exchange layer (sulfonated polyethersulfone, SPES) onto a polysulfone support. The mechanical stability and adhesion of the ion-exchange material to the hydrophobic support membrane (polysulfone) has been studied by a systematic approach of initial proof-of-principle experiments, followed by single layer and double-layer flat sheet casting. Critical parameters quantified by the latter experiments are translated into the co-extrusion spinning process. The composite hollow fiber membrane has low flux as a supported liquid membrane for the copper removal due to the low ion exchange capacity of the SPES. The coating layer of the composite membrane is porous as indicated by gas pair selectivity close to unity. However, our new composite membrane has good nanofiltration properties: it passes mono and bivalent inorganic salts but rejects larger charged organic molecules. The experimental work demonstrates that co-extrusion can be a viable process to continuously prepare surface tailored hollow fiber membranes in a one-step process, even if the support and coating material differ significantly in hydrophilicity.     

DHA-induced changes of supported lipid membrane morphology

Docosahexaenoic acid (DHA) is a polyunsaturated long fatty acid known to have fundamental effects on cell membrane function. Here, the effect of DHA on phosphocholine-supported lipid bilayers was measured using the quartz crystal microbalance with dissipation monitoring (QCM-D) technique. Above a concentration of 60 muM (i.e., near the critical micelle concentration), DHA had drastic effects on the viscoelastic properties of the supported membranes, suggesting a more complex process and structure than simple insertion of molecules in the bilayer. Fluorescence microscopy revealed the spontaneous formation of elongated out-growths from the bilayers, which were remarkable for their length ( approximately 100 mum) and extensive coverage of the surface. These results demonstrate the applicability of QCM-D as a method to screen for conditions where membrane remodeling occurs but also that complementary techniques are required to describe in more detail the changes in viscoelastic properties of the membrane. These results are highly relevant for the present rapid development in the field of model lipid membranes aiming toward increased knowledge about processes occurring at biological surfaces.     

Structural and performance studies of poly(vinyl chloride) hollow fiber membranes prepared at different air gap lengths

Poly(vinyl chloride) hollow fiber membranes were prepared by the dry/wet and wet/wet spinning technique at different air gap lengths keeping all other spinning parameters constants. Mean pore size, pore size distribution and mean roughness of both the internal and external surfaces of the hollow fibers were determined by atomic force microscopy. Cross-sectional structure was studied by scanning electron microscopy. Ultrafiltration experiments of pure water and aqueous solutions of different solutes having different molecular weights (bovine serum albumin, polyethylene glycol and polyvinyl pyrrolidone) were carried out. It was found that the inner and outer diameters of the PVC fiber membranes decreased with the increase of the air gap distance due to the gravitational force effect. The hollow fiber membranes prepared without and with air gap distances up to 7 cm exhibited a quite symmetric cross-structure consisting of four layers, two small finger-like structure layers at both edges of the hollow fibers and two larger finger-like voids mixed with macrovoids layers in the middle of the cross-section. The outer-middle layer thickness decreased when the air gap distance was increased to 10 cm and disappeared from the cross-section of the hollow membranes prepared with higher air gap lengths than 15 cm. For all dry/wet spun PVC hollow fibers, the outer pore size and the pure water permeation flux both increased with the increase of the air gap distance. In contrast, the solute separation factor decreased with the air gap distance. This was related to the pore size of the external surface of the PVC hollow fibers.     

Latest advances in zwitterionic structures modified dialysis membranes

End-stage renal diseases are affecting many patients and as a result, demand to receive dialysis service is growing annually. Morbidity and mortality rates are reported to be higher in comparison with healthy humans. The reason is reported to be the hemoincompatiblity of blood purification membranes, which hinders patients’ lives. Activation of different immune systems in the body, in case of blood-membrane interaction, results in several side effects, of which cardiovascular shocks have been mentioned to be a major one. Efforts to solve this issue have resulted in different generations of dialysis membranes. Zwitterionic immobilized membranes are the latest (third) generation, which owns a higher degree of hemocompatiblity with more stability of immobilized structures. This critical review intends to cover recent efforts conducted over the zwitterionization of polymeric membrane surfaces with the goal of improving hemocompatibility. Different aspects of third-generation membranes are discussed for a better understanding of the current gap and gathering the knowledge to further develop the field. Accordingly, this critical survey provides an in-depth understanding of blood purification membranes zwitterionization for paving the way for the optimum enhancement of hemodialysis membrane hemocompatibility.     

Insights into the surface property and blood compatibility of polyethersulfone/polyvinylpyrrolidone composite membranes: toward high‐performance hemodialyzer

Applications of blood purification membranes are fuelled by diverse clinical needs, such as hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis, and plasma collection. For clinical usage, the adding of polyvinylpyrrolidone (PVP) is the general protocol for the design of antifouling and antithrombotic properties integrated artificial membranes. In the present work, to insight into the detailed surface properties and blood compatibilities of the PVP blended composite membranes, we synthesized a series of PVP polymers with different molecular weights using reversible addition fragmentation chain transfer polymerization and designed a series of polyethersulfone (PES)/PVP composite membranes by a physically blending method. The effects of PVP molecular weights and blending ratios on the surface properties and the blood compatibilities of the composite membranes were investigated in detail. The surface attenuated total reflection Fourier transform infrared spectra and scanning electron microscopy pictures indicated that the PVP was successfully immobilized into the membranes, and the composite membranes exhibited morphology transformation from finger‐like structure to sponge‐like structure, which indicated that the composite membrane had tunable porosity and permeability by adding PVP. The blood compatible tests revealed that the composite membranes showed increased hydrophilicity, decreased plasma protein adsorption, suppressed platelet adhesion, and prolonged blood clotting time compared with pristine PES membrane. These results indicated that the PES/PVP composite membranes exhibited enhanced antifouling and antithrombotic properties than the pristine PES membrane. Meanwhile, the results also suggested that the composite membranes with larger molecular weight PVP and higher blending ratios might show better blood compatibility. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of Dry-Jet Wet Spinning Parameters on Properties of Polysulfone Hollow Fiber Membranes

Russian Journal of Applied Chemistry - The influence of parameters of the dry-jet wet spinning process was studied on properties of porous polysulfone hollow fiber membranes. The air gap distance,...     

Improved Membranes for Hemodialysis

Asymmetric membranes of cellulose acetate and cellulose acetate modified with pendant amino groups have been evaluated for ultrafiltration and dialysis properties. Ultrafiltration rates from 4 to 30 times that of Cuprophan were obtained. During the ultrafiltration test, up to 89% of inulin in the test solution permeated with the ultrafitrate in contrast to the 14% permeation of inulin through a Cuprophan membrane. In spite of the apparently facile permeation of high molecular weight species (e.g., inulin) through the experimental membranes, human albumin was quantitatively reflected. Dialysis tests indicate that cellulose acetate membranes 38 μ or less in thickness should surpass 23-μ-thick (wet) Cuprophan in purely diffusional transport of blood solutes of low molecular weight.

In addition to their promising ultrafiltration and dialysis properties, membranes made from a blend of cellulose acetate and N,N-diethylaminoethylcellulose acetate were found to sorb heparin strongly. The clotting time of rabbit blood in contact with the heparinized membranes was extended, in some cases indefinitely.     

Effect of γ irradiation on the surface properties of wet polysulfone films containing poly(vinylpyrrolidone)

In Japan, hemodialyzers are usually sterilized by γ irradiation. However, the polymer materials used in the dialysis membrane, such as polysulfone (PSf) and poly(vinylpyrrolidone) (PVP), undergo crosslinking or degradation on exposure to γ radiation. In the present study, we prepared PSf/PVP films (PVP content, 0–50 wt%) and used atomic force microscopy (AFM) to perform nanoscale evaluations of the effect of γ irradiation (25 and 50 kGy) on the surface properties of wet PSf/PVP surfaces. Force‐curve measurements were used to evaluate the hardness of and fibrinogen adsorbability on the wet PSf/PVP surface; fibrinogen adsorbability on the wet PSf/PVP surface was evaluated using AFM probes with fibrinogen immobilized on the tips of the probes. At PVP levels greater than 5 wt%, the wet PSf/PVP film surface was completely covered with hydrated and swollen PVP particles. The surface hardness of the wet PSf/PVP films exposed to 25‐kGy γ irradiation greatly decreased with increasing PVP content, whereas the surface hardness of the wet PSf/PVP films exposed to 50‐kGy γ irradiation did not decrease significantly. At higher PVP levels, the reduction in the fibrinogen adsorbability on a wet PSf/PVP film exposed to 25‐kGy γ irradiation was more significant than that on a wet PSf/PVP film exposed to 50‐kGy γ irradiation. PVP particles on the wet PSf/PVP film surface exposed to 50‐kGy γ irradiation did not show significant hydration and swelling because the polymer materials PVP–PSf and PVP‐PVP in these membranes has undergone excessive crosslinking due to γ irradiation. Copyright © 2010 John Wiley & Sons, Ltd.     

PVDF and HYFLON AD membranes: Ideal interfaces for contactor applications

Super-hydrophobic fluorinated membranes were tailored by combining traditional dry-wet phase inversion and wet chemical treatment techniques. PVDF and HYFLON AD 60X were selected as raw polymers for their chemical and mechanical resistance as well as hydrophobic and solvophobic properties. Membranes with modulated pore size, narrow distribution and high overall porosity were manufactured without using additional additives or modifiers. High resistance to liquid water entry pressure (LEPw), high mass transfer and low surface free energy of the membrane surfaces were fully achieved. The combination of these two fluorinated polymers improved dramatically the mechanical resistance and the water repellence of the PVDF membranes. Well-controlled structure combined with aimed supra-molecular chemistry makes these porous layers ideal interfaces to be processed in membrane contactor devices.     

Effect of membrane preparation on the lifetime of supported liquid membranes

A new observation on the stability of supported liquid membranes (SLMs) is reported. Membranes prepared with ‘dry’ outer surfaces, free from organic wetting, were found to be more stable than the conventional SLM prepared with external surfaces wetted with a film of the organic membrane liquid phase. For copper transport the ‘dry’ surface SLM had a similar initial flux to the ‘wet’ surface SLM, and 2 to 4 times the flux after 100 h. Over a 50 h period the ‘dry’ SLM lost about 10% of its membrane liquid, whereas the ‘wet’ SLM lost about 50%. The difference is ascribed to the loss of membrane by emulsion formation at one of the aqueous-organic interfaces which would be greater for the ‘wet’ SLM with a continuous liquid film over the surface of the support.     

Mimicking the cell membrane with block copolymer membranes

Cell membranes are essential barriers in Nature. To understand their properties and functions and to develop desirable applications, a simple and elegant approach is to study membranes that mimic the cell membrane. Lipid bilayers represent simple models that are physiologically representative when in the form of mixtures of various lipids, but they are not adequately stable even when covered with amphipathic proteins or when combined with polymers, thus preventing technological applications. This makes necessary the design of completely synthetic membranes. In this respect, amphiphilic copolymers that self‐assemble under dilute aqueous conditions and generate supramolecular polymer vesicles or films are ideal candidates for synthetic membranes. Their versatility in terms of chemistry and properties (permeability, mechanical stability, thickness), if appropriately designed, enable the insertion of biological molecules, such as membrane proteins and biopores, or the attachment of biomolecules at their surfaces. Here, we present the domain of synthetic membranes based on amphiphilic copolymers beginning with their generation and up to their applications in medicine, the food industry, and technology. Even though significant progress has been made in combining them with membrane proteins, open questions remain with respect to desired properties that could accommodate biological molecules and support further development of the field, from both the point of view of fundamental understanding and of applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Fabrication study of polysulfone hollow-fiber microfiltration membranes: Optimal dope viscosity for nucleation and growth

Fabrication of polysulfone hollow-fiber microfiltration membranes through non-solvent induced phase separation (NIPS) by dry–wet spinning was studied. For all sample preparations, we used N-methylpyrrolidone (NMP) as solvent, polyethylene glycol (PEG) as additive, aqueous NMP solution as bore liquid, and water as coagulation bath. Particular focus was placed on the influence of PEG molecular weight (Mw) on membrane structure. Characterization of the obtained membranes was performed by measuring pure water permeate flux, tensile strength, and tensile elongation at break, and by analyzing scanning electron microscope (SEM) images of hollow-fiber cross-sections, outer surfaces, and inner surfaces.