Surface modification using photocrosslinkable chitosan for improving hemocompatibility

Immobilization of the anticoagulative or antithrombogenic biomolecule has been considered as one of the important methods to improve the blood compatibility of artificial biomaterials. In this study, a novel immobilization reaction scheme was utilized to incorporate O-butyrylchitosan (OBCS) onto the activated glass surface with an aim to develop an anticoagulative substrate. Activation of the glass surface was carried out by silanization and then OBCS was grafted to the silanized surface via a radiation grafting technique. The OBCS-grafted glass surfaces were characterized by electron spectroscopy for chemical analysis (ESCA) and atomic force microscopy (AFM). The blood compatibility of the OBCS-grafted glass was evaluated by platelet rich plasma (PRP) contacting experiments and protein adsorption experiments in vitro. These results have demonstrated that the surface with immobilized OBCS shows much less platelet adhesive and fibrinogen adsorption compared to the control surface. Therefore, the novel reaction scheme proposed here is very promising for future development of an anticoagulative glass substrate.     

New biocompatible polypyrrole-based films with good blood compatibility and high electrical conductivity

A novel O-butyryl chitosan (OBCS)-grafted polypyrrole (PPy) film was described. The immobilization was accomplished by photocrosslinking the OBCS onto PPy films under ultraviolet light irradiation. The surfaces of OBCS-grafted PPy film were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). The blood compatibility of the OBCS-grafted PPy film was evaluated by platelet-rich plasma (PRP) contacting experiments and protein adsorption experiments in vitro. These results have demonstrated that the surface with immobilized OBCS shows much less platelet adhesive and fibrinogen adsorption compared to the control surface. The bulk conductivity values of PPy films were measured by a modified four-probe method. The composite films have both good blood compatibility and high electrical conductivity that make them suitable for using as potential biomaterials, such as electrically conducting blood vessel and functionally haemocompatible substrate of biosensor used directly in whole blood.     

Introduction of O-butyrylchitosan with a photosensitive hetero-bifunctional crosslinking reagent to silicone rubber film by radiation grafting and its blood compatibility

Based on an in vitro test for an improvement of the blood compatibility of silicone rubber (SR) films by grafting O-butyrylchitosan (OBCS), OBCS was covalently immobilized onto SR film surface using the photosensitive hetero-bifunctional crosslinking reagent, 4-azidobenzoic acid, which was previously bonded to OBCS by reaction between an acid group of the crosslinking reagent and a free amino group of OBCS. Surface properties of SR film were investigated by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA) and the water contact angle measurements. The blood compatibility of SR film was evaluated by platelet rich plasma (PRP) contacting experiments and the results were observed by scanning electron microscopy (SEM). The state of platelet adhesion was described. The suitable modifications could be carried out to tailor SR films biomaterial to meet the specific needs of different biomedical applications. These results suggest that the blood compatible of SR films/OBCS films show their suitability as potential biomaterials.     

PEG-grafted PVA Membrane and Its Blood Compatibility

Preparation and blood compatibility of different shape polyvinyl alcohol(PVA) membrane were investigated. Firstly, the tabular and tubular[polytetrafluoroethylene(PTFE) capillary as supporter] PVA membranes were prepared; then, methoxy polyethylene glycol(mPEG) was grafted onto the surface of the PVA membranes. The effects of the shape, structure and properties of the membrane surface on blood compatibility were studied in detail. The experiment results show that mPEG modified PVA membranes, especially mPEG modified tubular membrane, could availably repel the adhesion of the platelets. In addition, the anticoagulant mechanism of mPEG with a steric repulsion effectiveness was confirmed further via different grafting methods.     

Grafting of regenerated cellulose membrane by surface‐initiated atom transfer radical polymerization and its pH‐resposive behavior

Regenerated cellulose (RC) membranes which have pH modulated permeability have been prepared by anchoring the hydroxyl groups on the membrane surface with 2‐bromoisobutyryl bromide, followed by grafting with acrylic acid (AA) using atom transfer radical polymerization (ATRP). The obtained membranes were analyzed by X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared attenuated total reflection spectrometer (ATR‐FTIR), scanning electron microscopy (SEM), TGA and the results showed that AA had been grafted onto the membrane surfaces successfully. Then the pH modulated permeability properties were tested by water flux measurement. All results show that the pH modulated permeability properties of a RC membrane can be obtained by surface‐initiated ATRP. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of conjugated linoleic acid grafting on the hemocompatibility of polyacrylonitrile membrane

Polyacrylonitrile (PAN) membrane was hydrolyzed with NaOH_(aq) and grafted with conjugated linoleic acid (CLA) via esterification with 1,3‐propanediol. The resulting CLA grafted PAN membranes were characterized using Fourier transform infrared spectrometry (FT‐IR) and X‐ray photoelectronic spectroscopy (XPS). The effects of CLA grafting on the blood coagulation, platelet aggregation, and oxidative stress were evaluated using human blood. The complete blood count (CBC) and coagulation time (CT) was evaluated in vitro for hemocompatibility. After CLA grafting, the proliferation of human umbilical vein endothelial cells (HUVECs) on the membranes were improved. In addition, the production of reactive oxygen species (ROS) was measured by the chemiluminescence (CL) method to evaluate the oxidative stress. The results showed that the CLA‐grafted PAN membrane could keep the CBC values more stable than unmodified PAN membrane. The CLA‐grafted PAN membranes also showed longer CT. CLA‐grafted PAN membrane could keep the CL counts of hydrogen peroxide and superoxide values more stable than unmodified PAN membrane. These results suggest that a CLA‐grafted PAN membrane could offer protection for patients against oxidative stress and would be helpful for reducing the dosage of anticoagulant during hemodialysis. Copyright © 2006 John Wiley & Sons, Ltd.     

Novel cellulose acetate membrane blended with phospholipid polymer for hemocompatible filtration system

To improve the blood compatibility of cellulose acetate (CA) membranes for hemofiltration, a novel CA membrane blended with 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer was designed for a hemocompatible filtration system. The MPC copolymer (PMB30) was synthesized from MPC and n-butyl methacrylate. The polymer solution for making the membrane was prepared from a solvent mixture composed of N,N-dimethylformamide, acetone, and 2-propanol. The CA and CA/PMB30 blended membranes with an asymmetric and porous structure were prepared by a phase inversion process. The mechanical properties and solute permeability of the CA/PMB30 blended membrane could be controlled by preparation conditions such as the composition of the solvents and the solvent evaporation time. The CA/PMB30 blended membrane showed both good water and solute permeabilities in comparison with the CA membrane. Also, the molecular weight of the solute passed through the membrane was changed by the addition of PMB30, and good permselectivity could be obtained. Moreover, the CA/PMB30 blended membranes had excellent blood compatibility such as protein adsorption resistivity compared to the CA membrane due to location of the MPC units in the PMB30 at the surface.     

Preparation of high-capacity,weak anion-exchange membranes for protein separations using surface-initiated atom transfer radical polymerization

This contribution describes a method to prepare high-capacity anion-exchange membranes for chromatographic bioseparations. Surface-initiated atom transfer radical polymerization was used to graft poly(2-dimethylaminoethyl methacrylate) (poly(DMAEMA)) nanolayers from the pore surfaces of commercially available regenerated cellulose membranes. Initial measurements were made to determine the thickness evolution of the poly(DMAEMA) nanolayers, using a model flat substrate designed to mimic the three-dimensional nature of initiator incorporation into the membrane. Thereafter, polymerization time was used as the independent variable to control the mass of polymer grafted from the membrane surfaces and, thus, the protein binding capacity. ATR-FTIR, AFM, and SEM were used to characterize changes in the chemical functionality, surface topography, and pore morphology of membranes as a result of modification. Bovine serum albumin was used to evaluate the static protein binding capacity of poly(DMAEMA)-modified membranes. Maximum static binding capacities increased with increasing polymerization time in a linear fashion for short polymerization times (<6 h). For longer polymerization times, capacity increased non-linearly, eventually reaching a plateau value of 66.3 mg/mL.     

IMPROVING NONTHROMBOGENICITY OF CHITIN WITH ZWITTERIONIC STRUCTURE OF SULFOBETAINE

In order to improve the nonthr0mbogenicity of chitin, a new monomer, N, N-dimethyl(β-hydroxyethyloxyethyl) ammonium propanesulfonate (DHAPS) was designed, synthesized and grafted onto the chitin membrane by using hexamethylene diisocyanate (HDI) as a coupling agent. Surface analysis of the grafted membranes by ATR-FTIR and XPS confirms that DHAPS has been successfully grafted onto the membrane surface. The platelet resistant property of the grafted membranes was evaluated by a platelet-rich plasma adhesion method. The results showed that platelet-adhesive resistance of the modified membrane has been greatly improved.     

Protein adsorption and platelet adhesion of polysulfone membrane immobilized with chitosan and heparin conjugate

Polysulfone (PSF) membranes were treated with ozone to introduce peroxides, and then grafted with either acrylic acid or chitosan, followed by the immobilization of heparin. The effect of spacer arm on blood compatibility was investigated using three chitosans of different molecular weight [1170 (water soluble), 160 000, and 400 000] and similar degrees of deacetylation (75%). The hydrophilicity was evaluated by measuring the contact angle of water. Blood compatibility was evaluated using the activated partial thromboplastin time (APTT) as well as the adhesion of platelets. The protein affinity was determined by the absorption of human serum albumin (HSA) and human plasma fibrinogen (HPF). The results show that by the coupling of chitosan, the amount of heparin immobilized can be increased by four times. Water contact angle (from 78 ° to 41 °) decreased with the increase of the amount of heparin immobilized, showing increased wettability. The heparinized PSF membrane showed longer APTT and decreasing platelet adhesion, compared to that of unmodified PSF membrane. The adsorption of HSA and HPF were reduced to 17 and 6%, respectively. This suggests that longer spacer binding to heparin can increase the opportunity of anti‐coagulation on contacting blood. These results demonstrated that the hydrophilicity and blood compatibility of PSF membrane could be improved by chitosan and heparin conjugate. Copyright © 2003 John Wiley & Sons, Ltd.     

Hemocompatibility of poly(vinylidene fluoride) membrane grafted with network-like and brush-like antifouling layer controlled via plasma-induced surface PEGylation

In this work, the hemocompatibility of PEGylated poly(vinylidene fluoride) (PVDF) microporous membranes with varying grafting coverage and structures via plasma-induced surface PEGylation was studied. Network-like and brush-like PEGylated layers on PVDF membrane surfaces were achieved by low-pressure and atmospheric plasma treatment. The chemical composition, physical morphology, grafting structure, surface hydrophilicity, and hydration capability of prepared membranes were determined to illustrate the correlations between grafting qualities and hemocompatibility of PEGylated PVDF membranes in contact with human blood. Plasma protein adsorption onto different PEGylated PVDF membranes from single-protein solutions and the complex medium of 100% human plasma were measured by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies. Hemocompatibility of the PEGylated membranes was evaluated by the antifouling property of platelet adhesion observed by scanning electron microscopy (SEM) and the anticoagulant activity of the blood coagulant determined by testing plasma-clotting time. The control of grafting structures of PEGylated layers highly regulates the PVDF membrane to resist the adsorption of plasma proteins, the adhesion of platelets, and the coagulation of human plasma. It was found that PVDF membranes grafted with brush-like PEGylated layers presented higher hydration capability with binding water molecules than with network-like PEGylated layers to improve the hemocompatible character of plasma protein and blood platelet resistance in human blood. This work suggests that the hemocompatible nature of grafted PEGylated polymers by controlling grafting structures gives them great potential in the molecular design of antithrombogenic membranes for use in human blood.     

Immobilization of bovine serum albumin onto porous polyethylene membranes using strongly attached polydopamine as a spacer

Based on the self-polymerization and strong adhesion characteristics of dopamine in aqueous solution, a novel and convenient approach was developed to immobilize protein onto porous polyethylene (PE) membranes. A thin polydopamine (pDA) layer was formed and tightly coated onto PE membrane by dipping simply the membrane into dopamine aqueous solution for a period of time. Subsequently, bovine serum albumin (BSA) was bound onto the obtained PE/pDA composite membranes via the coupling between BSA and the reactive polydopamine layer. The firm immobilization of polydopamine layer and BSA was verified by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The results of water contact angle measurement showed that the hydrophilicity of PE membrane was significantly improved after coating polydopamine and binding BSA. The experiments of blood platelet adhesion indicated that BSA-immobilized PE membrane had better blood compatibility than the unmodified PE and the PE/pDA composite membranes. The investigations on hepatocyte cultures and cell viability revealed that the polydopamine coating endowed PE membrane with significantly improved cell compatibility. Compared to BSA surface, polydopamine surface is more favorable for cell adhesion, growth, and proliferation.     

Preparation of pH-responsive phenolphthalein poly(ether sulfone) membrane by redox-graft pore-filling polymerization technique

In this communication, a simple method for the preparation of environmentally responsive membrane, in situ redox-graft pore filling polymerization, was reported. Phenolphthalein poly(ether sulfone) dissolved in dimethyl sulfoxide was used to prepare porous membranes by means of classical phase inversion method. After that, methylacrylic acid was grafted successfully onto the membranes using the method reported here. Then, surface chemical changes and membrane morphology changes before and after graft polymerization were investigated by the ATR–FTIR and FESEM, respectively, to ascertain the formation and location of graft. Besides, the graft yield was also determined gravimetrically under different monomer concentrations. At last, in the hydraulic permeability experiments and diffusional permeability experiments using VB₁₂ and KCl as solutes, the grafted membranes prepared using the reported method exhibited marked, rapid and reversible pH-response.     

Photochemical modification of 10 kDa polyethersulfone ultrafiltration membranes for reduction of biofouling

Poly(ether sulfone) 10 kDa ultrafiltration membranes were modified by photolysis using ultraviolet light and graft polymerization of hydrophilic monomers onto the membrane surface to create more hydrophilic and lower fouling membrane surfaces. The modified membrane surfaces were characterized by FTIR/ATR and captive bubble contact angle measurements to determine chemical and hydrophilicity changes during modification. The modified membranes were compared with an unmodified poly(ether sulfone) (control) membrane as well as a commercial regenerated cellulose and a low protein adsorbing poly(ether sulfone) membrane using a newly developed standardized filtration protocol with 1 wt% bovine serum albumin. The best performing modified membrane was with N-vinyl-2-pyrrolidinone and showed a 25% increase in hydrophilicity, a 49% decrease in bovine serum albumin fouling, and a 4% increase in bovine serum albumin retention compared to the unmodified poly(ether sulfone) membrane. While the regenerated cellulose membrane had the lowest fouling and the low protein adsorbing membrane had the highest flux of all tested membranes, the N-vinyl-2-pyrrolidinone-modified membranes had the best combination of low fouling and high flux.     

Functionalization of regenerated cellulose membrane via surface initiated atom transfer radical polymerization for boron removal from aqueous solution

In this study, an adsorptive membrane was prepared for efficient boron removal. Poly(glycidyl methacrylate) was grafted on the surfaces of the regenerated cellulose (RC) membrane via surface-initiated atom transfer radical polymerization, and N-methylglucamine was used to further react with epoxide rings to introduce polyhydroxyl functional groups, which served as the major binding sites for boron. The pristine and modified membranes were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), dynamic water contact angle measurement, and scanning electron microscopy. It was shown that the designed functional groups were successfully grafted onto the RC membrane, and surface modification contributed to higher boron binding capability. The optimal pH range for boron adsorption was 4-8. Under a neutral pH condition, the maximum adsorption capacity of the modified membrane was determined to be 0.75 mmol/g, which was comparable with those of commercial resins. Studies of electrolyte influence indicated the formation of inner-sphere surface complexes on the membrane surface. The ATR-FTIR and XPS analyses showed that secondary alcohol and tertiary amine groups were mainly involved in boron adsorption, and tetrahedral boron complexes were found on the membrane surface.     

A novel method of surface modification on thin-film-composite reverse osmosis membrane by grafting hydantoin derivative

Membrane degradations by biofouling and free chlorine oxidation are the major obstacles for aromatic polyamide thin-film-composite (TFC) reverse osmosis (RO) membranes to realize high performance over a long period of operation. In this work, a hydantoin derivative, 3-monomethylol-5,5-dimethylhydantoin (MDMH), was grafted onto the nascent aromatic polyamide membrane surfaces by the reactions with active groups (e.g., acyl chloride groups) in the surfaces. The grafted MDMH moieties with high reaction activity and free chlorine could play as sacrificial pendant groups when membranes suffer from chlorine attacks, and the chlorination products N-halamines with strong antimicrobial function could sterilize microorganisms on membrane surfaces and then regenerate to MDMH. This was designed as a novel means to improve both chlorine resistances and anti-biofouling properties of the aromatic polyamide TFC RO membranes.Attenuated total reflectance mode Fourier transform infrared spectroscopy (ATR-FTIR) revealed that the MDMH-modified membranes had two characteristic bands at 1772 and 1709 cm⁻¹ corresponding to two carbonyl groups in hydantoin ring. This suggested the successful grafting of MDMH onto the membrane surfaces, which was further confirmed and quantified by X-ray photoelectron spectroscopy (XPS) analysis. After modification with MDMH, the membrane surface hydrophilicity increased obviously as contact angles decreased from 57.7° to 50.4–31.5°. But, there was no obvious change in membrane surface roughness after modification. The MDMH-modified membranes were shown to possess high chlorine resistances with small changes in water fluxes and salt rejections after chlorination with 100–2000 ppm h chlorine at pH 4. The chlorinated MDMH-modified membranes demonstrated obvious sterilization effects on Escherchia coli and substantial preventions against microbial fouling. Therefore, the MDMH-modified membranes offer a potential use as a new type of chlorine resistance and anti-biofouling TFC RO membranes.     

Novel poly-glutamic acid functionalized microfiltration membranes for sorption of heavy metals at high capacity

Various sorbent/ion exchange materials have been reported in the literature for metal ion entrapment. We have developed a highly innovative and new approach to obtain high metal pick-up utilizing poly-amino acids (poly-l-glutamic acid, 14,000 MW) covalently attached to membrane pore surfaces. The use of microfiltration (0.2–0.6 μm) membrane-based sorbents containing multiple functional groups is a novel technique to achieve high metal sorption under convective flow conditions. For our studies, both commercial membranes and laboratory prepared cellulose membranes containing aldehyde groups were used for the attachment of poly-amino acids. Cellulose membranes were prepared by converting cellulose acetate microfiltration membranes to cellulose (using alkali treatment), subsequent oxidation of hydroxyl groups to aldehyde using sodium periodate, and attachment of poly-l-glutamic acid via Schiff base chemistry. Extensive experiments (pH 3–6) were conducted (under convective flow mode) with the derivatized membranes involving the heavy metals: lead, cadmium, nickel, copper, and selected mixtures with calcium in aqueous solutions. Metal sorption results were found to be a function of derivatization (aldehydes) density of membranes and degree of attachment of the polyfunctional groups, number of functional groups per chain, membrane surface area, and the type of metals to be sorbed. We have obtained metal sorption capacities as high as 1.5 g metal/g membrane. Of course, depending on the desired goals the membrane containing metal could be regenerated or stabilized for appropriate disposal.     

Influence of pore structure and architecture of photo-grafted functional layers on separation performance of cellulose-based macroporous membrane adsorbers

New weak cation-exchange membrane adsorbers were prepared via UV-initiated heterogeneous graft copolymerization on Hydrosart^® macroporous regenerated cellulose membranes. The dynamic performance was investigated in detail with respect to the pore size and pore size distribution of the base membranes, ion-exchange capacity and architecture of the grafted functional layers as well as binding of target proteins. Main characterization methods were pore analysis (BET and permporometry), titration, analysis of protein binding under static conditions including visualization by confocal laser scanning microscopy and chromatographic analysis of dynamic protein binding and system dispersion. The trade-off between static binding capacity of the membrane adsorber and its permeability has partially been overcome by adapted architecture of the grafted functional layer achieved via the introduction of uncharged moieties as spacers and via stabilization of the binding layer by chemical cross-linking. The resulting membranes show only negligible effects of flow rate on dynamic binding capacity. There is no considerable size exclusion effect for large proteins due to mesh size of functional cross-linked layers. Investigation of system dispersion based on breakthrough curves confirms that the adapted grafted layer architecture has drastically reduced the contribution of the membrane to total system dispersion. The optimum pore structure of base membranes in combination with the best suited architecture of functional layers was identified in this study.     

Lipase-immobilized biocatalytic membranes for enzymatic esterification: Comparison of various approaches to membrane preparation

In this paper, lipase-immobilized membranes were prepared by both non-covalent and covalent immobilization methods using (i) lipase adsorption on membranes, (ii) inclusion of enzyme in membrane structure by filtration and (iii) covalent attachment of lipase to membrane. The catalytic properties of these membranes have been studied in reaction of butyloleate synthesis through esterification of oleic acid with n-butanol in isooctane. Ultrafiltration membranes made of regenerated cellulose (C030F) and polyethersulphone (PM30) were used for lipase immobilization. It was found that the lipase inclusion in the wide porous supporting layer of membrane was the most efficient method in preparing highly effective biocatalytic membranes. The degree of oleic acid conversion using these membranes was about 70–72% with a reaction time of 8 h. It was shown that the distribution profile of the lipase in the membrane was important for the effective enzyme utilization.The profile imaging atomic force microscopy (AFM) technique was used to visualize surfaces of lipase-immobilized biocatalytic membranes. AFM has also been used to directly quantify interactions between lipase-coated tip and membrane surfaces. It was concluded that the direct measurements of the interaction force between the enzyme-coated tip and the membrane surface would be a useful and practical approach for the choice of membranes as porous polymeric support for lipase immobilization through adsorption.     

纳米羟基磷灰石表面接枝聚合左旋丙交酯

为了改善HA纳米粒子与有机PLGA的相容性,分别采用六亚甲基二异氰酸酯加乙二醇、左旋乳酸改性纳米粒子表面后或直接原位接枝聚合左旋丙交酯等3种不同方法,制备了表面修饰聚乳酸的纳米羟基磷灰石(PLLA-g-HA).FTIR、XPS、TEM、TGA测试表明PLLA成功接枝到HA的表面.其中六亚甲基二异氰酸酯加乙二醇改性HA纳米粒子所获得的PLLA接枝率远高于其它两种方法达25%,调整有机相和无机相的比例对PLLA接枝率的影响较小,其在氯仿中可以稳定分散2天以上.共混电纺丝后的拉伸测试表明PLLA-g-HA/PLAG复合纤维膜的力学性能高于HA/PLGA膜,当两者之间的比例为5%拉伸性能达到最大值.