Nano-scale surface modification of a segmented polyurethane with a phospholipid polymer

Nano-scale modification of a segmented polyurethane (SPU) with cross-linked 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was performed to obtain a biocompatible elastomer. To control the domain size and the depth of the modified layer, various compositions of monomers, including MPC, 2-ethylhexyl methacrylate (EHMA), and glycerol 1,3-diglycerolate diacrylate, were examined. SPU film was immersed in the monomer solution and visible light irradiation was applied to initiate polymerization to the SPU film that was held by mica to condense MPC units at the surface. The surfaces of the obtained film were analyzed by X-ray photoelectron spectroscopy and water contact angle measurement. The surface density of MPC units changed with the monomer concentration, and the density was the highest when the ratio between MPC and EHMA was 7:3. In modified SPU films, 6- to 25-nm MPC unit-enriched domains were observed and the density of these domains gradually decreased with depth. The sizes of the domains depended on the MPC composition in the monomer solution. The mechanical properties of the modified films as evaluated by tensile strength measurement under wet conditions were not significantly different from those of SPU. With increase in the existence of MPC unit-enriched domains on the MEG film surface, platelet adhesion and activation were remarkably reduced compared to the SPU film. This nano-scale surface modification may be a useful technique for applying elastic polymer biomaterials.     

Competitive adsorption between phospholipid and plasma protein on a phospholipid polymer surface

Abstraet-The competitive adsorption of proteins and phospholipids on ω-methacryloyloxyalkyl phosphorylcholine (MAPC) polymer was evaluated in this study. Albumin, fibrinogen, and dimyrstoyl phosphatidylcholine (DMPC) were used as model components. The amount of DMPC adsorbed on the MAPC polymers increased with an increase in the MAPC unit composition of the polymer. The methylene chain length of the MAPC unit was another factor influencing the DMPC adsorption when the MAPC unit composition of the MAPC polymer was low. The state of albumin and DMPC liposome adsorbed on the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was determined by dynamic contact angle (DCA) measurement. The adsorption strength of albumin on the MPC polymer was weaker than that on the poly[n-butyl methacrylate (BMA)], that is, the albumin was detached from the MPC polymer during the rinsing process. On the poly(BMA) surface, no difference in the shape of the DCA loops before and after contact with the DMPC liposomal suspension was observed. Fibrinogen adsorption on the MAPC polymer was detected by gold-colloid labeled immunoassay. The amount of fibrinogen adsorbed on every MAPC polymer surface was reduced by addition of the DMPC liposome in the fibrinogen solution. The number of platelets adhered on the MAPC polymer was also decreased when the DMPC liposome was present in the fibrinogen solution during pretreatment. We concluded that phospholipids were preferentially adsorbed on the MAPC polymer surface compared with plasma protein and that the adsorbed phospholipids played an important role in showing an excellent blood compatibility on the MAPC polymer.     

Competitive adsorption between phospholipid and plasma protein on a phospholipid polymer surface.

The competitive adsorption of proteins and phospholipids on omega-methacryloyloxyalkyl phosphorylcholine (MAPC) polymer was evaluated in this study. Albumin, fibrinogen, and dimyrstoyl phosphatidylcholine (DMPC) were used as model components. The amount of DMPC adsorbed on the MAPC polymers increased with an increase in the MAPC unit composition of the polymer. The methylene chain length of the MAPC unit was another factor influencing the DMPC adsorption when the MAPC unit composition of the MAPC polymer was low. The state of albumin and DMPC liposome adsorbed on the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was determined by dynamic contact angle (DCA) measurement. The adsorption strength of albumin on the MPC polymer was weaker than that on the poly[n-butyl methacrylate (BMA)], that is, the albumin was detached from the MPC polymer during the rinsing process. On the poly(BMA) surface, no difference in the shape of the DCA loops before and after contact with the DMPC liposomal suspension was observed. Fibrinogen adsorption on the MAPC polymer was detected by gold-colloid labeled immunoassay. The amount of fibrinogen adsorbed on every MAPC polymer surface was reduced by addition of the DMPC liposome in the fibrinogen solution. The number of platelets adhered on the MAPC polymer was also decreased when the DMPC liposome was present in the fibrinogen solution during pretreatment. We concluded that phospholipids were preferentially adsorbed on the MAPC polymer surface compared with plasma protein and that the adsorbed phospholipids played an important role in showing an excellent blood compatibility on the MAPC polymer.     

Importance of a biofouling-resistant phospholipid polymer to create a heparinized blood-compatible surface

Heparinization is believed to be one of the methods to suppress thrombus formation on blood-contacting surfaces. However, this study hypothesizes that heparinization alone might not be sufficient to provide a blood-compatible surface; that is, a surface property that resists biofouling is necessary to obtain an effective heparin-modified surface. 2-Methacryloyloxyethyl phosphorylcholine (MPC) polymers with 2-aminoethyl methacrylate (AEMA) were synthesized to immobilize heparin through ionic bonding. The primary amino groups of AEMA were considered to be the polymer surface because the ζ-potential of the surface was positive when the mole fraction of the AEMA units was above 0.2. The antithrombogenic character of the polymer surface modified with heparin was evaluated by both Lee-White and microsphere column methods. The coagulation period of human whole blood in the absence of anticoagulant in glass tubing coated with the MPC polymer was longer than that in the original glass tube. Cell adhesion was completely inhibited on the MPC polymer surface after contact with human whole blood without anticoagulant. However, many adherent blood cells were observed on poly(2-ethylhexyl methacrylate-co-AEMA) (no MPC unit) even after heparinization. These results strongly indicate that the MPC polymer is a useful substrate where the heparin works well and that the heparin-immobilized MPC polymer has superior blood compatibility to the simple MPC polymer.     

Importance of a biofouling-resistant phospholipid polymer to create a heparinized blood-compatible surface

Heparinization is believed to be one of the methods to suppress thrombus formation on blood-contacting surfaces. However, this study hypothesizes that heparinization alone might not be sufficient to provide a blood-compatible surface; that is, a surface property that resists biofouling is necessary to obtain an effective heparin-modified surface. 2-Methacryloyloxyethyl phosphorylcholine (MPC) polymers with 2-aminoethyl methacrylate (AEMA) were synthesized to immobilize heparin through ionic bonding. The primary amino groups of AEMA were considered to be the polymer surface because the zeta-potential of the surface was positive when the mole fraction of the AEMA units was above 0.2. The antithrombogenic character of the polymer surface modified with heparin was evaluated by both Lee-White and microsphere column methods. The coagulation period of human whole blood in the absence of anticoagulant in glass tubing coated with the MPC polymer was longer than that in the original glass tube. Cell adhesion was completely inhibited on the MPC polymer surface after contact with human whole blood without anticoagulant. However, many adherent blood cells were observed on poly(2-ethylhexyl methacrylate-co-AEMA) (no MPC unit) even after heparinization. These results strongly indicate that the MPC polymer is a useful substrate where the heparin works well and that the heparin-immobilized MPC polymer has superior blood compatibility to the simple MPC polymer.     

Towards a methodology for the effective surface modification of porous polymer scaffolds

A novel low-pressure radio-frequency plasma treatment protocol was developed to achieve the effective through-thickness surface modification of large porous poly (d,l-lactide) (PDLLA) polymer scaffolds using air or water: ammonia plasma treatments. Polymer films were modified as controls. Scanning electron micrographs and maximum bubble point measurements demonstrated that the PDLLA foams have the high porosity, void fraction and interconnected pores required for use as tissue engineering scaffolds. The polymer surface of the virgin polymer does contain acidic functional groups but is hydrophobic.

Following exposure to air or water: ammonia plasma, an increased number of polar functional groups and improved wetting behaviour, i.e. hydrophilicity, of wet surfaces was detected. The number of polar surface functional groups increased (hence the decrease in water contact angles) with increasing exposure time to plasma. The change in surface composition and wettablility of wet polymer constructs was characterised by zeta potential and contact angle measurements. The hydrophobic recovery of the treated PDLLA polymer surfaces was also studied. Storage of the treated polymer constructs in ambient air caused an appreciable hydrophobic recovery, whereas in water only partial hydrophobic recovery occurred. However, in both cases the initial surface characteristics decay as function of time.     

UV surface modification of a new nanocomposite polymer to improve cytocompatibility

A novel modified nanocomposite was studied for the adhesion and proliferation of the human umbilical vein endothelial cell (HUVEC) line EA.hy926. The nanocomposite under investigation was poly(carbonate-urea)urethane with silsesquioxane nano-cages, here in the form of a mixture of two polyhedral oligomeric silsesquioxanes. The nanocomposite surfaces were exposed to ultraviolet (UV) light of a Xe(*)(2)-excimer lamp at a wavelength of 172 nm in an ammonia atmosphere. The effects of the irradiation were characterized by atomic force and scanning electron microscopy (AFM, SEM), X-ray photo-electron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) using an attenuated total reflection (ATR) device and measurements of advancing water contact angle (CA). The irradiation resulted in the introduction of new hydrophilic N- and O-containing groups into the surface, which was initially amphiphilic, while surface morphology remained mainly unchanged. Slight chemical changes were also observed for the silsesquioxane nano-cages at the surface. Onto the untreated and irradiated samples HUVECs were seeded and grown for various durations in culture. Standard tissue-culture polystyrene (PS) was employed as a positive control to check the efficiency of the cell-culture methods. Viability and proliferation of the cells were then assessed using a non-radioactive assay. Compared to the untreated nanocomposite polymer, irradiation times of at least 5 min resulted in a significantly increased cell proliferation between 3 and 8 days after seeding with the HUVEC line EA.hy926.     

UV surface modification of a new nanocomposite polymer to improve cytocompatibility

A novel modified nanocomposite was studied for the adhesion and proliferation of the human umbilical vein endothelial cell (HUVEC) line EA.hy926. The nanocomposite under investigation was poly(carbonate-urea)urethane with silsesquioxane nano-cages, here in the form of a mixture of two polyhedral oligomeric silsesquioxanes. The nanocomposite surfaces were exposed to ultraviolet (UV) light of a Xe^* ₂-excimer lamp at a wavelength of 172 nm in an ammonia atmosphere. The effects of the irradiation were characterized by atomic force and scanning electron microscopy (AFM, SEM), X-ray photo-electron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) using an attenuated total reflection (ATR) device and measurements of advancing water contact angle (CA). The irradiation resulted in the introduction of new hydrophilic N- and O-containing groups into the surface, which was initially amphiphilic, while surface morphology remained mainly unchanged. Slight chemical changes were also observed for the silsesquioxane nano-cages at the surface. Onto the untreated and irradiated samples HUVECs were seeded and grown for various durations in culture. Standard tissue-culture polystyrene (PS) was employed as a positive control to check the efficiency of the cell-culture methods. Viability and proliferation of the cells were then assessed using a non-radioactive assay. Compared to the untreated nanocomposite polymer, irradiation times of at least 5 min resulted in a significantly increased cell proliferation between 3 and 8 days after seeding with the HUVEC line EA.hy926.     

Asymmetrically functional surface properties on biocompatible phospholipid polymer membrane for bioartificial kidney

To obtain a bioartificial kidney composed of a porous polymer membrane and renal cells, a polysulfone (PSf) membrane (PSM) blended with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was prepared. The PSM flat membrane with a porous structure could be prepared from the polymer blend containing 1 wt % of the MPC polymer in PSf by the phase inversion technique in a dry-wet process. Asymmetrical surface properties were observed on both sides of the membrane surfaces. That is, the sponge layer formed at the substrate-contacting surface of the membrane had 10-20 microm pores, but the pores in the micrometer range could not be observed for a skin layer formed at the air-contacting surface of the membrane. At the sponge layer surface, the MPC unit composition was 7 times larger than that at the skin layer surface. The amount of proteins adsorbed on the surface corresponded to the MPC unit composition. On the skin layer, a small amount of adsorbed proteins and platelet adhesion could be suppressed compared with those on the sponge layer. However, the skin layer had a moderate protein adsorption, so it showed a sufficient cytocompatibility to enable renal tubule epithelial cells to adhere and proliferate in the membrane. Thus, it functioned well as a renal tubule. Therefore, because of both its hemocompatibility and cytocompatibility, we could conclude that the PSM membrane is useful for as a renal tubule device for a bioartificial kidney.     

Effects of molecular architecture of phospholipid polymers on surface modification of segmented polyurethanes

To modify the surface properties of segmented polyurethane (SPU), effects of the molecular architecture of the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers on the performance of the SPU/MPC polymer membrane were investigated. We combined the random-type, block-type, and graft-type of the MPC polymers with a typical SPU, Tecoflex^® using double solution casting procedure. The graft-type MPC polymers composed of a poly(MPC) main chain and poly(2-ethylhexyl methacrylate (EHMA)) side chains were synthesized through the combination of two different living radical polymerization techniques to regulate the density and chain length of the side chains. The SPU membranes modified with the MPC polymers were characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results revealed that the MPC units were located on the SPU surface. Although the breaking strength of the SPU membranes modified with block-type poly(MPC-block-EHMA) and graft-type poly(MPC-graft-EHMA) was lower than that of SPU membranes modified with random-type poly(MPC-random-EHMA), their breaking strengths were adequate for manufacturing medical devices. On the other hand, better stability was observed in the MPC polymer layer on the SPU membrane after immersion in an aqueous medium, wherein the SPU membrane had been modified with the poly(MPC-graft-EHMA). This was because of the intermixing of the hydrophobic poly(EHMA) segments in the domain of the hard segments in the SPU membrane. After this modification, each SPU/MPC polymer membrane showed hydrophilic nature based on the MPC polymers and a dramatic suppression of protein adsorption. From these results, we concluded that the SPU membrane modified with the poly(MPC-graft-EHMA) was one of the promising polymeric biomaterials for making blood-contacting medical devices.     

Controlled drug release from multilayered phospholipid polymer hydrogel on titanium alloy surface

Here we describe the functionalization of a multilayered hydrogel layer on a Ti alloy with an antineoplastic agent, paclitaxel (PTX). The multilayered hydrogel was synthesized via layer-by-layer self-assembly (LbL) using selective intermolecular reactions between two water-soluble polymers, phospholipid polymer (PMBV) containing a phenylboronic acid unit and poly(vinyl alcohol) (PVA). Reversible covalent bonding between phenylboronic acid and the polyol provided the driving force for self-assembly. Poorly water-soluble PTX dissolves in PMBV aqueous solutions because PMBV is amphiphilic. Therefore, our multilayered hydrogel could be loaded with PTX at different locations to control the release profile and act as a drug reservoir. The amount of PTX incorporated in the hydrogel samples increased with the number of layers but was not directly proportional to the number of layers. However, as the step for making layers was repeated, the concentration of PTX in the PMBV layers increased. The different solubilities of PTX in PMBV and PVA aqueous solutions allow for the production of multilayered hydrogels loaded with PTX at different locations. In vitro experiments demonstrated that the location of PTX in the multilayered hydrogel influences the start and profile of PTX release. We expect that this rapid and facile LbL synthesis of multilayered hydrogels and technique for in situ loading with PTX, where the location of loading controls the release pattern, will find applications in biomedicine and pharmaceutics as a promising new technique.     

A soft and flexible biosensor using a phospholipid polymer for continuous glucose monitoring

A flexible biosensor using a phospholipid polymer to immobilization of glucose oxidase (GOD) was fabricated and tested. At first, an enzyme membrane formed by immobilizing GOD onto a porous polytetrafluoroethylene (PTFE) membrane using the phospholipid polymer (2-methacryloyloxyethyl phosphorylcholine (MPC) copolymerized with 2-ethylhexylmethacrylate (EHMA) : PMEH) was evaluated. According to the result of amperometric measurement, average density of GOD to be immobilized was optimized to 38.9 units cm⁻². Temperature and pH dependences were also investigated. Then, a flexible glucose sensor was fabricated by immobilizing GOD onto a flexible hydrogen peroxide electrode using PMEH. The flexible glucose sensor showed a linear relationship between output currents and glucose concentration in 0.05–1.00 mmol L⁻¹, with a correlation coefficient of 0.999. The calibration range covered the normal tear glucose level of 0.14–0.23 mmol L⁻¹. This indicates that the flexible biosensor is considered to be useful for monitoring of glucose in tear fluids.     

The effect of the chemical structure of the phospholipid polymer on fibronectin adsorption and fibroblast adhesion on the gradient phospholipid surface.

The interaction between biocomponents and the polyethylene (PE) surface modified with poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)] was considered taking into account the surface characteristics, i.e., density, mobility, and orientation of the poly(MAPC). The PE surface, grafted gradually with the poly(MAPC) was prepared by corona irradiation method. The amount of peroxide produced on the PE surface which was determined with 1,1-diphenyl-2-picryl-hydrazyl, increased with an increase in the energy of the corona. The surface density of the poly(MAPC) was increased with an increase in the amount of the peroxides produced by the corona irradiation. The orientation and mobility of the poly(MAPC) grafted on the PE surface was evaluated with 1,6-diphenyl-1,3,5-hexatriene. The orientation of the poly[6-methacryloyloxyhexyl phosphorylcholine (MHPC)] which has six methylene chains between the phospholipid polar group and the backbone was higher than that of other poly(MAPC)s. The mobility of the poly(MAPC) decreased with an increase in the methylene chain length in the MAPC unit. The fibronectin adsorption on the gradient PE sheet grafted with poly(MAPC) was determined with enzyme-labeled immunoassay. The amount of adsorbed fibronectin on the PE grafted with poly[2-methacryloyloxyethyl phospohorylcholine(MPC)] and poly(MHPC) decreased with an increase in their surface density. Especially, the PE sheet grafted with the poly(MHPC) was effectively reduced compared with other poly(MAPC)s. On the poly[10-methacryloyloxydecyl phosphorylcholine (MDPC)], there is a minimum amount of adsorbed fibronectin. The fibronectin adsorption pattern on the PE sheet grafted with poly(MAPC) was quite different from the chemical structure of the MAPC unit. The human normal diploid fibroblasts (WI-38 cells) were cultured on the gradient PE sheet grafted with poly(MAPC) changing the concentration of seeded WI-38 cells. The adhesion behavior of the WI-38 cells was different depending on the concentration of the seeded WI-38 cells. When the concentration was low, the number of the adherent WI-38 cells had the same tendency as fibronectin adsorption. The gradient PE sheet grafted with the poly(MHPC) effectively reduced WI-38 cells adhesion even when the concentration of the WI-38 cells was high. The biocompatibility of polymer surfaces can be improved by highly oriented phosphorylcholine group.     

肿瘤坏死因子-α的光化学修饰及其固定化研究

肿瘤坏死因子-α（TNF-α）是具有强大抗肿瘤作用的蛋白质型的细胞因子，与4-叠氮苯甲酸反应，经红外光谱确认生成物在2127cm^-1处有叠氮基团的典型吸收，证明合成得到了光活性的肿瘤坏死因子。采用光固定法将这种光活性蛋白质固定到组织培养聚苯乙烯膜上，制成生物材料。实验进一步表明，种植TNF和固定化TNF量之间的关系以及紫外辐射时间对固定化的影响。通过扫描电子显微镜（SEM）和原子力显微镜（AFM），对光固定化TNF的微观形态的观察结果表明，光活性的肿瘤坏死因子在聚苯乙烯膜表面处于高度有序状态，且固定化的肿瘤坏死因子的粗糙度约为200～300nm。     

Semi-interpenetrating polymer networks composed of biocompatible phospholipid polymer and segmented polyurethane

2-Methacryloyloxyethyl phosphorylcholine (MPC) polymers, which have excellent biocompatibility, have been receiving increasing attention in biomedical and bioengineering fields; however, the mechanical strength of the hydrated MPC polymers is not sufficient for use in these fields as a bulk material. Therefore, we hypothesized that a novel material might be realized by reinforcing the MPC polymer network with segmented polyurethane (SPU). Semi-interpenetrating polymer networks (IPNs) composed of crosslinked MPC polymer and SPU were prepared. The mechanical properties of the IPN membrane were significantly improved compared with those of the MPC polymer membrane. Three-dimensional polymer networks of the MPC polymer in the IPNs were observed after solvent extraction of SPU. An X-ray photoelectron spectrum analysis revealed that the MPC units were exposed on the IPN surface. When the IPN was alternately soaked in water and ethanol, the swelling ratio was found to be completely reversible and no disintegration of the network structure was observed. The permeation coefficient of 1, 4-di(2-hydroxyethoxy)benzene through the IPN membrane was 1.11 x 10(-7) cm(-2)s(-1). The amount of adsorbed protein and the number of adherent platelets on the IPN membrane were effectively reduced compared with those on SPU. We concluded that IPNs composed of the MPC polymer and SPU are a new bulk biomaterial, which possesses both blood compatibility and good mechanical properties.     

Control of staphylococcal adhesion to polystyrene surfaces by polymer surface modification with surfactants.

The adherence of three clinical isolates of Staphylococcus epidermidis to model polystyrene surfaces was studied in vitro using epifluorescent image analysis. A series of 16 Pluronic surfactants (A-B-A block copolymers where A is poly(ethylene oxide) (PEO) and B is poly(propylene oxide) (PPO)) were used as surface modifiers for the model polystyrene surfaces. Substantial reductions (up to 97%) in bacterial adhesion levels were achieved with all copolymers tested, irrespective of the PPO or PEO block lengths. It appears likely that such treatments create a sterically stabilized surface with adsorbed PEO chains, conferring nonspecific anti-adhesive properties which can limit bacterial attachment.     

Effect of surface modification of polymer beads on the mechanical properties of acrylic bone cement

The effect of surface modification of polymer filler on the static mechanical properties of acrylic bone cement was studied. The surface of polymer beads was modified with carboxylic and amino groups by photochemical reaction with azide compounds. Monomer modifiers (maleic anhydride, methacrylic acid and p-aminostyrene) are attached to the functionalized surface of polymer beads. Functional allyl groups, which are capable of the graft polymerisation reaction, are attached to the surface via photochemical reaction with N-(2-nitro-4-azidophenyl)-N-(-propen) amine. This approach to bone cement provides the additional covalent bonds between the polymer beads and the inter-bead matrix. The static mechanical properties of bone cements containing modified polymer beads were investigated and compared with the static mechanical properties of unmodified cements. The absolute values of compressive strength for the modified and unmodified cements were found to be similar. An increase in flexural strength for the modified cements (dry and after water storage) was observed. The structure of the surface functional groups affects the methyl methacrylate grafting resulting in a higher value of flexural strength for the maleic anhydride- and p-aminostyrene-modified cements. The scanning electron microscopy examination of the fracture surface of the cement samples showed an improvement of the adhesion between the beads and the matrix after modification.     

Effect of surface modification of polymer beads on the mechanical properties of acrylic bone cement

The effect of surface modification of polymer filler on the static mechanical properties of acrylic bone cement was studied. The surface of polymer beads was modified with carboxylic and amino groups by photochemical reaction with azide compounds. Monomer modifiers (maleic anhydride, methacrylic acid and p-aminostyrene) are attached to the functionalized surface of polymer beads. Functional allyl groups, which are capable of the graft polymerisation reaction, are attached to the surface via photochemical reaction with N-(2-nitro-4-azidophenyl)-N-(-propen) amine. This approach to bone cement provides the additional covalent bonds between the polymer beads and the inter-bead matrix. The static mechanical properties of bone cements containing modified polymer beads were investigated and compared with the static mechanical properties of unmodified cements. The absolute values of compressive strength for the modified and unmodified cements were found to be similar. An increase in flexural strength for the modified cements (dry and after water storage) was observed. The structure of the surface functional groups affects the methyl methacrylate grafting resulting in a higher value of flexural strength for the maleic anhydride- and p-aminostyrene-modified cements. The scanning electron microscopy examination of the fracture surface of the cement samples showed an improvement of the adhesion between the beads and the matrix after modification.     

Preparation of a chemically anchored phospholipid monolayer on an acrylated polymer substrate

This paper describes a strategy for designing a chemically anchored phospholipid monolayer that could be used as coating materials for biomedical implants. To make a chemically anchored phospholipid monolayer on the polymer substrate, we prepared the mono-acrylated phospholipid (1-palmitoyl-2-[12-(acryloyloxy)-dodecanoyl]-sn-glycero-3-phosphocholine; acryloyl-PC) and the acrylated polymer (poly(octadecylacrylate-co-4-acryloyloxy butylacrylate)), which was synthesized by the acrylation of poly(octadecyl acrylate-co-hydroxybutyl acrylate, poly(OA-co-HA)) with acryloyl chloride. The chemically anchored phospholipid monolayer was prepared by using in situ photopolymerization of a pre-assembled phospholipid monolayer, produced by lipid vesicle fusion, onto the acrylated polymer coated silicon wafer. Optimal condition of vesicle fusion and irradiation time was determined from the degree of hydrophilicity rendered by the polymerized phospholipid surface. The physicochemical properties of polymerized phospholipid monolayer on the substrate were evaluated using water contact angle, field-emission scanning electron micrograph (FE-SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). These results confirmed that the polymerized phospholipid monolayer was chemically anchored on the acrylated polymer substrate. The chemically anchored phospholipid monolayer was stable in aqueous condition for 2 weeks, but the physically adsorbed phospholipid monolayer got removed within 1 day. Moreover, the polymerized phospholipid monolayer also suppressed albumin absorption and platelet adhesion, in vitro. This polymerized phospholipid monolayer provides a new biomimetic system for coating medical devises.     

Synthesis of photoreactive pullulan for surface modification

Photoreactive pullulan was prepared, the polymer was photoimmobilized on polymeric or organic surfaces, and its interactions with a protein and a cell type were investigated. The photoreactive pullulan was synthesized by a coupling reaction with 4-azidobenzonic acid. Surface modification was carried out in the presence or absence of a micropatterned photomask containing 100 microm transparent stripes with 150 microm gaps, making it easy to confirm the immobilization. By the micropatterning method, immobilization of the photoreactive pullulan on polystyrene, polyethylene, and silane-coupled glass was confirmed. Contact angles were measured on the unpatterned surfaces. Although the original surfaces have different contact angles, the contact angle on Az-pullulan-immobilized surface was the same on all surfaces. This result demonstrated that photoimmobilization completely covered the surface with Az-pullulan. Protein adsorption was investigated using fluorescently labeled albumin applied to the micropatterned surface: fluorescence microscopy demonstrated that adsorption was reduced on the pullulan-immobilized regions. Culture of RAW264 cells, derived from mouse leukemic monocytes, on the micropatterned surface for 22 h showed that cells did not adhere to the immobilized pullulan regions. In conclusion, photoreactive pullulan was covalently immobilized on various surfaces and tended to reduce interactions with proteins and cells.