Protein adsorption and platelet adhesion on polymer surfaces having phospholipid polar group connected with oxyethylene chain

Surface functionalization of polytetrafluoroethylene substrate with hybrid processes comprising plasma treatment and chemical reactions

Polytetrafluoroethylene (PTFE) exhibits excellent mechanical properties and chemical stability and has been widely used in medical fields for the preparation of implantable medical devices. However, the implantation of PTFE in living systems results in inflammation reactions and infections at the surface thus limits its long-term applications. For PTFE surface modification, we examined the effects of mussel-inspired polydopamine (PDA) coating and the further introduction of functional groups. During PDA coating, the plasma pretreatment on PTFE enhanced the stability of the PDA coating layer. Furthermore, the introduction of functional groups on the PDA layer was carried out using reactive functional groups for the photoinduced graft polymerization of methacrylate. For instance, 2-methacryloyloxyethyl phosphorylcholine (MPC) could be polymerized from the surface of the substrate. These chemical modifications were confirmed step by step using spectroscopes to obtain the hydrophilic surface of the poly(MPC)-modified PTFE. The protein adsorption behaviors on PTFE and poly(MPC)-modified PTFE were compared to understand biocompatibility characteristics of these substrates. The surface of PTFE was immediately covered with albumin and the contact between the substrate and the serum resulted in an increase in the fibrinogen composition with time. On the other hand, fewer proteins were adsorbed on the poly(MPC)-modified PTFE substrate. Thus, this modification procedure would serve as a strategy for safer alterations in PTFE surfaces to expand the life span of the PTFE-carrying medical devices in living systems.

Clickable and Antifouling Platform of Poly[(propargyl methacrylate)-ran-(2-methacryloyloxyethyl phosphorylcholine)] for Biosensing Applications

A functional copolymer platform, namely, poly[(propargyl methacrylate)-ran-(2-methacryloyloxyethyl phosphorylcholine)] (PPgMAMPC), was synthesized by reversible addition-fragmentation chain-transfer polymerization. In principle, the alkyne moiety of propargyl methacrylate (PgMA) should serve as an active site for binding azide-containing molecules via a click reaction, i.e., Cu-catalyzed azide/alkyne cycloaddition (CuAAC), and 2-methacryloyloxyethyl phosphorylcholine (MPC), the hydrophilic monomeric unit, should enable the copolymer to suppress nonspecific adsorption. The copolymers were characterized using Fourier transform infrared (FTIR) and (1)H NMR spectroscopies. Thiol-terminated, PPgMAMPC-SH, obtained by aminolysis of PPgMAMPC, was immobilized on a gold-coated substrate using a "grafting to" approach via self-assembly. Azide-containing species, namely, biotin and peptide nucleic acid (PNA), were then immobilized on the alkyne-containing copolymeric platform via CuAAC. The potential use of surface-attached PPgMAMPC in biosensing applications was shown by detection of specific target molecules, i.e., streptavidin (SA) and DNA, by the developed sensing platform using a surface plasmon resonance technique. The copolymer composition strongly influenced the performance of the developed sensing platform in terms of signal-to-noise ratio in the case of the biotin-SA system and hybridization efficiency and mismatch discrimination for the PNA-DNA system.

Optimized molecular structure of photoreactive biocompatible block copolymers for surface modification of metal substrates

Poly(2-methacryloyloxyethyl phosphorylcholine)-b-poly(2-methacryloyloxyethyl phosphate-co-2-cinnamoyloxyethyl methacrylate) (PMPC-b-P(MPA/CMA)) was prepared by reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. The block copolymers were coated on stainless steel (SUS316L) and other metal substrates, and then the surface was subsequently irradiated with UV light. The wettability of a specimen surface treated with a block copolymer was improved in comparison with that of an untreated SUS316L plate. From X-ray photoelectron spectroscopy (XPS) data, it was clear that the P(MPA/CMA) block worked as a binding site on the SUS316L surface. The surface density of the block copolymer-immobilized SUS316L surface was influenced by the molecular weight of the PMPC block. The stability of the immobilized layer was improved by UV irradiation, which induced intermolecular dimerization of the CMA. In addition to the SUS316L surface, various other metal surfaces could be modified by surface immobilization of block copolymers. Serum protein adsorption and fibroblast adhesion were effectively reduced by surface immobilization of block copolymers with optimal molecular weight of PMPC block. The nonfouling property was preserved after 1 week of cell cultivation.

Antibody immobilization to phospholipid polymer layer on gold substrate of quartz crystal microbalance immunosensor

To modify gold electrode for immunosensor to construct an artificial cell membrane structure, water-soluble amphiphilic phospholipid polymer, poly[2-methacryloyloxyehtyl phosphorylcholine-co-n-butyl methacrylate-co-p-nitrophenyloxycarbonyl poly(ethylene glycol) methacrylate (PMBN)] was applied. The polymer had active ester groups for immobilization of biomolecules and it was converted partially to thiol groups for binding to gold substrates. The partially thiolated PMBN was adsorbed on a gold electrode of quartz crystal microbalance (QCM). Surface characterization of adsorbed PMBN layers was thoroughly investigated with reflectance anisotropy spectroscopy, ellipsometry spectroscopy, dynamic contact angle and X-ray photoelectron spectroscopy measurements. Among several PMBN, having different degree of thiolation, it was concluded that 21.5% thiolated PMBN layer had the most well-ordered phosphorylcholine groups in its outer surface. The proteins adsorption test revealed that the phosphorylcholine group on the outer side of PMBN layers, which was substituted their active ester groups by glycine, showed suppress the non-specific adsorption of proteins, such as bovine serum albumin and gamma-globulin. Also, through antigen-antibody binding evaluation, the anti-C-reactive protein antibody immobilized on the PMBN surface worked well and it was confirmed that denaturation of the antibody on the PMBN layers was hardly occurred in spite of 60 days storage at 4 degrees C. The antibody conjugated phospholipid polymer layer with well-ordered phosphorylcholine group could be outstanding functional membrane for biomedical diagnostic devices without non-specific binding and reduction of immunologic activity of immobilized antibody.

Solution pH-regulated interfacial adsorption of diblock phosphorylcholine copolymers

Spectroscopic ellipsometry has been used to examine the pH-responsive interfacial adsorption of a series of biocompatible diblock copolymers incorporating 2-methacryloyloxyethyl phosphorylcholine-based (MPC) residues and 2-(dialkylamino)ethyl methacrylate residues, with a specific focus on 2-(diethylamino)ethyl groups (referred to as MPCm-DEAn, where m and n refer to the mean degrees of polymerization of each block) at the hydrophilic silicon oxide/water interface. For all the copolymers studied the surface excess shows only weak concentration dependence. Increasing the length of the DEA block has little effect on the dynamic or equilibrated adsorption at pH 7, indicating that the DEA block adopts a flat conformation on the silicon oxide surface at this pH. With increasing pH, however, the surface excess shows a dramatic increase, followed by a subsequent decline. The observed maximum in surface excess represents a balance between charge over-compensation of the copolymer with the oppositely charged surface and the subsequently reduced charge density of the copolymer. Variations in the observed maxima for various MPCm-DEAn diblock copolymers indicate different surface conformations at high pH. Salt addition does not affect copolymer adsorption. This behavior is attractive for biomedical applications in which the ionic strength is variable. It was also found that the preadsorbed diblock copolymers immobilized DNA from solution to an extent that is proportional to the relative charge ratio between the anionic DNA and the cationic DEA block of the copolymer.

Reduced adhesion of blood cells to biodegradable polymers by introducing phosphorylcholine moieties

Aliphatic polyesters are believed to be good biocompatible polymers for tissue engineering because of their biodegradability and nontoxicity of the degradated products. However, it is necessary to reduce the nonspecific protein adsorption for the application of biodegradable polymers to drug delivery systems or antiadhesive membranes. We hypothesized that novel biodegradable polymers could be synthesized by introducing phosphorylcholine moieties into aliphatic polyesters. The L-lactide was polymerized in the presence of L-alpha-glycelophosphorylcholine (LGPC) using stannous octate as the catalyst. The molecular weight and crystallinity of poly(L-lactide) (PLLA)-based phospholipid polymers (PLLA-PC) decreased with an increase in the composition of the LGPC unit in the PLLA-PC. The hydrolysis of the PLLA-PC was evaluated by soaking the polymer membranes in a phosphate buffer solution. The rate of weight loss was increased with increasing the LGPC units in PLLA-PC. The surface analysis of the membranes using an X-ray photoelectron microscope showed the composition of phosphorylcoline groups on the surface. The amount of adsorbed protein and adherent blood cell on the polymer surface was decreased with introducing LGPC unit. PLLA-PC is a promising biodegradable polymer having blood compatibility and antiadhesive property.

Cell adhesion on supported lipid bilayers

The cell and protein repellent properties of supported phospholipid bilayer (SPB) membranes were investigated. The SPBs were prepared by vesicle adsorption on SiO(2) surfaces. The vesicles of phosphatidylcholine fuse and rupture, and form a supported bilayer covering the surface. We carried out cell culture experiments on several surfaces, including SPBs, using two types of epithelial cells to address the cell adhesional properties. The Quartz Crystal Microbalance Dissipation (QCM-D) technique was used to monitor the SPB formation and subsequent protein adsorption. Neither cell type adhered or proliferated on SiO(2) surfaces coated with SPBs, whereas both cell types adhered and proliferated on the three control surfaces of SiO(2), tissue culture glass, and TiO(2). The QCM-D measurements showed that about two orders of magnitude less mass adsorbed on a SPB surface compared to a TiO(2) surface, from serum-containing media (10% fetal bovine serum). The reduced adsorption on the SPB is a likely explanation for the nondetectable epithelial cell adhesion on the SPB surface. Biomembranes are therefore attractive candidate systems to achieve alternating cell-resistant and cell-interacting regions on surfaces, by including specific cell-binding proteins in the latter regions.

Integrin-dependent interaction of human vascular endothelial cells on biomimetic peptide surfactant polymers

Biomimetic surfactant polymers designed by molecular grafting of pendant RGD peptides (Pep) and dextran oligosaccharides (Dex) in different ratios onto the backbone of poly(vinyl amine) (PVAm) were examined for their ability to promote endothelial cell (EC) growth. Adhesion, formation of focal contacts, and expression of integrin receptors were examined in EC seeded onto a series of novel surfactants containing 100% dextran (PVAm[Pep (0%)]) to 100% peptide (PVAm[Pep (100%)]) compared to fibronectin control. Interaction of EC on polymer was specific, as soluble GRGDSP, but not GRGESP, was able to inhibit both adhesion and spreading of EC. At three hours, EC attachment and spreading were rapid and comparable on fibronectin and PVAm[Pep (100%)], rounded on PVAm[Pep (0%)], and intermediate on PVAm[Pep (25%)], (PVAm[Pep (50%)], and PVAm[Pep (75%)], with increasing peptide ratio favoring more spreading, although all the substrates had similar hydrophilicity. Cells that spread well on fibronectin and PVAm[Pep (100%)] had sharp spikes of vinculin localized at the termination point of actin stress fibers. Formation of stress fibers and focal adhesions on other substrates were correlated with spreading pattern of EC and the peptide content. EC seeded on fibronectin expressed alpha5beta1 integrins all along the stress fibers and throughout the entire cytoskeleton, but this distribution pattern was less prominent on PVAm[Pep (100%)]. However, expression and distribution of vitronectin receptors (alpha(v)beta3) were similar on both fibronectin and PVAm[Pep (100%)], suggesting a strong cell adhesion on PVAm[Pep (100%)]. Viability of EC was also comparable on both fibronectin and PVAm[Pep (100%)] at 24 h. Substrates with high proportion of dextran limited cell adhesion, probably by decreasing protein adsorption. These results suggest that it may be possible to engineer substrates that promote cell adhesion in a receptor-dependent manner while blocking nonspecific protein adsorption, which may have potential as interface materials for prostheses used in cardiovascular system.

Study of blood compatibility with poly(2-methoxyethyl acrylate). Relationship between water structure and platelet compatibility in poly(2-methoxyethylacrylate-co-2-hydroxyethylmethacrylate)

Previously, we reported that poly(2-methoxyethylacrylate) (PMEA) showed excellent blood compatibility and implied that the water structure in PMEA contributed to the blood compatibility. In this study, the relationship between the water structure and the blood compatibility is clarified by studying the influence of the monomer composition of poly(MEA-co-HEMA) on the water structure and the blood compatibility of the copolymers. The water in the polymer was classified into three types: free water, freezing bound water, and nonfreezing water. The polymers with 0-30 mol % of HEMA content had a significant amount of freezing bound water, and the amount decreases greatly when the composition of HEMA exceeded 30 mol %. On the other hand, the amount of other water increased simply with an increase of HEMA content. The evaluation of the platelet compatibility of poly(MEA-co-HEMA) revealed that the adhesion number and the morphological change of platelet on the copolymer surface were least when the HEMA content was 0-20 mol %. These two results strongly suggest that the freezing bound water relates to the platelet compatibility of the polymers.

Shear-induced platelet activation and adhesion on human pulmonary artery endothelial cells seeded onto hydrophilic polymers

We evaluated platelet activation and adhesion on two plasma polymerized surfaces, N-vinyl pyrrolidone (NVP) and gamma-butyro lactone (GBL), which have been shown previously to promote endothelial cell growth and adhesion as well as fibronectin-coated glass (1 microg/cm(2)) coverslips. Human pulmonary artery endothelial cells were seeded onto coverslips at a low density ( approximately 20,000 cells/cm(2)) and grown to confluence (3-5 days). The materials, both with and without ECs, were then exposed to a shear rate of 400 s(-1) in a closed loop recirculating flow system containing human platelet-rich plasma. Plasma samples were taken at 0, 5, 15, 30, and 60 min and analyzed for platelet and coagulation activation. The coverslips were examined for EC coverage and platelet adherence. EC retention over a 1-h period was approximately 75% for all three materials. All three materials without ECs were highly platelet activating having similar P-selectin expression, platelet factor 4 (PF4) release, mepacrine uptake, and microparticle production. Both microparticle production and platelet adhesion were significantly lower in EC-seeded materials. Dense granule and PF4 release were both slightly diminished in all three materials seeded with ECs. P-selectin expression was reduced slightly for GBL, but remained the same for the other two materials. The EC-seeded materials displayed favorable characteristics with respect to platelet activation and adhesion; however, they still demonstrated some thrombogenic tendencies due to EC loss and exposure of the underlying substrate. Therefore, both EC coverage and EC hemostatic function are important factors in determining the thromboresistance of an EC-seeded surface.

Grafted poly(ethylene oxide) brushes as nonfouling surface coatings

The identification of design criteria for the prevention of surface fouling by protein adsorption has been an elusive research goal. The current ideas in this domain assume two different directions. One focuses on correlating protein adsorption with macroscopic surface properties such as the water wettability. The second approach involves tailoring the molecular interactions between the adsorbing proteins and the surface. In this paper, we focus on the experimental results and theoretical ideas concerned with tuning the interfacial forces by means of terminally grafted PEO chains.

The Denaturation of Lysozyme Layers Adsorbed at the Hydrophobic Solid/Liquid Surface Studied by Neutron Reflection

We have studied the adsorption of lysozyme layers at a hydrophobic silicon water interface using specular neutron reflection. The hydrophobic surface was obtained by self-assembly of a densely packed monolayer of octadecyltrichlorosilane (OTS) onto the natural silica layer on the smooth surface of a (111) silicon block. The effect of pH on the adsorbed lysozyme layer was examined at a constant lysozyme concentration of 0.03 g dm-3 and at a constant ionic strength of 0.02 M. Reflectivity profiles at different pH show that adsorption is irreversible with respect to pH, the composition and structure of the final layer being dependent on the route by which the pH was achieved. The adsorbed protein layer was found to divide into approximately two regions, a densely packed thin layer next to the OTS surface and a diffuse thicker layer extending into the bulk solution. None of the dimensions of this structure corresponds to those of the globular protein in solution, suggesting that, unlike its adsorption at the hydrophilic silica/water interface, lysozyme is denatured at the OTS/water surface. The irreversible adsorption is explained by the combined interaction of the hydrophobic attraction of the hydrophobic fragments in lysozyme to the OTS surface and electrostatic repulsion within the adsorbed layer. The hydrophobic surface induces the exposure of hydrophobic fragments from the lysozyme assembly. The thickness of the dense layer suggests that the denatured protein adsorbs in the form of peptide chains with the hydrophobic amino acid side chains attached to the OTS surface with the hydrophilic side chains extending into the bulk solution. Since lysozyme is more stable at pH 7 than at pH 4, the difference in initial adsorption is dominated by the greater relative stability of lysozyme to denaturation at the higher pH. A change of pH from 7 to 4 reduces the stability of the protein to unfolding and results in more adsorption than when the pH is changed in the opposite direction. Solution pH also affects the net charges within the hydrophilic tail region and the structural distribution of the tail region was found to vary with pH. Copyright 1998 Academic Press.

Influence of thrombus components in mediating Staphylococcus aureus adhesion to polyurethane surfaces

The role of protein and cellular components of thrombi in mediating bacterial adhesion on artificial surfaces was investigated in this study. The attachment of Staphylococcus aureus on polyurethane surfaces was observed directly using an automated video microscopy system. Surfaces were preconditioned with components of platelet-fibrin thrombi, including fibrinogen, thrombin, plasma, and isolated platelets. Experiments were performed in a radial flow chamber, and attachment rate constants were compared on the preconditioned surfaces in an effort to understand the complex relationship that exists between bacterial infection and thrombosis on synthetic biomaterials. Preadsorption of fibrinogen to surfaces significantly increased S. aureus adhesion compared to those preadsorbed with albumin alone while the presence of fibrin dramatically increased bacterial attachment compared to plasma preadsorbed surfaces. While the presence of adherent platelets also increased bacterial attachment, fibrin appeared to play a larger role in mediating bacterial adhesion on polyurethane surfaces. Striking results were obtained on the zwitterionic phosphonated polyurethane for a number of pretreatment conditions with regard to decreased bacterial adhesion and fibrinogen deposition.