Effect of 2-methacryloyloxyethyl phosphorylcholine concentration on photo-induced graft polymerization of polyethylene in reducing the wear of orthopaedic bearing surface

Photo-induced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) on cross-linked polyethylene (CLPE) has been developed as a novel technology for reducing wear of orthopaedic bearings. In this study, the effect of MPC concentration on graft polymerization and the resultant properties of the grafted poly (MPC) layer have been investigated. The grafted poly (MPC) layer thickness increased with the MPC concentration in feed. The hip simulator wear test confirmed that CLPE-g-MPC cups exhibited minimal wear compared with untreated CLPE cups. Since MPC is a highly hydrophilic methacrylate, the water-wettability of CLPE-g-MPC was greater than that of untreated CLPE due to the formation of a poly(MPC) nanometer-scale layer. The CLPE-g-MPC orthopaedic bearing surface exhibited high lubricity, because of the present of the poly(MPC) layer even at a thickness of 10 nm. This layer is considered responsible for the improved wear resistance. Nanometer-scale modification of CLPE with poly(MPC) is expected to significantly increase the durability of the orthopaedic bearings. Poly (MPC) layer thickness can be controlled by changing the MPC concentration in feed. In order to achieve nanometer-scale modification of poly(MPC) in this manner, it is necessary to use a long photo-irradiation time for the MPC graft polymerization system, which contains a high-concentration monomer without its gelation.     

Platelet compatible blood filtration fabrics using a phosphorylcholine polymer having high surface mobility

To obtain a novel polymer for coating on blood filtration devices, which can reduce platelet adhesion and activation when the polymer is in contact with blood under a dry condition, a phosphorylcholine polymer with high mobility of the polymer side chain was designed. The polymer possesses 2-methacryloyloxyethoxyethyl phosphorylcholine unit (PMEO2B) having a diethylene oxide chain between the phosphorylcholine group and the backbone. The surface density of the phosphorylcholine groups and their orientation under aqueous conditions were analyzed with an X-ray photoelectron spectroscope. On the PMEO2B surface, the surface density of phosphorylcholine groups was much higher than that of the theoretical value even when the surface was in air atmosphere. The period for equilibrating the surface of PMEO2B by hydration was shorter than that of the 2-methacryloyloxyethyl phosphorylcholine polymer (PMB). The mobility of the polymer chain with hydration was remarkably improved with the addition of a diethylene oxide chain as a bridging unit.The platelet activation and adhesion were evaluated using a non-woven fabric made from poly(ethylene terephthalate) fibers and that coated with these phosphorylcholine polymers. Even when the platelets were passed through the PMEO2B-coated fabric without prehydration, the activity of the platelets eluted was similar to that of native platelets. Moreover, adherent cells were not observed on the fabric. On the other hand, the platelets adhered to the PET fabric and to that coated with PMB. Based on these results, we concluded that the higher mobility of the polymer chain is very important to reduce interactions with platelets.     

Biomimetic glucose recognition using molecularly imprinted polymer hydrogels

Non-covalent molecular imprinting of poly(allylamine hydrochloride) (PAA.HCl) with D-glucose 6-phosphate monobarium salt (GPS-Ba) produced molecularly imprinted polymer hydrogels (MIP) having an affinity to glucose over fructose. The hydrogels were formed by ionic association of the template molecule, GPS-Ba, to the polymer, prior to covalent crosslinking using epichlorohydrin (EPI). The template was removed by an aqueous base wash. Batch equilibration studies using different MIP hydrogels and non-molecularly imprinted polymers (NIPs) were performed in aqueous and buffered media to determine the binding capacities and isomeric selectivities with respect to the sugars, glucose and fructose. MIP glucose hydrogels exhibited binding capacities in excess of 0.6g of glucose per g of dry gel in a 100% DI H(2)O glucose solution, and in a 50-50% glucose-fructose solution mixture. Equilibrium binding capacities of fructose were lower than those observed with respect to glucose, indicating an isomeric preference for the binding of glucose over fructose. These hydrogels demonstrated a remarkable degree of biomimetic sugar recognition to specifically and selectively bind glucose in their swollen state in environments mimicking physiological conditions.     

Biomimetic scaffolds fabricated from apatite-coated polymer microspheres

The deposition of a bonelike mineral on the surface of polymer scaffolds results in the formation of hybrid biomaterials, possessing enhanced osteoconductivity while retaining appropriate biodegradability. However, current methods of fabricating such composite scaffolds use a prolonged incubation process, which permits scaffold deformation and premature loss of incorporated macromolecules. We hypothesized that the fabrication of biomineralized polymer scaffolds could be achieved using premineralized polymer microspheres generated through incubation in a modified simulated body fluid (mSBF). We explored the material characteristics of these substrates and characterized the in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs) when cultured on these novel scaffolds. Unlike scaffolds prepared using the conventional approach, premineralized scaffolds maintained their initial conformation after fabrication, achieved improved mineral distribution throughout the substrate, and enabled significantly greater incorporation efficiency of a model protein. We did not detect differences in osteogenic differentiation as determined by alkaline phosphatase activity and osteopontin secretion. However, we did observe a significant increase in cell-secreted calcium by hMSCs seeded on scaffolds prepared from premineralized polymer. These results demonstrate that the use of premineralized polymeric materials to fabricate biodegradable polymer scaffolds is an improved method for composite scaffold formation and may have numerous advantages for use in bone tissue engineering.     

A substrate-independent method for surface grafting polymer layers by atom transfer radical polymerization: reduction of protein adsorption

A general method for producing low-fouling biomaterials on any surface by surface-initiated grafting of polymer brushes is presented. Our procedure uses radiofrequency glow discharge thin film deposition followed by macro-initiator coupling and then surface-initiated atom transfer radical polymerization (SI-ATRP) to prepare neutral polymer brushes on planar substrates. Coatings were produced on substrates with variable interfacial composition and mechanical properties such as hard inorganic/metal substrates (silicon and gold) or flexible (perfluorinated poly(ethylene-co-propylene) film) and rigid (microtitre plates) polymeric materials. First, surfaces were functionalized via deposition of an allylamine plasma polymer thin film followed by covalent coupling of a macro-initiator composed partly of ATRP initiator groups. Successful grafting of a hydrophilic polymer layer was achieved by SI-ATRP of N,N'-dimethylacrylamide in aqueous media at room temperature. We exemplified how this method could be used to create surface coatings with significantly reduced protein adsorption on different material substrates. Protein binding experiments using labelled human serum albumin on grafted materials resulted in quantitative evidence for low-fouling compared to control surfaces.     

Quasi-living surface graft polymerization with phosphorylcholine group(s) at the terminal end

A surface graft polymer with one or two phosphorylcholine (PC) polarheads at the terminus of the growing chain end was prepared by sequential reactions on a glass substrate. The dithiocarbamate group covalently bound to glass surfaces was derivatized with one or two PC groups and then irradiated with ultraviolet light in the presence of N,N-dimethylacrylamide (DMAAm). X-ray photoelectron spectroscopy, wettability measurements and dye staining experiment for the PC group showed that the resultant graft copolymers were produced via iniferter-based quasi-living radical polymerization, in which the polyDMAAm graft chain contains one or two PC groups at the terminal end of the graft chain. These polymer surface grafts may help provide biocompatibility.     

High lubricious surface of cobalt-chromium-molybdenum alloy prepared by grafting poly(2-methacryloyloxyethyl phosphorylcholine)

Osteolysis caused by wear particles from polyethylene in artificial hip joints is of great concern. Various bearing couple combinations, bearing material improvements, and surface modifications have been attempted to reduce such wear particles. With the aim of reducing the wear and developing a novel artificial hip-joint system, we created a highly lubricious metal-bearing material: A 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was grafted onto the surface of the cobalt-chromium-molybdenum (Co-Cr-Mo) alloy. For ensuring the long-term retention of poly(MPC) on the Co-Cr-Mo alloy, we used a 4-methacryloxyethyl trimellitate anhydride (4-META) intermediate layer and photo-induced graft polymerization technique to create a strong bonding between the Co-Cr-Mo substrate and the poly(MPC) chain via the 4-META layer. The Co-Cr-Mo alloy was pretreated with nitric acid and O(2) plasma to facilitate efficient interaction between the 4-META carboxyl group and the surface hydroxyl group on the Cr oxide passive layer of the Co-Cr-Mo alloy. After MPC grafting, the MPC unit peaks were clearly observed in the Fourier-transform infrared spectroscopy with attenuated total reflection (FT-IR/ATR) and X-ray photoelectron spectroscopy (XPS) spectra of the Co-Cr-Mo surface. Tribological studies with a pin-on-plate machine revealed that surface MPC grafting markedly lowered the friction coefficient. We concluded that the grafted poly(MPC) layer successfully provided high lubricity to the Co-Cr-Mo surface.     

Preparation of blood-compatible hollow fibers from a polymer alloy composed of polysulfone and 2-methacryloyloxyethyl phosphorylcholine polymer

Blood-compatible hollow fibers were successfully prepared from a polymer alloy composed of polysulfone (PSf) and the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer. To improve the hydrophilicity, fouling-resistance characteristics, and blood compatibility of the PSf hollow fiber in a hemodialyzer, an MPC polymer that can be blended with PSf was synthesized in order to prepare the polymer alloy (PSf/MPC polymer). The contents of the MPC polymer blended in the PSf were 7 and 15 wt%. The PSf/MPC polymer hollow fiber could be prepared by both wet and dry-wet processing methods. The hollow fiber took an asymmetric structure, that is, the hollow-fiber membrane had a dense skin layer on the porous sponge-like structure. The mechanical strength was higher than that of conventional PSf hollow fibers for hemodialysis. The surface characterization of the PSf/MPC polymer hollow fiber by x-ray photoelectron spectroscopy revealed that the MPC units were concentrated at the surface. The permeability for solutes through the PSf/MPC polymer hollow fibers was measured for 4 h. The permeabilities of both a low-molecular-weight compound and protein were greater than those of the PSf hollow fibers. The amount of adsorbed protein was lower on the PSf/MPC polymer hollow fiber when compared to that of the PSf hollow fiber. Moreover, platelet adhesion was also effectively inhibited on the PSf/MPC polymer hollow fiber. Based on these results, the addition of the MPC polymer to the PSf is a very useful method to improve the functions and blood compatibility of the hollow fiber.     

Group reorientation and migration of amphiphilic polymer bearing phosphorylcholine functionalities on surface of cellular membrane mimicking coating

Amphiphilic polymers bearing phosphorylcholine (PC) groups can form films of interfacial structure similar to that of the outer membrane of living cells. The films, as prepared, present PC groups to the external aqueous environment and exhibit good biocompatibility. However, under certain conditions, the surface structure can change irreversibly due to the reorientation and deep migration of the surface groups. X-ray photoelectron spectroscopy (XPS), dynamic contact angle measurements, and cell culture experiments were used to investigate the reorientation and migration of the surface groups of an amphiphilic PC-polymer coating. When the polymer surface is immersed into or drawn out of water, significant reorientation and group migration occurs, as suggested by the large difference between the advancing and receding contact angles. Angle-resolved XPS measurements indicate that the hydrophobic groups move to the air/film interface while the hydrophilic groups migrate towards the bulk of the polymer coating. Long periods of aging may result in irreversible changes of the surface structure and decrease the biocompatibility of the materials.     

Biomembranes as models for polymer surfaces. III. Characterization of a phosphorylcholine surface covalently bound to glass

A surface layer of phosphorylcholine has been chemically linked with the surface hydroxyl groups present on glass and silica by reaction with mono- and bifunctional reagents. Evidence for the structural integrity of the deposited group was provided by the equimolar association of phosphorus and choline with the reacted surfaces. Modified glass surfaces yielded contact angles which are consistent with those found previously for other models of biological membranes. Covalent modification of the treated surfaces was demonstrated by i.r. spectroscopy via the removal of surface hydroxyl groups. The modified surfaces were thermostable at temperatures up to 375 degrees C for extended periods. The relevance of these results to the generation of new biomaterials is discussed.     

Biomembranes as models for polymer surfaces. IV. ESCA analyses of a phosphorylcholine surface covalently bound to hydroxylated substrates

Using a simple chemical process, phosphorylcholine has been deposited covalently on the surface of a variety of hydroxylated polymers as a stable, monomolecular coating. Our goal was to obtain new biomaterials which, due to the chemical similarity of the modified interfaces to the phospholipid head groups present on the extracellular surfaces of blood cell membranes, should exhibit enhanced haemo- and biocompatibility. Our previous analyses by chemical and spectrophotometric methods indicated that sufficient quantities of phosphorylcholine were deposited on glass and silica surfaces to result in appreciable modification of their interfacial properties. In the present study, we have examined a series of modified hydroxylated substrates by ESCA and demonstrate specific chemical modifications on the molecular surfaces of polymeric substrates.     

Non-biofouling materials prepared by atom transfer radical polymerization grafting of 2-methacryloloxyethyl phosphorylcholine: separate effects of graft density and chain length on protein repulsion

Biomimetic poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) brushes with graft density 0.06-0.39 chains/nm2 and chain length 5-200 monomer units were prepared from silicon wafer surfaces by combining self-assembly of initiator and surface-initiated atom transfer radical polymerization (ATRP). Water contact angle, X-ray photoelectron spectroscopy, and atomic force microscopy were used to characterize the modified surfaces. These surfaces with well-controlled poly(MPC) brushes were tested for protein repelling performance. Fibrinogen adsorption from tris-buffered saline at pH 7.4 decreased significantly with increasing graft density and/or chain length of poly(MPC) and reached a level of < 10 ng/cm2 at graft density > or = 0.29 chains/nm2 and chain length > or = 100 units, compared to ca. 570 ng/cm2 for the unmodified samples. While the fibrinogen adsorption was determined by both graft density and chain length, it showed a stronger dependence on graft density than on chain length.     

Effects of mobility/immobility of surface modification by 2-methacryloyloxyethyl phosphorylcholine polymer on the durability of polyethylene for artificial joints

Surface modification is important for the improvement in medical device materials. 2-Methacryloyloxyethyl phosphorylcholine (MPC) polymers have attracted considerable attention as surface modifiable polymers for several medical devices. In this study, we hypothesize that the structure of the surface modification layers might affect the long-term stability, hydration kinetics, wear resistance, and so forth, of medical devices such as artificial joints, and the poly(MPC) (PMPC) grafted surface might assure the long-term performance of such devices. Therefore, we investigate the surface properties of various surface modifications by using dip coatings of MPC-co-n-butyl methacrylate (PMB30) and MPC-co-3-methacryloxypropyl trimethoxysilane (PMSi90) polymers, or photoinduced radical grafting of PMPC and also the effects of the surface properties on the durability of cross-linked polyethylene (CLPE) for artificial joints. The PMPC-grafted CLPE has an extremely low and stable coefficient of dynamic friction and volumetric wear as compared to the untreated CLPE, PMB30-coated CLPE, and PMSi90-coated CLPE. It is concluded that the photoinduced radical graft polymerization of MPC is the best method to retain the benefits of the MPC polymer used in artificial joints under variable and multidirectional loads for long periods with strong bonding between the MPC polymer and the CLPE surface, and also to retain the high mobility of the MPC polymer.     

In vivo release of testosterone from vinyl polymer composites prepared by radiation-induced polymerization

Polymer-testosterone composites with long periods of controlled slow release were made by radiation-induced polymerization in a supercooled state at low temperature using glass-forming monomers. The in vitro release of testosterone from various vinyl polymer composites was found to follow a matrix-controlled process (Q-t1/2). The rate of drug delivery was accelerated with increasing water content of polymers. In experiments in vivo, the composites were implanted subcutaneously in the back of castrated rats during the 30 day test period. The in vivo release rate of testosterone was a little smaller than in vitro. This difference between two releases also increased with the increase of hydrophilicity of polymer. The physiological response in rats was investigated by measuring the weight of ventral prostate and serum testosterone concentration with testosterone-containing composites. The weight of ventral prostate increased linearly with increasing rate of drug release and the serum testosterone concentration could be correlated with the release and with the weight increase of ventral prostate. It was found from microscopic observation that the used polymer carriers had relatively good biocompatibility to cause little foreign body reaction.     

Assessing embryonic stem cell response to surface chemistry using plasma polymer gradients

The control of cell-material interactions is the key to a broad range of biomedical interactions. Gradient surfaces have recently been established as tools allowing the high-throughput screening and optimization of these interactions. In this paper, we show that plasma polymer gradients can reveal the subtle influence of surface chemistry on embryonic stem cell behavior and probe the mechanisms by which this occurs. Lateral gradients of surface chemistry were generated by plasma polymerization of diethylene glycol dimethyl ether on top of a substrate coated with an acrylic acid plasma polymer using a tilted slide as a mask. Gradient surfaces were characterized by X-ray photoelectron spectroscopy, infrared microscopy mapping and profilometry. By changing the plasma polymerization time, the gradient profile could be easily manipulated. To demonstrate the utility of these surfaces for the screening of cell-material interactions, we studied the response of mouse embryonic stem (ES) cells to these gradients and compared the performance of different plasma polymerization times during gradient fabrication. We observed a strong correlation between surface chemistry and cell attachment, colony size and retention of stem cell markers. Cell adhesion and colony formation showed striking differences on gradients with different plasma polymer deposition times. Deposition time influenced the depth of the plasma film deposited and the relative position of surface functional group density on the substrate, but not the range of plasma-generated species.     

Immobilization of surface active compounds on polymer supports using a gas discharge process.

By applying an argon plasma treatment to a layer of a surface active agent pre-adsorbed on a polymer substrate, it is possible to covalently couple this layer to the substrate. This method offers a direct route to tailor the surface properties of polymers.     

Plasma-induced polymerization as a tool for surface functionalization of polymer scaffolds for bone tissue engineering: An in vitro study

A commonly applied strategy in the field of tissue engineering (TE) is the use of temporary three-dimensional scaffolds for supporting and guiding tissue formation in various in vitro strategies and in vivo regeneration approaches. The interactions of these scaffolds with highly sensitive bioentities such as living cells and tissues primarily occur through the material surface. Hence, surface chemistry and topological features have principal roles in coordinating biological events at the molecular, cellular and tissue levels on timescales ranging from seconds to weeks. However, tailoring the surface properties of scaffolds with a complex shape and architecture remains a challenge in materials science. Commonly applied wet chemical treatments often involve the use of toxic solvents whose oddments in the construct could be fatal in the subsequent application. Aiming to shorten the culture time in vitro (i.e. prior the implantation of the construct), in this work we propose a modification of previously described bone TE scaffolds made from a blend of starch with polycaprolactone (SPCL). The modification method involves surface grafting of sulfonic or phosphonic groups via plasma-induced polymerization of vinyl sulfonic and vinyl phosphonic acid, respectively. We demonstrate herein that the presence of these anionic functional groups can modulate cell adhesion mediated through the adsorbed proteins (from the culture medium). Under the conditions studied, both vitronectin adsorption and osteoblast proliferation and viability increased in the order SPCL ? sulfonic-grafted SPCL < phosphonic-grafted SPCL. The results revealed that plasma-induced polymerization is an excellent alternative route, when compared to the commonly used wet chemical treatments, for the surface functionalization of biodevices with complex shape and porosity.     

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.     

Emulsion polymerization of styrene using phospholipid as emulsifier. Immobilization of phospholipids on the latex surface

Emulsion polymerization of styrene using polymerizable and non-polymerizable phospholipids with double alkyl chains ( 1a , 1b ), and their single-chain analogues ( 2a , 2b ) as emulsifier gave polymer latices with narrow size distribution. The resulting latices, which were subjected to acid and enzymatic hydrolysis, and reprecipitation with methanol, were characterized by phosphorus analysis and X-ray photoelectron spectroscopy (XPS). The phospholipids remained mainly on the surface of the latices. The non-polymerizable emulsifiers were physically adsorbed on the latices, but the polymerizable emulsifiers were chemically bound to the latices. Phospholipid 1b on the latex prepared with a lipophilic radical initiator was hydrolyzed by phospholipase C.     

Human amniotic cell sheet harvest using a novel temperature-responsive culture surface coated with protein-based polymer

Human amniotic epithelial (hAE) and mesenchymal (hAM) cells are believed to have the potential to differentiate into various functional cells, such as neurons, hepatocytes, cardiomyocytes, and pancreatic beta cells. However, cell transplantation has been performed by injection of cell suspensions, and thus it is difficult to control shape, size, location, and functions of differentiated cells. To overcome these problems, we developed a novel temperature-responsive culture surface coated with elastic protein-based polymer. By reducing the temperature using a polyvinylidene difluoride (PVDF) membrane, the primary hAE and hAM cell sheet can detach from the coated surface. The recovered cell sheet can be transferred and can re-adhere and re-proliferate on another surface. This represents the first report of harvesting of primary hAE and hAM cell sheets using the novel temperature- responsive polymer. These findings suggest that this new technique of cell sheet detachment from noncytotoxic, highly biocompatible protein-based polymer-coated surfaces may be useful in tissue engineering, as well as in the investigation of hAE and hAM cell sheets for transplantation.