Improvement of blood compatibility on cellulose hemodialysis membrane: IV. Phospholipid polymer bonded to the membrane surface

Superhydrophilicity and strong salt-affinity: Zwitterionic polymer grafted surfaces with significant potentials particularly in biological systems

In recent years, zwitterionic polymers have been frequently reported to modify various surfaces to enhance hydrophilicity, antifouling and antibacterial properties, which show significant potentials particularly in biological systems. This review focuses on the fabrication, properties and various applications of zwitterionic polymer grafted surfaces. The "graft-from" and "graft-to" strategies, surface grafting copolymerization and post zwitterionization methods were adopted to graft lots type of the zwitterionic polymers on different inorganic/organic surfaces. The inherent hydrophilicity and salt affinity of the zwitterionic polymers endow the modified surfaces with antifouling, antibacterial and lubricating properties, thus the obtained zwitterionic surfaces show potential applications in biosystems. The zwitterionic polymer grafted membranes or stationary phases can effectively separate plasma, water/oil, ions, biomolecules and polar substrates. The nanomedicines with zwitterionic polymer shells have "stealth" effect in the delivery of encapsulated drugs, siRNA or therapeutic proteins. Moreover, the zwitterionic surfaces can be utilized as wound dressing, self-healing or oil extraction materials. The zwitterionic surfaces are expected as excellent support materials for biosensors, they are facing the severe challenges in the surface protection of marine facilities, and the dense ion pair layers may take unexpected role in shielding the grafted surfaces from strong electromagnetic field.

Construction of biomimetic long-circulation delivery platform encapsulated by zwitterionic polymers for enhanced penetration of blood–brain barrier

A core–shell protein-based long circulation delivery platform has been constructed for enhanced penetration of the blood–brain barrier.

Long-term hip simulator testing of the artificial hip joint bearing surface grafted with biocompatible phospholipid polymer

To prevent periprosthetic osteolysis and subsequent aseptic loosening of artificial hip joints, we recently developed a novel acetabular highly cross-linked polyethylene (CLPE) liner with graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) on its surface. We investigated the wear resistance of the poly(MPC) (PMPC)-grafted CLPE liner during 20 million cycles in a hip joint simulator. We extended the simulator test of one liner to 70 million cycles to investigate the long-term durability of the grafting. Gravimetric, surface, and wear particle analyses revealed that PMPC grafting onto the CLPE liner surface markedly decreased the production of wear particles and showed that the effect of PMPC grafting was maintained through 70 million cycles. We believe that PMPC grafting can significantly improve the wear resistance of artificial hip joints.

Near-monodisperse poly(2-(methacryloyloxy)ethyl phosphorylcholine)-based macromonomers prepared by atom transfer radical polymerization and thiol-ene click chemistry: novel reactive steric stabilizers for aqueous emulsion polymerization

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepared by the atom transfer radical polymerization (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addition, which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aqueous emulsion polymerization of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diameter. As a comparison, the disulfide-containing PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepared using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw experiments and the addition of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepared in the absence of any steric stabilizer and a PS latex prepared in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addition of an electrolyte, as expected.

Cartilage-mimicking, high-density brush structure improves wear resistance of crosslinked polyethylene: a pilot study

BACKGROUND

In natural synovial joints under physiologic conditions, fluid thin-film lubrication by a hydrated layer of the cartilage is essential for the smooth motion of the joints. The considerably less efficient lubrication of artificial joints of polyethylene is prone to wear, leading to osteolysis and aseptic loosening and limiting the longevity of THA. A nanometer-scale layer of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) with cartilage-mimicking brushlike structures on a crosslinked polyethylene (CLPE) surface may provide hydrophilicity and lubricity resembling the physiologic joint surface.

QUESTIONS/PURPOSES

We asked whether the photoirradiation time during graft polymerization would affect the density and stability of the PMPC layer and the PMPC-grafted surface would enhance the durability of artificial joints. We investigated the effect of photoirradiation time and the resultant characteristics of the PMPC layer on the durability of the CLPE.

METHODS

For each of the PMPC-grafted CLPE surfaces with various photoirradiation times (six groups: 0 [untreated CLPE], 11, 23, 45, 90, and 180 minutes), 18 sample pieces (total of 108 samples) were evaluated in surface analyses, and four cups (total of 24 samples) were evaluated in a hip simulator test.

RESULTS

The density of the PMPC layer increased with an increase in the photoirradiation time. The hip simulator test confirmed the PMPC-grafted CLPE with a high density of the PMPC layer exhibited minimal wear as compared with the untreated CLPE. High-density PMPC grafting appears essential for maintaining the high wear resistance of the PMPC-grafted CLPE. To obtain a high-density PMPC layer, the photoirradiation time must be greater than 45 minutes.

CONCLUSIONS

The cartilage-mimicking, density brushlike structure of the PMPC-grafted CLPE could extend high durability to acetabular cups in THA.

CLINICAL RELEVANCE

Our in vitro findings suggest the wear performance of CLPE acetabular cups in THA can be improved by this approach.

Reduction of Peritendinous adhesions by hydrogel containing biocompatible phospholipid polymer MPC for tendon repair

BACKGROUND

Peritendinous adhesions are serious complications after surgical repair of tendons. As an anti-adhesion material, we focused on 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, our original biocompatible polymer, and prepared an aqueous solution of MPC-containing polymer called poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate-co-p-vinylphenylboronic acid) (PMBV), which can be formed into hydrogel properties by mixture with another aqueous polymer, poly(vinyl alcohol) (PVA). The objective of the present study was to examine the possible application of the MPC hydrogel for the reduction of peritendinous adhesions.

METHODS

the effects of the hydrogel on peritendinous adhesions and tendon healing were examined by means of histological and mechanical analyses in a rat Achilles tendon model and a rabbit flexor digitorum profundus tendon model. Cell migration and viability were examined with use of fibroblastic NIH3T3 cells cultured in a double chamber dish.

RESULTS

among the concentrations examined, 2.5% and 5.0% PMBV formed hydrogel properties immediately after mixing with 2.5% PVA and maintained a honeycomb microstructure with nanometer-scaled pores for three weeks after implantation. In animal models, the hydrogel formed from 5.0% PMBV remained at the sutured site during the critical period up to three weeks and disappeared by six weeks. The MPC hydrogel reduced the peritendinous adhesions histologically and mechanically by >25% at three weeks, without impairing tendon healing as determined with mechanical analyses. In the cell culture, cell migration was reduced by the MPC hydrogel, although cell viability was unaffected, indicating physical prevention, rather than cytotoxicity, to be the anti-adhesion mechanism.

CONCLUSIONS

the MPC hydrogel that was formed by a local injection and mixture of two aqueous solutions, 5.0% PMBV and 2.5% PVA, reduced peritendinous adhesions without impairing tendon healing. This effect may be due to its excellent biocompatibility without a foreign-body reaction and the formation of a microstructure that physically prevents passage of cells but allows cytokines and growth factors to pass for healing.

CLINICAL RELEVANCE

this nanotechnology could potentially improve the quality of surgical repair of tendon, especially the zone-II area of the digital flexor tendon.

Surface grafting of biocompatible phospholipid polymer MPC provides wear resistance of tibial polyethylene insert in artificial knee joints

OBJECTIVE

Aseptic loosening of artificial knee joints induced by wear particles from a tibial polyethylene (PE) insert is a serious problem limiting their longevity. This study investigated the effects of grafting with our original biocompatible phospholipid polymer 2-methacryloyloxyethyl phosphorylcholine (MPC) on the insert surface.

METHODS

The hydrophilicity of the PE surface was determined by the contact angle of a water droplet, and the friction torque was measured against a cobalt-chromium alloy component. The wear amount was compared among PE inserts with or without cross-linking and MPC grafting during 5x10(6) cycles of loading in a knee joint simulator. The surfaces of the insert and the wear particles in the lubricant were subjected to electron and laser microscopic analyses. The mechanical properties of the inserts were evaluated by the small punch test.

RESULTS

The MPC grafting increased hydrophilicity and decreased friction torque. In the simulator experiment, the wear of the tibial insert was significantly suppressed in the cross-linked PE (CLPE) insert, and even more dramatically decreased in the MPC-grafted CLPE insert, as compared to that in the non-cross-linked PE insert. Surface analyses confirmed the wear resistance by the cross-linking, and further by the MPC grafting. The particle size distribution was not affected by cross-linking or MPC grafting. The mechanical properties of the insert material remained unchanged during the loading regardless of the cross-linking or grafting.

CONCLUSION

Surface grafting with MPC polymer furnished the PE insert with wear resistance in an artificial knee joint through increased hydrophilicity and decreased friction torque.

Structure of Water Incorporated in Amphoteric Polymer Thin Films as Revealed by FT-IR Spectroscopy

The structure and hydrogen bonding of water incorporated in a thin film of amphoteric terpolymers composed of various ratios of MA, DMAPMA, and BMA were analyzed using the band shapes of the O--H stretching in the IR spectra. At an early stage of sorption of water, the IR spectrum for the water incorporated in the film with comparative contents of MA and DMAPMA residues was similar to that for free water. This is consistent with the tendency for zwitterionic polymers, but is in contrast with the drastic change in the IR spectrum of water incorporated in non-ionic polymer films such as polyBMA. These results suggest a correlation between the mildness of the charge-balanced polymers to the structure of incorporated water and their blood compatibilities.

2006 Frank Stinchfield Award: grafting of biocompatible polymer for longevity of artificial hip joints

Aseptic loosening induced by wear particles from the polyethylene liner is likely the most common cause of long-term total hip arthroplasty failure. We developed a novel hip polyethylene liner with the surface graft of a biocompatible phospholipid polymer, 2-methacryloyloxyethyl phosphorylcholine (MPC), and previously reported the grafting decreased the short-term production of wear particles and the subsequent bone resorptive responses. For clinical application, we investigated the stability of the 2-methacryloyloxyethyl phosphorylcholine grafting during sterilization and the wear resistance of the sterilized liner during longer loading comparable to clinical usage. Radiographic spectroscopy confirmed the stability of the 2-methacryloyloxyethyl phosphorylcholine polymer on the liner surface after the gamma irradiation. We used a hip wear simulator up to 1 x 10(7) cycles to test sterilized cross-linked polyethylene liners with and without 2-methacryloyloxyethyl phosphorylcholine grafting. The 2-methacryloyloxyethyl phosphorylcholine grafting markedly decreased the friction, the production of wear particles, and the wear of the liner surface. These data suggest a marked improvement in the wear resistance of the polyethylene liner by the 2-methacryloyloxyethyl phosphorylcholine grafting for clinically relevant periods after sterilization, indicating 2-methacryloyloxyethyl phosphorylcholine grafting is a promising technology for extending longevity of artificial hips.

Coating of a surface with 2-methacryloyloxyethyl phosphorylcholine (MPC) co-polymer significantly reduces retention of human pathogenic microorganisms

The present study compares the retention of four species that are often isolated in association with biomedical device-related infections - Staphylococcus aureus, Streptococcus mutans, Pseudomonas aeruginosa, and Candida albicans - to three different surfaces. All four bacterial species were found to bind significantly less well to MPC-coated surfaces than to non-coated surfaces. We attribute this effect to the "superhydrophilicity" of MPC-coated surfaces, whereas hydrophobic surfaces are well known to reduce bacterial retention and thus to inhibit a crucial step in the formation of bacterial biofilms that lead to biomedical device-related infections and complications.

Raman spectroscopic study of the structure of water in aqueous solutions of amphoteric polymers

Methacrylic acid (MA) and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC) were polymerized to give amphoteric copolymers with various compositions. The structure and H-bonding of water in an aqueous solution of the copolymer were analyzed using the contours of the O-H stretching in the polarized Raman spectra. For comparison, the H-bonded network structure of aqueous solutions of homopolymers (polyMA and polyMAPTAC) was also examined. From the relative intensity of the collective band (C value) corresponding to a long range coupling of the O-H stretching in the aqueous polymer solutions, the number of H-bonds disrupted due to the presence of one monomer residue of the polymers (Ncorr) was determined. The Ncorr value for polyMA was largely positive, and with an increase in the content of the MAPTAC residue, the Ncorr value became smaller, and after passing a minimum (which was still slightly positive) at a roughly equivalent molar ratio, the Ncorr value increased again. This is in significant contrast with the larger positive Ncorr values for the homopolymers (both polyMA and polyMAPTAC), and other ordinary polyelectrolytes such as sodium polyethylenesulfonate, poly-L-lysine hydrobromide and sodium polyacrylate. Furthermore, the Ncorr value for the copolymer (MA ratio MAPTAC = 56:44) became much smaller by the neutralization of MA residues in the copolymer with sodium hydroxide, and comparable to those for neutral polymers such as poly(ethylene glycol) and poly(N-vinylpyrrolidone) and zwitterionic polymers such as poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly[3-sulfo-N,N-dimethyl-N-(3'-methacryloylaminopropyl)propanaminium inner salt]. The present results clearly indicate that the amphoteric polymers with comparative contents of cationic and anionic groups do not significantly disturb the H-bonded network structure of water, probably due to the counteraction of the electrostatic hydration effect by the proximity between the anionic and cationic side groups.

Photoiniferter-based thermoresponsive graft architecture with albumin covalently fixed at growing graft chain end

The aim of this study was to develop a novel surface graft architecture in which albumin is covalently fixed at the growing chain end of the hydrophilic polymers: poly(N, N-dimethylacylamide), PDMAM, and poly(N-isopropylacrylamide), PNIPAM. Photoiniferter-based surface-grafted polymers were prepared using either an albuminated iniferter or a nonalbuminated iniferter, both of which were derivatized on glass surfaces, and ultraviolet (UV)-light-irradiated in the presence of a DMAM or NIPAM monomer. Surface chemical composition analysis by X-ray photoelectron spectroscopy, contact angle measurement, immunostaining using fluorescence labeled antibody and the measurement of graft thickness, as determined from force-distance curves obtained in water at 25 degrees C and 37 degrees C by atomic force microscopy, evidenced that the thickness of graft layer increased with photoirradiation time and albumin molecules exist at growing chain ends. For PNIPAM-grafted surfaces, the interconversion between swollen and collapsed graft chains was observed below and above the lower critical solution temperature of PNIPAM. The potential application of a thermoresponsive graft with albumin covalently fixed at its growing chain end was discussed in terms of "active" nonfouling surface design based on the temperature-dependent switching of phase transition.

Surface grafting of artificial joints with a biocompatible polymer for preventing periprosthetic osteolysis

Periprosthetic osteolysis-bone loss in the vicinity of a prosthesis-is the most serious problem limiting the longevity of artificial joints. It is caused by bone-resorptive responses to wear particles originating from the articulating surface. This study investigated the effects of graft polymerization of our original biocompatible phospholipid polymer 2-methacryloyloxyethyl phosphorylcholine (MPC) onto the polyethylene surface. Mechanical studies using a hip-joint simulator revealed that the MPC grafting markedly decreased the friction and the amount of wear. Osteoclastic bone resorption induced by subperiosteal injection of particles onto mouse calvariae was abolished by the MPC grafting on particles. MPC-grafted particles were shown to be biologically inert by culture systems with respect to phagocytosis and resorptive cytokine secretion by macrophages, subsequent expression of receptor activator of NF-kappaB ligand in osteoblasts, and osteoclastogenesis from bone marrow cells. From the mechanical and biological advantages, we believe that our approach will make a major improvement in artificial joints by preventing periprosthetic osteolysis.

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.

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.

Preparation of non-thrombogenic materials using 2-methacryloyloxyethyl phosphorylcholine

This review addresses the non-thrombogenic characteristics of copolymers based on 2-methacryloyloxyethyl phosphorylcholine (MPC), originally developed by Nakabayashi and colleagues. The hypothesis underlying these developments was that such materials would adsorb phospholipids from blood, yielding surfaces with good natural blood compatibility. Methacrylates were found to have excellent properties for this copolymerisation. The characteristics of the MPC copolymers relevant to the improved blood compatibility were minimisation of protein adsorption through an increase in the amount of free water in the MPC hydrogels, which prevents protein conformational change and increased protein stability in solution. Non-thrombogenicity has been evaluated by in vitro, ex vivo and in vivo procedures. Non-thrombogenic dialysis membranes and a durable glucose biosensor have been developed using this MPC copolymer.

Preparation of a stable phospholipid monolayer grafted onto a methacryloyl-terminated substrate as blood compatible materials

We have prepared a surface-grafted phospholipid monolayer by in situ polymerization carried out at the interface between a pre-assembled phospholipid monolayer and a methacryloyl-terminated substrate. The phospholipid containing an acryloyl moiety, 1-stearoyl-2-[12-(acryloyloxy)-dodecanoyll-sn-glycero-3-phosphocholine (acryloyl-PC), was pre-assembled by vesicle fusion onto methacryloyl-terminated substrates which were silanized with 3-(trimethoxysilyl)propyl methacrylate (TSM). The acryloyl-PC monolayer and methacryloyl-terminated substrates were then polymerized in situ by adding a water-soluble initiator, 2,2-azobis(2-methylpropionamidine) dihydrochloride (AAPD), at 60 degrees C for 15 min. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements indicated that the polymerized phospholipid surface on the TSM-silanized substrates formed a lipid monolayer structure with some defects. The polymerized phospholipid surfaces also showed good stability in methanol due to chemical bonding to solid surfaces. The grafting efficiency of acryloyl-PC monolayer on the TSM substrate, which was calculated by the relative carbon ratio of the polymerized acryloyl-PC monolayer on TSM substrate before and after methanol washing, was 94.5%. For comparative analysis, the acryloyl-PC monolayer was also polymerized onto dimethyl-terminated substrates silanized with dichlorodimethylsilane (DCM). In the absence of surface grafting moieties on solid substrates, the laterally polymerized acryloyl-PC monolayer physically adsorbed on substrates was easily removed in an organic solvent. The surface-grafted phospholipid monolayer was also greatly effective in the prevention of platelet adhesion.

Protein adsorption-resistant hollow fibers for blood purification

Nonfouling polysulfone (PSf) hollow fiber membranes resistant to protein adsorption and deposition were newly developed by the addition of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer. To improve hydrophilicity, permeability, and nonfouling characteristics of the PSf hollow fiber in a hemodialyzer, we synthesized a MPC polymer which can be blended with PSf for preparing the polymer alloy (PSf/MPC polymer). The composition of the MPC polymer blended in the PSf was in the range between 7.0 and 15 wt%. From the PSf/MPC polymer solution, flat membranes and hollow fibers could be prepared. These membranes took an asymmetric structure, and its mechanical strength was good. The surface characterization of the PSf/MPC polymer hollow fiber membrane by X-ray photoelectron spectroscopy revealed that the MPC units were concentrated at the surface. The permeability for solutes through the PSf/MPC polymer membrane was higher, and the amount of protein adsorbed on the PSf/MPC polymer membrane was lower than those of the PSf membrane. Moreover, platelet adhesion was also effectively inhibited on the PSf/MPC polymer membrane.

A nonthrombogenic gas-permeable membrane composed of a phospholipid polymer skin film adhered to a polyethylene porous membrane

Polymer membranes are widely used in biomedical applications such as hemodialysis, membrane oxygenator, etc. When the membranes come in contact with blood or body fluids, protein adsorption and cell adhesion occur rapidly. Nonspecific protein adsorption and cell adhesion on the membranes induce not only various bio-rejections but also a decrease in their performance. We hypothesized that a blood compatible gas-permeable membrane could be prepared from polyethylene (PE) porous membranes modified with phospholipid polymers. In this study, poly[(2-methacryloyloxyethyl phosphorylcholine) (MPC)-co-dodecyl methacrylate] (PMD) skin film adhered to a PE porous membrane (PMD/PE porous membrane) was prepared. Elution of PMD was not detected meaning that the PMD film did not detach from the PE porous membrane even after soaking in water for more than 6 months. The permeation coefficient of oxygen gas through the PE membrane with the adhered PMD containing more than 0.20 mole fraction of the MPC unit, was the same as that of the original PE porous membrane. The PMD surface effectively reduced biofouling. We concluded that the PMD/PE porous membrane is useful as a novel membrane oxygenator due to its excellent gas-permeability and blood compatibility.

Characterization of the spontaneously forming hydrogels composed of water-soluble phospholipid polymers

Spontaneously forming hydrogels composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymers, poly(MPC-co-methacrylic acid) (PMA), and poly(MPC-co-n-butyl methacrylate) (PMB) were examined. The MPC copolymer hydrogel was observed to have a spontaneous gelation property. To determine the properties of the hydrogels and why the gelation takes place, we have studied the properties of the hydrogels by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC). The morphologies of the hydrogels were spongelike with a homogeneous structure. By XPS analysis in terms of the molecular distributions in the hydrogels, it was observed that a stabilization time was required for the hydrogel to undergo chain rearrangement. DSC thermograms of the hydrogels were different from their components, PMA and PMB. For the hydrogel, a crystallization peak around -30 degrees C was observed. This result indicated that some ordered structures existed in the hydrogels. To determine the role of the MPC groups, aqueous solutions of poly(methacrylic acid) (PMAc) and PMB were mixed. The mixture of PMAc-PMB turned into a sol state, and the sol state remained for a week. When the mixture was cooled, a very weak hydrogel was prepared. This result suggested that the MPC groups were the dominant unit for spontaneously forming the hydrogels.

Antithrombogenic polymer alloy composed of 2-methacryloyloxyethyl phosphorylcholine polymer and segmented polyurethane

To evaluate the antithrombogenicity of a new polymeric biomaterial in vivo, a polymer alloy tube composed of poly[2-methacryloyloxyethyl phosphorylcholine(MPC)-co-2-ethylhexyl methacrylate](PMEH) polymer and a segmented polyurethane (SPU) was prepared by a solvent evaporation method on a Teflon rod from a homogeneous solution containing both the PMHE and SPU. The composition of the PMEH vs the SPU was 10 wt%. The inner and outer surfaces of the polymer alloy tubing were characterized by X-ray electron spectroscopic (XPS) measurements. The MPC units were located on the inner surface of the polymer alloy tubing rather than the outer surface. After immersion in aqueous media, a higher concentration of the MPC units was observed on both surfaces. Selective staining of the MPC units with osmium tetraoxide was carried out to observe the morphology of the PMEH domain on the surface of the polymer alloy. There were large-sized PMEH domains on the inner surface of the tubing but small-sized domains were found on the outer surface. This result was in good agreement with the XPS results. Blood compatibility of the polymer alloy was evaluated by observation of fibrinogen adsorption and platelet adhesion from human plasma. A lot of fibrinogen was adsorbed and many platelets adhered to the inner surface of the original SPU tubing. On the other hand, the PHEH/SPU polymer alloy tubing suppressed these adsorptions and adhesions. When the PMEH/SPU polymer alloy tubing was implanted into a rabbit's artery, thrombus could not be observed even after a 7-day implantation but the original SPU tubing was almost totally occluded only after a 90-min implantation due to serious thrombus deposition on the surface. These results clearly indicated that the PMEH in the SPU matrix acted as an antithrombus reagent by suppression of protein adsorption and platelet adhesion and activation. Particularly, the MPC units played a significant role in this function.

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.

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.