Water absorption and surface properties of novel poly(ethylmethacrylate) polymer systems for use in bone and cartilage repair

The surface and bulk properties of novel methacrylate polymers prepared by gelling poly(ethyl methacrylate) (PEMA) powder with different ratios of tetrahydrofurfuryl methacrylate (THFMA) and hydroxyethyl methacrylate (HEMA) monomers were investigated. The water adsorption and desorption characteristics of these polymers were measured in water and phosphate buffered saline (PBS). The desorption diffusion coefficients were higher than the adsorption coefficients in both water and PBS. Linear relationships between the equilibrium mass of water taken up and the mass of water desorbed with the concentration of HEMA in the polymer were established. Polymer surfaces were analysed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Surface features varied with polymer composition; during hydration only selective areas of the surface hydrated indicating a heterogeneous surface. Contact angle data showed no trend between the different polymers indicating that contact angles are not an acceptable method of assessing hydrophobicity/wettability of a material which does not have a homogeneous surface. The effect of these bulk and surface characteristics on biological interactions were examined using bovine chondrocytes and human osteoblast (HOB) cell cultures. Cell attachment decreased when HEMA was present in the copolymer.     

Surface characterizations of copolymer films with pendant monosaccharides

We copolymerized a monomer with a pendant glucose unit (GEMA) with methyl methacrylate (MMA) and prepared copolymer films with pendant monosaccharides by casting the copolymer solution on glass plates. The surfaces of the copolymer films were characterized by contact angle measurements, X-ray photoelectron spectroscopy (XPS) and protein adsorption measurements, and compared with the surface of 2-hydroxyethyl methacrylate (HEMA)-MMA copolymer films. The surface free energy of the GEMA-MMA and HEMA-MMA copolymer was calculated from the contact angle of methylene diiodide and glycerol on the copolymer films. The surface free energy of the films increased gradually with increasing GEMA or HEMA content. The surface free energy of GEMA-MMA copolymers was larger than that of HEMA-MMA copolymers in the whole range of composition. The results of XPS measurements suggest that the fraction of GEMA at the copolymer surface increases as the content of GEMA in the copolymer increases. This indicates that introduction of GEMA makes the copolymer surface more hydrophilic. Further more, the higher the GEMA content is, the smaller amounts of fibrinogen and γ-globulin are adsorbed at the copolymer surface. The copolymer with a GEMA content of 20 mol-% hardly adsorbs fibrinogen and γ-globulin at all.     

The effect of RAFT-derived cationic block copolymer structure on gene silencing efficiency

In this work a series of ABA tri-block copolymers was prepared from oligo(ethylene glycol) methyl ether methacrylate (OEGMA(475)) and N,N-dimethylaminoethyl methacrylate (DMAEMA) to investigate the effect of polymer composition on cell viability, siRNA uptake, serum stability and gene silencing. Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization was used as the method of polymer synthesis as this technique allows the preparation of well-defined block copolymers with low polydispersity. Eight block copolymers were prepared by systematically varying the central cationic block (DMAEMA) length from 38 to 192 monomer units and the outer hydrophilic block (OEGMA(475)) from 7 to 69 units. The polymers were characterized using size exclusion chromatography and (1)H NMR. Chinese Hamster Ovary-GFP and Human Embryonic Kidney 293 cells were used to assay cell viability while the efficiency of block copolymers to complex with siRNA was evaluated by agarose gel electrophoresis. The ability of the polymer-siRNA complexes to enter into cells and to silence the targeted reporter gene enhanced green fluorescent protein (EGFP) was measured by using a CHO-GFP silencing assay. The length of the central cationic block appears to be the key structural parameter that has a significant effect on cell viability and gene silencing efficiency with block lengths of 110-120 monomer units being the optimum. The ABA block copolymer architecture is also critical with the outer hydrophilic blocks contributing to serum stability and overall efficiency of the polymer as a delivery system.     

Adhesion of cultured human endothelial cells onto methacrylate polymers with varying surface wettability and charge

The adhesion of human endothelial cells (HEC) onto a series of well-characterized methacrylate polymer surfaces with varying wettabilities and surface charges was studied either in serum-containing (CMS) or in serum-free (CM) culture medium. HEC adhesion in CMS onto (co)polymers of hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) was found to be optimal on the moderately wettable copolymer (mol ratio 25 HEMA/75 MMA). Positively-charged copolymers of HEMA or MMA with trimethylaminoethyl methacrylate-HCl salt (TMAEMA-Cl), both with mol ratios of 85/15 and a negatively-charged copolymer of MMA with methacrylic acid (MAA), mol ratio 85/15, showed high numbers of adhering HEC. In CM, HEC adhered onto the three charged copolymers mentioned above, but neither onto the copolymer of HEMA and MAA (mol ratio 85/15) nor onto the HEMA/MMA co- and homopolymers. Complete cell spreading in CM was only observed on the positively-charged copolymers.     

The effect of two hydrophilic monomers on the water uptake of a heterocyclic methacrylate system

The room temperature polymerising system poly(ethyl methacrylate) (PEM)/tetrahydrofurfuryl methcrylate (THFM) has been modified by replacing some of the THFM by hydroxyethyl methacrylate (HEMA) and hydroxypropyl methacrylate (HPM), respectively. In both cases, the equilibrium uptake of the parent system is reduced substantially, in spite of the hydrophilic nature of these monomers. The effect is less with HPM. Corresponding to these decreases in uptake are substantial increases in the diffusion coefficients. This points to changes from a cluster-dominated process, to a more continuum-based process in the dual monomer systems. Addition of chicken serum albumin to these systems increases water uptake. At higher levels of HEMA addition, there is a substantial increase in polymerisation exotherm.     

Effect of hydrophilic polymer conjugation on heat-induced conformational changes in a protein

End-functional 2-methacryloyloxyethyl phosphorylcholine (MPC) co-polymers containing two different monomer units, 2-hydroxyethyl methacrylate (HEMA) and n-butyl methacrylate (BMA), with varying hydrophilicities were synthesized to investigate the effect of the conjugated hydrophilic polymer on the heat-induced conformational changes of a protein. MPC co-polymer-conjugated proteins containing the HEMA unit (PMH) could withstand thermal conformational changes better than those containing the more hydrophobic BMA unit (PMB). The changes in protein tertiary structures were estimated via the excitation of tryptophan. PMH-conjugated proteins could withstand heat-induced intensity changes better than the PMB-conjugated proteins. Thus, hydrophilic units in the conjugated polymer are probably essential in suppressing the heat-induced conformational changes of a protein. The changes in secondary and tertiary structures of poly(MPC)-(PMPC) and poly(HEMA) (PHEMA)-conjugated proteins were compared to validate the effect of MPC units on heat-induced conformational change. Although the thermally induced conformational changes in the secondary and tertiary structures of PHEMA-conjugated proteins were partially suppressed, the effect on PMPC-conjugated proteins was much greater, with significant conformational preservation. This is due to the specific hydration state of the hydrophilic PMPC chain, which reduces interaction between the protein molecules.     

Surface characteristics of block-type copolymer composed of semi-fluorinated and phospholipid segments synthesized by living radical polymerization

A series of random and block copolymers composed of hydrophilic and hydrophobic monomer units have been synthesized by the free and living radical polymerization methods, respectively. The hydrophilic monomer unit, 2-methacryloyloxyethyl phosphorylcholine (MPC), was selected because the MPC polymers are well-known for their excellent bio- and blood compatibilities. The semi-fluorinated monomer, 2,2,2-trifluoroethyl methacrylate (TFEMA), was used as the hydrophobic monomer unit. Several analyses of the copolymer surface showed that the TFEMA unit was concentrated at the outermost surface on the random copolymer surface and characteristics of MPC unit was dominant on the block copolymer with a low-MPC-unit composition in the dry state. A reorientation of the MPC unit occurred dynamically in the wet state because of the strong hydrophilicity of the MPC units. In the case of the block copolymer with a low-MPC-unit composition, the surface was covered with the MPC units in the wet state. As a result, the amount of the adsorbed bovine plasma fibrinogen and bovine serum gamma-globulin on the block copolymer surface was reduced dramatically.     

Inhibition of fibroblast cell adhesion on substrate by coating with 2-methacryloyloxyethyl phosphorylcholine polymers

Fibroblast adhesion and growth behavior were examined on various polymers coated on a poly(ethylene telephthalate) (PET) substrate. The polymers are poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate copolymer (PMB)s with different MPC unit compositions, and poly(2-hydroxyethyl methacrylate). Surface analysis by dynamic contact angle measurement revealed that the mobility of the polymer chain on the PET substrate depended on the MPC unit composition, but there was no significant difference between the PMBs with 3-10 mol% MPC units and poly(HEMA). Fibronectin adsorption on the polymer surface from a cell culture medium was determined by immunoassay. The adsorbed fibronection was evenly distrubuted in every polymer, however, the amount was reduced with an increase in the MPC unit composition in the PMB. This result suggested that the MPC unit could weaken the interaction between the polymer surface and proteins. When fibroblast L-929 cells, were cultured on the polymers, the cells adhered and the number of cells increased on not only the hydrophobic poly(BMA) but also on the hydrophilic poly(HEMA). However, the number of cells that adhered on the PMB surface decreased with an increase in the MPC unit composition. This was a result of the fibronectin adsorption behavior. Thus, it could be concluded that since the PMB could suppress cell adhesion proteins e.g. fibronectin, the PMB showed excellent cell adhesive resistance properties.     

Adhesion of coagulase-negative staphylococci to methacrylate polymers and copolymers

Adhesion of coagulase-negative staphylococci (CNS) was studied onto a homologous series of methacrylate polymers and copolymers. The materials varied in wettability (contact angles) and were either positively or negatively charged (zeta-potential). Bacterial adhesion experiments performed in a parallel-plate perfusion system showed that positively charged TMAEMA-Cl copolymers significantly promoted the adhesion of CNS as compared with all other methacrylate (co)polymers tested. The bacterial adhesion rates onto the positively charged surfaces are diffusion-controlled, whereas those onto the surfaces with a negative zeta-potential are more surface-reaction-controlled due to the presence of a potential energy barrier. The bacterial adhesion rates onto various poly (alkyl methacrylates) were similar. The number of adhering bacteria onto the negatively charged MMA/MAA copolymer did not differ from that onto pMMA, indicating that sufficient sites on the copolymer surface with the same potential energy barrier as that on pMMA, were available for adhesion. Decreasing rates of adhesion of CNS were observed onto MMA/HEMA copolymers with increasing HEMA content coinciding with increasing hydrophilicity. Low plateau values for the bacterial adhesion were observed on 50MMA/50HEMA, pHEMA, and 85HEMA/15MAA, indicating that the adhesion onto these materials was reversible. Four CNS strains with different surface characteristics all showed higher numbers of adhering bacteria onto 85MMA/15TMAEMA-Cl than onto 85MMA/15MAA and pMMA.     

Using pH-sensitive hydrogels containing cubane as a crosslinking agent for oral delivery of insulin

The goal of oral insulin delivery devices is to protect the sensitive drug from proteolytic degradation in the stomach and upper portion of the small intestine. Copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) based hydrogels containing 2, 4, and 6% of a crosslinking agent (CA) were studied as drug delivery systems. Cubane-1, 4-dicarboxylic acid (CDA) was linked to two HEMA groups as CA. Radical copolymerizations of HEMA and MAA with the various ratios of CA were performed at 70 degrees C. The compositions of the crosslinked three-dimensional polymers were determined using Fourier transform infrared spectroscopy. Glass-transition temperature of the network polymers was determined calorimetrically. The effect of copolymer composition on the swelling behavior and hydrolytic degradation was studied in simulated gastric fluid (pH 1) and simulated intestinal fluid (pH 7.4). The swelling and hydrolytic behavior of the copolymers was dependent on the content of MAA groups and caused a decrease in gel swelling in simulated gastric fluid or an increase in gel swelling in simulated intestinal fluid. The drug-release profiles indicate that the amount of drug release depends on their degree of swelling and crosslinking.     

Rat peritoneal macrophage adhesion to hydroxyethyl methacrylate-ethyl methacrylate copolymers and hydroxystyrene-styrene copolymers

Macrophage adhesion to a wide variety of substrates has been measured, but no systematic study of the influence of specific substrate chemical properties on adhesion is available. These studies were conducted using two series of materials, copolymers of hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) and copolymers of hydroxystyrene and styrene, to determine the effect of a single chemical property, polar character, on adhesion. Rat peritoneal macrophages were allowed to contact polymer substrates for periods ranging from 1 to 240 min before being subjected to a shear stress of 60-120 dynes/cm2 in a thin-channel flow cell. Percentage adhesion was calculated from the number of cells that remained adherent to the substrate after 30 s of applied shear stress. Macrophages remained adherent to 100% EMA and all hydroxystyrene-styrene copolymer surfaces after only 1 min of contact. In copolymers of the HEMA-EMA series, the time required to attain peak adhesion levels increased with increasing substrate hydrophilicity (increasing HEMA content). Cells did not attach to the 20% EMA/80% HEMA copolymer and the 100% HEMA polymer. The results demonstrate that there is a time delay between contact and adhesion of the cells to surfaces of increasing hydrophilicity within the HEMA-EMA series and no time delay with the hydroxystyrene-styrene series. The time delay is thought to be a function of the excluded volume provided by polymers that are able to undergo significant chain rotation and or swelling in the solvent, water. Small excluded volumes present in copolymers of high EMA content and all hydroxystyrene-styrene copolymers offer little or no resistance to formation of adhesive bonds by macrophages, whereas copolymers with large excluded volumes (high HEMA content) prevent contact and/or adhesion. A mechanism based on the net excluded volumes of both the cell and substrate surface macromolecule is proposed to explain this phenomenon.     

Effect of bifunctional comonomers on mechanical strength and water sorption of amorphous calcium phosphate- and silanized glass-filled Bis-GMA-based composites

This study seeks to elucidate structure-property relationships in a series of unfilled dental copolymers and their composites. The copolymers/composites were derived from photo-activated binary monomer systems based on 2,2-bis[p-2'-hydroxy-3'-methacryloxypropoxy)phenyl] propane (Bis-GMA) and equimolar amounts of a bifunctional, surface-active comonomer, i.e., 2-hydroxyethyl methacrylate (HEMA), glycerol dimethacrylate (GDMA) or ethylene glycol methacrylate phosphate (PHEMA). Triethyleneglycol dimethacrylate, a widely used comonomer for Bis-GMA, was used as a control. Two types of fillers were investigated: (1) a hydrophilic, silica-modified amorphous calcium phosphate (Si-ACP) and (2) a more hydrophobic, silanized nanosized silica (n-SiO(2)). Both the unfilled copolymers and their composites were evaluated for biaxial flexure strength (BFS), both dry and wet after 30 days immersion in buffered saline, and for water sorption (WS) and their WS kinetic profiles. The Bis-GMA copolymers and composites derived from HEMA and GDMA had BFS and WS values, as well as WS kinetic profiles, similar to the controls. Copolymers and composites based on Bis-GMA/PHEMA had lower BFS and higher WS values. Si-ACP composites had significantly lower BFS values (that were further diminished on soaking) than their copolymers. WS increased as the level of this filler was increased except for Bis-GMA/PHEMA composites. With n-SiO(2) as the filler, a more moderate reduction in BFS occurred compared to the unfilled copolymers. By contrast to Si-ACP composites, the WS of all the n-SiO(2) composites decreased with increasing filler level. From this study it is evident that both the chemical structure of the polymer matrix and the type of filler system can have significant effects on the strength and water-related properties of dental composites.     

Inhibition of fibroblast cell adhesion on substrate by coating with 2-methacryloyloxyethyl phosphorylcholine polymers

Fibroblast adhesion and growth behavior were examined on various polymers coated on a poly(ethylene telephthalate) (PET) substrate. The polymers are poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylatel copolymer (PMB)s with different MPC unit compositions, and poly(2-hydroxyethyl methacrylate). Surface analysis by dynamic contact angle measurement revealed that the mobility of the polymer chain on the PET substrate depended on the MPC unit composition, but there was no significant difference between the PMBs with 3-10 mol% MPC units and poly(HEMA). Fibronectin adsorption on the polymer surface from a cell culture medium was determined by immunoassay. The adsorbed fibronection was evenly distrubuted in every polymer, however, the amount was reduced with an increase in the MPC unit composition in the PMB. This result suggested that the MPC unit could weaken the interaction between the polymer surface and proteins. When fibroblast L-929 cells, were cultured on the polymers, the cells adhered and the number of cells increased on not only the hydrophobic poly(BMA) but also on the hydrophilic poly(HEMA). However, the number of cells that adhered on the PMB surface decreased with an increase in the MPC unit composition. This was a result of the fibronectin adsorption behavior. Thus, it could be concluded that since the PMB could suppress cell adhesion proteins e.g. fibronectin, the PMB showed excellent cell adhesive resistance properties.     

MPC-BMA共聚物的合成及其血小板粘附行为研究

本研究首先合成了含有磷酸胆碱基团的单体2-甲基丙烯酰氧乙基-2′-三甲胺乙基磷酸酯.内盐(MPC)和甲基丙烯酸正丁酯(BMA)的共聚物,采用红外光谱对其主要基团进行了表征分析,利用血小板粘附实验研究了磷脂聚合物膜的血小板粘附性,通过扫描电镜对血小板在聚合物膜上的形态和粘附量进行观察。结果表明:MPC含量越高,血小板的粘附量和变形程度越小;与其它亲水性单体如HEMA、HPOEM360、HPOEM526相比,等量MPC更能有效的降低其聚合物膜的血小板粘附性。     

Surface characterization of 2-hydroxyethyl methacrylate/styrene copolymers by angle-dependent X-ray photoelectron spectroscopy and static secondary ion mass spectrometry

The surface composition and structure of three structurally distinct amphiphilic copolymers of 2-hydroxyethyl methacrylate (HEMA) and styrene have been examined with angle-dependent X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS). The phase-separated block copolymer made by anionic living polymerization, HSH-A50, showed significant surface enrichment of styrene. The outermost 2-3 Å appeared to be ~100% styrene, with the styrene concentration decreasing to its bulk value at a depth of ~50 Å from the surface. However, HEMA was detected in the outer 20 Å of this copolymer. The presence of HEMA in the surface region implies this copolymer may undergo significant restructuring when hydrated in a hydrophilic environment (as opposed to the hydrophobic environment in which the sample was prepared and analyzed). The phase-separated block copolymer made by telechelic coupling of free radical polymerized functionalized oligomers, HSH-B60, showed only slight styrene enrichment at the surface. Both HEMA and styrene were detected at all sampling depths, including the outermost surface layer, consistent with the presence of discrete HEMA and styrene domains at the copolymer surface. Since both components are already present at the surface under hydrophobic conditions, the degree of restructuring this copolymer may undergo upon hydration should be minor. The random HEMA-styrene copolymer made by conventional free radical initiation techniques, HS-RAN50, had a surface composition that was similar to the bulk composition and independent of depth, as expected for a homogeneously mixed copolymer film.     

Hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) copolymers for cell microencapsulation: effect of HEMA purity

Thermoplastic copolymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) (molar ratio: 75/25 HEMA-MMA) were synthesized using HEMA containing different amounts of ethylene glycol dimethacrylate (EGDMA) to investigate their suitability for cell microencapsulation. Pure HEMA (0.0% EGDMA) was obtained with preparative chromatography to prepare a linear copolymer. Microcapsules (with a diameter of 300-400 microm) were readily made with the copolymers by interfacial precipitation. Smaller and more transparent capsules were obtained using the copolymer prepared from purer HEMA. Chinese hamster ovary (CHO) fibroblasts, as model cells, were microencapsulated in the linear copolymer. The CHO cells survived the microencapsulation process and the metabolic activity of the encapsulated cells increased within the 14 days observation period.     

Surface characterization of 2-hydroxyethyl methacrylate/styrene copolymers by angle-dependent X-ray photoelectron spectroscopy and static secondary ion mass spectrometry.

The surface composition and structure of three structurally distinct amphiphilic copolymers of 2-hydroxyethyl methacrylate (HEMA) and styrene have been examined with angle-dependent X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS). The phase-separated block copolymer made by anionic living polymerization, HSH-A50, showed significant surface enrichment of styrene. The outermost 2-3 A appeared to be approximately 100% styrene, with the styrene concentration decreasing to its bulk value at a depth of approximately 50 A from the surface. However, HEMA was detected in the outer 20 A of this copolymer. The presence of HEMA in the surface region implies this copolymer may undergo significant restructuring when hydrated in a hydrophilic environment (as opposed to the hydrophobic environment in which the sample was prepared and analyzed). The phase-separated block copolymer made by telechelic coupling of free radical polymerized functionalized oligomers, HSH-B60, showed only slight styrene enrichment at the surface. Both HEMA and styrene were detected at all sampling depths, including the outermost surface layer, consistent with the presence of discrete HEMA and styrene domains at the copolymer surface. Since both components are already present at the surface under hydrophobic conditions, the degree of restructuring this copolymer may undergo upon hydration should be minor. The random HEMA--styrene copolymer made by conventional free radical initiation techniques, HS-RAN50, had a surface composition that was similar to the bulk composition and independent of depth, as expected for a homogeneously mixed copolymer film.     

Synthesis and characterization of polyamine graft copolymers with a poly(2-hydroxyethyl methacrylate) backbone

Radical copolymerizations were carried out with 2-hydroxyethyl methacrylate (HEMA) and a polyamine macromonomer ( 1 ). ¹H NMR, IR, liquid chromatography and turbidity measurements showed the polymer obtained to be poly[(HEMA)-graft-polyamine]. The monomer reactivity ratio for the polyamine macromonomer was found to be similar to that of a low-molecular-weight analogous monomer. Microphase separated structure was observed on thin films of the copolymer by means of transmission electron microscopy. Using the column method, the biomedical behavior of the copolymer was estimated in terms of its interaction with rat lymphocytes. Strikingly, the copolymer surface was found to differentiate the lymphocyte subpopulations without any added adjuvant protein.     

Controlled release of cyclosporine from VP-HEMA copolymer systems of adjustable resorption monitorized by MEKC

Soluble, uncrosslinked and high molecular weight copolymers of vinylpyrrolidone, VP, with 2-hydroxyethyl methacrylate, HEMA, prepared by free radical copolymerization, are proposed as supports for the modulated release of drugs, taking cyclosporine as a model system. The copolymerization parameters described as reactivity ratios, rVP = 0.08 and rHEMA = 7.97, indicate that the copolymer systems prepared at high conversion have two main components with a microstructural arrangement which depends on the average composition, i.e., an initial HEMA-rich copolymer and a final PVP homopolymer or VP-rich copolymer. This microstructural distribution controls the resorption rate of the polymeric support and therefore the release process of cyclosporine which is demonstrated experimentally by the application of a modern technique known as micellar electrokinetic capillary chromatography (MEKC).     

The short-term blood biocompatibility of poly(hydroxyethyl methacrylate-co-methyl methacrylate) in an in vitro flow system measured by digital videomicroscopy

An in vitro flow system for short-term blood biocompatibility testing of solution-castable polymeric biomaterials was developed. This system was relatively free of artefacts resulting from blood contact with materials other than the test material itself. In conjunction with epifluorescence videomicroscopy and digital image processing, this method provided a high resolution, quantitative, continuous analysis of platelet adhesion, aggregation, thrombus formation, and embolization on the biomaterial surface. This system was well suited for performing biochemical assays on post-contact blood for assessment of platelet activation and release as additional measures of the thrombogenicity of the test material. This method for biomaterials evaluation in vitro was demonstrated by a detailed examination of copolymers of hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA). Videomicroscopic analysis of fluorescently labelled platelets adhering per unit area of the polymer surface after 5 min of flow at a wall shear rate of 500 s-1 showed a dramatic decrease with increasing HEMA fraction in the polymer. The release of serotonin and thromboxane A2 by platelets decreased with increasing HEMA fraction. Reflection interference contrast microscopy was used to examine focal contacts of platelets on the copolymer surfaces as a qualitative measure of the platelet-surface interaction. A polymer-dependent gradation in contact extent and morphology was observed, ranging from large contacts on P(MMA) to none on P(HEMA).