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Increased crosslink density increases the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) acetabular components used in total hip reconstructions. However, increasing crosslink density can reduce the mechanical properties of UHMWPE. Other researchers have tried to limit the crosslinking to a superficial layer on the articulating surfaces to retain the properties of the virgin polymer. We present here a method of producing a gradient of crosslink density across the acetabular component. Acetabular liners with 26 mm inner diameter were machined from the UHMWPE. The liners were then irradiated at 140 degrees C in the molten state of the polymer using a 2 MeV electron beam with limited penetration of the effects of radiation into polyethylene. The liners were then machined to an inner diameter of 32 mm to remove the radiation induced oxidized surface layer. The limited penetration of the e-beam resulted in a gradient of crosslink density with a crosslink density of 0.15 +/- 0.01 mol/dm3 near the articulating surfaces and 0.12 +/- 0.01 mol/dm3 near the backside. The concentration of the trans-vinylene unsaturations decreased gradually as a function of depth from the articulating surfaces to the backside of the liners. The wear resistance of the melt-irradiated liners was contrasted with those of conventional liners using the Boston hip simulator. The gravimetric wear rate was 27 +/- 5 mg million cycles with the conventional liners, while the melt-irradiated acetabular liners did not show any weight loss.

Molecular rearrangements and alterations in supermolecular structure of ultra high molecular weight polyethylene (UHMWPE) due to cross-linking and oxidation-induced chain scission following irradiation and subsequent storage in air at room temperature have been studied over a period of 29 months. The techniques that were used are: equilibrium swelling in decalin, differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR) and electron spin resonance (ESR). The experimental results indicate that immediately after irradiation, cross-linking and an increase in crystallinity are the important processes. With time, chain scission induced by oxidation takes place resulting in a new phase of thinner crystallites in the amorphous region. In the absence of oxygen diffusion limitations, the free radicals survive for 30 months in the form of peroxides. The effect produced by higher doses and shorter aging times correspond to those produced by lower doses and longer aging times, thus, suggesting a superposition law between dose and aging time.

A new method was developed for binding poly-(ethylene oxide) (PEO) to polymer surfaces that involves the use of electron beam irradiation in two steps. In the first, methacrylic acid was grafted and polymerized to a polymer surface, changing it from hydrophobic to hydrophilic. Exposure of this surface to aqueous PEO solutions resulted in strong hydrogen bonding of the PEO, which was covalently grafted in a second radiation step. The PEO grafts were stable; they could not be removed with extensive washing with water, soaking in basic solution, or gentle mechanical scraping. Both monolayers and multilayers of PEO were formed. The density of the monolayers were found to have little dependence on the molecular weight or concentration of the PEO solution; multilayers could be controlled by varying the viscosity of the PEO solution and the method of application. The PEO-grafted monolayers were tested for their ability to prevent protein adsorption of cytochrome-c, albumin, and fibronectin. Monolayers of star PEO were the most effective, at best showing a 60% decrease in adsorption from untreated controls. One million molecular wight linear PEO monolayers were almost as effective as star monolayers, and 35,000 g/mol linear PEO was bound too closely to the surface, owing to its small size, to have much impact in preventing protein adsorption. The reason for the continued protein adsorption was believed to be due to a close grafting of the PEO to the surface, as well as the grafted methacrylic acid chains being long enough to extend through the PEO monolayer, thus being accessible on the surface.

Gamma irradiation of Ultrahigh Molecular Weight Polyethylene (UHMWPE) leads to long-lived free radicals which react with oxygen. Diffusion of oxygen, occurring over months or years, controlled by the permeability characteristics of the polymer, results in progressive oxidation, breaking of polymer chains, alteration of the crystalline portion of the polymer, and deterioration of the mechanical properties of the polymer. This paper reviews the observations in the literature on this issue and then presents a conceptual model concerning the interplay of radical diffusion, oxygen diffusion, non-uniform permeability, and free-radically driven chain reactions in order to explain these observations. The suggested model is based on literature that is available on the oxidation of linear polyethylenes during and after irradiation. The model directs the attention of researchers in the field of orthopaedic implants to the complexity of the process and the variety of issues and parameters to be considered while studying the long-term effects of radiation sterilization on UHMWPE.

This study involves an examination of the changes in the rheological behavior (specifically the non-Newtonian viscosity) of blends of various starches with a synthetic polymer (polyethylene-co-vinyl alcohol) as a result of irradiation-modification. The results are generally consistent with fact that starch degrades substantially upon irradiation, while the synthetic polymer is relatively unaffected. However, the high-amylose starch-containing blends are less sensitive to irradiation than we would expect ; this is attributed to possible interactions between the linear molecules from the high-amylose starch and the synthetic polymer.

Irradiation-modification of the blends of various starches with a synthetic polymer [poly(ethylene-co-vinyl alcohol)] was carried out using an electron beam. The effect of irradiation on neat starches was studies using gel permeation chromatography. Changes in the thermal and mechanical properties of the blends, as well as in their microstructures, were also evaluated. The data indicate, consistent with other reports in literature, that starch molecules fragment under the effect of ionizing radiation, while the EVOH is relatively unaffected. These substantial (mainly physical) modifications to the starch molecules manifest themselves in changes in the thermal behavior of the blends. Furthermore, the mechanical properties of filaments obtained from molten irradiated pellets were quite different from those of control filaments, at least for some starches. Micrographic examination of some blends indicated a correspondence between a modification in the microstructure of the filaments and a change in their mechanical properties. It seems likely that the enhanced mobility of the fragmented starch molecules in the melt is responsible for these changes in the microstructure and concomitantly, the mechanical properties of the blend. Such an irradiation-based physical modification of starch may be of use in tailoring the properties of commercial blends of starches with synthetic thermoplastics. © 1996 John Wiley & Sons, Inc.

Under ionizing radiation aqueous solutions of water-soluble polymers become cross-linked and form hydrogels, primarily by radiolysis of water-generating hydroxyl radicals which attack the polymer chains. The chain radicals thus formed create cross-links by coupling. In particular, hydrogels formed from poly(ethylene oxide) are of interest for biomedical applications, including those in which it is necessary to transport large molecules such as growth factors, in addition to nutrients, to cells attached to the surface. We sought a rapid and simple method for estimating diffusion coefficients by observing the diffusion of two red-coloured proteins: cytochrome C and hemoglobin of respective molecular weights 12,000 and 67,000. In the course of this we discovered a previously unreported effect of the primary molecular weight of the polymer, before cross-linking, on the cross-link density finally achieved and on the diffusion coefficient of the proteins.

This work examines the properties of starch esters for their possible application as environmentally degradable thermoplastics. The rheological, thermal, and mechanical properties of a series of fatty-acid esters of high-amylose starch (as well as the effects of adding plasticizer on some selected properties) were evaluated. The ester group acts like an internal plasticizer, with an increase in the size of the fatty-acid chain, resulting in greater internal plasticization. This is reflected in the rheological and thermal measurements as well as in the mechanical properties. Overall, larger ester groups and the addition of external plasticizer make these starch-based materials more processable and more ductile. However, comparing their properties and cost to commodity thermoplastics leads us to believe that their commercial applications are likely to be limited, at least in the near future. © 1995 John Wiley & Sons, Inc.

We demonstrate that a bilayer composite hydrogel composed of corneal stroma crosslinked to poly(ethylene oxide) provides a substrate suitable for wound healing behavior of corneal epithelial cells and for formation and maintenance of a stable multilayered epithelium. Potential diffusion-limitation of nutrients or regulatory molecules across the hydrogel was investigated experimentally with a new in vitro ocular assay, using epithelial cell migration as an index of molecular diffusion limitations. Corneal epithelial cells explanted on the composite hydrogel in vitro exhibited morphology similar to those in vivo, and migrated effectively over the stromal surface. Importantly, our system yielded multilayered epithelium like that found in normal corneal tissue under conditions that closely simulate the in vivo physiologic arrangement. In addition, our results indicate that molecules of substantially greater molecular weight than glucose appear to control the cell migration rate. Thus, engineering design of this composite hydrogel system may allow it to be useful in corneal wound healing applications.

This study focuses on the molecular fragmentation of starch as a result of extrusion-based thermomechanical processing. Gel permeation chromatography-light scattering and bulk intrinsic viscosity measurements were used for the macromolecular characterization. The data indicate that the extrusion processing of starch results in a reduction in its molecular weight. Such a fragmentation of the starch polymer could be attributed, at least partly, to debranching of the molecules.

An analytical method for estimating the lag between concentration and molecular-mass-sensitive detectors has been developed. This method is simple in its approach and does not require any knowledge about the molecular mass distribution of the polymer sample used in the analysis. The elution behavior results obtained using the lag value from this method correlate well with those obtained from the traditional gel permeation chromatography peak calibration method.

Whereas it has been commonly thought that adding polyethylene oxide PEO to a surface would diminish the capacity of the surface to cause deposition of platelets and of fibrinogen, and to activate complement C3, we present data showing exactly the opposite. These unexpected results are obtained with low molecular weight (2000) PEO, and are not found with higher molecular weight (20,000) PEO.

A series of crosslinked polymer networks formed from hydrophilic polyethylene oxide (PEO) and a hydrophobic polysiloxane (PGPMDMS) were studied with respect to the partitioning and release of five tricyclic antidepressants (TCAs) at pH 7.4. The TCAs, chemical analogues of one another, have both nonpolar and ionic characteristics at pH 7.4, but differ considerably in hydrophobicity. In PEO-PGPMDMS copolymer networks, the partition coefficient of protriptyline (the TCA studied most extensively) was observed to be higher than in networks of PEO or PGPMDMS singly. This finding, which may represent adsorption of the amphiphilic drug at interfacial sites between hydrophilic and hydrophobic phases within the copolymeric network, shows that in some cases, higher drug loadings of amphiphilic drugs can be obtained with a hydrophilic-hydrophobic copolymer compared with a material made of only one polymer. As the PEO content in PEO-PGPMDMS networks was increased from 20 to 100%, the release rate of protriptyline increased by greater than 1000-fold. Thus, a key variable in achieving a desired release rate is the PEO content of the copolymer. On the other hand, release rates of the five TCAs from PEO-PGPMDMS networks containing 50% PEO varied by a factor of less than 3. Thus, minimal effect on drug release rates was obtained by using a different TCA analogue.

Networks of cross-linked poly(ethylene oxide) and a polyether-substituted polysiloxane were synthesized containing (i) variations of PEO content, (ii) PEO systematically varied from low to high molecular weight, and (iii) pentafunctional glycidoxy derivitized siloxane oligomers which acted as cross-linking units for both polymer components. Surface chemical analysis by ESCA demonstrated improved PEO surface coverage with increasing PEO content and molecular weight. This observation and the relative enhancement of surface silicon content with respect to the calculated bulk value were interpreted in terms of free energy minimization, chain overlap, and phase mixing.

Interpenetrating polymer networks (IPNs) of poly(ethylene oxide) (PEO) and a polyether substituted polysiloxane were synthesized containing variations of PEO content (35 and 65% dry network weight) and PEO systematically varied from low to high molecular weight (2,000, 8,000, and 20,000). Biocompatibility was assessed by measureing 111In platelet deposition in a baboon femoral ex vivo shunt. Mass transfer analysis revealed that platelet transport to PEO/polysiloxane surfaces was kinetically limited and correlated with both PEO content and molecular weight. Differences in material performance were noted particularly after the initial 30 min blood contact period. In mid and high PEO molecular weight networks (8,000 and 20,000), reduced platelet deposition was noted with increased PEO content. In materials of high PEO content (65%), mid and high PEO molecular weight samples had significantly lower levels of platelet adsorption than PDMS (60 min; p< 0.05) or networks of low PEO molecular weight, coded 2K-65 (30 and 60 min; p < 0.05). The lowest level of platelet deposition was noted on 20K-65 networks, less than one platelet per 1,000 μm2.

In this paper, we describe the synthesis of copolymeric networks made from poly(ethylene oxide) (PEO) and a derivative of low-molecular-weight polydimethylsiloxane containing multiple glycidoxy functions (PGPMDMS). Upon addition of boron trifluoride etherate to homogeneous dichloromethane solutions of PEO and PGPMDMS, networks form via cationic ring opening of the glycidoxy groups, which add the terminal PEO hydroxyl and also homopolymerize. The molecular weight of PEO in the networks was varied from 690 to 17 700 and the PEO content was varied from 0 to 84 wt%. The reaction is sensitive to traces of water and the final network structure is affected by catalyst concentrations above 0.030 M. The networks containing PEO swell in water, and equilibrium swelling increases as the content of PEO increases. Equilibrium swelling does not increase with increases in PEO molecular weight because of intermolecular homopolymerization of PGPMDMS. Intentional oxidative degradation of the PEO component in these networks demonstrates that, for certain PEO-PGPMDMS compositions, a continuous PGPMDMS phase is formed. Because of the wide range of compositions that can be obtained, these networks are being used as a model system for studies on drug-releasing properties of hydrogels and on the blood compatibility of PEO-based materials.

A variety of affinity cross-flow filtration (ACFF) experiments were conducted to evaluate the technique as a means of effectively separating biomolecules. Agarose particles, which contained a specific affinity ligand for the targeted protein, were used as “affinity escorts” in the ACFF process. Both conventional agarose particles (40–150; μm) and small agarose particles (Superose, 11–15 μm.) were used as the basis for affinity escorts. Batch ACFF washing experiments were conducted in both constant-volume and volume-reduction modes and compared with model predictions. The different affinity ligand-adsorbate systems studied include Cibacron Blue and human serum albumin, Cibacron Blue and lysozyme, protein A and immunoglobulin G, and concanavalin A and horseradish peroxidase.

The present work discusses the grafting by electron beam irradiation of poly(ethylene oxide) (PEO) star-shaped polymers onto porous expanded polytetrafluoroethylene (EXPTFE) surfaces. The resulting materials are intended to combine the good biocompatible properties of PEO with the outstanding mechanical properties of PTFE. The star-shaped PEOs were synthesized via anionic polymerization. 3 Mev electron beam irradiation was applied to graft these PEO stars onto porous EXPTFE surfaces. The hydrophobic EXPTFE surface had to be pre-modified with N-vinylpyrrolidone. ESCA was used to quantify the amount of grafted star-shaped PEO. Unmodified EXPTFE surfaces are well known, when implanted in a body, to be rapidly covered by a layer of cells and fibrin. The EXPTFE coated with PEO were implanted in the peritoneal cavity of rats (or under the back skin). This implantation did not induce any inflammation reactions and SEM analysis had attested the absence of adsorbed cells and fibrin. The glucose diffusion properties of these membranes were studied by a lag time analysis method and compared to those of pure PEO hydrogels. As expected, glucose diffuses through the hydrogel coated membrane and diffusion is not affected by the presence of the EXPTFE membrane.

Poly(ethylene oxide) (PEO) polymer, in linear and star form, was covalently grafted to silicon surfaces, and the surfaces were tested for their ability to adsorb proteins. Linear PEG of molecular weight 3400, 10 000, and 20 000 g/mol and star PEO molecules were coupled via their terminal hydroxyl groups activated by tresyl chloride to aminosilane-treated silicon wafers. The amount of PEO coupled to the surface was varied by changing the concentration of the tresyl-PEO solution. The dry PEO thickness on the surface was measured using X-ray photoelectron spectroscopy (XPS) and ellipsometry, from which the grafting density was calculated. The PEO surfaces were exposed to solutions of each of three proteins: cytochrome-c, albumin, and fibronectin. The degree of adsorption of each protein was determined by XPS and ellipsometry and recorded as a function of PEO grafting density. All three proteins were found to reach zero adsorption at the highest grafting densities on all three PEG surfaces, which for all three PEG surfaces was a PEO content of 100 +/- 10 ng/cm2. On both star PEO surfaces, albumin and fibronectin decreased to zero adsorption at intermediate values of grafting density, whereas cytochrome-c continued to adsorb at all grafting densities, although with a decreasing trend. A physical model of the surface helped explain these protein adsorption results in terms of the spacing and degree of overlap of grafted PEO chains.

We describe the synthesis and in vitro biological characterization of a new class of carbohydrate-modified hydrogels based on radiation-cross-linked star polyethylene oxide (PEO). Hydrogels were synthesized from either of two types of PEO star molecules in order to vary the terminal hydroxyl content of the gels while keeping other gel properties such as molecular weight between cross-links and water content constant. The resulting gels were covalently modified with monosaccharide ligands and the behaviour of primary rat hepatocytes on the modified gels was evaluated under culture conditions. Hepatocytes exhibited a sugar-specific adhesion to the modified gels, adhering to gels bearing galactose but not glucose. Cell spreading was observed on both types of galactose-modified PEO star gels; moreover, the gels supported long-term (6 d) culture and differentiated function of primary hepatocytes. Further, on comparing the cell spreading behaviour observed on the PEO star gels with that reported previously for galactose-modified polyacrylamide, we find that our gels elicit spreading at ligand concentrations lower by an order of magnitude. A simple mechanistic analysis indicates that this enhanced ability of PEO star gels to support spreading of primary hepatocytes on low concentrations of immobilized galactose derives from freedom of the immobilized ligands to come within sufficiently close proximity to mimic a high-affinity branched oligosaccharide.

Two ‘families’ of polymers applicable to preservation and restoration are discussed: (i) polysiloxane networks generated by platinum catalyzed addition of vinyl silane precursors to hydrogenosilane precursors; and (ii) acrylic compositions generated by redox initiated polymerization of acrylic monomers in the presence of fine spherical acrylic polymer particles. In both cases the end result is achieved at temperatures between ambient and 60°C, and with negligible volumetric shrinkage.

A new method has been developed for the covalent attachment of poly(ethylene oxide) to various polymeric surfaces for use in biomedical applications. Methacrylic acid (MA) monomer was first grafted to low-density polyethylene (LDPE) or polystyrene (PS) sheets by placing them in a solution of 10–20% (v/v) methacrylic acid in water followed by electron beam irradiation of 2–4 megarads. The methacrylic acid was grafted to the surface and polymerized, resulting in the polymer surface being extremely hydrophilic. The MA-treated samples were placed in a solution of PEO in water (MW 8000 – lx106 g/mol, concentration 0.05–15 % w/v), where the PEO strongly hydrogen bonds to the MA on the surface. The pieces were either rinsed with water (monolayer formation) or drained of excess solution (multilayer formation), then placed under the electron beam for a dose of 2 megarads to graft the PEO to the MA-treated surface. The grafted PEO was stable on the surface, unable to be removed despite extensive washing with water, soaking in basic solution (which would break the hydrogen bonding of the PEO with the acid), or scraping of excess hydrogel from the surface. The monolayer thickness was found to have no dependence on the molecular weight or concentration of the PEO in solution, nor did it have any dependence on the time that the MA-treated samples were soaking in the PEO solution before the second irradiation. This indicates that the PEO molecules immediately lie flat on the surface with few loops or tails, with no exchange taking place after the initial adsorption. All surfaces were analyzed using X-ray photoelectron spectroscopy (XPS), with high resolution carbon Is scans being the principle means of MA and PEO detection in the top 50 angstroms of the surface.

Hydrogels were created by electron beam irradiation of aqueous solutions of poly(ethylene oxide) (PEO) having a nominal molecular weight of 35,000. The molecular weight between cross-links Mc varied from 3000 to 15,000, and the equilibrium volume fractions of polymer V2,s from 0.01 to 0.08. These hydrogels were exposed to aqueous solutions of solutes: tricyclic antidepressants, cyanocobalamin, four globular proteins and three linear species of PEO. Partition coefficients and diffusion coefficients were determined. For each solute the ratio diffusion coefficient in hydrogel/diffusion coefficient in free solution was determined, and related to the hydrogel parameters Mc and v2,s and to the solute effective radius rE (Einstein radius). The diffusion coefficient ratio is greater for the flexible random coiling PEO than for the 'rigid' solutes at a given set of Mc, v2s and rE, and the disparity increases rapidly as rE increases. Among the globular proteins the diffusion coefficient ratio decreases by orders of magnitude with small changes in rE (20.6-27.6 A) and was found to be nearly zero for albumin (rE = 36.1 A). The tricyclic antidepressants had partition coefficients of around 2, whereas the other solutes had partition coefficients of about unity. By reason of the partition coefficient of around 2, the diffusion coefficient ratio of a tricyclic antidepressant having a value of rE = 5.5 A is half that of the larger cyanocobalamin, for which rE = 8.5 A.

Festschrift remark-It was an honor to be invited to honor Allan Hoffman on the occasion of his 60th birthday. It seems like yesterday that Allan and I shared an office in old Building 12 on the M.I.T. campus. At that time Allan had lost a bout with a snow covered mountain while on skis, and consequently moved about awkwardly in our already small room on crutches with a heavy cast. Despite these impediments, he carried on his classroom activities with typical energy. It was even earlier that at M.I.T., under the supervision of Ed Gilliland and myself, he carried out his doctoral research on the radiation grafting of styrene to polyethylene. Both he and I have dabbled in radiation chemistry on and off since then-he far more than I. Neither of us at that epoch had much idea about biomaterials or medical applications of materials-at least I did not-perhaps Allan had it in the back of his mind. The University of Washington, Seattle, is recognized as one of the great centers of biomedical engineering in the wor...

This brief resume is a personal view, offered as a historical narrative to complement the other contributions to this volume dealing with the role of PEO in blood-surface interactions.

A two-layer composite material composed of a thin-layer of corneal tissue and a synthetic polyethylene oxide (PEO) hydrogel is described. The material is designed to provide a suitable substrate for corneal epithelial cell growth while maintaining the desirable characteristics of hydrogels, i.e. clarity, flexibility, and ability to allow diffusive flow of nutrients. The gels are synthesized via electron irradiation induced crosslinking of an aqueous solution of PEO onto a thin layer of collagenous tissue substrate. light microscopic studies indicate that the interface between the corneal tissue and PEO gel appears well adherent with no gaps in the interface. SEM studies of the material surface show an architecture similar to that of normal corneal tissue. Surface analytical techniques were used to identify amino-acids covalently bound to the gel at the gel/collagen interface after the proteinaceous material was removed. ESCA survey scans identified the presence of nitrogen on exposed gel/collagen interfaces and amino acid labelling confirmed the presence of amino acids. ATR-IR studies identifed increased absorption for the gel collagen interfaces at 1640 cm− 1and 1540 cm−1indicative of bound amino acids.

Segmented polyurethanes (SPU) were synthesized with polyethylene oxide (PEO), polypropylene oxide, or polytetramethylene oxide as the “soft segment,” from the respective polyether diols, of which molecular weight varied from 600 to 2000. The “hard segment” was created from ethylene diamine and tolylene diisocyanate or 4,4′-diphenylmethane diisocyanate. Platelet activation was assessed using columns packed with beads coated with each of the SPU by solutions from which the solvent was subsequently evaporated. Citrated whole human blood was passed through the columns and the platelet count in aliquots leaving the columns was compared with the platelet count in blood that had not contacted the column surface. By this method the fraction of platelets retained in the column averaged for several donors, ρ, was determined. In parallel experiments, SPU surfaces formed under identical conditions by evaporation of solvent were examined by X-ray electron spectroscopy for carbon, oxygen, and nitrogen content of the surface. The carbon C1s spectra proved to be particularly useful, when analyzed for the components with peaks respectively at 286 eV (carbon not bonded to an ether oxygen) and at 288 eV (carbon bonded to an ether oxygen). The platelet retention index ρ was found to increase nearly linearly with the ratio of the 286-eV intensity to the 288-eV intensity, and extrapolated to nearly zero for zero value of the intensity ratio, which would correspond to amorphous PEO, suggesting that if a surface were only amorphous PEO it would be remarkably inactive toward platelets. In contrast, nitrogen spectra show no systematic relationship with ρ.

Aqueous poly(vinyl alcohol) solutions were crosslinked via electron-beam irradiation to form transparent hydrogels of varying crosslinking densities. Typical crosslinked hydrogels with anti M/sub c/ between 3500 and 8000 were weak, easily shattered, nonextensible materials with very low tensile moduli (up to 70 psi) and tensile strengths at break (less than 10 psi). Reinforcement by induction of partial crystallization was accomplished by a two-stage drying process, consisting of a slow dehydration stage at room temperature and an annealing stage at elevated temperatures, which was mainly responsible for the introduction of the crystallites. The swollen hydrogels after the annealing process had crystallinities widely varying between 30 and 65 percent and polymer volume fractions between 30 and 60 percent, depending on the temperature--time history of the specimen. These materials showed greatly improved mechanical properties (modulus, ultimate tensile strength, tear strength), as compared to the uncrystallized hydrogels.

The protein film adsorbed at an artificial surface ultimately affects platelet adhesion and activation. This study examines the role of fibrinogen in platelet adhesion at the surface of crosslinked polypropylene glycol (PPG)/polyglycidoxy propyl methyl siloxane (PGPMS) networks which contain polyethylene glycol monomethyl ether (PEGME) chains. These crosslinked networks were produced by reacting the epoxy groups of PGPMS with the hydroxyl groups of the polyethers. PEGME chains were attached covalently to the network at only one end while PPG chains were attached at both ends. The incorporation of PEGME resulted in a substantial reduction in fibrinogen adsorption as compared to the model network (PPG + PGPMS only), but the expected concomitant decrease in platelet adhesion was not observed.