Immobilized polyethylene glycol (PEG) reduced the amount of bovine serum albumin (BSA) adsorbed on polyvinyl alcohol (PVA) hydrogel, but did not reduce the platelet reactivity of the hydrogel surface. PEG, molecular weight (MW) 2000 or 5000, with or without a monomethoxy end group, was covalently bound to glutaraldehyde-crosslinked PVA either through a cyclic acetal or an urethane functional group with a surface coverage of 70% (as measured by x-ray photoelectron spectroscopy [XPS]). Immobilization of monomethoxy-PEG via a cyclic acetal reduced BSA adsorption to PVA from 11 t 2 nmol/mz to 3.9 2 0.3 nmol/m2 and 3.3 2 0.3 nmol/m2 for MW 2000 and 5000, respectively. Similarly, urethane bound PEG reduced adsorption to 3.5 % 1.6 nmol/m2 for MW 2000 and 5.4 +-1.0 nmol/m2 for MW 5000. Whole blood clotting times of PVA (using a Chandler loop) were not affected by covalently linked PEG, although the initial rate of thrombin generation at the surface, measured using a fluorogenic substrate, was marginally reduced; a rate constant of 4.2 2 0.1 cm/sec and 3.5 t 0.1 cm/sec were obtained for MW 2000 and 5000, respectively, compared to 5.6 2 1.0 cm/sec for PVA. Ex vivo evaluation using a canine arteriovenous shunt revealed that the hydrogel, with or without bound PEG, reduced circulating platelet levels by 35-70% after 4 days. The initial fractional rate of platelet destruction determined from measurement of platelet cyclooxygenase activity, indicated that cyclic acetal or urethane bound PEG of either molecular weight had no effect on platelet consumption produced by PVA.
The PEG hypothesis at least as it relates to platelet interactions may need to be evaluated further in the light of these results.