Surface modification with PEO-containing triblock copolymer for improved biocompatibility:: In vitro and ex vivo studies

Poly(ethylene oxide) (PEG) has been frequently used to modify biomaterial surfaces for improved biocompatibility. We have used PEO-polybutadiene-PEO triblock copolymer to graft PEG to biomaterials by gamma-irradiation for a total radiation dose of 1 Mrad. The molecular weight of PEG in the block copolymer was 5000. In vitro study showed that fibrinogen adsorption to Silastic(R) polyethylene, and glass was reduced by 70 similar to 95% by PEO grafting. On the other hand, the reduction of fibrinogen adsorption was only 30% on expanded polytetrafluoroethylene (e-PTFE). III vitro platelet adhesion study showed that almost no platelets could adhere to PEG-coated Silastic(R), polyethylene, and glass, while numerous platelet aggregates were found on the ePTFE. The platelet adhesion in vitro corresponded to the fibrinogen adsorption. When the PEG-grafted surfaces were tested ex vivo using a series shunt in a canine model, the effect of the grafted PEG was not noticeable. Platelet deposition on ePTFE was reduced by PEO grafting from 8170 +/- 1030 to 5100 +/- 460 platelets 10(-3) mu m(2), but numerous thrombi were still present on the PEG-grafted surface. The numbers of platelets cumulated on Silastic(R), polyethylene, and glass were 100 +/- 80, 169 +/- 35, and 24 +/- 22 platelets 10(-3) mu m(2) respectively. This is about 35% reduction in platelet deposition by PEO grafting. While the numbers of deposited platelets were small, the decreases were not as large as those expected from the in vitro study. This may be due to a number of reasons which have to be clarified in future studies, but it appears that in vitro platelet adhesion and fibrinogen adsorption studies may not be a valuable predictor for the in vitro or ex vivo behavior of the PEG-grafted surfaces.