Grafting of ethylene glycol-butadiene block copolymers onto dimethyl-dichlorosilane-coated glass by gamma-irradiation.

Amphipathic ethylene glycol-butadiene block copolymers (PEG-PB) with different chain lengths of poly(ethylene glycol) (PEG) were synthesized by reacting poly(ethylene glycol methyl ether) (m-PEG, mol. wt = 350, 550, 750, 2000 and 5000) with telechelic polybutadiene (PB). The PEG-PB copolymers formed were covalently grafted to dimethyldichlorosilane-coated glass (DDS-glass) by gamma-irradiation. The PEG-grafted surface was characterized by measuring advancing and receding contact angles, fibrinogen adsorption, the number of adherent platelets and the area of spread platelets. The grafting efficiency was measured indirectly from the ability of the surface to prevent platelet adhesion. The total dose of gamma-irradiation necessary for grafting of PEG-PB onto DDS-glass in aqueous solutions was less than 0.24 Mrad at atmospheric pressure and ambient temperature. For successful grafting, the surface-adsorbed copolymers should be gamma-irradiated in the presence of water. gamma-Irradiation in the dried state did not result in copolymer grafting. The adsorption of copolymers for 30 min before exposure to gamma-irradiation was enough for effective grafting. The grafting was equally effective whether or not DDS-glass was exposed to the air-copolymer solution interface when the DDS-glass was introduced into the copolymer solution. The copolymers were able to prevent platelet adhesion only when they were adsorbed onto DDS-glass at certain bulk concentrations. Too low or too high copolymer concentrations in the adsorption solution resulted in a surface where platelets could adhere and activate. The range of copolymer concentration which prevented platelet adhesion was larger as the PEG chain length of the grafted copolymers became longer. Our data indicate that platelet-resistant surfaces can be made by grafting PEG-PB onto chemically inert surfaces by a simple gamma-irradiation process.