Surface characterization and platelet adhesion studies of aliphatic polyurethanes grafted by fluorocarbon oligomers: effect of fluorocarbon chain length and carboxylic acid group.

The surfaces of aliphatic polyurethane films, which were synthesized by 1,6 hexamethylene diisocyanate, poly(tetramethylene glycol) and 1,4 butanediol, were modified by grafting different chain length of fluorocarbon oligomers. The fluorocarbon oligomers on polyurethane surfaces were terminated with trifluorocarbon or carboxylic acid functionality. The alkyl groups were also grafted onto polyurethane surfaces for comparison. The surface characterization and platelet-contacting property were studied using electron spectroscopy for chemical analysis (ESCA), static contact angle analysis and in vitro platelet adhesion experiments. The effects of fluorocarbon oligomers and their terminal functionalities are discussed. The ESCA results demonstrate the fluorocarbon enrichment at the outmost layer in fluorocarbon oligomer grafted polyurethanes. The fluorocarbon content at the surface increases with increasing the chain length of fluorocarbon oligomers. The fluorocarbon oligomer grafted polyurethanes exhibit highly hydrophobic surfaces, while alkyl groups grafted polyurethanes show relatively hydrophobic surfaces compared with the untreated polyurethane. The in vitro platelet adhesion experiments indicated that the fluorocarbon oligomer and carboxylic acid functionality significantly reduced the number and the degree of activation of the adherent platelets.