Amidine surface modification of poly(acrylonitrile-co-vinyl chloride) reduces platelet adhesion

The surface nitrile groups of solvent-cast polyacrylonitrile-co-vinyl chloride (PAN-VC) films were converted into amidine groups through a two-step process analogous to Pinner's method of 1877. The amidine groups were hypothesized to reduce platelet adhesion and activation through the inhibition of the classical complement pathway, as was noted for benzamidine and pentamidine in earlier studies. A slightly higher nitrogen content was detected on the amidine-surface modified (ASM) samples by X-ray photoelectron spectroscopy relative to the solvent-treated and unmodified controls. Reaction with pentafluoroaldehyde resulted in increased fluorine and decreased nitrogen contents (relative), consistent with the formation of a Schiff base with the primary nitrogen of the amidine on ASM PAN-VC surface. The corresponding yield was 17.2% based on nitrile groups and 9.6% based on all repeating units of the base polymer. Despite this low degree of amidine modification, platelet adhesion was approximately 40% lower on the amidine-modified film compared to the solvent-treated and unmodified controls. The scanning electron micrographs also showed less activation in the adherent platelets. A small reduction in C1s binding was also noted on the amidine-modified surface. Taken together, these results support the notion that amidine modification may be a useful approach to improve the nonthrombogenicity of a biomaterial. However, much effort is required to improve the degree of surface modification and to provide unequivocal evidence linking amidines to the improved thrombogenicity.