Polytetrafluoroethylene-N-vinylpyrrolidone graft copolymers: affinity with plasma proteins

N-vinylpyrrolidone was grafted onto films, grains, and tubes of polytetrafluoroethylene (PTFE) using a radiation procedure. By controlling the experimental conditions, it was possible to obtain an analogous grafting percentage on films and grains. Kinetic grafting onto a tube might be used under certain conditions to preserve both size and water tightness. Poly(vinylpyrrolidone) (PVP)-grafted material became hydrophilic and slightly swollen according to the grafting percentage obtained. A scanning electron microscope (SEM) analysis of polymer surfaces showed preferential polymerization sites at a low radiation dose. A regular, velvet-like surface was obtained for a high grafting percentage induced at a low radiation intensity. Biological properties of PTFE were compared before and after PVP grafting. PTFE appeared to be a nonreactive polymer with respect to the blood-clotting proteins. No significant change was observed using different granulometric sizes of PTFE grains, and its noteworthy inertness was preserved after PVP grafting. Interactions between polymer surfaces and human plasma proteins were analyzed using 125I-isolated proteins. Fibrinogen and immunoglobulins have a high affinity for PTFE; on the other hand, albumin was weakly adsorbed on the polymer surface. Marked changes in protein adsorption were observed after PVP grafting. Hydrophilic group grafting induced an increase of albumin adsorption and a decrease of fibrinogen adsorption. Prothrombin affinity was not significatly affected by modified PTFE. Studies of serum protein adsorption using solid-phase radioimmunoassays were developed with monospecific and polyvalent antisera. After incubation of the whole serum protein and polymer, immunoglobulins were found to exhibit the major part of bound protein radioactivity on the polymer surface. No evidence of increasing adsorption of immunoglobulins from rabbit serum after immunization by PTFE or PTFE/PVP was observed. The immunoglobulin adsorption was submitted to a competitive effect with the other serum proteins. It was possible to postulate the competitive action of albumin, particularly after biological property changes induced by chemical grafting.