In vitro platelet adhesion and in vivo antithrombogenicity of heparinized polyetherurethaneureas

We investigated in-vitro platelet adhesion to polyetherurethaneureas, to which heparin was bound covalently or by ionic bonding. When heparin was bound to polymers, platelet adhesion and platelet activation upon adhesion were suppressed with the increasing content of bound heparin in the polymer. Platelets were activated upon adsorption to different degrees according to the method of heparinization. The platelet adhesion and the platelet activation upon adhesion appeared to be regulated by the electrostatic repulsion between platelet and anionic surface of covalently or ionically heparinized polymer, rather than by the physiological action of bound heparin. The effect of the method of heparinization seemed to be related to the molecular heterogeneity of heparin. Heparinized polyurethanes which interacted very weakly with platelets in vitro were tested for in-vivo antithrombogenicity. The test was carried out by the implantation of a suture of the heparinized polyurethane into canine veins. Ionically heparinized polyurethane did not form a thrombus and maintained a smooth surface over a long period. On the other hand, covalently heparinized polyurethane formed a small amount of thrombus and grew endothelial cells from the insertion point.