Improvement of haemocompatibility of metallic stents by polymer coating.

An alternative to open heart surgery in treating arterial diseases causing restricted blood flow is the implantation of intracoronary metallic stents. In spite of the advances in implantation and in spite of the excellent mechanical properties of metallic stents, there are still limitations because of the thrombogenicity of the metal. We have, hence, directed our attention to the coating of metallic stents with an ultrathin polymer layer by chemical vapor deposition (CVD) polymerization of 2-chloroparacyclophan. In a second step of surface modification the poly(2-chloroparaxylylene) layer is modified by treatment with a sulfur dioxide plasma in order to obtain a more hydrophilic surface with new functional groups. The results demonstrate the stable polymer coating of the stents and the improvement of haemocompatibility after treatment with sulfur dioxide plasma. Platelet adhesion is decreased from 85% for the metal surface to 20% for the CVD-coated and sulfur-dioxide-plasma treated surface.