Design of nonthrombogenic polymer surfaces for blood-contacting medical devices.

Although significant progress has been made in the design of blood-compatible polymers in the past decades, there is no ideal polymer surface which is comparable with a natural endothelial surface in preventing surface-induced thrombosis and maintaining hemostasis. This is due to the complex pattern of protein and cellular interactions with foreign surfaces, which still demands defining a proven hypothesis to develop non-thrombogenic surfaces. Synthesis of new polymers with optimal mechanical properties and the in vitro and in vivo characterization of these surfaces will require many more years of work. In this article, the surface modification of existing medical polymers for the improvement of blood compatibility is introduced. Surface immobilizing of heparin onto polyurethane, coatings of a polyurethane-poly(ethylene oxide)-heparin graft copolymer, and a coating of thermosensitive polymers on polyurethane will be discussed. All modified surfaces demonstrated superior blood compatibility both in vitro and in vivo. The biological response of these designed systems in vitro, ex vivo and in vivo should provide state-of-the-art materials for the specific application of controlling thrombosis and solving biocompatibility problems.