Safety and intracardiac function of a silicone-polyurethane elastomer designed for vascular use.

No ideal prosthetic heart valve exists. While polyurethane copolymers possess excellent physical properties, thrombosis and embolism remain a problem and compounds designed to be less thrombogenic have been prone to biodegradation and failure ('cracking'). We tested a new material which has an elastomeric silicone applied to the polymer surface. A hydrophilic film of protamine and gelatin is covalently bonded to the silicone--this obviates the need for preclotting and should permit endothelial growth. The material was tested by implantation during cardiopulmonary bypass as patches in the mitral valve of six weanling sheep (weanling sheep provide a standard model of accelerated calcification for bioprosthetic heart valves). Prosthetic valves constructed from the material were implanted in an additional four animals, but all of these died within 30 days with heavily calcified valves. Four of the six animals with patches survived and were sacrificed 180 days after surgery when the patches were found to be well healed to native tissue, with collagenous ingrowth and partial endothelial covering. Scanning electron microscopy confirmed good healing, tissue ingrowth and good surface endothelium. The material functioned well as a patch in the mitral valve, allowing tissue ingrowth and endothelial growth on the surface of the patch. The material is not able to resist the strains experienced by a mitral valve prosthesis. Prospects for improved polymers for intravascular applications are good.