Experience with compliant polyurethane and polyurethane/fibrin microvascular prostheses

Compliance is viewed as a critical factor for the success of microvascular prostheses. In the present study, biodurable, porous, distensible grafts were compared to partially resorbable, porous, distensible grafts under the assumption that a bioresorbable compound (e.g. fibrin) could stimulate the progressive replacement of the graft material by the cellular elements of a normal artery. Porous tubes (1 .5 mm 10, 2.0 mm 00) were fabricated by spraying either a polyurethane solution (PU) or a 1:1 blend of polyurethane and human fibrin (PU-F) over a rotating mandrel according to a phase inversion technique. The prostheses, 1.5 cm long, were inserted in the rat infrarenal aortic position using microsurgical techniques. All 6 PU and PU-F grafts appeared functional and pulsating at the time of implantation. Upon retrieval 4 weeks later, 5 out of 6 PU grafts were patent and free of intraluminal clot and one was occluded. Three out of 6 PU-F grafts were patent, but 2 of those were aneurysmal and partially thrombosed. The internal tissue capsule was 20 micron thick, well organized and consisted of layers of mainly longitudinally oriented smooth muscle-like cells with substantial elastin deposition. A lining of endothelial-like cells covered most of the luminal surface. PU-F grafts showed significant resorption of the graft material with marked tissue invasion. However, the regenerated arterial wall was not as well organized and differentiated as in the PU grafts. In the rat model, porous, distensible micro-prostheses allow a high patency rate with the development of a thin, well organized internal capsule with significant elastin deposition. Blending the elastomer with fibrin leads to greater tissue invasion but poorer organization and patency. An optimal balance between prosthesis degradation and tissue replacement remains to be identified.