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Biodegradable polyurethane-based (PU) nerve guides, instilled with or without ACTH4-9 analog (a melanocortin) were used for bridging an 8 mm gap in the rat sciatic nerve and were evaluated for function and histological appearance after 16 weeks of implantation. Autologous nerve grafts functioned as controls. The guides successfully enabled the sciatic nerve to regenerate across the 8 mm gap, thus effectively reestablishing the contact between the proximal and distal nerve ends. The mean conduction velocity, motor latency, and muscle action potentials of all the nerve guides did not differ significantly from the autografts. The histological quality of the regeneration in the nerve guides was significantly better than in the autografts; in the nerve guides, a well-defined nerve cable of normal architecture had regenerated without extensive endoneural scarring as seen in the autografts. ACTH4-9 instilled in the nerve guides showed a slight, but significant, increase in the number of myelinated axons. It is concluded that biodegradable PU nerve guides result in similar functional recovery when compared with autografts, but their histological quality is significantly better. ACTH4-9 showed only slight, but significant, improved nerve growth promoting activity. Therefore biodegradable PU nerve guides with ACTH4-9 would appear to be promising alternatives to autografts for bridging nerve defects.

A biodegradable microporous small-caliber vascular prosthesis has been developed that consists of two layers. The inner layer has been made highly antithrombogenic by cross-linking of a mixture of linoleic acid and an alipharic polyetherurethane with dicumylperoxide. Microporosity was introduced by adding sodiumfluoride crystals of about 5 I~m in diameter prior to cross-linking and leaching them out afterwards.The outer ply has been constructed by precipitating a (95/5) physical mixture ofpolyesterurethane and poly(L-lactide) from solution in the presence of sugar crystals with dimensions in the range 30-90 t~m which were removed by exposing the graft to water.The two-ply grafts were tested in vivo by replacing I cm of the abdominal aorta of rats. All the grafts remained patent at least up to 1 year and did not exhibit any aneurismal formarion. The inner layer was covered with endothelial cells and several layers of smooth muscle cells.

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The sleeve anastomotic technique was used to enhance the longer term patency and healing of polyurethane-based (PU) microvenous prostheses (ID: 1 mm, length: 5 mm, wall thickness: 0.2 mm; n = 34) in the rat femoral vein. In the control group, PU prostheses (n = 12) were implanted by means of the conventional end-to-end technique, and all were found to be occluded after one day (n = 6) and three weeks (n = 6). In the other experimental groups, the prostheses were evaluated after one day (n = 6), three weeks (n = 10), and six weeks (n = 18) of implantation by means of routine light- and scanning-electron microscopy. The occluded prostheses in the control group demonstrated a firmly attached mural thrombus at the anastomoses at one day and a completely organized thrombus at three weeks after implantation. Thirty-one of the 34 PU prostheses implanted by means of the sleeve technique were patent. At one day, all patent PU prostheses (five out of six) demonstrated minimal thrombus accumulation and a smooth transition at the anastomotic sites. At three and six weeks, all patent PU prostheses (16 out of 18) were covered by a complete endothelial layer. Underneath the endothelial layer, a subendothelial layer, composed of two to four layers of smooth muscle cells, could be observed. The wall of the prostheses were penetrated by fibrohistiocytic tissue. Stenosis was not observed. These results demonstrate that the sleeve anastomotic technique not only improves the short-term patency of PU microvenous conduits, but also the longer-term patency rate.(ABSTRACT TRUNCATED AT 250 WORDS)