Long-term biologic fate of neoarteries regenerated in microporous, compliant, biodegradable, small-caliber vascular grafts in rats.

Microporous, compliant, biodegradable vascular grafts prepared from a mixture of polyurethane [( PU], 95% weight) and poly-L-lactide [( PLLA] 5% weight) can function as temporary scaffolds for the regeneration of the arterial wall of small-caliber arteries. The purpose of this study was to determine the long-term biologic fate of these neoarteries that were regenerated in PU/PLLA vascular grafts. The PU/PLLA vascular grafts (1.5 mm internal diameter [ID]) were implanted into the abdominal aortas of rats (N = 8) and were evaluated 1 year after implantation by means of macroscopic inspection, light microscopy, and electron microscopy. All implants were patent; three implants were normally shaped, two were slightly dilated (+/- 10% of the original ID), and three implants were aneurysmal. Arterial pulsations were reduced but still visible in the normally shaped implants and absent in the other implants. In all implants, the neointima was complete. The neomedia varied among the implants: In the normally shaped implants, smooth muscle cells were predominantly circularly arranged as in normal arterial tissue; in the other implants, smooth muscle cells were predominantly longitudinally arranged. The neoadventitia showed a completely fragmented graft lattice, which was organized by fibrohistiocytic tissue. These results suggest that the pattern of arrangement of smooth muscle cells in the neomedia determines the ultimate biologic fate of neoarteries regenerated in microporous, compliant, biodegradable vascular grafts. Only those neoarteries with predominantly circularly arranged smooth muscle cells in the neomedia were able to function normally as an arterial substitute for a 1-year period after implantation into the rat abdominal aorta.