Microporous, complaint, biodegradable vascular grafts for the regeneration of the arterial wall in rat abdominal aorta

Microporous, complaint, biodegradable vascular grafts prepared from mixtures of polyurethane (PU) and poly-L-lactic acid (PLLA) can function as temporary scaffolds for the regeneration of the arterial wall in small-caliber arteries. This study was undertaken to determine the most suitable composition for PU/PLLA vascular grafts to ensure an optimal regeneration. Four types of PU/PLLA vascular grafts differing in percent weight of the PU/PLLA mixture, molecular weight of PLLA, and pore size were implanted into the abdominal aorta of rats (n = 32). Six weeks after implantation two implants of each graft type were evaluated by means of scanning electron microscopy and six implants were evaluated by means of light microscopy. In two types of the PU/PLLA vascular grafts, both of which were prepared from a 95%/5% weight PU/PLLA mixture with PLLA of molecular weight 500,000 but which had a different pore size, there was (I) absence of aneurysm formation and maintenance of arterial implant pulsations, (II) regeneration of a complete antithrombogenic neointima, (III) regeneration of a neomedia of comparable thickness to the media of normal rat abdominal aorta with the regeneration of elastic laminae almost throughout its thickness, and (IV) regeneration of a sufficiently supporting neoadventitia. These results demonstrate that a 95%/5% weight PU/PLLA mixture with PLLA of molecular weight 500,000 is the most suitable composition for PU/PLLA vascular grafts to ensure an optimal regeneration of a neoarterial wall that is of sufficient strength, compliance, and thromboresistance to function as a small-caliber arterial substitute. Pore size of these PU/PLLA grafts does not affect regeneration.