Longterm study of a compliant biological vascular graft.

Clinically implanted prostheses of biological origin have recently been shown to develop aneurysms within several years. To study this process, recently developed bovine heterografts that were implanted in canine ilio-femoral arteries for 27 to 45 months, were studied in vivo and in vitro. Seven out of seven grafts were patent with only one showing evidence of focal aneurysm. Measurements of mechanical properties, including water permeability, compliance, and burst pressure, and of heat shrink temperature and dry weight were obtained before and after a period of controlled exposure to bacterial collagenase; all data suggested that much of the original graft had been replaced with host tissue. However, enzyme susceptibility was less than that of fresh bovine arteries, indicating that at least some of the grafts' crosslinked collagen was preserved. The compliance of these explants was similar to that reported for autogenous vein. Histological examination of the graft wall revealed cellular "intimal" and adventitial zones containing host-generated collagen surrounding a central zone devoid of cellular infiltration, which appears to be unmodified graft "media" highly resistant to degradation. We conclude that, when properly processed, biological prostheses can act as a bioresorbable scaffold for the orderly replacement of structural elements during healing, promoting continued mechanical integrity of the graft. These promising results encourage the further development of prostheses of biological origin.