Newly designed compliant hierarchic hybrid vascular graft wrapped with microprocessed elastomeric film--II: Morphogenesis and compliance change upon implantation.

Hierarchic structured hybrid tubular vascular media composed of endothelial cells (ECs), which covered the luminal surface, and smooth muscle cells (SMCs), which resided in the tubular collagen gel, were wrapped with thin segmented polyurethane elastomeric films designed to provide compliance matching with native arteries and transmural tissue permeability using a laser-directed ablation technique to provide different pore densities. Two hybrid grafts with high and low pore densities (inner diameter: 150 microm and length: 4 cm), and exhibiting pressure-dependent distensibility in response to pulsatile pressure, were bilaterally implanted into canine common arteries for up to 6 months. Irrespective of the pore density, high patency was achieved and no dilation and bursting occurred. Maintenance of full endothelialization during the entire course of implantation period was observed for the graft wrapped with the film with higher pore density. On the other hand, the graft wrapped with the film with lower pore density exhibited markedly reduced endothelialization at a later period of implantation, probably due to delamination of neoarterial tissue from the segmented polyurethane (SPU) surface. There were some differences in transmural tissue ingrowth between the two grafts. At anastomotic sites, neoarterial thickness for type A graft was smaller than that for type B graft regardless of the implantation period. Slightly reduced compliance was observed for both types of grafts at the sixth month of the implantation period. This study indicates that a hybrid vascular graft minimally supported with a thin elastomeric film can be used to replace diseased arteries if micropores are well designed for tissue permeability and anchoring.