The challenge of small diameter vascular grafts

Symptomatic vascular disease involving blood vessels smaller than 6 mm internal diameter constitutes the majority of vascular disease cases. In many cases the only correction for the condition is vascular reconstruction, or bypass surgery. The only adequate replacement for these vessels at the present time are autologous arteries, or more commonly veins. The availability of a reliable small diameter artificial graft would greatly increase the number of patients that could be treated surgically. Three materials are used for present grafts, tanned natural vessels, and artificial vessels constructed of knitted Dacron or expanded Teflon. All three types eventually fail due to thrombosis, either because of their inherent thrombogenicity or because of encroachment of tissue (intimal hyperplasia) (IH) into the lumen of the graft at the point where the natural and prosthetic vessel join. The exact reasons for thrombosis and IH are poorly understood and constitute a major area of current research. Attempts to alleviate the problem involve: designing non-thrombogenic grafts, lining grafts with the living cells (endothelial cells) that form the inner surface of natural vessels, designing grafts that are elastic like natural vessels, providing biodegradable grafts that are replaced by tissue that reconstitutes a natural vessel, and producing living vessels in vitro. An overview of the problems and current research reveals some promising approaches to the solution, but all are still in the developmental stages.