Abstract: A polypeptide growth factor is associated with a substrate to promote population of the substrate with endothelial cells. In a preferred approach, the growth factor is associated with the substrate by crosslinking under suitably mild conditions such that the growth factor is active following the crosslinking process. Thus, a prosthesis is formed with growth factor crosslinked to the substrate.

Abstract: A composite matrix has a first layer and a second layer. The first layer includes at least about 5 dry weight percent flexibility modifying agent. The second layer includes at least about 5 dry weight percent less flexibility modifying agent than the first layer. A valved prosthesis with flexible leaflets supported by a wall can be formed from the composite materials. In some embodiments, the wall of the prosthesis includes a first layer with at least about 60 weight percent collagen and a second layer with at least about 25 weight percent collagen and at least about 5 weight percent elastin. The leaflets preferably include a first layer with at least about 60 weight percent collagen and a second layer with at least about 25 weight percent collagen and at least about 5 weight percent proteoglycans.