Because the cell mass in a bioartificial tissue exceeds relatively small numbers, there is a requirement to incorporate a convective transport system that provides nutrients and removes waste products. This function is provided by the vascular tree in vivo, and it may be desirable that endothelial cells be used in the design of the vascular tree in the bioartificial tissue, because endothelial cells provide a nonthrombogenic surface inside normal blood vessels. Furthermore, there is an ongoing effort in the area of vascular graft development, and the development of these applications requires a reliable source of endothelial cells.