In cardiovascular medicine, there is an urgent need for improved heart valve prostheses, since traditional designs are either subject to rapid degeneration (tissue valves) or have a high risk of blood clot formation (mechanical prostheses). As part of an innovative heart valve design, we have manufactured biomaterial/polymer composite materials based on decellularized vascular matrix scaffolds that are coated with biodegradable polymers. The goal is to improve the mechanical strength of the decellularized matrix so that is able to withstand hemodynamic forces. The polymer is then subject to slow degradation, while the matrix scaffold is repopulated with the recipients own cells. Here, we describe a series of experiments that assess the biocompatibility of such composite materials, which is prerequisite for successful in vivo application.