In one aspect the present invention provides methods for promoting endothelial morphogenesis. The methods of this aspect of the invention include the step of providing to one or more endothelial cells an amount of an osteoprotegerin sufficient to promote endothelial morphogenesis. The methods of this aspect of the invention can be practiced in vivo or in vitro. In another aspect, the present invention provides implantable medical devices that each include: (a) a device body; and (b) a layer attached to a surface of the device body, the layer comprising a molecule selected from the group consisting of osteoprotegerin and a nucleic acid molecule encoding osteoprotegerin, wherein the device is adapted to be completely or partially implanted into an animal body. The implanted medical device thus promotes the growth of blood vessels in the surrounding tissue, thereby reducing or preventing the formation of a collagenous capsule around the implanted medical device.