Nowadays there are innummerable materials available to replace soft tissue. Polytetrafluorethene, for example, can be used to weae a strong yet flexible blood vessel. Pacemakers and synthetic valves restore functional ability a diseased heart. Even a complete artificial heart seems nearly within reach by the pioneering efforts of W.J. Kolff who once introduced teh artificial kidney. In the field of microsurgical transplantation rapid progress has been made, partly due tothe use of bioactive material.