Conventional medical technologies to address tissue and organ dysfunction have resulted in a host of approaches, largely device-based. Examples include maintenance dialysis for renal dysfunction, use of pacemakers, stents, oxygenators, and valves to neutralize the effects of cardiovascular dysfunction, and replacement of large joints with mechanical substitutes. Advances in transplantation science have led to increasing success in replacing diseased kidneys, livers, hearts, pancreata, and lungs. There are, however, significant and severe limitations to these conventional therapies, most notably the demand by a growing and aging population. There is a well-recognized limitation in the supply of tissues and organs. In the year 2000, for example, 77,000 people were awaiting organ transplants, while only 23,000 were performed. High tech medicine is costly; U.S. healthcare expenditures as a percent of gross domestic product are expected to reach 16.7% by 2007…