If a salamander can grow a new limb, Dr. Anthony Atala likes to say, why can't a person? It's hardly an idle question. Atala, 50, is at the forefront of the study of growing human tissue, an emerging field also known as regenerative medicine. He made headlines around the world in 2006 when he announced that he had grown a handful of human bladders in the lab and that the patients who'd received them were still healthy after five years. No one had bio-engineered an organ before, much less implanted one. But today, Atala and his staff at North Carolina's Wake Forest Institute for Regenerative Medicine, the world's largest such facility, are working to replicate their success with other body parts. They're currently growing 22 different tissues--from heart valves to muscle to fingers.