This could happen. Printing bone, muscle, and cartilage—even an ear—is easy. Anthony Atala, who heads the Wake Forest Institute for Regenerative Medicine, has done that. Organs are harder. They need to grow slowly, generating massive networks of nerves and blood vessels. Atala’s plan is to print organ molds instead. The molds have tiny holes for nutrients and oxygen to flow through as injected cells blossom into organs.