Anthony Atala and his colleagues at the Wake Forest Institute for Regenerative Medicine, in North Carolina, have printed ears, bones and muscles in this way, and have implanted them successfully into animals. The crucial part of the process is ensuring the printed tissue survives and then integrates with the recipient when transplanted. Some types of tissue, such as cartilage, are easy to grow outside the body. Infusing nutrients into the medium they are kept in is sufficient to sustain them, and they tend to take well when transferred to a living organism. More complex structures, though, like hearts, livers and pancreases, require a blood supply to grow beyond being tiny slivers of cells. Dr Atala and his colleagues therefore print minute channels through their structures, to let nutrients and oxygen diffuse in. This encourages blood vessels to develop. The next step, probably within a few years, will be to test such bioprinted material on people.
