USING 3D PRINTING to build human tissue. “Unlike some experimental approaches that have used ink-jet printers to deposit cells, Organovo’s technology enables cells to interact with each other much the way they do in the body. They are packed tightly together and incubated, prompting them to adhere to each other and trade chemical signals. When they’re printed, the cells are kept bunched together in a paste that helps them grow, migrate, and align themselves properly. ­Muscle cells, for example, orient themselves in the same direction to create tissue that can contract.”