An MIT research team has spent years asking living tissues to do something familiar: exercise. Stretched and tugged with a gentle back-and-forth motion, the artificial muscles and nerves in their lab changed how they grew in response. Their newest experiment turned that same approach on blood vessels.

Labs can already grow muscle, skin, liver, and kidney tissue from scratch, but most of it stays small and thin because cells only survive within a few hundred micrometers of a blood supply.

The team’s latest results show exercise may work on blood vessels, too. Gently and repeatedly stretching a lab-grown vessel caused it to sprout entirely new capillaries. Researchers could also choose which direction the new vessels grew, simply by changing which way they pulled.