The researchers previously stimulated bio-bots with electrical signals, but those can adversely affect a biological setting and don't allow for selective control. "Light is a noninvasive way to control these machines," says the school's bioengineering head Rashid Bashir. "It gives us flexibility in the design and motion." By strategically positioning the rubber-band like rings of muscle on the backbone, the team was able to make bio-bots that perform a variety of functions. "We can have multiple legs and multiple rings. With the light, we can control which direction things move," says Bashir.

Previous bots used thicker pieces of muscle, but the thin tissue can more easily absorb light and nutrients. The researchers also exercised the muscle daily using light, making it stronger and able to move farther when contracted. The next step will be to design different types of 3D-printed skeleton designs and use them as "building blocks" for larger bots. "People can now use this to build higher-order systems," says grad student Ritu Raman. Not too high-order, though, please.