It was just a couple of years ago that we heard about how scientists at the University of Illinois were using electrical fields to activate tiny muscle-powered "walking" biological robots – or "bio-bots." Ultimately, it was hoped that such devices could be used for applications such as targeted drug delivery within the body. Recently, however, the researchers made an improvement: the bio-bots can now be steered using light.

Each of the tiny devices measures no more than 7 mm to 2 cm in length, and is made from a 3D-printed hydrogel skeleton with a ring of bioengineered muscle tissue looped around it. That tissue is grown from mouse cells, with a gene added that causes it to contract when exposed to a certain wavelength of blue light.

After the rings are first created, they're then subjected to regular pulses of that light, allowing them to become bigger and stronger by "exercising." When placed on the skeleton, they can move its legs forward – or do other things – simply by having the light flashed at them. In fact, a more complex skeleton could conceivably be outfitted with multiple muscle rings, each one responsible for moving a certain appendage.

While the electrical stimulation approach also worked, using light has its advantages. For one thing, exposing biological tissue to electrical currents can damage it, whereas the blue light is harmless. For another, the light can be focused on particular parts of the bio-bots, causing just that area to contract – this allows for finer steering control, and can even be used to guide the bots toward a light source. By contrast, an electrical current causes the whole muscle ring to contract, all at once.

"Light is a noninvasive way to control these machines," says lead scientist Prof. Rashid Bashir. "It gives us flexibility in the design and the motion. The bottom line of what we are trying to accomplish is the forward design of biological systems, and we think the light control is an important step toward that."

The bio-bots can be seen in action, in the following video.