Tiny robots powered by living muscle tissue

Creating an articulated robot usually involves putting together a series of parts and utilising one or more technologies to make it move, including hydraulics, rubber bands and wheels. These are often fairly limited; omni-directional, for example, or unable to adjust to uneven terrain -- one of the biggest challenges for locomotive robots.

If, however, robots could use muscles, like a biological body does, they would be able to get around much more easily -- and could be controlled with greater finesse. An entirely muscular robot is, of course, a long way off; but researchers at the University of Illinois at Urbana-Champaign, led by head of bioengineering Professor Rashid Bashir, have created a series of tiny walking robots powered by muscle tissue.

Previously, Professor Bashir's team had developed a robot powered by beating heart cells from rats -- an imperfect solution, since heart cells contract constantly, making the movement of the robot difficult to control. The team's new robots, however, are powered by a strip of skeletal muscle, which can be controlled using an electric pulse -- easy to administer and program.

"Skeletal muscles cells are very attractive because you can pace them using external signals," Professor Bashir said. "For example, you would use skeletal muscle when designing a device that you wanted to start functioning when it senses a chemical or when it received a certain signal. To us, it's part of a design toolbox. We want to have different options that could be used by engineers to design these things."

The robot is put together in a system similar to bone-muscle-tendon. A 3D-printed hydrogel base forms the robot's "backbone", strong enough to maintain structure, but flexible enough to move with the muscle. The strip of muscle is anchored to the backbone by two posts, which act like tendons, but also serve as the robot's feet. Electric pulses are then administered; the higher the frequency, the faster the robot moves.

At the moment, it can only move in one direction, and the team's next challenge is taking steps to integrate the ability to turn: a more flexible backbone, and perhaps even neurons integrated into the robot so that it can be steered using light or chemical gradients.

These robots could one day be used in a variety of applications, the team believes, particularly medical; precision surgical robots, smart implants, even environmental surveying.

"The idea of doing forward engineering with these cell-based structures is very exciting," Bashir said. "Our goal is for these devices to be used as autonomous sensors. We want it to sense a specific chemical and move towards it, then release agents to neutralise the toxin, for example. Being in control of the actuation is a big step forward toward that goal."

The full paper, "Three-dimensionally printed biological machines powered by skeletal muscle", can be found in the journal PNAS.