Bio-bots that walk on command

Engineers have developed walking ‘bio-bots’ powered by muscle cells and controlled with electrical pulses, giving researchers unprecedented command over their function.

We’re trying to integrate these principles of engineering with biology in a way that can be used to design and develop biological machines and systems for environmental and medical applications, said Rashid Bashir, Abel Bliss Professor and head of bioengineering at the University of Illinois at Urbana-Champaign.

Previously, Bashir’s group demonstrated bio-bots that ‘walk’ on their own, powered by beating heart cells from rats. However, heart cells constantly contract, denying researchers control over the bot’s motion. This makes it difficult to use heart cells to engineer a bio-bot that can be turned on and off, sped up or slowed down.

The new bio-bots are powered by a strip of skeletal muscle cells that can be triggered by an electric pulse. This gives the researchers a simple way to control the bio-bots and opens up possibilities for other forward design principles, so engineers can customise bio-bots for specific applications.

“Skeletal muscles cells are very attractive because you can pace them using external signals,” 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 design is inspired by the muscle-tendon-bone complex found in nature. There is a backbone of 3D printed hydrogel, strong enough to give the bio-bot structure but flexible enough to bend like a joint. Two posts serve to anchor a strip of muscle to the backbone, like tendons attach muscle to bone, but the posts also act as feet for the bio-bot.

A bot’s speed can be controlled by adjusting the frequency of the electric pulses. A higher frequency causes the muscle to contract faster, thus speeding up the bio-bot’s progress.

Next, the researchers will work to gain even greater control over the bio-bots’ motion, like integrating neurons so the bio-bots can be steered in different directions with light or chemical gradients. On the engineering side, they hope to design a hydrogel backbone that allows the bio-bot to move in different directions based on different signals. Thanks to 3D printing, engineers can explore different shapes and designs quickly. Bashir and colleagues even plan to integrate a unit into the undergraduate lab curriculum so that students can design different kinds of bio-bots.

“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 National Science Foundation supported this work through a Science and Technology Center grant, in collaboration with the Massachusetts Institute of Technology, the Georgia Institute of Technology and other partner institutions. Mechanical science and engineering professor Taher Saif was also a co-author.