Think of a traditional robot and you probably imagine something made from metal and plastic. Such “nuts-and-bolts” robots are made of hard materials. As robots take on more roles beyond the lab, such rigid systems can present safety risks to the people they interact with. For example, if an industrial robot swings into a person, there is the risk of bruises or bone damage.

Researchers are increasingly looking for solutions to make robots softer or more compliant – less like rigid machines, more like animals. With traditional actuators – such as motors – this can mean using air muscles or adding springs in parallel with motors. For example, on a Whegs robot, having a spring between a motor and the wheel leg (Wheg) means that if the robot runs into something (like a person), the spring absorbs some of the energy so the person isn’t hurt. The bumper on a Roomba vacuuming robot is another example; it’s spring-loaded so the Roomba doesn’t damage the things it bumps into.

But there’s a growing area of research that’s taking a different approach. By combining robotics with tissue engineering, we’re starting to build robots powered by living muscle tissue or cells. These devices can be stimulated electrically or with light to make the cells contract to bend their skeletons, causing the robot to swim or crawl. The resulting biobots can move around and are soft like animals. They’re safer around people and typically less harmful to the environment they work in than a traditional robot might be. And since, like animals, they need nutrients to power their muscles, not batteries, biohybrid robots tend to be lighter too.