Sophia, a robot created by Hanson Robotics, has fascinated many with her human-like characteristics, appearance, and witty comments. She became a global media sensation overnight and even appeared on The Tonight Show Starring Jimmy Fallon (1). While it may be hard to believe that robots can get anymore human-like than Sophia, the integration of living tissue and muscle into robots makes that possibility more real than ever before.
The growing field of biohybrid robotics involves the use of live muscle in robots to improve robot movement and function. Scientists have begun to prefer living tissue over plastic and metal because muscles provide a better range of motion and overall increased flexibility (2).
A major biohybrid robot breakthrough occurred when researchers from Harvard University created a stingray robot that was 1/10 the size of a normal stingray. They took cardiomyocytes, or cardiac muscle cells, from rat embryos and grew them on a stingray-shaped mold to make the muscles similar to those of an actual stingray (3). They used rat cardiomyocytes as actuators to power the movement of the stingray. As these cardiomyocytes were engineered to respond to light cues, the stingray robot was able to move based on the light frequencies (4).
Researchers from Case Western Reserve University have accomplished similar feats when they created a robot using the mouth muscle of a California sea slug and 3D printed pieces (5). The muscle provided movement for the robot when stimulated by electrical currents. The robot’s intended purpose is to search for items or areas underwater, such as an oil leak.
A variety of muscles can be used for robots. Skeletal and cardiac muscle are particularly good choices because both can contract with the use of external stimuli like electricity (6). However, problems have arisen due to the spontaneous shrinkage of skeletal muscle, which makes the muscle shorter and therefore incapable of proper contractions. This particular problem of spontaneous shrinkage has been overcome by researchers from the University of Tokyo Institute of Industrial Science. They first made the robot skeleton, which is similar to that of a human finger, by using a 3D printer. Then, the research team built a muscle from scratch, using hydrogel sheets containing myoblasts, or cells that develop into muscle cells, and layering them onto the robot skeleton (2). The muscles had been lined up as antagonistic pairs, meaning that they were parallel to each other. This allowed the muscles to work together: while one muscle contracted, the other expanded, mimicking the actions of muscles in the human body (7). By applying voltage, the muscles contract, allowing the robot to move. This robot works in a finger-like manner by being able to pick up and place down items.
These biohybrid robots bring new benefits and opportunities. Professor Shoji Takeuchi, from the Institute of Industrial Science at the University of Tokyo, hopes that their findings will help in creating a complete biohybrid robot (7). Takeuchi proposes that pharmaceutical researchers will eventually be able to benefit from biohybrid robots by testing developing drugs on the living tissues of these robots instead of living animals.
Biohybrid robots have the potential to revolutionize the world, whether it’s in the ocean or in the lab. One day, Sophia might no longer be simply silicon, plastic, and metal disguised as a human. She might actually be part human.
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