Frog Leg Muscle Powers a Wireless, Light-Controlled Robotic Manta Ray

Researchers at the Shenyang Institute of Automation (SIA) of the Chinese Academy of Sciences have built a wireless, light-controlled robotic manta ray whose fins are driven by real biological muscle from a bullfrog's leg. The work falls under biosyncretic robotics, a field of biohybrid robotics that uses living tissue instead of motors, pneumatics, or hydraulics inside machines.

The team isolated the gracilis, a long skeletal muscle from the frog's leg, instead of the lab-grown tissue used for an earlier manta-inspired swimmer in 2022. Native muscle keeps its naturally organized fiber arrangement, giving better contractile performance than the comparatively weak lab-grown kind, the researchers say. At an optimized stimulation of 1 Hz, 5 V and 10 milliseconds per pulse, the muscle produced a stable contractile force of 6.5 newtons and shortened by about 25%; peak force reached 9.4 newtons under more extreme stimulation. The tissue stayed electrically responsive for up to 11 days and reliably drove the robot for seven days.

To move without wires, tiny gallium arsenide photovoltaic modules sit on the robot's back. An operator shines an 808-nanometer near-infrared laser onto them; the cells convert the light into electricity, which reaches nerves on the muscle's surface and triggers contraction. Controlling when and where the laser hits the left and right photovoltaic sections lets the researchers trigger contractions on each side separately. The muscles are mechanically linked to the robot's pectoral fins, so contraction and relaxation create a flapping motion that drives it forward or steers it.

The robot reached an average straight-line speed of 0.54 body lengths per second, about 2.7 centimeters per second, and briefly hit two body lengths per second — the fastest relative forward speed yet reported for a skeletal-muscle-driven biosyncretic robot, the researchers say. It could turn within one-eighth of its own body length, reach a maximum turning speed of 21 degrees per second, and complete a full circular trajectory in about 17 seconds.