Little turns lead to big steps for biohybrid robots

(CN) — A fusion of biology and mechanics, a new biohybrid robot can make small turns thanks to silicone, muscle tissue and electricity.

Conventional biohybrid robots walk while moving forward so they can only make large trajectory turns, which prevents them from navigating areas with many obstacles that require small circle turns, according to a study published Friday in Matter. With that concern in mind, the study authors from the University of Tokyo took inspiration from human bipedal movement when building their own biohybrid robot. Namely, the purpose of muscle contractions in movement.

The researchers’ robot consists of two 3D-printed legs kept afloat by a foam buoy top which allows it to stand upright underwater. The liquid medium was necessary to preserve the lab-grown skeletal muscle tissues attached to the bendable silicone rubber on each leg. To shorten the turns and the direction length of the robot’s movement axis, the team gave the robot short, weighted legs that also anchored the ground contact by giving their creation a physical rotation center.

Then came the manual zapping.

A researcher applied electrical pulses that caused the muscle to contract and lift the leg up, with the heel landing forward when the electricity dissipated. To move the robot, a researcher alternated the electrical stimulation between the left and right leg every five seconds, which moved the robot at a speed of 0.002 mph. To make it turn, the researchers repeatedly zapped the right leg every five seconds as the left leg acted as an anchor, with the study reporting one instance of the robot performing a 90-degree left turn in 62 seconds.

While pleased with their robot's progress, study co-author Shoji Takeuchi of the University of Tokyo said there is room for improvement.

“Our robot currently does not have joints,” Takeuchi said in an email. “We're working on designing robots with joints and additional muscle tissues to enable more sophisticated walking capabilities. Also, at present, the robot is only capable of operating underwater, so we will develop a structure that can move in the air. In addition, the thicker the muscle tissue, the more force it generates, but this also makes nutrient supply to the interior more challenging. Therefore, introducing a nutrient supply system to the muscle tissues is one of our challenges.”

Another obstacle is that the electrical pulses that drive the robot must be manually applied, so the researchers hope to remove this operability issue in the future. One possibility could involve integrating a system that automatically applies electrical stimulation to the biohybrid robot and into the robotic skeleton. Another alternative the researchers suggest involves the use of optimal stimulation based on remote-controlled optogenetics and electrical stimulation to control muscle contractions.

However, the researchers do not focus solely on what the robot cannot yet do. Takeuchi said they are also eager to explore what their current findings can do for future studies on biohybrid robots and human locomotion.

“These findings offer valuable insights for the advancement of soft robots powered by muscle tissue and have the potential to contribute to a deeper understanding of biological locomotion mechanisms,” said Takeuchi. “This constructive approach may pave the way for further mimicking of the intricacies of the human gait mechanism in biohybrid robotics development.”

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