Researchers at the National University of Singapore have developed a method for strengthening lab-grown skeletal muscle tissue by allowing paired muscle strips to mechanically train each other during maturation, and used the approach to power a biohybrid swimming robot that the team says achieved the highest speed reported for its class.
The work, published in Nature Communications, addresses a constraint in biohybrid robotics, where living muscle is used as an actuator in place of conventional motors. While muscle-based systems offer advantages including softness, low noise and efficiency at small scales, their performance has been limited by the relatively low force generated by cultured muscle tissue.
The NUS team’s approach relies on the spontaneous contractions that engineered skeletal muscle tissues produce as they mature. Instead of treating those contractions as a byproduct, the researchers connected two muscle tissues through a sliding mechanism so that contraction in one tissue stretches the other, which then contracts in return. This created repeated cycles of shortening and lengthening without external stimulation or manual input during the early stages of development.
According to the researchers, the self-trained muscles generated a maximum force of 7.05 millinewtons and a stress of 8.51 millinewtons per square millimetre. The team said those figures exceed previously reported results for the same cell line used in biohybrid robotics. Because the method uses a commercially available muscle cell line, the researchers said it could be reproduced at lower cost than more specialised alternatives.
The muscle tissues were incorporated into OstraBot, a swimming robot modelled on boxfish locomotion, in which a rigid body is propelled by tail movement. Guided by a physiology-based model linking electrical stimulation to calcium signalling, muscle activation and force output, the design used a single trained muscle to drive two flexible tails. At a stimulation frequency of 3 hertz and optimal tail stiffness, the robot reached a swimming speed of 467 millimetres per minute, more than three times the speed of an otherwise identical version built with conventionally cultured muscle, the researchers said.
The study also focused on control as well as propulsion. The robot’s speed could be adjusted by changing electrical field strength, and the team demonstrated a sound-triggered start-and-stop response using clapping signals. Assistant Professor Tan Yu Jun, who led the research, said the result showed that muscle-powered robots could combine higher force output with controlled response to external inputs.
The researchers said the findings could support future applications in areas such as environmental sensing and minimally invasive biomedical tools. The team is also working on systems built entirely from biodegradable structural materials, with the aim of producing devices that can perform a task and then safely break down. Possible uses under consideration include temporary implantable tools and monitoring devices for sensitive environments such as wetlands and coral reefs.
Future work will focus on biodegradable materials, improved control systems, and greater durability and energy efficiency in muscle-powered robotic platforms.
Photo credit: National University of Singapore
