Biohybrid robots powered by cultured muscle have been held back by the weakness of laboratory-grown tissue, which lacks the mechanical loading that builds strength in a living body. Researchers in the NUS Department of Mechanical Engineering found a way to supply that loading without external stimulation. Two muscle tissues are mechanically linked so that each pulls against the other, converting the spontaneous contractions muscle produces anyway into a continuous training regime.
The strengthening is measurable. Trained muscle reached a maximum force of 7.05 millinewtons and a stress of 8.51 millinewtons per square millimetre, achieved using a commercially available cell line rather than specialised primary tissue. That last detail matters a great deal for reproducibility, since results obtained with hard-to-source cells are difficult for other laboratories to build on, and biohybrid robotics has suffered from exactly that kind of fragmentation across groups.
The tissue was then used to drive OstraBot, a boxfish-inspired swimmer that reached 467 millimetres per minute. This is the fastest speed reported for a skeletal-muscle-driven biohybrid robot, more than three times that of an equivalent device powered by conventionally cultured muscle. Speed can be adjusted through electrical field strength, and the robot starts and stops in response to sound. The study was published in Nature Communications.
Soft, biodegradable actuators are attractive for environmental monitoring, where devices may not be recoverable, and for temporary medical implants that should disappear once their work is done. Both applications depend on muscle strong enough to be useful, which has been the binding constraint. The group plans to move next to fully biodegradable structural materials so that the whole device, not only its actuator, is transient.