MIT Researchers Build Swimming Robot Powered by Thin Muscle Films

CAMBRIDGE, Mass. -- Researchers at the Massachusetts Institute of Technology (MIT) have developed thin films of living skeletal muscle that can power a swimming robot, reporting a 20-fold increase in force density compared with earlier three-dimensional muscle actuators.

The approach replaces the bulky engineered muscle tissues commonly used in biohybrid robots with a single layer of muscle cells grown on a flexible hydrogel. The researchers published the work in Advanced Functional Materials.

The team, led by MIT mechanical engineering professor Ritu Raman, developed muscle films that remained functional for more than 30 days after removal from their supports. Previous two‑dimensional actuators stopped working after about 10 minutes, according to the study.

The new design extended the untethered actuator's lifespan by about 4,500 times - this refers to the actuator, not the robot's runtime.

The key change is how the muscle cells are arranged. Typically, biohybrid robots generally use three-dimensional muscle tissues, which require substantial cell volumes and make it difficult to precisely align individual muscle fibers.

MIT's researchers instead grew mouse skeletal muscle cells on micropatterned hydrogel structures. Those cells followed microscopic grooves to form aligned fibers, enabling contractions to produce measurable forces.

The resulting centimeter-scale actuators generated forces in milinewtons and movements in milimeters. Their force density was twenty times more contractile force per unit volume than earlier 3D skeletal muscle actuators.

The team used the films to construct a small swimming robot with two independently controlled fins. Its muscle cells were light-sensitive to blue light, allowing researchers to control each fin independently and adjust its beating frequency.

In laboratory experiments, the robot traveled in straight lines at speeds of up to four body lengths per minute. It reached rotations of 1,200 degrees per minute, showing controlled turning rather than involuntary muscle contractions.
The system is still experimental and hasn’t been shown to work outside controlled conditions; it also depends on living muscle, which needs an appropriate biological environment.