A small swimming robot from MIT has a surprising source of movement: a thin layer of living muscle. Researchers can make its two fins contract by directing light at them, guiding the soft machine through a simple maze in a dish.
MIT described the demonstration on September 29. The robot reached about four body lengths per minute at its fastest; the maze video accompanying the announcement is sped up. Researchers manually positioned the light source to control its route. MIT’s announcement and demonstration.
Building a better support for muscle
The study, first published September 28 in Advanced Functional Materials, examines how a muscle-powered machine’s supporting material affects its performance. The researchers grew skeletal muscle on patterned hydrogel and varied the gel’s stiffness and microscopic grooves.
Their optimized thin-film actuators produced more force per unit of muscle volume than previously reported three-dimensional muscle actuators. They also remained functional for more than 30 days in culture. That longevity result concerns the muscle-actuator system under laboratory conditions; it does not establish that a robot can swim continuously for a month. The research paper.
The path from patterned cells to a swimmer
This work follows an earlier step in the same research program. In March 2025, MIT described a method for arranging muscle cells into patterns that could pull in multiple directions.
That team pressed stamps containing cell-scale grooves into a soft gel, then added muscle cells. As the cells grew into fibers, the grooves helped determine their orientation. Stimulating the resulting tissue produced movement that followed the pattern.
One demonstration resembled the arrangement of muscles in a human iris, combining circular and radial patterns. The researchers used skeletal muscle cells, while a real iris contains smooth muscle. The point was to test whether fabrication could reproduce a more complex arrangement of pulling forces. The method gave the team a way to design muscle architecture, alongside choosing the material on which the cells grow. MIT’s account of the 2025 work.
What “untethered” means here
The swimming demonstration used a robot released from its supporting mount. Other experiments measured actuator movement with one edge still attached, a configuration the paper calls half-tethered.
Even during free movement, control depended on an external light source. The authors identify that reliance on outside stimulation, along with simple body shapes and use of a single cell line, as limitations. They propose more complex geometries as one route toward improving performance. Study methods and limitations.
Ritu Raman’s team next wants to refine the body for faster swimming. Environmental monitoring is a possible future application. For now, the result is a controlled laboratory demonstration of thin muscle tissue doing useful mechanical work. MIT’s next steps.
