Swimming through water requires considerable force, but a new experiment from MIT shows that even a single thin layer of living muscle cells can propel a tiny robot through water. Engineers have developed a paper-thin, muscle-powered swimming robot that uses genetically engineered cells and flashes of light to move, turn and navigate.
The research, published September 28 in Advanced Functional Materials, introduces a new type of two-dimensional biohybrid robot—a machine that combines living biological tissue with engineered materials.
Unlike conventional swimming robots that rely on motors, batteries and rigid mechanical parts, this tiny machine is powered by living skeletal muscle cells.
A Robot Powered by Living Muscle
At the heart of the new robot is a thin film of gel roughly the length and width of a stick of gum. The film acts as the robot's skeleton, while its two sides form flexible fins.
Each fin is covered with a layer of living muscle cells that is thinner than a human hair. The cells have been genetically engineered to contract when exposed to light.
When researchers shine light on one side of the robot, the muscle cells on that fin twitch. Their contraction causes the fin to flap, generating enough force to push the robot through water.
The researchers can control the robot's movement simply by changing where and when the light is applied.
Lighting one fin can make the robot turn, while stimulating both sides can produce forward swimming. By adjusting the timing of the light pulses, the researchers can also control its speed.
This creates a remarkably simple control system: light becomes the command, and living muscle becomes the motor.
Tiny Robot Can Navigate a Water Maze
The MIT team demonstrated that the robot could swim and rotate through a simple underwater maze.
Its maximum speed was about four body lengths per minute. That is extremely slow compared with human competitive swimmers, who can reach around 65 body lengths per minute.
However, the researchers point out that the robot's performance is notable considering its extremely small size and the fact that its propulsion comes from only a single layer of muscle cells.
"It takes a lot of force to move through water versus air," said Ritu Raman, an associate professor of mechanical engineering at MIT and an author of the study. "The robot's quite strong, given its size."
The experiment demonstrates something important for biohybrid robotics: living muscle does not necessarily need to be arranged into a thick, three-dimensional structure to generate useful movement.
Why Making the Robot Thin Matters
Previous biohybrid robots developed by Raman's group and other researchers generally relied on relatively bulky pieces of lab-grown skeletal muscle.
These structures can require millions of cells to fabricate.
The MIT team's new approach takes a different direction. Instead of building a thick muscle-powered machine, the researchers created an extremely thin structure with muscle cells arranged in a carefully engineered pattern.
A thinner robot could potentially require fewer biological materials and may be easier to manufacture.
It could also interact with its surroundings differently from conventional machines.
Living tissue is soft and responsive, and biological muscle can potentially heal itself. These properties could eventually make biohybrid robots useful for operating in environments where traditional rigid machines may be difficult to deploy.
Raman suggests that future versions could perform delicate tasks, including exploring environments that are fragile or unpredictable.
The Key Was the Robot's "Skeleton"
The idea for the swimming robot came from earlier research by Raman's group.
In previous work, the researchers created an artificial-muscle structure inspired by the human eye's iris. They built a thin gel disk containing concentric and radial grooves and placed living muscle cells onto its surface.
The cells naturally aligned with the grooves.
When exposed to light, the muscle cells contracted and moved the disk in different directions, creating a motion similar to the opening and closing of the eye's pupil.
That experiment demonstrated that muscle cells could be grown as a very thin layer and arranged into complex patterns.
However, there was a problem.
The cells moved only about 100 micrometers. While that movement was impressive at the biological scale, it was not enough to produce the force required for practical robotic movement.
The researchers therefore focused on one major question: How could they make the same thin layer of muscle generate much more force?
Engineering the Perfect Surface for Muscle
The answer turned out to involve the material underneath the muscle cells.
In the earlier design, the researchers used fibrin, an extremely soft gel. But they discovered that the material could shrink or deform when the muscles contracted.
That meant some of the muscle's force was effectively lost.
For the new robot, the researchers experimented with the properties of the underlying gel. They adjusted its composition, stiffness, thickness and surface pattern.
They tested different groove shapes, including narrow square-shaped channels and curved valleys.
The muscle cells behaved differently depending on the pattern.
Cells placed inside the more square-shaped grooves became better aligned. This alignment allowed them to form stronger muscle fibers that could contract together more effectively.
The square grooves therefore became an important part of the final design.
A Stronger Gel Made Stronger Muscle
The researchers also replaced fibrin with gelatin methacrylate, or GelMA, a material commonly used in tissue engineering.
By changing the formulation of GelMA, they produced gels with different levels of stiffness.
The experiments showed that muscle cells grew with better alignment and generated greater force when placed on stiffer gels.
The researchers also tested different film thicknesses.
They found that a GelMA film approximately 0.5 millimeters thick provided enough structural support while remaining thin enough for the muscle cells to stay attached during contraction.
This balance was critical.
If the skeleton was too soft, it could deform under the muscle's force. If the structure was not properly designed, the contracting cells could pull away from the surface.
Training the Living Muscle
The team did not simply grow the muscle cells and immediately put them into the robot.
They also trained them.
Using repeated flashes of light, the researchers exercised the muscle cells to strengthen their contractions.
After optimizing the material, groove pattern and muscle training, they built the final two-finned swimming robot.
The robot effectively has two independently controlled biological muscles.
When light is directed toward one side, that fin moves. When both sides are illuminated, both fins contract.
The researchers then placed the robot in a large petri dish filled with water and moved a light source above it.
The robot responded to the light and followed its path, using its fins to navigate through a maze.
A New Direction for Biohybrid Robotics
The current machine is deliberately simple. The researchers' main goal was to prove that a very thin layer of muscle could generate enough force to move a robot through water.
The next challenge is increasing its swimming speed and improving the overall body design.
Even without becoming dramatically faster, however, the technology could have potential applications.
Future versions could potentially be designed for tasks such as monitoring aquatic environments, where small and flexible machines could move through water without relying entirely on conventional motors and batteries.
The work also demonstrates a broader idea in robotics: the future of machines may not always involve making stronger motors or smaller electronics. Sometimes, the answer could be using biology itself.
By combining living muscle with precisely engineered materials, MIT researchers have shown that a robot thinner than a conventional mechanical structure can still produce meaningful movement.
The tiny swimmer is only an early prototype, but it demonstrates a fascinating possibility—robots that move not because an electric motor spins, but because living cells contract when they receive a signal.
Reference: Maheera Bawa et al., 2D Skeletal Muscle Thin Film Actuators Enhance Efficiency of Biohybrid Robots, Advanced Functional Materials (2026), DOI: 10.1002/adfm.78065.
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