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| MIT engineers developed a soft robot that can flap through water in response to flashes of light. Photo Credit: Melanie Gonick, MIT (CC BY-NC-ND 3.0) |
Scientific Frontline: Extended "At a Glance" Summary: Biohybrid Aquabot
The Core Concept: A paper-thin, biohybrid swimming robot powered by a single layer of genetically engineered, living muscle cells that flap in response to light.
Key Distinction/Mechanism: Unlike previous biohybrid robots that use bulky, three-dimensional chunks of lab-grown muscle requiring millions of cells, this robot utilizes a two-dimensional, ultra-thin film of live muscle cells cultured on an optimized gel skeleton, allowing for more efficient movement with fewer resources.
Major Frameworks/Components:
- Gelatin Methacrylate (GelMA) Skeleton: A tunable, half-millimeter-thick gel film serving as the structural base, optimized for stiffness to support cell growth without shriveling.
- Square-Bottomed Grooves: Microscopic channels stamped into the gel that encourage muscle cells to align and fuse into stronger, coordinated fibers.
- Genetically Engineered Muscle Cells: A single layer of live cells programmed to contract ("twitch") when exposed to flashes of light.
- Optical Navigation: The ability to control the robot's speed and direction by selectively shining light on specific fins.
Branch of Science: Mechanical Engineering, Biological Engineering, Robotics (Biohybrid Robotics).
Future Application: The development of highly efficient, self-healing biohybrid robots capable of navigating fragile, unpredictable, or tightly constrained aquatic environments, such as for environmental monitoring or delicate biological exploration.
Why It Matters: This represents the first successful demonstration of locomotion powered by a thin, two-dimensional layer of muscle cells, proving that biological materials can be engineered at microscopic scales to create functional, responsive machines that are cheaper and more efficient than bulky 3D tissue models.
This video, which has been sped up, shows how the swimming robot responds to light.
Swimming requires significant muscular effort. However, Massachusetts Institute of Technology (MIT) engineers have discovered that even a single layer of muscle cells can propel a structure through water if it is properly designed.
In a paper published in the journal Advanced Functional Materials, the team presents a design for a thin, muscle-powered swimming robot. The “skeleton” of the aquatic robot consists of a gel film approximately the length and width of a stick of chewing gum. The two halves of the gel form the robot’s “fins.” Each fin is covered with a layer of live muscle cells that is much thinner than a single strand of human hair. The cells are genetically engineered to contract in response to light.
When the researchers illuminate one fin, the surface muscles contract in response, causing the entire fin to flap with sufficient force to propel the robot through the water. By exposing one fin or the other to flashes of light at various intervals, the researchers can control the swimming robot’s direction and speed.
The engineers demonstrated that the paper-thin robot could swim and maneuver through a simple aquatic maze. At its fastest, the robot can swim a distance of approximately four body lengths in one minute. Although this pace is significantly slower than that of Olympic swimmers, who can cover up to 65 body lengths per minute, the robot performs comparably to more leisurely swimmers, such as the cow shark, which explores the ocean at approximately the same rate.
“It takes a lot of force to move through water versus air,” said study author Ritu Raman, an associate professor of mechanical engineering at MIT. “The robot’s quite strong, given its size.”
The new robot is the first example of a very thin, two-dimensional, muscle-powered robot capable of locomotion.
“Currently, biohybrid robots from our group and others’ are built from bulky, three-dimensional chunks of lab-grown skeletal muscle that require millions of cells to fabricate,” said Raman. She noted that thinner, less bulky designs, such as the team’s new robot, could be more economical to build and could move more efficiently. “We believe that biohybrid robots powered by living muscle could one day perform delicate tasks, such as exploring environments too fragile or unpredictable for conventional hardware, because living tissue is soft, responsive to its surroundings, and can heal itself.”
Video Credit: Massachusetts Institute of Technology
Maximizing Movement
Last year, Raman’s group developed an iris-inspired disk of artificial muscle tissue. They stamped a gel disk with a pattern of concentric and radial grooves and deposited live muscle cells onto the gel’s surface. The cells formed a thin layer that grew along the grooves; when stimulated with light, the cells moved in patterns that stretched and squeezed the disk, much like the way a human iris dilates and constricts the eye’s pupil.
That work was the first to demonstrate that muscle cells could be grown in a very thin layer and in complex patterns that, when stimulated, could move in multiple, controllable directions.
“People hadn’t seen this muscle architecture engineered from scratch before,” Raman said. “And the cells were moving in multiple directions. But they only moved about 100 microns. From a robotics perspective, their movements were tiny.”
In their new work, the team aimed to maximize muscle movements to produce more force—enough, say, to power a swimming robot. The key, they found, was to optimize the skeleton on which the cells grew.
In their previous iris-inspired design, they grew muscle cells on fibrin, an ultrasoft gel that the team realized could quickly shrivel in response to the forces generated by the muscles. To better support the cells and maximize their force, the researchers focused on fine-tuning the underlying gel by changing three properties: the gel’s composition, its stiffness, and the size and shape of the grooves stamped into it.
“For engineering any type of tissue, it’s known that these are knobs you can tune,” Raman said. “And we wanted to optimize all these parameters to support live muscle cells.”
Tuning a Skeleton
To find an optimal “skeleton” on which to grow muscle cells, the team experimented with multiple gel formulations of varying stiffnesses, stamped with grooves of different geometries. For instance, one groove type resembled a narrow, square trough, whereas another was more of a long, curved valley. They found that when they deposited muscle cells onto each type of grooved gel, the cells settled into alignment in grooves that were more square than curved. More aligned cells tend to fuse into fibers that then form stronger, more coordinated muscle tissue. Square grooves, they found, were the optimal choice.
Instead of using fibrin, they utilized gelatin methacrylate (GelMA), a material frequently used in tissue engineering. They created different formulations of GelMA to produce skeletons of varying stiffnesses and observed how muscle cells grew when deposited on the gel’s surface. They found that the cells grew in better alignment and produced the most force on stiffer gels.
The team also varied the gel thickness and found that a 0.5-millimeter film of GelMA offered substantial support for a single layer of muscle cells. The film was light enough that the cells were able to adhere to the gel when they contracted, rather than peeling away.
Finally, the team “exercised” the cells, employing a training routine of flashing lights to strengthen the resulting muscle tissue.
With the strengthened cells and the optimized gel, the team designed a thin, two-finned robot comprising the gel, stamped on both sides with square-bottomed grooves, and lined with muscle cells. The cells fused into fibers, eventually forming strong, aligned muscle tissue.
“You can think of the robot as having two independent muscles,” Raman said. “If we shine a light on just one, only that muscle moves. If we shine a light on both, they both flap.”
The researchers submerged the robot in a large Petri dish of water and manually maneuvered a light source over the robot. The robot followed the light, flapping its fins in response to navigate through a maze that the team had placed in the dish.
Published in journal: Advanced Functional Materials
Title: 2D Skeletal Muscle Thin Film Actuators Enhance Efficiency of Biohybrid Robots
Authors: Maheera Bawa, Arielle Berman, Laura Schwendeman, Ferdows Afghah, Seanbiron Johnson, and Ritu Raman
Source/Credit: Massachusetts Institute of Technology | Jennifer Chu
Edited by: Scientific Frontline
Reference Number: eng092926_01