It’s a bizarre sight: With a short burst of light, a sponge-shaped robot scoots across a tiled surface. Flipped on its back, it repeatedly twitches as if doing sit-ups. By tinkering with the light’s frequency, scientists can change how fast the strange critter moves—and how long it needs to “rest” after a long crawl.
Soft robots are nothing new, but the spongy bot stands out in that it blends living muscle and brain cells with a 3D-printed skeleton and wireless electronics. The neurons, genetically altered to respond to light, trigger neighboring muscles to contract or release.
Watching the robot crawl around is amusing, but the study’s main goal is to see if a biohybrid robot can form a sort of long-lasting biological “mind” that directs movement. Neurons are especially sensitive cells that rapidly stop working or even die outside of a carefully controlled environment. Using blob-like amalgamations of different types of neurons to direct muscles, the sponge-bots retained their crawling ability for over two weeks.
Scientists have built biohybrid bots that use electricity or light to control muscle cells. Some mimic swimming, walking, and grabbing motions. Adding neurons could further fine-tune their activity and flexibility and even bestow a sort of memory for repeated tasks.
These biohybrid bots offer a unique way to study motion, movement disorders, and drug development without lab animals. Because their components are often compatible with living bodies, they could be used for diagnostics, drug delivery, and other medical scenarios.
Squishy But Powerful
The word robot often conjures images of Terminator’s metal T-800. Soft robots have the potential to be far more flexible and agile. Being able to slightly deform lets them squeeze through tiny spaces, monitor fragile ecosystems like coral reefs, explore the deep sea, and potentially snake through the body with minimal damage to surrounding tissues.
In addition to synthetic materials and mechanisms, another way to build soft robots is inspired by nature. From blue whales to rodents and humans—all rely on similar biological machinery to move. Motor neurons in muscles receive directions from the brain and spinal cord. They then release chemicals that trigger muscles to contract or relax.
The process is energy efficient and rapidly adapts to sudden changes in the environment—like stepping over an unexpected doorstep instead of tripping. Though today’s robots are getting more agile, they still struggle with unexpected landmines in uneven terrain. Adding neuromuscular junctions could lead to more precise and efficient robots.
Last year, in a proof of concept, one team engineered a swimming “stingray” bot using stem cell-derived neurons, heart muscle cells, and an electronic “brain.” Scientists combined the cells, and brain with an artificial skeleton to make a soft robot that could flap its fins and roam a swimming pool.
There was a surprise too—the junctions between the two cell types developed electrical synapses. Usually, neurons release chemicals to direct muscle movements. These connections are called chemical synapses. While electrical networks are faster, they’re generally less adaptable.
Back to Basics
The new study aimed to create chemical synapses in robots.
The team first 3D printed a skeleton shaped roughly like a figure eight, but with a wider middle section. Each side formed a trough with one side slightly deeper than the other. The troughs were intended to function as legs. The researchers then embedded muscle cells from mice in a nutritious gel contained in each trough. After five days, the cells had formed slivers of muscle capable of contracting throughout the legs.
The robot’s “brain” sat in the middle part of the figure eight. The team made tiny blobs of neural tissue, called neurospheres, out of stem cells genetically engineered to activate with light. The blobs contained a mix of brain cells, including motor neurons to control muscles.
The neurospheres connected with muscle tissue days after transplantation. The cells formed neuromuscular junctions similar in form and function to those in our bodies, and the biohybrid robots began pumping out chemicals that control muscle function.
Then came an electronic touch. The team added a hub to wirelessly detect light pulses, harvest power, and drive five tiny micro-LED lights to change brain cell activity and translate it into movement.
The robot moved at turtle speed, roughly 0.8 millimeters per minute. However, the legs twitched in tandem throughout the trials, suggesting the neurons and muscles formed a sort of synchrony in their connections.
Surprisingly, some bots kept moving even after turning off the light, while other “zombie” bots spontaneously moved on their own. The team is still digging into why this happens. But differences in performance were expected—living components are far less controllable than inorganic parts.
Like after tough workout, the robots also needed breaks. And when flipped on their backs, their legs moved for roughly two weeks but then failed. This is likely due to a buildup of metabolic toxins, which gradually accumulate inside the robots, but the team is looking for the root cause.
Despite their imperfections, the bots are essentially built from living mini neural networks and tissue connected to electronics—true cyborgs. They “provide a valuable platform for understanding…the emergent behaviors of neurons and neuromuscular junctions,” wrote the team.
The researchers are now planning to explore different skeletons and monitor behavior to fine-tune control. Adding more advanced features like sensory feedback and a range of muscle structures could help the bots further mimic the agility of our nervous system. And multiple neural “centers,” like in sea creatures, could control different muscles in robots that look nothing like us.
Shelly Fan
Dr. Shelly Xuelai Fan is a neuroscientist-turned-science-writer. She's fascinated with research about the brain, AI, longevity, biotech, and especially their intersection. As a digital nomad, she enjoys exploring new cultures, local foods, and the great outdoors.