An international team of researchers has developed an eerily realistic robotic stingray that blurs the line between animal and machine. Fuelled by light-activated heart cells, the cyborg fish could inspire the development of futuristic medical devices and incredibly life-like synthetic animals. The tissue-engineered soft-robotic ray. (Image: Karaghen Hudson & Michael Rosnach)
Like an actual stingray, this miniature robot features a flat body with long wing-like fins. And like the real thing, it swims by flapping its fins up and down. Its polymer "skin" is wrapped around a gold skeleton and laced with about 200,000 rat heart muscle cells called cardiomyocytes. At just 16mm long and weighing just 10g, it is a cyborg in the truest sense — a hybrid of biological and synthetic components.
The effort to build the robotic stingray was headed by Kit Parker, a professor of bioengineering and applied physics at Harvard University. His "eureka" moment for the project came while visiting the New England Aquarium with his daughter, Caroline.
"She was trying to pet a stingray and she put her hand in the water and the stingray quickly moved away from her hand in a very elegant way," Parker told Gizmodo. "It struck me like a thunderbolt that I could build that system in the musculature, and that it would look very much like the [muscular] layer of the heart."
Image: Sung-Jin Park et al., 2016/Science
Parker took this idea to his team, and they began to build their miniature, soft tissue robot. After creating a neutrally charged gold skeleton, the researchers overlaid it with a thin layer of flexible polymer. A series of light-sensitive (photovoltaic) cardiomyocytes were strategically aligned along the top.
When exposed to light, the muscle cells collectively caused the fins to contract in a downward motion. To create the upward motion, the researchers designed the gold skeleton such that it naturally stores some downward energy, which is later released when the cells relax.
To develop a guidance system, Parker once again turned to his daughter for inspiration. "When my daughter was little, I used to point a laser pointer at the ground and she would try to stomp on it," he said. "We would go for a walk down the street and I could lead her along the footpath safely by just pointing a laser pointer at the ground. It occurred to me that we could use optogenetics to mimic this with the tissue engineered stingray."
So that's what they did. Leveraging the power of the light-sensitive cells, Parker's team was able to steer the stingray using asymmetrical pulses of light. As the stingray moves forward, the pulses can guide it either to the left or right. Different frequencies of light can be used to control its speed. They tested the light-driven navigation system by having the cyborg stingray navigate through an obstacle course.
The cyborg stingray (left) compared to the real thing. (Image: Karaghen Hudson)
There's more to this project than just creating a life-like fish. Parker's primary interest is in understanding the heart and how various parts of the anatomy can help with blood flow. "With the exception of crustaceans, almost all marine life forms have muscles designed to move fluid," said Parker. "To advance our studies of the heart we have started looking at marine life forms and the muscular pumps they represent." Parker hopes to gain better insight into the human heart and heart disease by reverse engineering other forms of muscular pumps found in nature.
This research could also lead to even better, and more useful, automated and semi-automated robots. When it comes to building better robots, biology has its advantages. For instance, this particular bot is faster than other similar devices; its cells function as both actuator and sensor. "Living muscle cells are much more energy efficient than synthetic actuators and can be programmed to do cool things," said Parker.
Of course, biology isn't perfect. A disadvantage of using cells as a building material is that they're vulnerable, fragile and they eventually die. But the potential for tissue engineering and soft robotics is huge. This tiny cyborg stingray is a sure sign of bigger and better things to come.