July 8, 2016 report
Tiny soft robot stingray propelled by rat heart cells is guided by light
The impetus for developing the biohybrid was to learn more about ways to construct an artificial human heart—that is the specially of team lead Kit Parker. While at the aquarium with his daughter he noticed the similarity between the muscles a stingray used to propel itself through the water and muscles used by the human heart. Turning that insight into a swimming soft robot, the team notes, was a four-year journey into new territory that started with dissecting stingrays.
The researchers wound up making a skeleton out of gold because they found it the easiest material to use to connect to silicone rubber, which was used to form the body and because it is chemically inert. To make the robot move, the researchers coated the underside of their creature with approximately 200,000 live rat heart muscle cells (cardiomyocytes)—printed on in a serpentine radiating pattern similar to the muscles of a real stingray. The rat muscle cells had been genetically engineered to contract when exposed to light. Thus, to control the movement of their robot stingray, all they had to do was shine a light on different parts of its body—its speed could be changed by altering the frequency. Also, to lessen complexity, the researchers relied on the spring action of the gold skeleton to cause the muscles to rebound after the was light is removed—in real stingrays, there are two sets of pectoral muscles that work together to allow for swimming
The finished product was a very small soft robot, less than the size of a penny—but as can be seen in a video the team created, it is able to swim like a real stingray through a liquid salt and sugar solution (which serves as food for the heart cells) guided by a blue light held in the hand of a researcher—marking yet another step forward in robot technology and perhaps a milestone in developing an artificial heart.
Inspired by the relatively simple morphological blueprint provided by batoid fish such as stingrays and skates, we created a biohybrid system that enables an artificial animal—a tissue-engineered ray—to swim and phototactically follow a light cue. By patterning dissociated rat cardiomyocytes on an elastomeric body enclosing a microfabricated gold skeleton, we replicated fish morphology at scale and captured basic fin deflection patterns of batoid fish. Optogenetics allows for phototactic guidance, steering, and turning maneuvers. Optical stimulation induced sequential muscle activation via serpentine-patterned muscle circuits, leading to coordinated undulatory swimming. The speed and direction of the ray was controlled by modulating light frequency and by independently eliciting right and left fins, allowing the biohybrid machine to maneuver through an obstacle course.
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