From the abstract of “Phototactic guidance of a tissue-engineered soft-robotic ray”, published in Science Vol. 353, Issue 6295:
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.
From the article published on Popular Science:
The stingray bot is composed of four sequential layers of material. The top layer is a 3D body of a silicone material—”the same thing as the outer coating of a breast implant,” says Parker—that’s been cast in a titanium mold. This flexible, bendy body holds the other materials together.
The second layer down is a simple gold skeleton. “The skeleton’s there because we needed some recoil, so that the pectoral fins bounce back to their original positions” once they’re done undulating, Parker says. Why gold? The team found the material had just the right stiffness and flexibility to bend and bounce, “and it’s really easy to work with,” he says.
The third layer down is another hyper-thin layer of silicone. This prevents the heart muscle from having direct contact with the gold, but also plays another huge role. Along with that top 3D layer, the silicone is cast with just the right small-scale patterns so that the next layer, the rat cells, “grow with the exact muscular architecture we want,” says Parker. “With the right geometric design, we can guide these cells to form the tissue we want.”