The robot, whose development is seen as a stepping-stone towards engineering a biomechanical human heart, is comprised of a silicone skin enclosing cells cultured from rat hearts, with a gold support structure.
Research leader Kevin Kit Parker, a former army officer, has been building biomechanical hybrid structures for some years, after initial work on growing films of heart muscle cells on silicone films. His first was a jellyfish-like ‘medusoid’ in which the cells were induced to contact using an electric current, forcing the cup-shaped silicone structure to contract and expel some water. Moving up the evolutionary chain to stingrays, the latest project incorporates some genetic engineering into the mix as well.
Using data gathered by another team studying how stingrays’ muscles are arranged, Parker devised a springy gold skeleton as a support structure, and embedded a template of the protein fibronectin into a silicone sheet shaped like a very small ray (a tenth of the size of a living juvenile ray). This template encouraged 200,000 cells taken from the hearts of embryonic rats to grow in a pattern radiating from the skeleton to the edge of the ray shape’s fins. The team then infected the cells with a virus designed to implant a gene into the cell that would make them contract in response to the light of a blue laser. Another sheet of silicone completes the assembly.
Immersed in a bath of warmed nutrient solution, the robot is made to ‘swim’ by directing a laser onto each fin. Changing the frequency of the light speeds up the cells’ contraction rate, allowing the robot’s builder, post-doctoral student Sung-Jin Park, to steer it around the tank and even through an obstacle course. The cells only deflect the fin in one direction, with the spring action of the skeleton returning it to its original shape; this simplifies the real ray’s muscle structure, which as two muscle layers to control the fins’ rippling motion. The research is described in a paper in the journal Science.
Parker is now turning his attention to a new biohybrid, whose nature he has not yet revealed, but his true goal is the bioengineered heart, he said. “I’m trying to get better and better at building muscular pumps,” he told Science
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