A team of researchers from Harvard have developed a light-sensitive robot out of rat heart cells. The robot, whose movement and shape is inspired by a stingray, is composed of four distinct layers; a silicone substrate that forms its body, a skeletal system made of gold wire, a second layer of silicone that insulates the skeleton and a final layer of 200,000 genetically-engineered rat cardiomyocytes (muscle cells that make up the cardiac muscle). The light controls the robot’s movement while the stingray shape allows more efficient navigation through body fluids.

The cardiomyocytes are engineered in such a manner that they contract under a specific wavelength of light. When the muscles contract, the robot is propelled forward using its fins similar to a stingray. The robot automatically finds the source of light as it swims through the nutrient-rich liquid that keeps its cells alive, allowing it to be remotely controlled. Each wing is tuned to a different light pattern, allowing the stingray to turn and maneuver.

To test the robot’s maneuverability in real-life scenarios, researchers challenged the tissue-engineered ray to swim through an obstacle course using gait control mechanism, which involved modifying the frequency of light and by asynchronously or synchronously triggering the right and left wing circuits.  Synchronous triggering resulted in the ray moving forward while asynchronous triggering resulted in directional turns.

Scientists guided the ray through obstacles using alternating turning and forward motions at an average approximate speed of 1.5 mm/s over an estimated distance of 250 mm, 15 times longer than its body length. Moreover, the ray was able to maintain 80% of its initial speed for up to 6 consecutive days, indicating its superiority over other bio-hybrid systems in terms of speed, durability, and distance travelled. The demonstration successfully showed the potential of self-propelled, phototactically activated tissue-engineered robots. The bio-hybrid’s test results were published in Science.

This is not the first time a nature-inspired robot has been built. Kevin Kit Parker, the study’s lead researcher and Founding Core Faculty Member, Wyss Institute at Harvard University, was inspired by his daughter’s love for aquatic life. His first foray into robotics came after being mesmerized by a jellyfish during a visit to the New England aquarium in Boston in which the creature’s rhythmic pumping reminded him of a beating heart. Parker’s team had already procured heart muscle cells to grow into thin films on silicone, what remained was how to use the cells which he incorporated into a jellyfish-like “pump.”

The result was a “medusoid”—a simple artificial creature built up of cardiomyocytes overlaid on a silicone sheet, molded into a shallow cup rimmed with flaps. A bath of salt-sugar solution sustained the cells, and tiny jolts of electricity made the cells contract, changing the shape of the silicone cup so that the “jellyfish” expelled liquid, propelling it through its bath.

The idea of using light to navigate the stingray was again thanks to his daughter, as he remembered using a laser pointer to guide her down the sidewalk. When Parker’s daughter touched a stingray in the petting tank, it flicked one side of its body and swerved away.

Nature and aquatic life form-inspired design, as applied to robotics, aims at utilizing naturally occurring features such as soft materials, organism structures, gaits, and control mechanisms in artificial settings in order to improve efficiency. The recent trend of nature-inspired robots is leading to a shift in soft polymer material from rigid elements to mimic the flexibility of animal muscles.  Therefore it is no surprise that nature-inspired design played such a major role in Parker’s vision.

Once the stingray’s design has been refined, it can play a vital role in modern medicine techniques. Recently a team of scientists from ETH Zurich and Technion-Israel Institute of Technology, have created a new breed of nanobots able to navigate the body using magnetic fields. Due to the rigidness of these nanobots, they can be a bit difficult to control and maneuver, especially through thicker liquids. But due to Parker’s vision, tasks such as delivering medicine, fighting bacterial cells and performing localized surgery can be performed comparatively quickly due to the bio-hybrid’s fluid movements and reliable maneuverability.

Currently, the bio-hybrid cannot survive outside of a clinical environment. Even if it was not unable to rely on its salt-solution liquid, its rat cells have no immune system and would be immediately attacked by bacteria and fungal pathogens. Despite these setbacks, Parker is adamant that it will lead others to develop a complete, genetically-engineered heart among other things.