When cardiac physiologist Kit Parker saw a stingray retract from his daughter's hand while she reached out to it on an aquarium visit three years ago, he had a revelation. The marine animal had contracted just like a heart muscle.
"With the exception of crustaceans, almost all marine life's muscles exist to move fluid—either as they swim through water, or to move fluid through their bodies. They're muscular pumps just like the heart is," Parker, who works at Harvard University, told me over the phone.
Parker's realisation led to a research project which saw him focus on mimicking the architecture of stingrays with a robot powered by living rat cells and guided by light. The results were published Thursday in a study in the journal Science on a robotic stingray powered by rat cells. Parker's aim was to show that in the future it might be possible to build artificial hearts from scratch.
"We had reverse-engineered the stingray to figure out what its anatomy was like so we could build a template," explained Parker. "We thought we could substitute for the kinds of computations done by the real stingray's brain by using a special tissue architecture and light to get the undulatory motions."
The robotic stingray, which Parker dubbs a "synthetic beast," is 16 mm long, weighs 10 grams, and contains around 200,000 rat cardiomyocytes—cardiac muscle cells. The researchers overlaid these cells on top of their robotic stingray; they draw energy from the salty-sugary solution they swim in.
The team engineered the cardiomyocytes to respond to light cues. This lets them use pulses of light to control the robotic stingray's side-to-side and up-and-down movements, allowing it to even weave its way around an obstacle course. The robotic stingray moves at roughly two millimeters per second.
"This robot is alive. It's functionally and morphologically a stingray, but genetically it's a rat," said Parker. "We spent over a decade trying to understand how to use cells as a building material."
Next up, the researchers will start building other marine life forms, and perhaps even model a real heart.
"This is like a training exercise for us, we want to get better and better at building muscular pumps so that ultimately we can build hearts for sick kids," said Parker.