The last time we checked in with engineering professor Kit Parker, his students had finished building a brisket-smoking robot. It's easy to see why they did that: Brisket is tasty, brisket is hard to cook, and Harvard kids are wicked smaht.
His latest project is no less impressive, but it requires greater mental gymnastics to parse. Here's the easily understood cool part: A team led by Parker created artificial stingrays that use a rat's heart cells as motors, and the rays can be controlled with a blinking light. Here's another cool part that's harder to grok: One day, the team's techniques could help build artificial human organs.
Parker, the Tarr Family Professor of Bioengineering and Applied Physics at Harvard University, often draws inspiration from animals and seemingly random objects. His past projects include spinning artificial tissues out of modified cotton candy machines, camouflage clothing that changes colors like a chameleon, and cyborg jellyfish.
As fascinating as those things are, Parker’s real goal is to build an artificial four-chamber heart that can help diagnose ailments and replace malformed hearts in babies and young children. Parker, a researcher at SEAS, looks to the seas for ideas. “In the ocean, most creatures with the exception of crustaceans, almost all their musculature exists to pump fluids," Parker says. "Either to swim through water or pump it through their body."
Parker sees a link between sea critters and how the human heart works. "Most muscular pumps---stingrays, jellyfish, the heart---do have similar design features," he says. You see a jellyfish, and Parker sees a simple muscular pump. A few years ago, his team built an artificial jellyfish using a rat’s heart cells, a relatively easy feat compared to the cyborg rays. The jellyfish didn’t have any type of navigational control. A trip to the aquarium with his daughter Caroline inspired this far more complex project.
The New England Aquarium features a petting tank of rays and small sharks. Children can feel the fish as they swim by. That's how it's supposed to work, anyway. When Caroline, who was 4 at the time, put her hand in the tank, a ray that wasn't in a petting mood easily evaded her with a quick flip of its wing. “When I saw it happen, it hit me like a lightning strike,” Parker says. “The musculature in that fin, in order to change direction, must have been like the musculature we see in the endocardial surface of the heart, the inside layer of the heart. If I could replicate or build this, then I might have a deeper understanding of why the heart is built the way it is.”
Like most people, Parker lacks the skills to build a light-guided tissue-engineered stingray using rat parts, even if he does have a background in biomedical and mechanical engineering. But he knows people who do have those skills---specifically, Sung-Jin Park, who'd recently started his postdoctoral fellowship on Parker’s disease biophysics team at SEAS. Finding Park was easy; convincing him was a different matter.
“I said, 'Hey, Sung-Jin, we’re going to take a rat, tear it apart, and rebuild it as a stingray. We can publish it in Science, and we’re going to get the cover,'" Parker says. "He looked at me like a hog staring at a wristwatch. It took me about a year to convince Sung-Jin that it wasn’t professional suicide.”
Within three years, the project went from a far-out scheme to, yes, the cover of Science. Park was able to steer the mini rays---about one tenth the size of the real deal---through obstacle courses using a pulsing blue light. The team worked with Stanford researcher Karl Deisseroth on the optical genetics to make heart cells "see." When the creatures sense a certain wavelength of light, their heart muscles contract, flap their wings, and make them swim.
The recipe for these artificial sea creatures consists of “a pinch of breast implant, a pinch of gold, and a pinch of rat,” says Parker. The bodies are made of polydimethylsiloxane, the flexible outer coating of a breast implant. It also provides a friendly substrate for the rat heart cells. That gold isn’t just to give the rays baller status; it provides a spring-loaded skeleton, one that makes its wings recoil to a ready position after each muscle contraction. The artificial tissues containing the rat’s heart cells are built into a layer of polydimethylsiloxane; they flap the stingray’s wings upon contraction and recoil due to the golden skeleton.
So how does this impressive creature advance the greater goal of building a full-on artificial heart? Parker calls it a training exercise, a way for scientists and engineers to practice their craft and build a control experiment. And Parker hopes the light-guided portion can lead to a kinder, gentler pacemaker. Instead of having to insert electrodes into a heart, brief flashes of light could help it keep the beat.
He also sees this as the first step toward safer drug testing, as researchers could test potentially toxic pharmaceuticals on an artificial human heart. Pharmaceutical companies, regulators, and physicians could see the effect of cancer treatments and experimental drugs without endangering anyone. But the primary goal remains building a full tissue-engineered heart.
“We’re doing a crawl, walk, run approach to building the heart,” Parker says. “Replacing a heart, that is a long term goal. That’s blue sky, way off in the future. But along the way we can replace parts of a baby’s malformed heart with something tissue-engineered. It might be valves, it might be a ventricular chamber.”
At the moment, it’s simply a sweet light-guided cyborg mini-stingray with high hopes. One you won't find in any aquarium's petting zoo.
