It was the aquarium that sent Kit Parker down an unexpected path with his heart research. He was there with his daughter watching jellyfish pulsing through the water. The jellyfish, he realized, looked a lot like hearts pumping blood.
So he went back to his lab to build a jellyfish-inspired robot, powered by muscles made of living heart cells from a rat. The heart cells squeezed and relaxed, squeeze and relaxed, pumping water to propel the artificial jellyfish. It was a rat heart, radically simplified to its most basic function.
Parker, a bioengineer at Harvard, has taken an unconventional approach to mimicking the human heart. On one hand, he’s a leader in the field of organs-on-chips, mimicking human organs in miniature to test new drugs and chemicals. His lab is out with a new paper in Nature Materials today showing a cheap and fast way to 3D-printed chips with heart cells growing on them.
But he also has a more ambitious project: growing a whole living human heart—not for drug testing but for transplant. A new heart grown out of a patient’s own cells would do away with the immunosuppressant drugs transplant recipients have to take for the rest of their lives. And it would leapfrog the bulky mechanical hearts—made of plastic and metal—that patients waiting for transplants currently use.
That’s all very far off, but the jellyfish-inspired robot is a step down Parker’s nontraditional path to figuring out how to grow a heart.
The traditional way scientists have tried to grow hearts, pioneered by the Texas Heart Institute’s Doris Taylor, is by starting with a heart. Taylor uses detergents to strip a heart of all living tissue, leaving only a scaffold of proteins and sugars. She then seeds it with new cells, which grow to fill that protein scaffold. The rat and human hearts grown this way look passable, but they don’t beat with the vigor necessary to pump blood through the whole body. It’s not clear exactly why these lab-grown hearts are so weak, but it may have to do with missing signals that teach heart cells to beat together in one synchronized rhythm.
Rather than grow something very heart-like right away, Parker is taking the indirect approach, starting with simple forms and getting them to beat. “What we’ve done is take a flanking maneuver. I’m assuming the whole herd is going to miss something, and we can find a better angle on the problem.” (Before becoming a professor, Parker served in the military in Afghanistan.)
To make the jellyfish-inspired robot pump properly, Janna Nawroth, then a graduate student advised by Parker, analyzed the circle and spoke-shaped musculature of real moon jellies, patterning the robot’s heart cells in the same way.
On another visit to the aquarium, Parker decided to built a stingray inspired robot out of rat heart cells. He had watched his daughter reach out to touch a stingray, which immediately flicked away—a split second maneuver not unlike how the heart changes the direction of blood flow. So he tasked another researcher in his lab, Sung-Jin Park, to build a robot patterned off of stingray musculature.
Getting heart cells to grow in the right orientation is key. In humans, the heart’s muscle fibers grow in a spiral arrangement. “That’s because the heart has to squeeze itself like a washcloth to wring all the blood out of it when it pumps,” says Taylor. As Parker’s group goes from simple forms with a single layer of heart cells to multiple layers, getting the orientation right will become more challenging, as will getting to all the cells to beat in a synchronized way.
Nevertheless, Taylor says she welcomes these different approaches to growing an artificial heart. The heart is such a complicated machine, growing an artificial one will require uniting people from cell biology and physics and physiology and all different backgrounds. And maybe even a kid who likes going to aquariums.