Scientists Build an Artificial Fish That Swims on Its Own Using Human Heart Cells

The experiment could advance pacemaker technology and bring science closer to developing artificial hearts for people

Image of the fish built using human heart cells
Scientists built this synthetic fish using paper, plastic, gelatin and human heart cells. Michael Rosnach, Keel Yong Lee, Sung-Jin Park, Kevin Kit Parker

Harvard scientists have engineered a school of fish that uses the contractions of human heart cells to swim autonomously. Researchers say the experiment could advance pacemaker technology and improve the development of artificial hearts for humans, writes CNET’s Monisha Ravisetti. The team published their results in the journal Science

Researchers built the fish using paper, gelatin, two layers of cardiac muscle tissue—one on the left side and one on the right—and a plastic fin, per the study. Muscle contractions propelled the fish through the water. A contraction on one side caused the muscle on the other side to stretch. The stretching then triggered those cells to contract, which moved the tail from side to side and allowed it to swim on its own. The muscle cells were derived from human stem cells, the authors write in the paper. They also engineered an autonomous pacing node, which acted like a pacemaker by controlling the rhythm and frequency of the contractions, per a statement.

"It's a training exercise," Kit Parker, a professor of bioengineering and applied physics at Harvard and senior author of the paper, tells NPR’s Jon Hamilton. "Ultimately, I want to build a heart for a sick kid."

The fish moved autonomously for over 108 days, which is equivalent to 38 million beats, the study states. Because heart cells constantly rebuild themselves, which takes about 20 days, Parker tells NPR the fish cells rebuilt themselves a total of about five times over. 

"The really interesting thing about these fish, which we weren't expecting, is how long they would swim and how fast they would swim in the dish," Parker says to NPR.

Several years ago, Parker, who is interested in pediatric heart disease, was frustrated by the state of heart therapeutics, he told the Daily Beast’s Neel V. Patel. 

“It occurred to me in 2007 that we might have failed to understand the fundamental laws of muscular pumps,” he said in a 2012 statement. He began looking at marine organisms for inspiration. Then, on a trip to the aquarium with his daughter, he spotted a jellyfish. 

“I’m looking at it, and thinking, ‘It pumps, it looks like a heart pump,’” he tells the Daily Beast. “I’m thinking, ‘I could build that damn thing.’” 

In 2012, his team created a jellyfish that swam using rat heart cells, and then a ray fish with rat heart cells in 2016. The new biohybrid fish built off this previous research, per a statement

Three engineered fish, showing their movements
Muscle contractions of the heart cells moved the fish tails from side to side, propelling it through the water.  Michael Rosnach, Keel Yong Lee, Sung-Jin Park, Kevin Kit Parker

Though the researchers say the fish is a step forward for heart research, it could be years before it leads to the creation of an artificial heart, Michael Schneider, a professor of regenerative cardiology at Imperial College London, who was not involved in the study, tells Insider’s Marianne Guenot. He tells the publication that the transplantation of genetically altered pig hearts is more promising.

But that doesn’t discourage Parker. 

"I think that other methods will be faster than us," Parker tells Insider. “But in the long run, creating tissue that relies on the patient's own cells could offer unexpected benefits over pig organs or synthetic alternatives”