Watch robotic fish swimming to the beat of human heart cells

To uncover the secrets of the human heart, we need to be clever.

And building a school of robotic fish powered by human heart cells is just one way of doing that.

A school of robotic fish created with this technique by a team of researchers at Harvard University and Emory University has come "alive": They can swim by recreating the contractions of a pumping heart. The heart cells in their body contract and stretch, causing their tails to move autonomously.

This shows how lab-grown heart tissue can be designed to maintain a rhythmic beat indefinitely, taking science one step closer to building an artificial heart and offering a unique platform to investigate cardiac illness like arrhythmia.

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Aquatic hearts beating to their own drum

The idea behind the fish is geniusly simple: These zebrafish-based biohybrids are made of paper, plastic, gelatin, and two strips of living heart muscle cells. One strip runs along the robot's left side, while the other runs along the right. When the muscle cells on one side contract, the tail moves in that direction. This propels the fish through the water. The opposite side's muscle cell strip similarly stretches as a result of the action. This stretching then sends a signal to the cells, causing them to contract, which keeps the swimming motion going.

The researchers also created an autonomous pacing node, similar to a pacemaker, that regulates the frequency and rhythm of these spontaneous contractions. The two muscle layers and the autonomous pacing node work together to generate continuous, spontaneous, and coordinated back-and-forth fin movements.

"We don't need any external stimulation," co-first Sung-Jin Park, a former postdoctoral fellow at Harvard's Disease Biophysics Group, explains in a press release. "They stimulate themselves, they exercise by themselves and they get stronger."

This closed-loop system can propel the fish for more than 100 days. Furthermore, the biohybrid fish age like fine wine -- unlike the fish in your fridge. Over the first month of the experiment, the amplitude of muscle contractions, maximal swimming speed, and muscular coordination increased as the cells grew. The biohybrid fish eventually reached speeds and swimming efficiency comparable to wild zebrafish.

Heart treatments of the future

The researchers also examined data like the rhythm and frequency of each contraction, which could help us understand how the hearts of people suffering from cardiac arrhythmia, or irregular heartbeats, work. Furthermore, these findings could aid in the advancement of pacemaker technology.

The researchers also intend to eventually construct a completely functioning heart; however, there are limitations to this, as the biohybrid fish tissue "beats" spontaneously, with little control over its behavior. To overcome such drawbacks, the team plans to create an even more complicated biohybrid organism next, progressing toward more lifelike artificial hearts.

In the future, such biohybrid robotic systems may even fly to space, as researchers believe they are the perfect approach to study microgravity-induced muscle atrophy, or the breakdown of muscle tissue caused by space's lack of gravity, which is something that dangers astronauts. The possibilities are truly limitless, and these squirmy tiny fish are an excellent starting point for grander breakthroughs.