Scientists have created a school for robotic fish powered from human heart cells.
Scientists report that the fish can swim independently on their own and how lab-grown heart tissue can be used to keep a rhythmic beat for indefinite periods.
Kit Parker, a Harvard professor of applied physics and bioengineering, said that it was a "training exercise." "Ultimately, I want a heart to heal a sick child."
These tiny biohybrids are based on zebrafish and made from plastic, paper, gelatin, and two strips of live heart muscle cells. One strip runs along one side of the robot's body and the other along its right.
The tail moves in the direction of the contracted muscle cells, propelling the fish through water.
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The movement causes muscle cells on the opposite end to stretch. The signal from the stretching causes cells to contract. This perpetuates the swimming motion.
Parker states, "Once that cycle begins, these things just begin to motor."
Parker says that the fish have a unique cluster of cells that triggers the cycle of stretching or contracting.
Park says that the robotic fish were built by a team including Keel Yoon Lee from Harvard and Sung Jin Park from Emory University and Georgia Tech. They activated muscle cells to test some of their early samples. They then put the fish leftovers in an incubator, and left them alone for a few weeks.
Park said that the fish started swimming independently when they opened the incubator. They were fed nutrients and kept swimming for three months.
Park says that scientists were sad when it was time to kill the tiny swimmers. Park says, "We have an emotional attachment to the fish."
From healing hearts to synthetic fish
It is important to show that it is possible to make human heart tissue that beats independently. This is because the body cannot replace lost heart cells due to inflammation or disease.
Parker states that once you are born, approximately two days after leaving the womb and the number of cardiac muscles cells you have at that time is all you will have for the rest your life."
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Parker says that the team decided to test the lab-grown heart cells in robot fish due to the similarity between swimming and pumping, Parker explains.
He says that a fish can be thought of as a pump. It pumps its own blood through the water, instead of pumping it through the body.
Parker states, "I believe there is a common design scheme. There are some fundamental laws of muscular pump that can be conserved from marine life forms and the human heart."
Parker's lab created a rodent-heart cell-powered stingray in 2016. The light was used to control the cells so that the robot's fins would undulate and propel it through the water.
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His team used stem cell technology to convert human skin cells into heart muscle.
Parker says, "The most interesting thing about these fish is how long and fast they would swim in this dish."
He says that heart cells are constantly rebuilding their own health, which takes around 20 days. He says that each cell in the fish's body has been rebuilt five times after swimming for more than 100 consecutive days.
Exercise can also make muscle cells stronger, just like the cells of a heart. These cells may eventually be used to fix a failing heart.
What's next for biohybrid robots?
This type of research, however, should be used to help scientists understand the heart and test drugs for heart disease, according to Ritu Raman (a mechanical engineer at MIT).
Raman states, "You need to understand how something is built in its native context and how we can recreate it in the laboratory as closely as possible."
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Raman's lab has created robots using skeletal muscle. One of these robots could even recover from injury.
She says, "This robot would be damaged and then we would repair it. After a few days it was able move and walk just like it did before."
Scientists are attempting to blur the line between living and machine by creating robots powered from living cells.
Raman states that these lines are still very clear for robots today. They lack awareness and cannot reproduce.
She says that all you are doing is replacing an engine, a rotor, or any other piece you would make in your machine.
Raman believes that biohybrids will become more sophisticated and may be worthy of the same ethical consideration as animals.
