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Scientists have created a synthetic fish - a sting ray. It's made of gold, silicone and muscle cells from a rat. It's not just a curiosity. As NPR's Jon Hamilton reports, it is part of an effort to build a better artificial heart.
JON HAMILTON, BYLINE: A heart and a sting ray may seem pretty different, but both need to overcome problems that involve fluid and motion. A sting ray has to propel itself through the water. A heart has to propel blood through the circulatory system. And all that was on Kit Parker's mind one day when he visited an aquarium. Parker is a biophysicist at Harvard's Wyss Institute. He'd taken his daughter Caroline to an exhibit where you can touch rays as they swim by.
KIT PARKER: Caroline had her hand down in the water, and the sting ray was coming at it. And it had a quick flick of its pectoral fin, and it just smoothly evaded her hand.
HAMILTON: Parker realized that this sort of split second adjustment is something the heart does all the time.
PARKER: As soon as it happened, the idea just hit me like a thunder bolt.
HAMILTON: His ultimate goal is to build a bioengineered heart out of living muscle tissue, but that's really tough. A sting ray, though - that seemed simpler to Parker, at least until he described his plan to a researcher named Sung-Jin Park.
PARKER: I sat down with him. I said, Sung-Jin, we're going take a rat apart. We're going to rebuild it as a sting ray, and then we're going to use a light to guide it. And the look on his face was both sorrow and horror.
HAMILTON: How was he going to take cells from a rat and make them swim like a fish? The team started working, though, and eventually they succeeded. Their synthetic ray has a transparent body made of silicone and a skeleton of sorts made of gold. The ray is propelled by 200,000 heart muscle cells taken from a rat. And those cells have been genetically altered to allow the hybrid creature to follow a pair of blue lights.
PARKER: And so then we put the sting ray down in the dish. It's shaped like a sting ray. It's about the size of a nickel, maybe a little bit bigger. And we can guide this thing around. It swims through obstacle courses.
HAMILTON: All with the rhythmic, undulating motion of a real sting ray. Parker says the success, published in the journal Science, is another small step toward his goal of building a better artificial heart.
PARKER: The heart's built the way it is for a reason. And we're trying to replicate as much of that function as we possibly can.
HAMILTON: In the meantime, the sting ray incorporates several advances. John Dabiri, a professor of engineering at Stanford, says one of these is the ability to trigger muscle cells in sequence, so that the fins undulate. Dabiri says the effect is like when the crowd at a soccer game does the wave.
JOHN DABIRI: You have one group standing up and then the next and then the next. Well, in the case of the muscle here, they're doing the same thing now. They're able to get a certain section of muscle to contract and then of the next and then the next.
HAMILTON: Which is exactly the way the heart pumps blood. Another advance is the ability to activate muscle cells with light, rather than electricity. That allows scientists to control precisely which part of a muscle contracts. Of course, experiments like the artificial sting ray can raise uncomfortable questions about things like when a machine becomes a living organism. In this case, it's pretty clear it isn't. It can't grow, adapt or reproduce. But Dabiri says scientists should be considering the possibilities.
DABIRI: We want to make sure we think about the ethical issues hand-in-hand with just asking what we can do as scientists and engineers.
DABIRI: Because in the future, machines made with living cells will become increasingly sophisticated and lifelike. Jon Hamilton, NPR News.
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