Synthetic Stingray May Lead To A Better Artificial Heart

Jul 7, 2016
Originally published on July 13, 2016 1:46 pm

Scientists have created a synthetic stingray that's propelled by living muscle cells and controlled by light, a team reports Thursday in the journal Science.

And it should be possible to build an artificial heart using some of the same techniques, the researchers say.

"I want to build an artificial heart, but you're not going to go from zero to a whole heart overnight," says Kit Parker, a bioengineer and physicist at Harvard University's Wyss Institute. "This is a training exercise."

Previous artificial hearts have been versions of mechanical pumps. An artificial heart made from living muscle cells would behave more like a natural heart, Parker says, and would be able to grow and change over time.

"The heart's built the way it is for a reason," he says. "And we're trying to replicate as much of that function as we possibly can."

A heart and a stingray may seem pretty different. But both need to overcome problems that involve fluid and motion, Parker explains. A stingray has to propel itself through the water. A heart has to propel blood through the circulatory system.

And all of that was on Parker's mind a couple of years ago when he visited an aquarium with his daughter. At an exhibit where visitors can touch rays as they swim by, his daughter put her hand in the water. "The stingray was coming at it," he says, "and with a quick flick of its pectoral fin it just smoothly evaded her hand."

Parker realized that this sort of split-second adjustment is something the heart does all the time as it senses changes in blood flow or pressure.

"The idea just hit me like a thunderbolt," he says.

By building an artificial stingray, Parker figured, he could learn how to replicate the animal's ability to respond instantly to changing conditions.

So he came up with a strategy and presented it to Sung-Jin Park, a researcher in his lab.

"I sat down with him," Parker says, "and I said, 'Sung-Jin, we're going to take a rat apart; we're going to rebuild it as a stingray; and then we're going to use a light to guide it.' And the look on his face was both sorrow and horror."

Parker's lab had previously built an artificial jellyfish. But a ray was much more complicated. And the team was facing tough questions like, how do you to take cells from a rat and make them swim like a fish?

Park and the rest of the team started working, though. And, eventually, they succeeded.

Their synthetic ray, which is about the size of a nickel, has a transparent body made of silicone and a rudimentary skeleton made of gold.

The ray is propelled by 200,000 heart muscle cells taken from a rat. The cells have been genetically altered to allow the hybrid creature to follow a pair of blue lights.

"We can guide this thing around," Parker says. "It swims through obstacle courses."

And the creature displays the rhythmic, undulating motion of a real stingray. Replicating that motion is one of the project's key accomplishments, says John Dabiri, a professor of engineering at Stanford who worked with Parker on the artificial jellyfish.

To get the ray's tail to undulate, the team had to come up with a way to trigger muscle cells in sequence. The effect is similar to when the crowd at a ballgame does the wave, Dabiri says.

"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," he says. "They're able to get a certain section of muscle to contract and then the next and then the next."

That coordinated movement is necessary for many biological functions, like swallowing. It's also the way the heart beats, with areas contracting in a precise sequence.

Another advance is the ability to activate muscle cells with light rather than electricity, Dabiri says. That allows scientists to control precisely which part of a muscle contracts. So light could act as a sort of pacemaker in an artificial heart that's made this way.

The artificial stingray is likely to make some people uncomfortable, Dabiri says, because it raises questions about when a machine becomes a living organism.

In this case, the artificial ray pretty clearly isn't an organism, he says. It can't grow, adapt or reproduce. But scientists should be considering the possibilities as they pursue other projects like this, he says.

"We want to make sure we think about the ethical issues hand in hand with just asking what we can do," Dabiri says.

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ROBERT SIEGEL, HOST:

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. Transcript provided by NPR, Copyright NPR.