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Sunday, March 3, 2024

A Bionic Jellyfish Swims With Manic Speed (for a Jellyfish)

No disrespect, but roboticists have got nothing on the animal kingdom. Birds cut through the air with ease, while our drones plummet out of the sky. Humans balance elegantly on two legs, while humanoid robots fall on their faces. It takes roboticists a whole lot of work to even begin to approach the wonders of evolution.

But maybe if you can’t beat ’em, hack ’em. Writing today in the journal Science Advances, researchers from Caltech and Stanford describe how they’ve equipped jellyfish with microchips and electrodes to turbocharge their swimming pace, from a leisurely 2 centimeters per second to a less leisurely 6. It’s a first step toward bionic jellyfish, which scientists might use as a sort of floating sensor network to sample water quality in the oceans. And, more generally, it’s a move toward giving animals powers that evolution hasn’t invented since life’s been on Earth.

Energy remains a major challenge in robotics: It takes a lot of power to run a robot’s sensors and get its limbs or propellers to move. That means bulky batteries, which add weight. And in turn, weight means it takes more power to get the thing moving. Animals, on the other hand, are inherently energy efficient—natural selection favors individuals that have surplus energy to mate and pass their genes down to the next generation.

Jellyfish happen to be not only extremely efficient swimmers, but are also devoid of a brain and pain receptors, making them ideal subjects for this research. “That's important because it allows us to manipulate their swimming in ways that might be ethically questionable in other organisms,” says mechanical engineer John Dabiri of Stanford University and Caltech, coauthor on the paper. But might the jellies be stressed? Unlikely, since jellyfish should secrete a mucus in response to stress, and these test subjects did no such thing. “In addition, it's reversible, so we can take out our device and the animals return to their normal functioning,” Dabiri says.

The researchers’ setup is fairly straightforward: A microchip controls a pair of electrodes inserted into the layer of muscle that powers the jellyfish’s bell. (The probes are made of wood, which sticks well in the tissue thanks to the material’s microscopic barbs.) These electrodes are analogous to the jellyfish’s own eight pacemakers—bundles of neurons positioned around the bell to coordinate movement.

Interestingly, while the human-made pacemaker makes the jellyfish swim three times as fast, the animals only used twice as much energy to do it. So if they’re capable of moving faster, and are more efficient that way, why don’t jellyfish just swim that fast naturally? Because that hypnotic pulsing of their bell does more than propel the animal: Dabiri’s previous research has found that a jellyfish’s methodical movements create vortices that suck in prey. Muck with a jellyfish’s speed and you might muck with its ability to eat.

The increased speeds they were achieving here, though, probably wouldn’t interfere with feeding, Dabiri says. And in the wild, some jellyfish might naturally step on the gas to avoid predators. “This would be analogous to driving a car at the speed limit on the freeway. You still have the ability to go faster, but maybe the preferred speed is slower than the maximum,” says Nick Gravish, who studies the intersection of biology and robotics at UC San Diego but wasn’t involved in this work. So like jellyfish do naturally, these bionic versions might save energy by cruising at normal speed, but use short, high-powered bursts as needed.

Which is much different than how traditional robots operate. Engineers have to supply power for everything—to control algorithms, to run the motors that move the limbs, to charge sensors. But for a jellyfish, says Dabiri, “the only energy we have to put into the system is for that little bit of electrical impulse the animal uses to contract its muscles.” The jellyfish’s default pulses already regulate its movement. So with this living robot, scientists just have to add an electric pulse to the muscle and it’s on its way.

“Overall, I think it's a very interesting test bed for working out rules of how we can rationally augment function of existing complex biological machines,” says Tufts University developmental biophysicist Michael Levin, who wasn’t involved in the work. “That is an essential knowledge gap to fill.”

The other nice thing about jellyfish is they come prebuilt for the life aquatic. Levin and his colleagues have cobbled robots together out of living cells in the lab, programming them for complex behaviors. But that’s in a controlled indoor environment. Because jellyfish are already adapted to swim the seas, Dabiri says, they might be outfitted with sensors that could relay information about salinity, oxygen levels, and other aspects of water quality, then deployed as part of an enormous underwater sensor array. “Jellyfish don't have a brain now, but this device has the potential to become a brain for the jellyfish for the first time,” says Dabiri.

Just don’t let it go to their heads.

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