Engineers have developed soft-bodied robots that can outswim their biological inspiration -- jellyfish.

The jellyfish robots, described this week in the journal Advanced Materials Technologies, were engineered with pre-stressed polymers, a new method that lends strength to soft-bodied robots.

"Our previous work focused on making soft robots that were inspired by cheetahs - and while the robots were very fast, they still had a stiff inner spine," Jie Yin, an assistant professor of mechanical and aerospace engineering at North Carolina State University and corresponding author on the newly published paper, said in a news release. "We wanted to make a completely soft robot, without an inner spine, that still utilized that concept of switching between two stable states in order to make the soft robot move more powerfully -- and more quickly. And one of the animals we were inspired by was the jellyfish."

To build the new jellyfish robots, researchers bonded two polymer layers derived from the same material. Scientists stretched one layer to pre-stress the polymer. The second unadulterated layer featured an air channel.

"We can make the robot 'flex' by pumping air into the channel layer, and we control the direction of that flex by controlling the relative thickness of the pre-stressed layer," Yin said.

By stretching the polymer layer -- pulling each end in opposite directions, for example -- scientists can create layers that want to assume different curved, or warped, shapes. When combined with a thicker unstressed layer, the warped layer assumes a smile-like bend as air is pumped through the air channel. If the second layer is thinner, the activated air channel causes the warped layer to accentuate its frown, each end curling downward.

To build the jellyfish robots, scientists stretched the pre-stressed layer in four different directions, combining it with thin second layer outfitted with a ring-like air channel.

In a relaxed state, the soft-bodied disk takes on a shallow bowl-like appearance, with the dome curving upwards. When the air channel is activated, the outside of the disk bends downward, propelling the jellyfish-bot through the water.

In tests, the jellyfish robots traveled more than two inches per second, nearly double the speeds of the three jellyfish species analyzed for the project.

Researchers used the same construction method for the jellyfish robot to create a gripping robot. Unlike most gripping robots, which require energy to maintain their hold, the new robot remains clenched shut during its relaxed state. Filling the air channel causes the robot to release its cargo.

"The advantage here is that you don't need energy to hold on to the object during transport -- it's more efficient," Yin said.

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