In a paper published Thursday in Science, engineers from Harvard University and the University of California at San Diego present a 3-D printed, hard-and-soft robot that can manage over 30 jumps without connection to an outside computer or power source. The little bot can leap two and a half feet into the air -- up to six times its body height.

The combination of hard and soft materials, which its designers say make it a more efficient jumper, is actually inspired by nature. But we think it looks kind of extraterrestrial. Right? Maybe it's just that smoky trail its leaving in its wake -- presumably from the butane and oxygen used to power it.

Soft robots are so hot right now: They're more durable than robots made out of "hard" materials and less likely to damage objects, animals and humans they come into contact with.

But some hard materials are just too good to pass up: Batteries, sensors and motors are still basically impossible to make well if you're set on squishiness.

"The vision for the field of soft robotics is to create robots that are entirely soft," senior study author Robert J. Wood of Harvard University said in a statement. "But for practical reasons, our soft robots typically have some rigid components -- things like batteries and control electronics."

This robot, Wood said, marries the hard and soft in a more organic way than most soft robots. Instead of making a soft robot that just has its necessarily hard components stuck on until something better comes along, the new design tries to integrate hard and soft to get the best of both worlds.

Inspired by things that go from soft to hard in nature -- like mussels that turn their squishy feet rigid when they use them to push against a surface -- the engineers made a robot that gradually goes from loose to rigid.

A soft, plunger-like body gives way in layers to a rigid core, giving it the stability of a hard robot and the durability of a soft one.

The robot has two hemispheres. The bottom one, which is totally flexible, inflates like a balloon when the butane and oxygen that powers the bot ignite. The resulting jump is made more efficient by the sturdy upper hemisphere, which has nine graduating levels of stiffness surrounding a rigid core. The more rigid the robot, the more efficient its jumps would be -- but the researchers dialed in to a level of flexibility that made it more resilient to impacts.

And sure enough, the robot comes down so gently you can practically hear it say "boop!"

"We believe that bringing together soft and rigid materials will help create a new generation of fast, agile robots that are more robust and adaptable than their predecessors and can safely work side by side with humans," Michael Tolley, an assistant professor of mechanical engineering at UC San Diego and another lead author of the paper, said in a statement.

"In nature, complexity has a very low cost. Using new manufacturing techniques like 3-D printing, we're trying to translate this to robotics," Tolley said.

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