Researchers have developed the first robot with a 3D-printed body that transitions from a rigid core to a soft exterior and is capable of more than 30 untethered jumps.

"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," said Michael Tolley, an assistant professor of mechanical engineering at University of California - San Diego. The idea of blending soft and hard materials into the robot's body came from nature, Tolley added. For example, certain species of mussels have a foot that starts out soft and then becomes rigid at the point where it makes contact with rocks.

Soft robots tend to be slow, especially when accomplishing tasks without being tethered to power sources and other electronics. Researchers hope that their work will allow rigid components to be better integrated within soft robots, which will then move faster without compromising the safety of the humans who would work with them. Rigid layers make for a better interface with the device's electronic brains and power sources. The soft layers make it less vulnerable to damage when it lands after jumping.

The robot is made of two nestled hemispheres. The top hemisphere is like a half shell, 3D-printed in once piece, with nine different layers of stiffness, creating a structure that goes from rubber-like flexibility on the exterior to full rigidity near to core. Researchers tried several versions of the design and concluded that a fully rigid top would make for higher jumps. But a more flexible top was more likely to survive impacts on landing, allowing the robot to be reused. They decided to go with the more flexible design. The bottom half of the robot is flexible and includes a small chamber where oxygen and butane are injected before it jumps. After the gases are ignited, this half behaves very much like a basketball that gets inflated almost instantaneously, propelling the robot into a jump. When the chemical charge is exhausted, the bottom hemisphere goes back to its original shape. The two hemispheres surround a rigid core module that houses a custom circuit board, high-voltage power source, battery, miniature air compressor, butane fuel cell and other components.

The research was published in the journal Science magazine.