Using the Japanese art of kirigami, scientists have designed a snakelike skin that could give robots a major mobility boost.
The bioinspired snakeskin, described in the journal Science Robotics, could help scientists build more effective robots that could plunge into disaster zones, explore distant planets and even work inside the body.
"Our kirigami-based strategy opens avenues for the design of new class of soft crawlers that can travel across complex environments for search and rescue, exploration and inspection operations, environmental monitoring, and medical procedures," the study authors wrote.
While the Japanese art of kirigami (a variation of origami that involves paper-cutting, not just folding) has been around for centuries, scientists within the last decade have been exploring it for more practical purposes. Researchers have found that that the paper-cutting art can produce stretchy, three-dimensional structures with remarkable physical properties.
"We believe that the proposed kirigami approach provides a simpler, faster, and cheaper technique to create them," they wrote.
Senior author Katia Bertoldi, a mechanical engineer at Harvard University, had been one of the researchers experimenting with different patterns to see if they had any special applications. (Scientists have already used kirigami to make batteries and stretchable electronics, and even improve solar cells.) She and her colleagues soon realized that the diamond-like patterns that they had made looked very similar to snakeskin.
"So we thought, why not try to use them as a snakeskin?" Bertoldi said.
Skin, at least on humans, is the body's largest organ, and it's constantly multitasking. It feels heat, pressure, helps us to gauge the force we should apply and protects us from disease.
Skin also provides a pliable-but-rough surface that actually helps give you enough traction to move around — think about the soles of your feet, for example. But unlike us, snakes don't have limbs, so in some ways their skin might be even more crucial for helping them move.
Snakeskin appears to have a three-dimensional texture to it that allows snakes to effectively grip a surface as they move forward. Soft robots with smooth bodies, however, don't have that kind of grip. Without some kind of texture, legless robots that move by inflating and deflating their bodies would just thrash around helplessly.
So for this project, Bertoldi and her colleagues took sheets of plastic and laser cut them into different patterns — circular, triangular and trapezoidal. They wrapped these kirigami sheets around tube-shaped crawlers that were powered by air movement. As the tube inflated, the folds and cuts in its kirigami wrapping popped out, giving it three dimensional texture to grip the surface. As the tube deflated, the folds flattened, allowing the bot to smoothly move forward.
The scientists then measured which pattern helped the tube-bot get around fastest. Out of all the patterns they tried, the most effective appeared to be the trapezoidal one — which also just happened to most closely resemble actual snakeskin.
"It's just because they are more extensible," Bertoldi said of the pattern. "Basically for each inflation-deflation, the actuator can extend more."
Right now, their little tube bot only moves forward; Bertoldi said the next steps would involve adapting this skin for bots that can move in different directions.
On top of that, a truly snakelike skin pattern is more complex, she pointed out.
"Right now the skin is homogeneous throughout the body," she said of their kirigami skin. "But if you look at the snake in different portions of the body, the shape of the scales is different."
This technique could be adapted to make very tiny foldable structures that could be useful for medical devices, as well as very big ones for use on Mars rovers and other large robots.
"Because the properties of the designed kirigami skins are primarily governed by the geometry of the structure rather than the constitutive properties of the material, the proposed principles can be applied to systems over a wide range of length scales and made of different materials," the authors wrote.
Bertoldi says she's already working with colleagues who are building robots in the hopes that her skins will make their bots even more mobile than before.