A grasshopper-like soft material can jump 200 times above its thickness

Superhumans don't exist in the real world, but someday you might see super robots. Obviously, robots can be made that are stronger, faster, and better than humans, but do you think there is a limit to how much better we can make them?

Thanks to the ongoing developments in material science and soft robotics, scientists are now developing new technologies that could allow future robotsto push the limits of non-human biology. For instance, a team of researchers at the University of colourado Boulder recently developed a material that could give rise to soft robots capable of jumping 200 times above their own thickness. Grasshoppers, one of the most astonishing leapers on Earth, can leap into the air only up to 20 times their body lengths.

Despite outperforming the insects, the researchers behind the rubber-like jumping material say they took their inspiration from grasshoppers. Similar to the insect, the material stores large amounts of energy in the area and then releases it all at once while making a jump.

Discovered by chance

The rubber-like film is made up of liquid crystal elastomers (LCEs), special materials that are composed of cross-linked polymer networks. These exhibit properties of elastomers (used to make tires, adhesives, and soft robots) and liquid crystals (used to make TV displays, artificial muscles, and microbots) and are highly responsive to different external stimuli. Overall, LCEs are stronger, more flexible, and better actuators than conventional elastomers.

The study's first author, Tayler Hebner, and her colleagues were examining LCEs and their shape-changing ability. They had no intention of creating a jumping robot at that time, but they observed an interesting behavior of LCEs. “We were just watching the liquid crystal elastomer sit on the hot plate wondering why it wasn’t making the shape we expected. It suddenly jumped right off the testing stage onto the countertop,” Hebner said in a news release.

On coming in contact with the hot place, the material first warped and flipped, and then suddenly, within the next six milliseconds, it leaped in the air to a height of about 200 times its thickness.

The researchers realized that LCEs are responsive to heat, which led to the development of the grasshopper-like material. While commenting on these findings, Hamed Shahsavan, a materials science expert at the University of Waterloo who wasn’t involved in the study, told Ars Technica, “LCEs are typically responsive to heat or light. This work also uses heat to generate the energy required for the deformation and jumping of LCEs.”

What makes the material jump?

According to the researchers, the grasshopper-like material is composed of three elastomer layers and liquid crystals. When the material is heated, the elastomer layers start shrinking but the rate of shrinking is faster in the upper two layers, which are less rigid than the bottom layer. Meanwhile, the liquid crystals also start contracting. As a result of these disproportional changes, a cone-like formation appears near the legs on the backside of the robot’s body.

The robot has four legs attached to its four corner sides: two short legs in the front and two long legs in the backside. According to the researchers, as compared to the short legs, the longer back legs offer a higher point of contact, causing the snap-through force to lift the material at the desired angle.

A large amount of energy gets stored in the cone and this leads to mechanical instability in the film. As the LCE is further heated, the cone-shaped formation rapidly inverts, and the material gets kicked up in the air. The study authors note, “The concentric packing of orientation in each of the LCEs programs a directional shape change into a cone. However, variation in the response of the LCE and the mechanical properties of the materials are shown to introduce a temporal instability that manifests as a snap-through in a freestanding film.”

The researchers claim they can change the configuration of their jumping material such that it leaps on cooling instead of heating. Plus, they can easily control the direction in which the material jumps by changing the alignment of its legs. Shahsavan suggests that such LCEs could be used to make a variety of mobile soft robots and devices.

He added, “Confining the jumping mechanism shown in this study provides a large amount of energy output density that can be harvested for the load-bearing functionality of small-scale soft robots. Jumping can also be utilized for the locomotion of small robots on uneven terrains, either directly or as a mechanism auxiliary to other locomotion mechanisms such as walking, crawling, inching, etc.”

LCEs were discovered about 42 years ago by a chemist named Heino Finkelmann, but this is probably the first time scientists have recognized their extraordinary jumping skills. The resulting grasshopper-like material could provide a potent means of mobility for soft robotics.

Science Advances, 2023. DOI: https://doi.org/10.1126/sciadv.ade1320 (About DOIs)

Rupendra Brahambhatt is an experienced journalist and filmmaker. He covers science and culture news, and for the last five years, he has been actively working with some of the most innovative news agencies, magazines, and media brands operating in different parts of the globe.