The researchers describe their achievement Jan. 18 in the journal Science Advances. They say that similar materials could one day help embody “soft robots” (those that don’t need gears or other hard components to move) to leap or lift.

The material composite responds a bit like how grasshoppers jump by storing and releasing energy in their legs, said study co-author Timothy White.

“In nature, a lot of adaptations like a grasshopper’s leg utilize stored energy, such as an elastic instability,” said White, Gallogly Professor of chemical and biological engineering at CU Boulder. “We’re trying to create synthetic materials that emulate those natural properties.”

The new research takes advantage of the unusual behavior of a class of materials called liquid crystal elastomers. These materials are solid and stretchy polymer versions of the liquid crystals found in laptops or TV displays.

In the study, the team fabricated small wafers of liquid crystal elastomers about the size of a contact lens, then set them on a hot plate. As those films heated up, they began to warp, forming a cone that rose up until, suddenly and explosively, it flipped inside out — shooting the material up to a height of nearly 200 times its own thickness in just 6 milliseconds.

“This presents opportunities for using polymer materials in new ways for applications like soft robotics where we often need access to these high-speed, high-force actuation mechanisms,” said study lead author Tayler Hebner who earned her doctorate degree in chemical and biological engineering at CU Boulder in 2022.

Serendipitous discovery

Hebner, now a postdoctoral researcher at the University of Oregon, and her colleagues discovered this leaping behavior almost by accident.

She was experimenting with designing different kinds of liquid crystal elastomers to see how they changed their shape under shifting temperatures. Joselle McCracken, a senior research associate in White’s lab, joined her to observe.

“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. “We both just looked at each other kind of confused but also excited.”

With careful experimentation and help from collaborators at the California Institute of Technology, the team discovered what was making their material do the high jump.

White explained that each of these films are made up of three layers of elastomer. These layers shrink when they get hot, he said, but the top two layers shrink faster than the bottom one. That incongruity, combined with the orientation of the liquid crystal molecules within the layers, causes the film to contract and form a cone shape. It’s a bit like how painted vinyl sidings can warp in the sun’s rays.

As the cone forms, strain builds up in the film until, all at once — snap! The cone inverts, slapping the surface and knocking the material up. The same film can also hop several times without wearing out.

“When that inversion happens, the material snaps through, and just like a kid’s popper toy, it leaps off the surface,” White said.

Leaps forward

Unlike those poppers, however, the team’s liquid crystal elastomers are versatile. The researchers can tweak their films so that they hop when they get cold, for example, not hot. They can also give the films legs to make them jump in a particular direction.

Most robots probably wouldn’t be able to use this kind of popping effect to make their parts move. But White said that the project shows what similar kinds of materials could be capable of — storing an impressive amount of elastic energy, then releasing it a single go. And, Hebner said, the project brought a bit of fun to the lab.

“It’s a powerful example of how the fundamental concepts we study can transform into designs that perform in complex and amazing ways,” she said.

Grasshoppers, meet your new competition.

Video: https://youtu.be/0iggefqpACQ

The hybrid “eBiobots” are the first to combine soft materials, living muscle and microelectronics, said researchers at the University of Illinois Urbana-Champaign, Northwestern University and collaborating institutions. They described their centimeter-scale biological machines in the journal Science Robotics.

“Integrating microelectronics allows the merger of the biological world and the electronics world, both with many advantages of their own, to now produce these electronic biobots and machines that could be useful for many medical, sensing and environmental applications in the future,” said study co-leader Rashid Bashir, an Illinois professor of bioengineering and dean of the Grainger College of Engineering.

Bashir’s group has pioneered the development of biobots, small biological robots powered by mouse muscle tissue grown on a soft 3D-printed polymer skeleton. They demonstrated walking biobots in 2012 and light-activated biobots in 2016. The light activation gave the researchers some control, but practical applications were limited by the question of how to deliver the light pulses to the biobots outside of a lab setting.

The answer to that question came from Northwestern University professor John A. Rogers, a pioneer in flexible bioelectronics, whose team helped integrate tiny wireless microelectronics and battery-free micro-LEDs. This allowed the researchers to remotely control the eBiobots.

“This unusual combination of technology and biology opens up vast opportunities in creating self-healing, learning, evolving, communicating and self-organizing engineered systems. We feel that it’s a very fertile ground for future research with specific potential applications in biomedicine and environmental monitoring,” said Rogers, a professor of materials science and engineering, biomedical engineering and neurological surgery at Northwestern University and director of the Querrey Simpson Institute for Bioelectronics.

To give the biobots the freedom of movement required for practical applications, the researchers set out to eliminate bulky batteries and tethering wires. The eBiobots use a receiver coil to harvest power and provide a regulated output voltage to power the micro-LEDs, said co-first author Zhengwei Li, an assistant professor of biomedical engineering at the University of Houston.

The researchers can send a wireless signal to the eBiobots that prompts the LEDs to pulse. The LEDs stimulate the light-sensitive engineered muscle to contract, moving the polymer legs so that the machines “walk.” The micro-LEDs are so targeted that they can activate specific portions of muscle, making the eBiobot turn in a desired direction.

The researchers used computational modeling to optimize the eBiobot design and component integration for robustness, speed and maneuverability. Illinois professor of mechanical sciences and engineering Mattia Gazzola led the simulation and design of the eBiobots. The iterative design and additive 3D printing of the scaffolds allowed for rapid cycles of experiments and performance improvement, said Gazzola and co-first author Xiaotian Zhang, a postdoctoral researcher in Gazzola’s lab.

The design allows for possible future integration of additional microelectronics, such as chemical and biological sensors, or 3D-printed scaffold parts for functions like pushing or transporting things that the biobots encounter, said co-first author Youngdeok Kim, who completed the work as a graduate student at Illinois.

The integration of electronic sensors or biological neurons would allow the eBiobots to sense and respond to toxins in the environment, biomarkers for disease and more possibilities, the researchers said.

“In developing a first-ever hybrid bioelectronic robot, we are opening the door for a new paradigm of applications for health care innovation, such as in-situ biopsies and analysis, minimum invasive surgery or even cancer detection within the human body,” Li said.

The National Science Foundation and the National Institutes of Health supported this work.

Video: https://youtu.be/MI__Nm6EzvA

“Although an athlete may experience a slow or delayed recovery, there is reason to believe recovery is achievable with additional time and injury management,” said study author Thomas W. McAllister, MD, of the Indiana University School of Medicine in Indianapolis. “This is an encouraging message that may help to relieve some of the discouragement that athletes can feel when trying to return to their sport. While some athletes took longer than 24 days to return to play, we found that three-quarters of them were able to return to sports if given just one more month to recover.”

The study looked at 1,751 college athletes who had been diagnosed with a concussion by a team physician. Of the athletes, 63% were male and 37% were female. Male athletes participated primarily in football, soccer and basketball. Female athletes participated primarily in soccer, volleyball and basketball.

Participants were evaluated five times: within six hours after their injury, one to two days later, once free of symptoms, once cleared to return to play and at six months.

Participants reported symptoms daily to medical staff, up to 14 days following injury and then weekly if they had not yet returned to play.

A total of 399 athletes, or 23%, had a slow recovery.

Researchers found that of the athletes who took longer than 24 days to return to play, more than three-fourths, or 78%, were able to return to play within 60 days of injury, and four-fifths, or 83%, were able to return to play within 90 days of injury. Only 11% had not returned to play six months after injury.

For the slow recovery group, the average time for returning to play was 35 days after injury, compared to 13 days in the overall group.

“The results of this study provide helpful information for athletes and medical teams to consider in evaluating expectations and making difficult decisions about medical disqualification and the value of continuing in their sport,” McAllister said.

A limitation of the study is that participants were all collegiate varsity athletes and may not be representative of other age groups or levels of sport, and the results may not apply to other types of mild brain injuries.

The study was supported by the Grand Alliance Concussion Assessment, Research, and Education Consortium, National Collegiate Athletic Association, and the Department of Defense.