NEWS
Skin that Crawls
A soft robotic skin that lets millimeter-scale vine robots navigate complex, fragile spaces.
Written by Annemarie Mannion
Researchers showed that the robot was able to navigate a model of a jet engine. Photo: David Baillot/UC San Diego Jacobs School of Engineering
CATERPILLARS HAVE A PARTICULAR WAY of crawling along branches. Soon, robots of a similar build could be climbing through their environments in much the same way because they’ll have just the right equipment—or skin—to do so.
Researchers at the University of California, San Diego have developed a new soft robotic skin that enables extremely small vine-style robots to move through highly complex and delicate environments, demonstrating capabilities that could one day be used in medical, industrial, and inspection applications.
The research team’s findings, which were published in the journal Science Advances, contribute to a growing body of work in soft robotics, a field that seeks to build machines that are more flexible, adaptable, and safer around humans compared to traditional rigid robots.
Soft robots are increasingly being investigated for roles in medical diagnostics, minimally invasive procedures, industrial inspection, environmental monitoring, and wearable technologies. By enabling fine steering at a very small scale, the new skin brings researchers closer to deploying soft robots in environments where they could perform tasks previously considered impossible.
The vine robot can be equipped with a camera on its tip to inspect difficult-to-reach locations. Photo: David Baillot/UC San Diego Jacobs School of Engineering
“We saw the potential of that material [liquid crystal elastomer] because it can provide very large forces and displacements,” said Sukjun Kim, a postdoctoral researcher and the paper’s first author. “It is also very soft and elastic, all of which are great properties for soft robots at a small scale.”
By manipulating both the pressure inside the robot’s body and the temperature of the actuators, the team can steer the robot along complex paths. Temperature-based control is achieved using small, flexible heaters installed underneath the actuators, while pressure is controlled through a system designed to precisely adjust the robot’s internal air flow. The researchers determined that controlling the actuators using both temperature and pressure together yields the best performance.
To evaluate the capabilities of the new robotic skin, the team tested it on flexible vine robots measuring between 3 and 7 millimeters—approximately 0.2 inches—in diameter and about 25 centimeters, or roughly 10 inches, in length. Vine robots grow from the tip by turning their skin inside out, a mechanism that helps minimize friction with surrounding surfaces. With the new skin in place, the researchers found that the robot could execute several turns of more than 100 degrees along its length when the actuators were activated.
The project’s greatest hurdle was creating the first prototype.
A vine robot equipped with the active skin navigates a model of a jet engine and a model of human arteries. Video: UC San Diego Jacobs School of Engineering
“Figuring out the design and materials for each robotic component, and finding the integration method to put them all together was probably the biggest challenge,” Kim said. “We had to explore many different robot materials and actuator compositions. Because the actuator is heat activated, you also need heaters integrated into it. We studied several materials and designs for heaters. There was a moment when we figured out the manufacturing process that tightly integrates the robot body heater and the actuator together and made it work. That was a Eureka moment.”
Researchers showed that the vine robot could squeeze through narrow gaps as small as half its own diameter. In one demonstration, they threaded the robot through a model of a human aorta and a connecting artery, simulating a path that requires precision and delicacy. This result highlights the robot’s potential usefulness in environments requiring tight turns and minimal interaction forces.
The team also tested the robot in a model of the interior of a jet engine. The robot, equipped with a small camera attached at its tip, maneuvered through the mock engine’s convoluted internal structure.
“We saw the potential of that material [liquid crystal elastomer] because it can provide very large forces and displacements. It is also very soft and elastic, all of which are great properties for soft robots at a small scale.”
— Sukjun Kim, a postdoctoral researcher at the University of California, San Diego
Researchers anticipate future work to focus on shrinking the robots even further while maintaining their steering abilities, as well as advancing control methods to allow more sophisticated movement.
“My background is in micro robotics so I like to make things very small,” Kim said. “I’d like to see if we can reduce the diameter even further so it can reach the distal end of vessels and perform treatments that are currently challenging.”
The team is also exploring ways to improve and customize the skin for broader categories of soft robots.
Researchers believe that any setting that requires movement through constrained pathways, or interaction with fragile materials, could make use of small robots outfitted with this soft skin.
Researchers showed that the robot could navigate a model of human arteries. Photo: David Baillot/UC San Diego Jacobs School of Engineering
Next steps for the research team include enabling remote operation, exploring autonomous navigation, and continuing to reduce the robot’s size without sacrificing control. They also plan to develop additional adaptations of the soft skin to broaden its potential uses across other robotic platforms.
Tania K. Morimoto, an associate professor in the Department of Mechanical and Aerospace Engineering at the university, said collaboration between the soft roboticists and materials expert Shengqiang Cai, professor of Mechanical and Aerospace Engineering at the university, fueled the project’s success.
“A tight working relationship with our collaborators on the materials side really pushed this forward,” she said. “Enabling new capabilities for soft robots is probably going to come from collaboration between materials experts and soft roboticists. That was key for us in this project.”
Annemarie Mannion is a technology writer in Chicago.
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