Soft robotics engineers have always drawn heavily on nature and living organisms to increase their flexibility and adaptability. But a team of Cornell University researchers has taken it a step further—inspired by mammals, they have created a soft robot muscle that can regulate its temperature through sweating, or perspiring.
It solves a long-standing problem in the robotics field, as managing a robot’s internal temperature was a sticky issue previously. Unlike rigid robots, soft robots are made of synthetic materials. While that makes them much more flexible, unlike their metal counterparts, the material holds its heat. A cooling mechanism, such as a fan, is not an integration option as it would make the robot heavy and rigid.
“Our research addresses a fundamental research problem without a specific application in mind,” postdoctoral associate and co-lead author Anand Mishra told Laboratory Equipment. “We know that as soft robots continue to develop, thermoregulation will become a more critical component to enabling high-power, long-duration applications.”
Using a 3-D printing technique, Rob Shepherd, associate professor of mechanical and aerospace engineering, Mishra and their team of engineers created actuators composed of two hydrogel materials that can retain water and respond to temperature.
According to the paper published in Science Robotics, the base layer, made of poly-N-isopropylacrylamide, reacts to temperatures above 30 C (86 F) by shrinking, which squeezes water up into a top layer of polyacrylamide that is perforated with micron-sized pores. These pores are sensitive to the same temperature range and automatically dilate to release the “sweat,” then close when the temperature drops below 30 C. The evaporation of this water reduces the actuator’s surface temperature by 21 C within 30 seconds, a cooling process that is approximately three times more efficient than in humans.
“The ability to perspire is one of the most remarkable features of humans,” said co-lead author T.J. Wallin, a research scientist at Facebook Reality Labs. “Sweating takes advantage of evaporated water loss to rapidly dissipate heat and can cool below the ambient environmental temperature. As is often the case, biology provided an excellent guide for us as engineers.”
When the Cornell engineers incorporated the actuator fingers into a soft robot hand developed to grab and lift objects, they realized the sweating system not only cooled the hand, but lowered the temperature of the object as well.
Mishra said he believes this is the first example of thermoregulation inspired by mammals, but it won’t be the last.
“We want to investigate the role of sensing with sweating where we can combine actuation, sensing, and sweating with the passive actuation,” he said.
While perspirating-soft robots is novel, engineers mimicking nature is not. One of the most famous examples is gecko-inspired adhesives that can support the weight of a person, developed by Stanford University researchers in 2014. The researchers went on to found a spin-off company and collaborate with NASA to develop robots that can “catch” space junk.
Even more examples come out of The Biomimicry Institute, which seeks to make nature a vital part of the design process. Founded in 2006 by Janine Benyus and Bryony Schwan, the Institute hosts youth design challenges, global design challenges, awards and prizes for designs, and even a startup launchpad.
“We see future soft robots that will be highly multifunctional with embodied sensing and intelligence, which could help to respond to diverse and sustainable needs,” said Mishra. “Additionally, soft robotics can highly benefit from novel material design, advanced manufacturing technologies and the mimicry of biological artifacts.”
Photo: The 3D-printed hand with hydraulically controlled fingers that can cool itself by sweating. Credit for photo and video: Cornell University