Researchers at Cornell University have developed a soft robot that can sweat using multi-material 3D printing. The human-inspired perspiration function enables the robot to efficiently regulate its temperature and avoid overheating.
Researchers are increasingly turning to nature for inspiration in designing next-gen robotics, materials and more. In this case, a research team from Cornell found the inspiration in how their own bodies acclimatize to hot weather: by sweating.
The human body—as well as those of only a few other types of mammals—regulates its temperature by releasing water through sweat glands. The evaporation of this water on the skin functions to cool the body temperature.
“The ability to perspire is one of the most remarkable features of humans,” explained T.J. Wallin, co-lead author and 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… So as is often the case, biology provided an excellent guide for us as engineers.”
In its research, the team wanted to find a way to manage the generation of heat in soft robots. Unlike metals, which can dissipate heat quickly, soft robots are made from synthetic materials which typically hold on to heat. Rather than using fans to dissipate the heat generated by soft robots—which can be bulky—the team devised a way to make them sweat.
The team used multi-material SLA 3D printing technology to create finger-like actuators for a soft robot. These actuators were printed from a combination of two hydrogel materials, which are likened to “smart sponges” because of their ability to retain water and react to temperature changes.
The first material, which makes up the base layer of the actuators, is poly-N-isopropylacrylamide. This material shrinks when exposed to temperatures over 30 degrees Celsius, which causes the water contained in the material to move upwards into the top layer of polyacrylamide material.
The top layer of the finger-like actuators integrates a number of micron-sized pores, which are designed to dilate when exposed to 30 degrees Celsius temperatures, releasing the water from the fingers. When the temperature drops below 30 degrees, the pores tighten again and the perspiration stops.
The robotic perspiring technique is remarkably effective. According to the research team, the release of the water and its evaporation cooled the actuator’s surface by 21 degrees Celsius in just 30 seconds. This cooling rate is about three times more efficient than human perspiration. Used in combination with a fan, the robotic actuators cooled down six times faster.
The researchers do still have some kinks to work out in the project. For one, the sweating actuators can limit a robot’s mobility. For another, the team needs to find a way for the robot to replenish its water supply as it sweats. Ultimately, the goal is to find a thermal management solution that will enable soft robots to work independently for long periods of time without overheating and shutting down.
The research project, led by Rob Shepherd, Associate Professor of Mechanical and Aerospace Engineering at Cornell, was recently published in the journal Science Robotics.