Engineering team develops self-powered mobile polymers

As robots become more and more advanced, researchers are tasked with dealing with design challenges to make them more efficient and improve mobility. When it comes to miniature, “squishy” robots, engineers are faced with a power-to-weight ration challenge. The robot itself needs a power source that doesn’t unnecessarily add weight making movement more difficult.

An azobenzene-functionalized liquid crystalline polymer moves when exposed to broadband ultraviolet-visible light. Credit: Jeong Jae Wie, Inha University/AFRL

An international engineering team believe they have found the right solution. Building on previous researcher, engineers from Inha University, University of Pittsburgh and the Air Force Research Laboratory have identified new materials that directly convert ultraviolet light into motion without the need for electronics.

The group includes M. Ravi Shankar, co-author and professor of industrial engineering at Pitt’s Swanson School of Engineering. Lead author is Jeong Jae Wie, assistant professor of polymer science and engineering at Inha University, South Korea. The experiments were conducted at the Air Force Research Laboratory’s (AFRL) Materials & Manufacturing Directorate at Wright-Patterson Air Force Base, Ohio, under the direction of Timothy J. White.

The new materials challenge traditional robotic design. Without the need for electronics or an energy source, the team believes that they can build robots without adding heavy devices or complex parts, which will increase the limits of mobility.

In this case, the team is using light as the energy source. Dr. Shankar explains that this is an appealing option for the team because of the speed, temporal control and the ability to effectively target the mechanical response.

For the material, the group zeroed in on monolithic polymer films prepared from a form of liquid crystalline polymer.

Other investigations have proposed the use of ambient energy resources such as magnetic fields, acoustics, heat and other temperature variations to avoid adding structures to induce locomotion. However, the team found that light was the best option and zeroed in on monolithic polymer films prepared from a form of liquid crystalline polymer for the material.

“Our initial research indicated that these flexible polymers could be triggered to move by different forms of light,” Dr. Shankar explained. “However, a robot or similar device isn’t effective unless you can tightly control its motions. Thanks to the work of Dr. White and his team at AFRL, we were able to demonstrate directional control, as well as climbing motions.”

One of the advantages of using certain polymers is the “photomotility” properties. According to Dr. Wie, when exposed to UV light, these materials spontaneously form into spirals. By controlling the exposure, the team is able to enable corresponding motion without the need for an external power source.

“Complex robotic designs result in additional weight in the form of batteries, limb-like structures or wheels, which are incompatible with the notion of a soft or squishy robot,” Dr. Wie said. “In our design, the material itself is the machine, without the need for any additional moving parts or mechanisms that would increase the weight and thereby limit motility and effectiveness.”

Being able to control a robot’s movement without the need of an external power source attached, opens up the doors for unique design specifications.

For the material itself, the team was able to demonstrate more complex movement beyond just simply moving forward and backwards. The collaboration showed that the polymers were able to climb a glass slide at a 15-degree angle.

While the flat polymer strips are small  (approximately 15mm long and 1.25mm wide) they can move at several millimeters per second propelled by light. The movement can be perpetual, as long as the material remains illuminated.

“The ability for these flexible polymers to move when exposed to light opens up a new ground game in the quest for soft robots,” Dr. Shankar said. “By eliminating the additional mass of batteries, moving parts and other cumbersome devices, we can potentially create a robot that would be beneficial where excess weight and size is a negative, such as in space exploration or other extreme environments.”

The research, “Photomotility of Polymers,” was published in the journal Nature Communications.

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