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A Soft Material that Moves When Exposed to Light Could be Ideal for Robotics

When exposed to non-uniform light, the SP-BZ gel moves. This diagram shows how the material moves over time when only the ends are exposed to light. (Photo Credit: University of Pittsburgh)
When exposed to non-uniform light, the SP-BZ gel moves. This diagram shows how the material moves over time when only the ends are exposed to light.
(Photo Credit: University of Pittsburgh)

Researchers at the University of Pittsburgh’s Swanson School of Engineering have designed a synthetic polymer gel that can generate enough chemical energy to shape-shift and propel itself forward. The researchers modeled their research after the single-celled organism euglena mutabilis, which processes energy to expand and contract its shape in order to move.

“Movement is a fundamental biological behavior, exhibited by the simplest cell to human beings. It allows organisms to forage for food or flee from predators. But synthetic materials typically don’t have the capability for spontaneous mechanical action or the ability to store and use their own energy, factors that enable directed motion,” Anna Balazs, one of the researchers on the project, said in a press release. “Moreover in biology, directed movement involves some form of shape changes, such as the expansion and contraction of muscles. So we asked whether we could mimic these basic interconnected functions in a synthetic system so that it could simultaneously change its shape and move.”

The researchers used two materials: polymer gels containing spirobenzopyran (SP), which can be morphed into different shapes with the use of light, and Belousov-Zhabotinsky (BZ) gels which undergo periodic pulsations and can also be made to move using light.

“The BZ gel encompasses an internalized chemical reaction so that when you supply reagents, this gel can undergo self-sustained motion,” researcher Olga Kuksenok said the release. “Although researchers have previously created polymer chains with both the SP and BZ functionality, this is the first time they were combined to explore the ability of “SP-BZ” gels to change shape and move in response to light.”

These combined material is distinctive it integrates the attributes of each of the components: it can be molded with light and has autonomous mechanical actions.

Interestingly, changing the pattern of the light affected it’s behavior. Some patterns even caused the gel move in a tumbling fashion. “We also found that if we placed the SP in certain regions of the BZ gel and exposed this material to light, we could create new types of self-folding behavior,” Balazs said. Now the researchers will work on different ways of patterning the light to create other movements, as well. Ultimately, Balazs believes the material could be useful for very small soft robots for microfluidic devices.

“Scientists are interested in designing biomimetic systems that are dissipative — they use energy to perform a function, much like our metabolism allows us to carry out different functions,” she said. “The next push in materials science is to mimic these internal metabolic processes in synthetic materials, and thereby, create human-made materials that take in energy, transform this energy and autonomously perform work, just as in biological systems.”

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