Hybrid material could enable 4D adaptive devices

Researchers at the University of Pittsburgh's Swanson School of Engineering and Clemson University have modelled a hybrid material that they claim can reconfigure itself multiple times when exposed to light and heat, allowing for the creation of devices that not only adapt to their environment, but also display different behaviour in the presence of different stimuli.

Dr Anna Balazs, Professor of Chemical and Petroleum Engineering at Pittsburgh, explained: "In 4D printing, time is the fourth dimension that characterises the structure of the material. The ability of a material to morph into a new shape alleviates the need to build a new part for every new application, and hence, can lead to significant cost savings."

Drs Balazs and Olga Kuksenok, Associate Professor of Materials Science and Engineering at Clemson, say they have resolved this issue by embedding light-responsive fibres, which are coated with spirobenzopyran (SP) chromophores, into a temperature-sensitive gel.

Dr Kuksenok said: "If we anchor a sample of the composite to a surface, it will bend in one direction when exposed to light, and in the other direction when exposed to heat. When the sample is detached, it shrinks like an accordion when heated and curls like a caterpillar when illuminated."

The researchers note that by localising the SP functionality specifically on the fibres, the composites can encompass ‘hidden’ patterns that are only uncovered in the presence of light, allowing the material to be tailored in ways that would not be possible by simply heating the sample. This biomimetic, stimuli-responsive motion could allow for joints that bend and unbend with light and become an essential component for new adaptive devices, such as flexible robots.

"Robots are wonderful tools, but when you need something to examine a delicate structure, such as inside the human body, you want a ‘squishy’ robot rather than the typical devices we think of with interlocking gears and sharp edges," Dr Balazs said. "This composite material could pave the way for soft, reconfigurable devices that display programmed functions when exposed to different environmental cues."

Future research with this discovery will focus on tailoring the arrangements of the partially-embedded fibres to create hand-like structures that could serve as a type of gripper.

Tom Austin-Morgan

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