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Hybrid material 'morphs' depending upon its environment

15 December 2015

Researchers have developed a new '4D' printable material that could reconfigure itself multiple times into different shapes when exposed to light and heat.

Researchers embedded light-responsive fibres, coated with spirobenzopyran chromophores, into a temperature-sensitive gel. The resulting material displays different behaviours in the presence of light and heat (image: University of Pittsburgh)

Combining photo-responsive fibres with thermo-responsive gels, researchers at the University of Pittsburgh's Swanson School of Engineering and Clemson University have modelled a new hybrid material that could reconfigure itself multiple times into different shapes when exposed to light and heat, allowing for the creation of devices that not only adapt to their environment, but also display distinctly different behaviour in the presence of different stimuli.

"In 4D printing, time is the fourth dimension that characterises the structure of the material; namely, these materials can change shape even after they have been printed," says Pittsburgh's Professor Anna Balazs who developed the computational modelling for this work. "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. The challenge that researchers have faced is creating a material that is both strong and malleable and displays different behaviour when exposed to more than one stimulus."

Drs Balazs and Olga Kuksenok, an associate professor of Materials Science and Engineering at Clemson, resolved this issue by embedding light-responsive fibres, which are coated with spirobenzopyran (SP) chromophores, into a temperature-sensitive gel. This new material displays distinctly different behaviour in the presence of light and heat.

"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," says Dr Kuksenok. "When the sample is detached, it shrinks like an accordion when heated and curls like a caterpillar when illuminated. This programmable behaviour allows a single object to display different shapes and hence functions, depending on how it is exposed to light or heat."

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.

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


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