New adaptive material responds differently to light and heat

By combining photo-responsive fibers with thermo-responsive gels, researchers at the University of Pittsburgh's Swanson School of Engineering and Clemson University have modeled a new hybrid material that can reconfigure itself multiple times into different shapes when exposed to light and heat. This could lead to the creation of devices that not only adapt to their environment but also display distinctly different behavior in the presence of different stimuli.

Computational modeling developed by Anna Balazs, distinguished professor of chemical and petroleum engineering at Pitt, and Olga Kuksenok, associate professor of materials science and engineering at Clemson, predicted these composites would be both highly reconfigurable and mechanically strong. This suggests they could potentially be used for biomimetic four-dimensional printing. A paper on their research is published in Materials Horizons.

"In 4D printing, time is the fourth dimension that characterizes the structure of the material; namely, these materials can change shape even after they have been printed, " explained Balazs. "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 behavior when exposed to more than one stimulus."

Balazs and Kuksenok resolved this issue by embedding light-responsive fibers coated with spirobenzopyran (SP) chromophores into a temperature-sensitive gel. This new material displays distinctly different behavior 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," said Kukseno. "When the sample is detached, it shrinks like an accordion when heated and curls like a caterpillar when illuminated. This programmable behavior 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 localizing the SP functionality specifically on the fibers, 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, 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," said Balazs. "This composite material could pave the way for soft, reconfigurable devices that display programmed functions when exposed to different environmental cues."

"The real significance of the work is that we designed a single composite that yields access to a range of dynamic responses and structures," she continued. "On a conceptual level, our results provide guidelines for combining different types of stimuli-responsive components to create adaptive materials that can be controlably and repeatedly actuated to display new dynamic behavior and large-scale motion."

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

This story is adapted from material from the Swanson School of Engineering, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.