A new hybrid material has been modeled that can respond to both heat and light, and which could lead to materials that present different behaviors depending on the stimuli involved, as well as biomimetic 4D-printed devices that adapt to their environment. Single materials that can be reconfigured many times into different shapes using different stimuli could also significantly change a host of manufacturing processes, especially in the field of sustainability.

Two researchers from the University of Pittsburgh’s Swanson School of Engineering and Clemson University, whose study was published in Materials Horizons [Kuksenok O. and Balazs A. C. Mater. Horiz. (2015) DOI: 10.1039/C5MH00212E], modeled the material based on a combination of photosensitive fibers and thermo-responsive gels to reconfigure itself many times into various shapes when exposed to heat and light. Anna Balazs and Olga Kuksenok used computational modeling to predict how the composites could be easily reconfigurable and also mechanically robust, with the results demonstrating how such single composite materials can offer access to a range of dynamic responses and structures.

They embedded light-responsive fibers coated with spirobenzopyran (SP) chromophores into a temperature-sensitive gel. If the sample is anchored to a surface, it was shown to bend in one direction when exposed to light and the opposite direction when exposed to heat. On becoming detached, the sample shrinks when heated and curls up when illuminated, thus displaying programmable functions that allow an object to present different shapes and functions from being exposed to different environmental cues.

"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"Anna Balazs

Inspired by complex biological movements such as the cooperative interactions between bone and muscle in the human body, the model helped identify how the fibers and the gels would combine to produce structural changes. As Anna Balazs pointed out, “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.”

By localizing the SP functionality on the fibers, the composites encompassed patterns that are only uncovered in the presence of light, so the material can be altered in ways not possible just through heating. It is thought that this biomimetic, stimuli-responsive motion could find applications in joints that can bend and unbend with light, and become a key component of new adaptive devices such as flexible robots.

The team now hopes to tailor the arrangements of the partially embedded fibers to design structures that mimic the motion of human hands, with the fibers acting as small fingers and the gel as the muscle. In this way, such micro-scale systems could one day be controlled to grip around objects using combinations of light and heat.