Researchers from the University of Pittsburgh’s Swanson School of Engineering and Clemson University announced last week they have developed a hybrid “4-D printed” composite material that can reconfigure itself multiple times into different shapes when exposed to different light and/or heat. According to the researchers, the real significance of the work is that they designed “a single composite that creates access to a range of dynamic responses and structures.”

Dr. Anna C. Balazs, professor of chemical and petroleum engineering at the University of Pittsburgh, and Dr. Olga Kuksenok, associate professor of materials science and engineering at Clemson University, determined in a recent research paper that in order for a material to be suitable for 4D printing, it would have to exhibit highly reconfigurable behavior while also being quite mechanically strong. This, according to Balazs, was a challenge.

“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.  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,” Dr. Balazs explained. “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.”

Drs. Balazs and Kuksenok resolved this issue with composites. They create a unique material by embedding light-responsive fibers, which are coated with spirobenzopyran (SP) chromophores (color-sensitive molecules), into a temperature-sensitive gel. This resulting composite displayed 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,” Dr. Kuksenok explained. “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 these type of special composites can encompass “hidden” patterns that are only uncovered in the presence of light, allowing the material to be customized in ways that would not be possible by simply heating the sample. This could allow for joints that bend and unbend with light and become an essential component for new adaptive devices, such as flexible robots.