Dec 14, 2015 | By Kira

Researchers from the University of Pittsburgh’s Swanson School of Engineering and from Clemson University in South Carolina have developed a new hybrid material that can actually reconfigure itself multiple times into different shapes when exposed to different light and/or heat stimuli. The research combines photo-responsive fibers with thermo-responsive gels, and has strong potential to be used in soft robotics and other biomimetic, 4D printed adaptive devices.

3D printing technology has already expanded manufacturing and design possibilities, allowing for multi-purpose materials to be transformed into a wide variety of functional devices, from electronics to mechanical metal alloy components to living biological cells. For the most part, however, 3D printed parts are designed, conceived, and manufactured to fulfill a singular and specific purpose.

The next revolution in additive manufacturing is 3D printed parts that can adapt on-demand and fulfill a range of different functions even after they have been printed. They can do this by opening up the ‘fourth dimension’—time—and utilizing environmental triggers such as light, heat, vibrations, or magnetic fields, to self-assemble, re-configure, and respond to existing needs in the manufacturing, packaging, robotics, and biomedical sectors. As Skylar Tibbits, one of the original and leading researchers in the 4D printing field put it: “Imagine robotics-like behavior without the reliance on complex electro-mechanical devices!”

In this latest advancement, led by Anna C. Balazs, Professor of Chemical and Petroleum Engineering at Pittsburgh, and Olga Kuksenok, Associate Professor of Materials Science and Engineering at Clemson, the researches developed computational modeling to design and composite that integrates thermo-responsive polymer gel and photosensitive fibers. The resulting ‘hybrid’ material was found to be highly reconfigurable and mechanically strong, not only able to reconfigure multiple times and into different shapes, but also displaying distinctly different behavior in the presence of different stimuli.

For instance, the Drs. Balazs and Kuksenok found that when anchored to a surface, their composite would bend in one direction when exposed to light, and in the other direction when exposed to heat. When detached, the sample “shrinks like an accordion when heated, and curls like a caterpillar when illuminated.” This means that a single object can fulfill as many functions as the number of shapes it can take on, and that its behavior is completely programmable, predictable, and manifold.

"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," explained Balazs. "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."

The issue of being able to ‘program’ multiple behaviors into a single object was achieved by embedding light-responsive fibers, coated with spirobenzopyran (SP) chromophores, into a temperature-sensitive gel. The researchers also noted that by localizing the SP functionality specifically on the fibers, the composites were able to encompass ‘hidden’ patterns uncovered only in the presence of light. This biomimetic, stimuli-responsive motion could, for example, prove extremely useful for flexible robotic joints that bend and unbend in different lighting conditions.

"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 research was recently published in the journal Materials Horizons by the Royal Society of Chemistry, in a paper titled “Stimuli-responsive behavior of composites integrating thermo-responsive gels with photoresponsive fibers.” Future research by Balazs, Kuksenok and colleagues will focus on customizing the arrangements of the fibers so that they form hand-like structures that could grip or perform other functions in response to environmental stimuli.

Previously, we have seen 4D printing technology used to create complex, self-folding structures, valves that open and contract in response to water temperature, and 3D printed, shape-shifting shoes.



Posted in 3D Printing Materials



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