In order to create a material that is both strong and malleable and displays different behavior when exposed to more than one stimulus, researchers embedded light-responsive fibers, which are coated with spirobenzopyran (SP) chromophores, into a temperature-sensitive gel. This new material displays distinctly different behavior in the presence of light and heat. Credit: University of Pittsburgh
Combining photo-responsive fibers with thermo-responsive gels, researchers have modeled a new hybrid material that could reconfigure itself multiple times into different shapes when exposed to light and heat, allowing for devices that not only adapt to their environment, but also display distinctly different behavior in different stimuli.
“In 4D printing, time is the 4th 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.”
Materials that could be reconfigured multiple times into different shapes with the use of different stimuli could dramatically impact manufacturing processes. As a step toward creating such useful, adaptive materials, we use computational modeling to design a composite that integrates a thermo-responsive polymer gel and photosensitive fibers.
Drs Balazs and Kuksenok resolved this issue by embedding light-responsive fibers, which are 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,” Dr. Kuksenok said. “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.”
By localizing 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 and become 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,” Dr. Balazs said. “This composite material could pave the way for soft, reconfigurable devices that display programmed functions when exposed to different environmental cues.”
As Dr. Balazs points out, “the real significant of the work is that we designed a single composite that yields access to a range of dynamic responses and structures. On a conceptual level, our results provide guidelines for combining different types of stimuli-responsive components to create adaptive materials that can be controllably and repeatedly actuated to display new dynamic behavior and large-scale motion.”
Future research with this discovery will focus on tailoring the arrangements of the partially-embedded fibers to create hand-like structures that could serve as a type of gripper. http://www.eurekalert.org/pub_releases/2015-12/uop-hmp121415.php
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