New Hydrogels Are Capable of Complex Movements

Hydrogels that can expand and contract in response to light could lead to new designs in robotics, artificial muscles, and other medical applications.

A new process using 2D hydrogels applies force to their surfaces in a space- and time-controlled way. The hydrogel materials, which were developed by a team at the University of Texas at Arlington, can be programmed to expand and contract like actual human soft tissues. This capability paves the way for new applications in soft robotics, medical applications, and other fields where programmable materials are useful.

This programming enables the formation of complex 3D shapes and motions that mimic how real human soft tissue moves, said Kyungsuk Yum, an assistant professor in the Materials Science and Engineering Department at UTA, who led the research. “We studied how biological organisms use continuously deformable soft tissues, such as muscle, to make shapes, change shape, and move because we were interested in using this type of method to create dynamic 3D structures,” he said in a UTA news release.

It has historically been difficult to replicate these types of movements in man-made materials, which is why the team’s work is significant and could potentially transform the way that soft engineering systems or devices are designed and fabricated, Yum said. The materials used in the research are temperature-responsive hydrogels with locally programmable degrees and rates of swelling and shrinking. It’s these properties that allow the researchers to program how the hydrogels expand or contract in response to temperature change, Yum said in the release.

moving hydrogel
These bio-inspired 3D structures were created in the lab of Kyungsuk Yum, an assistant professor in the Materials Science and Engineering Department of the University of Texas at Arlington (UTA). (Image source: UTA)

4D Printing

Researchers used a novel digital-light 4D-printing method that Yum developed to create movement in the materials. 4D printing—an emerging research field—goes beyond 3D printing in that it uses time as the fourth dimension. In the process, it mathematically programs the structures' shrinking and swelling to form 3D shapes—such as saddle shapes, wrinkles, and cones—and their direction of movement. The method allows the team to print multiple 3D structures simultaneously in a one-step process, Yum said.

What’s also unique about his work is that Yum has developed design rules based on the concept of modularity to create even more complex structures, he said. These include bio-inspired structures with programmed sequential motions that make the shapes dynamic so they can move through space.  Yum also can control the speed at which the structures change shape and thus create complex, sequential motion that hasn’t been possible before, he added.

“Unlike traditional additive manufacturing, our digital light 4D-printing method allows us to print multiple, custom-designed 3D structures simultaneously,” he said. “Most importantly, our method is very fast, taking less than 60 seconds to print, and thus highly scalable.” Researchers published a video of the process online. They also published a paper on the research in the journal Nature Communications.

Potential applications for the technology include bio-inspired soft robotics and artificial muscles that can change shape or move in response to external signals just as human muscles do, Yum said. The research also could be used to develop programmable matter and other programmable materials.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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