Bioinspired 3D structures created in Yum’s lab). (Credit: University of Texas – Arlington)

Researchers have developed a process by which 2D hydrogels can be programmed to expand and shrink in a space- and time-controlled way that applies force to their surfaces, enabling the formation of complex 3D shapes and motions.

This process could potentially transform the way soft engineering systems or devices are designed and fabricated. Potential applications for the technology include bioinspired soft robotics, artificial muscles — which are soft materials that change their shapes or move in response to external signals as our muscles do — and programmable matter. The concept is also applicable to other programmable materials.

The approach uses temperature-responsive hydrogels with locally programmable degrees and rates of swelling and shrinking. Those properties allow researchers to spatially program how the hydrogels swell or shrink in response to temperature change using a digital light 4D printing method he developed that includes three dimensions plus time.

Using this method, multiple 3D structures can be printed simultaneously in a one-step process. The structures’ shrinking and swelling are programmed to form 3D shapes, such as saddle shapes, wrinkles and cones, and their direction.

Design rules are based on the concept of modularity to create even more complex structures, including bioinspired structures with programmed sequential motions. This makes the shapes dynamic, so they can move through space. The speed at which the structures change shape can be controlled and thus create complex, sequential motion, such as how a stingray swims in the ocean.