Metamaterial Can Be Tuned to Take on Different Shapes

A cross-institutional research team used defects in the material as an advantage to creating specific forms.

Researchers already have developed materials that can react to stimuli to change shape; however, most of these to date have only been able to switch back and forth between two distinct forms.

Now scientists at the Technical University of California (Caltech), working with scientists at ETH Zurich, have taken this design further with the development of a new metamaterial that can change shape in a way that can be tuned to take on different physical properties, they said.

Metamaterial, Technical University of California, Caltech, micro-nanoscale building blocks
Defects in a new metamaterial developed by researchers at the California Institutes of Technology (CalTech) are strategically placed to cause it to take on a specific shape when the material deforms. (Image source: CalTech)

A team in the lab of Julia Greer--professor of materials science, mechanics, and medical engineering in Caltech's Division of Engineering and Applied Science, developed the material--which is unique in that its deformity is controlled through an electrochemically driven silicon-lithium alloying reaction.

This means researchers can control the material using stimuli to transform it into various shapes and then remain in those configurations until the stimuli is reversed, researchers said.

The change in shape depends on the amount of current applied to the material and, if the current is removed when a shape is achieved, the material can maintain that particular shape, they said.

Using Defects as an Advantage

Greer’s lab is known for building materials out of micro- and nanoscale building blocks arranged into sophisticated architectures that can be periodic, like a lattice, or non-periodic in a tailor-made fashion, researchers said.

The materials are designed with strategically placed defects that cause their specific shapes when the material deforms, giving them unique physical properties, said Xiaoxing Zia, a graduate student at Caltech who worked on the research.

Indeed, it’s the defects that researchers used to their advantage in the current work, he said. "The most intriguing part of this work to me is the critical role of defects in such dynamically responsive architected materials," Zia said.

To develop the materials, the team designed a silicon-coated lattice with microscale straight beams that bend into curves under electrochemical stimulation using an ultra-high-resolution 3D printing process called two-photon lithography.

This fabrication method allowed research to integrate defects in the architected material system based on a pre-arranged design, Greer said.

"This just further shows that materials are just like people; it's the imperfections that make them interesting,” she said. “I have always had a particular liking for defects, and this time Xiaoxing managed to first uncover the effect of different types of defects on these metamaterials and then use them to program a particular pattern that would emerge in response to electrochemical stimulus.”

Future in Energy Storage

Researchers tested the system by fabricating a sheet of the material that, under electrical control, reveals a Caltech icon.

The team published a paper on their work in the journal Nature.

Researchers envision myriad uses for the material, particularly for next-generation energy storage because it provides the ability to create adaptive systems, Greer said. Batteries, for example, could be significantly lighter, safer, and to have significantly longer lives, she said.

The material also could be well-suited to the development of bio-implantable micro devices that require form flexibility to perform tasks inside the body, researchers said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 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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