Metamaterial Morphs into New Shapes and Takes on New Properties

California Institute of Technology, Pasadena

While most reconfigurable materials can toggle between two distinct states, a new material’s shape can be finely tuned, adjusting its physical properties as desired. The material has potential applications in next-generation energy storage and bio-implantable microdevices.

The Ni-based alloy presents significantly better creep properties over current alloys (ME3 and LSHR) through phase transformation strengthening.

Most materials that are designed to change shape require a persistent external stimulus to change from one shape to another and stay that way; for example, they may be one shape when wet and a different shape when dry — like a sponge that swells as it absorbs water. By contrast, the new nanomaterial deforms through an electrochemically driven silicon-lithium alloying reaction, enabling it to be finely controlled to attain any in-between states, remain in these configurations even upon the removal of the stimulus, and be easily reversed. If a low current is applied, a resulting chemical reaction changes the shape by a controlled, small degree. If a high current is applied, the shape changes substantially. Remove the electrical control and the configuration is retained.

Defects and imperfections exist in all materials and can often determine a material’s properties. In this case, the team built in defects to imbue the material with the properties they wanted.

The researchers designed a silicon-coated lattice with microscale straight beams that bend into curves under electrochemical stimulation, taking on unique mechanical and vibrational properties. The materials were created using an ultra-high-resolution 3D printing process called two-photon lithography. Using this novel fabrication method, they were able to build in defects in the architected material system, based on a pre-arranged design. In a test of the system, a sheet of the material was fabricated that, under electrical control, revealed a Caltech icon.

A material with such a finely controllable ability to change shape has potential in future energy storage systems because it provides a pathway to create adaptive energy storage systems that would enable batteries to be significantly lighter, safer, and to have substantially longer lives. Some battery materials expand when storing energy, creating a mechanical degradation due to stress from the repeated expanding and contracting. Architected materials can be designed to handle such structural transformations.

For more information, contact Robert Perkins at This email address is being protected from spambots. You need JavaScript enabled to view it.; 626-395-1862.