Push to twist: Achieving the classically impossible in human-made material

Researchers have designed a metamaterial that can twist to the right or the left in response to a straight, solid push. Such a chiral response is counterintutitive from the viewpoint of ordinary solid mechanics, says Corentin Coulais in a related Perspective. Achieving this paradoxical mechanical behavior in metamaterial brings the field a step closer to designing artificial materials engineered to deform in unique ways. The development of human-made materials has opened the door to devising properties that would otherwise be unattainable, such as extremes of strength, reusability, shock-absorption, programmability and resilience. These properties are useful for space missions, optics and fluidics, among other applications. One of the challenges in the manipulation of metamaterials has been to achieve a mechanical response that's unexpected by classical standards; for example, making a solid expand, instead of shrink, when it's compressed. Here, by layering computer simulations, 3-D laser microprinting (allowing large-scale fabrication) and complex micromechanical experimental techniques, Tobias Frenzel and colleagues were able to optimize, manufacture and characterize 3-D metamaterials that twist when compressed. Inspired by the properties of light that allow for chiral-like movement from a linear force, Frenzel et al. effectively converted a linear motion (the push) into rotation (a twist), in a solid. As similar size effects have previously been reported in bones, these metamaterials could also be leveraged for prosthetics and bring invaluable insights into how biological solids function, Coulais adds.

American Association for the Advancement of Science