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

Credit: T. Frenzel et al., Science (2017)

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.


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