Triclinic metamaterials by tristable origami with reprogrammable frustration

Geometrical frustration is exploited to induce anisotropy and inhomogeneity in metamaterials, enabling properties beyond those of conventional materials. Guided by Neumann’s principle, a triclinic metamaterial with minimal symmetry is developed, based on a Trimorph origami unit cell comprising four tilted panels and creases. The intrinsic geometry leads to folding motions that couple shear and normal strains, resulting in a reversible auxetic Poisson’s effect, confirmed both experimentally and theoretically. Nonlinear folding produces three stable states, connected by snapping instabilities. When tessellated, the structure exhibits defect-like phenomena due to geometric frustration, which can be reprogrammed by introducing point defects. The Trimorph origami showcases the creation of origami metamaterials with novel symmetries and tunable anisotropy, promising for applications such as wave control and compliant micro-robots.