Bistable Isochoric Chiral Metamaterials with Reprogrammable Multiaxial Responses

ABSTRACT Reprogrammable materials enable post‐fabrication tuning of mechanical properties, yet existing concepts are largely confined to uniaxial responses. Engineering materials, on the other hand, are routinely subjected to loading in multiple directions, yet their mechanical responses along these directions cannot be tuned in situ. Here, we introduce a class of chiral metamaterials built from isochoric rotationally bistable units that unlock reprogrammable behavior across multiaxial loading states. Integrating theory, simulations, and experiments, we demonstrate that the bistable units can reversibly switch between open and closed states under clockwise or counterclockwise torque, enabling isochoric switching between soft and stiff responses without geometric reconfiguration of the surrounding architecture. Upon selective activation of given bistable cores, the metamaterial exhibits reprogrammable snap‐through instabilities that alter in situ global buckling modes and energy dissipation pathways. Under multiaxial loading, a set of volume‐dominated properties, including effective bulk modulus and volumetric instability, can be reprogrammed, enabling erasable and rewritable two‐dimensional snapping sequences that encode complex mechanical memory within the material. Beyond property tuning, the work suggests a scalable, reprogrammable framework that can be extended to Cosserat media to achieve multiaxial multifunctionality in soft robotics, fluidic devices, and mechanically intelligent systems.