Cellular materials with tunable bistability integrating prominent soft and stiff properties

Developing materials that combine both softness and stiffness is crucial for meeting the demands of complex and versatile applications. The realization of multistability through elaborate units has been demonstrated, but the trade-off between performance and light weight across different states remains underdeveloped. In this work, we pioneer the application of the soft-stiff responsive strategy to lightweight cellular materials through architecturally nesting two materials with contrasting properties. The proposed cellular materials can be reconfigured and switched between soft and stiff states, as demonstrated experimentally, theoretically and numerically. The soft state represents high perturbation sensitivity and prominent vibration isolation properties. The stiff state exhibits a strong load-carrying capability due to multi-synergistic mechanisms, with a crushing modulus and strength 668.78 and 1037.55 times as high, respectively, as the soft state in the cases of soft materials embedded in metal materials. The manipulable mechanical properties can be tuned across a broad design space while maintaining robust switchability. These advantages of the proposed bistate cellular materials offer promising application prospects from adaptive protection to shock absorption and beyond.