Minimal-surface-based multiphase metamaterials with highly variable stiffness

Variable-stiffness materials have a unique ability to change their stiffness reversibly in response to external stimuli or conditions. However, achieving ultrahigh stiffness change is often constrained by the geometric organization of the microstructures in most materials that exhibit variable stiffness. Therefore, to overcome this limitation, we introduce a metamaterial design inspired by triply periodic minimal surfaces for fabricating multiphase metamaterials. The specific geometric features of minimal surface designs facilitate interlocking bi- or tri-continuous interpenetrating phases such as air, resin, and alloy within a single multiphase metamaterial. These multiphase metamaterials are constructed by injecting a low-melting-point alloy (LMPA) into a 3D-printed elastic resin mold. The thermally-induced solid-liquid phase transition of the LMPA governs the stiffness change in multiphase metamaterials, ranging from Kilopascals to Gigapascals. Further contributing to this phenomenon, the superior resilience of the elastic resin enhances the shape-memory effect of the multiphase metamaterials. Applications of these materials in origami and deployable structures have been successfully demonstrated, highlighting their reconfigurability and volume compressibility. This innovative design strategy provides the foundation for crafting other metamaterials with intricately arranged internal phases. In conclusion, the proposed multiphase metamaterials have promising potential for various engineering applications where adaptability and morphing capabilities are essential.