Bioinspired, Rapidly Responsive Magnetically Tunable Stiffness Metamaterials.

Programmable mechanical materials often require dynamic stiffness adaptability, but existing solutions face challenges with slow response times and limited precision. This study introduces magnetically tunable stiffness metamaterials (MTSM) that utilize a bioinspired ternary programming framework to achieve rapid and precise stiffness modulation. Drawing inspiration from biological sarcomeres, which naturally adjust stiffness through structural changes, the MTSM design employs direct ink writing, a 4D printing method, to incorporate neodymium microparticles and a styrene-isoprene-styrene polymer matrix. This approach enables the metamaterial to transition between three distinct stiffness states-soft, moderate, and stiff-through structural deformation controlled by magnetic torque. Integration of MTSM into a 3D array further enhances its versatility, allowing multi-layer stiffness adjustments under magnetic fields. The MTSM array achieves an impressive 390 percent stiffness modulation range and rapid changes in response to an external magnetic field, surpassing the limitations of prior designs. These findings emphasize the potential of ternary programming in MTSM as a foundation for creating next-generation programmable mechanical systems capable of rapid and efficient adaptability.