Bilayer Gradient Hydrogel with Topological Crosslinking for High‐Sensitivity Tactile Perception and Information Encryption

Human fingers possess stable high sensitivity and a wide range of tactile perception, attributed to the gradient microstructure and the interlocking collagen fiber on the skin's surface. However, challenges persist in achieving simultaneous enhancement of multiple functionalities in artificial skin. Inspired by the unique structure of the skin, a two‐step process involving ion diffusion‐induced and strong‐weak topological crosslinking is synergistically employed to fabricate a bilayer gradient hydrogel. Zn2+ initially diffuses to induce the formation of weak bonds, imparting elasticity. Subsequently, Fe3+/Zn2+ diffusion constructs a strong‐weak topologically crosslinked network, enhancing the toughness of the gel while reducing the brittleness associated with robust bonds. Due to its distinctive design, the gel employs an adaptive energy dissipation strategy subjected to large and small stress, ensuring high sensitivity (3.31 kPa−1, 0–2 kPa), wide sensing range (0.4–40.6 kPa), and exceptional stability (500 cycles). This flexible approach enables programmable design in three dimensions, including ion diffusion type, direction, and shape. This gel can detect the gentle brushing of feathers and human body movements. It utilizes significant differences generated by magnitudes of stress to perform binary information encryption. This study introduces a novel strategy for preparing skin‐like gels, offering promising potential for expanding their applications in complex scenarios. The flexible network induced by weak Zn2+ diffusion undergoes simultaneous sacrifice and reconstruction when subjected to loading, endowing a bilayer gradient gel with high sensitivity. Through strong‐weak Fe3+/Zn2+ dual‐ion diffusion, a topological cross‐linked network is constructed, and the robust coordination imparts a wide detection range. Weak bonds, serving as a buffer, alleviate hysteresis induced by the fracture of brittle bonds.