Liquid Metal‐Reinfored Hierarchically Aligned Double‐Network Hydrogels: Ultrahigh Crack/Fatigue Resistance and Strain‑Responsive Sensing

Soft hydrogels are promising for wearable stretchable devices due to their flexibility, stretchability, and biocompatibility, but most existing soft hydrogels suffer from crack propagation and fatigue failure. Inspired by the structure-property relationships of biological tissues, we developed a pre-alignment and subsequent cross-linking strategy to fabricate a hierarchically anisotropic double-network (DN) hydrogel that exhibits remarkable toughness, exceptional fatigue resistance, and high conductivity. The anisotropically aligned polymer network, synergistically combined with deformable liquid metals (LM) particles, enables efficient stress transfers and crack propagation suppression. The hydrogels exhibit a high fracture energy of 60.6 kJ m^-2 and an ultrahigh fatigue threshold of 5560 J m^-2, while maintaining a human skin-matching modulus of 1.3 MPa. Furthermore, the LM particles impart relatively high conductivity, enabling the use of composite hydrogels as stretchable sensor devices for stable and reliable motion monitoring. This study provides a new strategy for fabricating anisotropic hydrogels with superior mechanical and conductive properties, advancing their applications in wearable electronics and soft robotics.