Freeze‐Casting Anisotropic Hydrogels with Multi‐Dynamic Bonding for Enhancing Fatigue Resistance and Environmental Stability

Engineering hydrogels are widely utilized as load-bearing components considering their excellent mechanical properties, biocompatibility, and environmental adaptiveness in the fields of wearable devices, soft robots, and human-machine interfaces. However, conventional functional hydrogels exhibit notable limitations in mechanical properties and environmental adaptability, particularly regarding insufficient fatigue resistance during long-term usage and performance degradation under extreme conditions. In this study, we innovatively developed a synergistic strategy combining freeze-casting with multi-dynamic hydrogen bonding networks. By constructing well-aligned anisotropic microstructures through directional freezing and incorporating multi-scale hydrogen-bond networks formed by cellulose nanofibers (CNFs) and tannic acid (TA), the high-strength polyvinyl alcohol (PVA)-based hydrogels with exceptional fatigue resistance and environmental adaptability are successfully fabricated. Typically, the resulting hydrogel demonstrates outstanding comprehensive properties, including tensile strength and elastic modulus reaching 15.26 and 15.84 MPa, with the threshold tearing energy and critical tearing energy achieving 0.1233 and 1935.14 kJ/m², respectively. Remarkably, after 14 days of storage under extreme conditions of high-pressure saline environment (20 MPa hydrostatic pressure, 35‰ salinity), the hydrogel retained over 100% of its initial mechanical properties and structural integrity, demonstrating excellent environmental stability. Such superior performance enables their application as load-bearing components in diverse extreme environments. The design and fabrication strategy of PVA-based hydrogels reported in this study provides a groundbreaking solution for hydrogel applications under extreme conditions, overcoming the inherent limitations of conventional hydrogels and paving a new avenue for expanding their engineering applications in demanding scenarios.