Architected Inverse Nacre Hydrogels With High Strength and Crack-Insensitive Toughness

The practical deployment of synthetic hydrogels in load-bearing applications has long been hindered by their intrinsically low fracture toughness, poor fatigue resistance, and the persistent strength-toughness trade-off. Here, we propose an "inverse nacre" design principle that fundamentally overcomes these limitations by integrating hierarchical alignment of poly(vinyl alcohol) (PVA) chains and MXene nanosheets via a scalable thermo-calendering process. In this inverted structure, a minimal quantity of aligned MXene nanosheets serves as continuous, high-stiffness "bricks", while the PVA hydrogel forms a ductile, energy-dissipating "mortar". This inversion introduces a dual-function reinforcement mechanism: MXene nanosheets impart stiffness, crack-bridging, and deflection capabilities, while simultaneously suppressing PVA crystallization, thereby promoting molecular alignment and enhancing deformability. The resulting cooperative architecture achieves an exceptional combination of tensile strength (63.48 MPa), work of fracture (54.79 MJ/m³), and record-high fracture toughness (115.98 kJ/m²) without compromising hydrogel water content. Strikingly, the composite exhibits crack-insensitive fracture behavior, where propagating cracks undergo extensive deflection and branching, activating an autonomous self-preservation mechanism. This biomimetic strategy not only resolves the strength-toughness paradox but also provides a generalizable route for designing structurally resilient soft materials with broad implications in biomedical and engineering applications.