Bioinspired cellulose nanofiber/brushite composite films with high strength, toughness, and flame retardancy

The extensive use of petroleum-based plastics has led to severe environmental pollution and resource depletion issues, driving an urgent need for sustainable material alternatives. In this work, we present an environmentally friendly approach to fabricating bioinspired composite films by integrating cellulose nanofibers with brushite microplates via blade assisted assembly. The resulting nacre-like brick-and-mortar architecture is stabilized through hydrogen bonding and dynamic Ca²⁺-carboxyl coordination, leading to a combination of exceptional mechanical and functional properties. The composite films exhibit a tensile strength of 288.15 MPa, a Young's modulus of 7.4 GPa, a fracture toughness of 19.82 MJ·m^-3, and a wet strength of 22.97 MPa, outperforming most previously reported cellulose-based and bioinspired composites. The incorporation of brushite microplates delayed thermal degradation and conferred intrinsic flame retardancy, while also reducing surface hydrophilicity and enhancing long-term water resistance. Furthermore, these films can be easily patterned or printed into complex geometries and have been demonstrated to function reliably as sensors, showing stable and reproducible electrical response under repeated loading and instantly changing humidity.