Rodent enamel-inspired hydroxyapatite nanocomposites with Fe3+-rich amorphous intergranular phases

Rodent enamel is primarily composed of hydroxyapatite (HAP) nanowires and Fe 3+ -rich amorphous intergranular phases (AIP). Inspired by rodent tooth enamel, this study successfully formed a layer of Fe 3+ -rich AIP on the outer layer of HAP nanowires by ion exchange between Fe 3+ and Ca 2+ within the HAP lattice. The thermal stability of Fe-HAP nanowires with Fe 3+ -rich AIP was enhanced. By bi-directional freezing of Fe-HAP nanowires with polyvinyl alcohol (PVA), rodent enamel-like nanocomposites (Fe-HEN) were obtained. Owing to the reinforcing and toughening effect of Fe 3+ -rich AIP, Fe-HEN exhibited a hardness of 1.66 ± 0.23 GPa, a Young's modulus of 48.8 ± 6.7 GPa in the longitudinal direction, as well as a hardness of 1.38 ± 0.16 GPa and a Young's modulus of 40.2 ± 3.0 GPa in the transversal direction. The flexural strength of the sample reached 153.5 ± 5.0 MPa, which is 2.9 times higher than that of samples without AIP, surpassing the performance of natural rodent enamel. The compressive strength reached 205 ± 4.3 MPa, representing a 1.5-fold increase over the sample without AIP and comparable to that of natural enamel. Compared to samples without AIP, Fe-HEN exhibits superior fracture toughness and crack deflection, better corrosion resistance, owing to the reinforcing effect of Fe 3+ -rich AIP at nanowire interfaces. This study demonstrates the incorporation of amorphous reinforced structures into the tooth enamel-like materials via ion exchange, offering a promising strategy for the development of high-performance multiscale composites.