Fabrication of bioinspired structured glass–ceramics with enhanced fracture toughness

Abstract

Nature has the amazing ability to evolve materials with combined strength and toughness that far exceed those of their individual constituents. This study aims to develop a bioceramic that mimics the hierarchical organisation of the structure of nacre on multiple scale levels by using a widespread ceramics processing technique and bioactive components. We synthesised hexagonal-shaped platelets of β-tricalcium phosphate (β-TCP) with high aspect ratio (diagonal length of ~800 nm and thickness of ~150 nm) to mimic the aragonite (CaCO3) platelets in nacre. Bioactive glass nanoparticles (BGn, median size of 50 nm) with composition (mol%) of: B2O3 9.98, SiO2 49.02, CaO 39.64, P2O5 1.54 were fabricated to mimic bridges and asperities on the surface of platelets in nacre. Hierarchically organised structures were achieved by freeze-casting of a suspension containing β-TCP platelets and various concentrations of BGn in a custom-designed mould by adjusting the casting parameters. Results demonstrated successful self-organisation of all structural features during the freezing stage, including local alignment of platelets and entrapment of BGn between the platelets. The most significant mechanical results were obtained for nacre-structured β-TCP/5 wt% BGn sintered at an unconventionally low temperature (900 °C), which showed an indentation fracture toughness of 1.6 MPa m1/2, compared to reported values of 0.3–1.1 MPa m1/2 for β-TCP sintered at 1100–1300 °C, as well as other conventional bioceramics and glasses.