The unique microstructure of Nacre inspires the fabrication of biomimetic composites with enhanced mechanical properties and biocompatibility to address the limitations of current bone implants.

One of the most ambitious goals for bone implants is to improve bioactivity, incapability, and mechanical properties; to reduce the need for further surgery; and increase efficiency. Hydroxyapatite (HA), the main inorganic component of bones and teeth, has high biocompatibility but is weak and brittle material. Cortical bone is composed of 70% calcium phosphate (CaP) and 30% collagen and forms a complex hierarchical structure with anisotropic and lamellar microstructure (osteons) which makes bone a light, strong, tough, and durable material that can support large loads. However, imitation of concentric lamellar structure of osteons is difficult to achieve in fabrication. Nacre from mollusk shells with layered structures has now become the archetype of the natural “model” for bio-inspired materials. Incorporating a nacre-like layered structure into bone implants can enhance their mechanical strength, toughness, and durability, reducing the risk of implant catastrophic failure or fracture. The layered structure of nacre-like HA/polymer composites possess high strength, toughness, and tunable stiffness which matches that of bone. The nacre-like HA/polymer composites should also possess excellent biocompatibility and bioactivity which facilitate the bonding of the implant with the surrounding bone, leading to improved implant stability and long-term success. To achieve this, a bi-directional freeze-casting technique was used to produce elongated lamellar HA were further densified and infiltrated with polymer to produce nacre-like HA/polymer composites with high strength and fracture toughness. Mechanical characterization shows that increasing the ceramic fractions in the composite increases the density of the mineral bridges, resulting in higher flexural and compressive strength. The nacre-like HA/(methyl methacrylate (MMA) + 5 wt.% acrylic acid (AA)) composites with a ceramic fraction of 80 vol.% showed a flexural strength of 158 ± 7.02 MPa and a Young’s modulus of 24 ± 4.34 GPa, compared with 130 ± 5.82 MPa and 19.75 ± 2.38 GPa, in the composite of HA/PMMA, due to the higher strength of the polymer and the interface of the composite. The fracture toughness in the composition of 5 wt.% PAA to PMMA improves from 3.023 ± 0.98 MPa·m^1/2 to 5.27 ± 1.033 MPa·m^1/2 by increasing the ceramic fraction from 70 vol.% to 80 vol.%, respectively.

This study aims to develop a bio-inspired nacre-like glass flake/polymer composite with enhanced mechanical properties, antibacterial function, and aesthetic appearance for potential dental applications. Self-assembly via vacuum filtration was used to align glass flakes into a layered structure. After heat treatment, monomers containing methyl methacrylate (MMA), acrylic acid (AA) and dimethylaminohexadecyl methacrylate (DMAHDM) were infiltrated into the glass flake scaffold and polymerised in situ. The nacre-like microstructure of the composites was characterised and mechanical tests, including flexural strength, elastic modulus and fracture toughness, were conducted to optimise the DMAHDM content (0, 1.5wt%, and 3 wt%). The antibacterial function of the optimised composite with 1.5 wt% DMAHDM was measured by viable colony-forming unit (CFU) count. Finally, the translucency of the composite with 1.5 wt% DMAHDM was determined. The glass flake/polymer composites with different DMAHDM contents all exhibited nacre-like layered microstructures. Adding 3 wt% DMAHDM was shown to significantly lower the flexural strength of the composites. The composite with 1.5 wt% DMAHDM exhibited a flexural strength of 126.97 MPa, comparable to the current benchmark aesthetic dental composite. Moreover, the elastic modulus of the composite with 1.5 wt% DMAHDM (24.75 GPa) was similar to that of human dentine, presenting bio-inspired mechanical property. Its unique crack resistance, characterised by a rising R-curve behaviour and a fracture toughness K_J up to 3.88 MPa.m^½, suggested excellent damage tolerance. With the addition of 1.5 wt% DMAHDM, the nacre-like composite demonstrated significant antibacterial function against Streptococcus mutans. Furthermore, the composite retained an aesthetic appearance with a translucency comparable to human enamel. A bio-inspired nacre-like glass flake/polymer composite with good mechanical properties, unique crack resistance, antibacterial function and translucency has been developed for aesthetic dental applications.