Combining crossed-lamellar structure and nacre-like nanoparticulate structure in conch shells for enhanced mechanical properties†

Crossed-lamellar design and nacreous structure are two common architected microstructures of mollusk shells that both exhibit excellent mechanical properties. Conch shells are commonly constructed from several macroscopic layers with the same crossed-lamellar structure, and adjacent layers are perpendicular to each other. It is the careful control of the hierarchical structure from nanoscale to macroscale that yields a significantly improved toughness versus abiotic aragonite. In this study, we reported the discovery of a novel nacre-like nanoparticulate layer underneath two crossed-lamellar layers in Babylonia areolata shells. The microstructure and mechanical properties of this nanoparticulate layer were systematically investigated and compared with those of crossed-lamellar layers. The nanoparticulate layer comprises multiple sublayers of densely packed nanoparticles, each approximately 20–50 nm in size, interspersed with thick layers of organic matter. The organic content of the nanoparticulate layer is 5.32 wt%, nearly 3 times higher than that of crossed-lamellar layers. While the hardness and elastic modulus of the nanoparticulate layer are slightly lower than the crossed-lamellar layers, it exhibits better resistance to crack formation under low force, owing to the nacre-like lamellar structure, the presence of organic matter as glue and the nanoparticulate morphology. Moreover, the presence of the nanoparticulate layer further improved the compressive strength of the conch shell. This study provides additional design guidelines for the development of bioinspired structural materials.