Tough and Strong: Cross-Lamella Design Imparts Multifunctionality to Biomimetic Nacre.

The creation of structural composites with combined strength, toughness, low density, and biocompatibility remains a long-standing challenge. On the other hand, bivalve marine shells-Clinocardium spp.-exhibit strength, stiffness, and toughness that surpass even that of the nacre that is the most widely mimicked model for structural composites. The superior mechanical properties of Clinocardium spp. shells originate from their cross-lamella design, comprising CaCO3 mineral platelets arranged in an "interlocked" herringbone fashion. Reproduction of such hierarchical designs could offer multifunctionality, potentially combining strength and toughness at low densities, and the capability for seamless integration with biological systems. Here, we demonstrate manufacturing of the cross-lamella design by biomineralizing aragonite films with sawtooth patterns and assembling them in a chitosan/fibroin matrix to generate a composite with interlocked mineral layers. The resultant composite, with a similar constitution to that of the biological counterpart, nearly doubles the strength of previous nacre-mimetic composites while improving the tensile toughness and simultaneously exhibiting stiffness and biocompatibility.