Nanomechanical Property Determination of Organic Matrix in Mollusc Shell Nacre: A Biocomposite

Abstract

Mechanical properties were determined from the organic matrix of a mollusc hard tissue using a nanomechanical testing instrument attached to an atomic force microscope (AFM). Shells of molluscs are two-tier functionally-gradient ceramic/polymer biocomposites used by organisms as impact resistant materials. The inner section of the red abalone (Haliotis refuscens)shell, nacre (mother-ofpearl), has a brick and mortar microarchitecture with pseudo-hexagonal-shaped bricks made of aragonitic (orthorhombic) CaCO3 platelets (0.25 μn thick, and 5 μm edge length) surrounded by a thin (10-25 nm thick) proteinaceous organic matrix (Fig. 1). This higly ordered biocomposite has submicron-layered structure that result in excellent bulk mechanical properties, not achieved by manmade composites with similar phase compositions and, therefore, offers biomimetic lessons for novel materials design. In this model biomimetic composite, mechanical properties of its constituents need to be evaluated in addition to the details of the microstructure. We previously determined nanomechanical properties (hardness and modulus) of individual (twinned, single crystalline) aragonitic platelets.