A Hierarchically Structured Model Composite: A Tem Study of the Hard Tissue of Red Abalone

Abstract

AbstractThe structure and crystallography of the nacre of red abalone, Haliotis rufescens, was studied by transmission electron microscopy imaging and diffraction. We found that the nacre structure is based upon hierarchical {110} twinning in aragonite with the following organization: (i) first generation twins between platelets having incoherent boundaries, (ii) second generation twins between domains having coherent boundaries within a given platelet, and (iii) nanometer-scale third generation twins within domains. Since the aragonite platelets nucleate and grow as separate crystals, this long-range crystallographic relationship between the inorganic units of a biological hard tissue indicates that the nucleation and growth process of crystals may be mediated by the organic matrix and that the organic template structure may also be long-range ordered. We propose a superlattice structure based on the possible twin variants and suggest that the organic matrix structure, or the arrangement of nucleation sites, is compatible with the superlattice. Multiple tiling based upon this superlattice allows all of the crystallographic and morphological platelet configurations observed in nacre.