CaCO3 nanostructured crystals induced by nacreous organic extracts

Abstract

Nanostructured CaCO₃ crystals are produced in vitro by adding the acid-soluble organic matrix (SOM) extracted from the nacreous layer of Pinctada margaritifera pearl oyster shell to a supersaturated solution of calcium carbonate. For SOM concentrations above 25 ppm, the produced calcite crystals show two structural features of nacre and, more generally, of calcareous biocrystals: structuring at the nanometer scale and a hierarchical structure at higher scales. More specifically, the produced polycrystals exhibit hierarchical structures with stacks of mineral layers, the thickness of which is about 200–400 nm. AFM and SEM microscopies supplemented by FTIR spectrometry allowed us to conclude that these nanostructured layers correspond to packed ‘nanograins’ embedded in an organic matrix. Besides, each layering plane exhibits a single crystal character under TEM and SAED characterizations and can be indexed to the {110} planes of calcite. The reported work sheds light on the crucial role of SOM in the formation of oriented nanostructures, which are generally observed in biological calcareous tissues, like nacre.