Octocoral sclerite ultrastructures and experimental approach to underlying biomineralisation principles

Abstract

Skeletal biominerals often show complex morphologies and ultrastructures that are important for their mechanical function. The production of these biomineral structures requires exact control over mineral precipitation, which takes place under physiological conditions in the presence of gel-like organic matrices. Understanding the pathway of reproducibly forming elaborate structures with specific mechanical properties may open a way for new technical applications. We have conducted a detailed investigation of the ultrastructural organisation of calcitic octocoral sclerites, which demonstrated that internal fibrous crystals grow by aligned aggregation and fusion of nanoparticles. These nanoparticles were initially precipitated as nano-granular layers on the sclerite surface, where they enabled the smooth shaping of the sclerites. Experimental calcite precipitation in polyacrylamide hydrogel demonstrated that crystal growth via precursor-nanoparticles can be induced by gelatinous networks. This finding indicates the organic matrices’ role in controlling the mineral precipitation and crystal growth in biomineralisation.