A New Paradigm for Biomineral Formation: Mineralization via an Amorphous Liquid-Phase Precursor

Biologically mineralized tissues are well recognized for their unusual crystal morphologies and hierarchically organized composite structures. The soluble acidic macromolecules associated with biominerals are thought to play an important role in modulating the mineral morphology. Our in vitro studies, which use acidic polypeptide additives to modify crystal growth of calcium-based minerals, have demonstrated a crystallization mechanism that proceeds via a liquid-phase mineral precursor. Various features of the crystals produced via this mechanism, such as "extruded" mineral fibers and mineralized collagen composites, have led us to propose the hypothesis that an amorphous, liquid-phase precursor could play a fundamental role in the morphogenesis of calcium-based biominerals. Although in vivo evidence of this process remains to be determined, we demonstrate crystallization features that mimic bone and dental enamel and suggest that this process could be relevant to biomineralization in both vertebrates and invertebrates.