On the Origin of Amorphous Cores in Biomimetic CaCO₃ Spherulites: New Insights into Spherulitic Crystallization

Spherulitic crystals are found in association with many materials and diseases, but the fundamental formation mechanism is not well understood. Using maleic chitosan to control CaCO3 crystallization, we have discovered a two-stage process that produces biomimetic CaCO3 spherulites. First, amorphous calcium carbonate (ACC) films are formed from which amorphous nanoparticles are precipitated, deposited, and stabilized to form an ACC core. This core then acts as a nucleus for the radial growth of needlelike calcite subunits. Accordingly, the resulting crystals combine the coexistence of calcite and ACC found in composite skeletal elements and the radially ordered structure of spherulitic biominerals. In conjunction with previous studies of spherulites in plants and animals, these findings may provide new insights into spherulitic crystallization, including the formation of spherulitic biominerals in nature. They may also have important implications for the understanding and potential treatment of diseases in which amorphous cores have already been observed, such as Alzheimer’s disease and kidney stones.