Diffusion-Controlled Crystallization of Fluorapatite Mesocrystals in a Hydrogel

A mesocrystal is a superstructural crystal formed based on the assembly and oriented attachment of primary crystals, which are explained based on a nucleation theory. Mesocrystals are often found in biominerals formed in biological environments. With regard to biomedical applications, they have been used to imitate bones and teeth, employing soluble macromolecules and insoluble matrices. However, slow and controlled ion transport in living organisms has not generally been imitated. We synthesized fluorapatite crystals using a hydrogel to mimic the slow and controlled ion transport in the biomineralization process. Flower-, rod-, and cross-like fluorapatite crystals are formed in a single hydrogel as a function of ion flux. In particular, rod-like mesocrystals with converging ends have been formed under specific conditions. Their morphologies are determined by nucleation and growth rates that are influenced by supersaturation levels. This study explains the fluorapatite mesocrystal formation mechanism based on the ion supply rate in the initial stage and the possibility of a hydrogel being a biomimetic scaffold.