Preparation of chitosan/apatite composite particles with core–shell structure

In this study, a novel sequential preparation process of core–shell particles with chitosan (CS) cores and hydroxyapatite (HAp) shells is presented. This process involved the formation of phosphorylated CS particles, followed by HAp precipitation. Importantly, the precipitation of HAp on the surface of phosphorylated CS was confirmed. Different CaCl2 concentrations during the HAp precipitation step resulted in different HAp contents in the particles. To confirm the formation of the core–shell structure, the particles were immersed in hydrochloric acid (pH 2) for 5, 10, and 30 min. Notably, samples with higher HAp content (59 wt % and 84 wt %) retained their core morphology after 30 min of immersion, whereas samples with lower HAp content (28 wt %) rapidly lost their morphology. These results indicate that higher HAp content contributes to improved morphological stability under acidic conditions, leading to the formation of more stable core–shell particles. Overall, these findings clarify the role of phosphorylated CS in inducing HAp precipitation and show that the proposed preparation process leads to the formation of CS/HAp core–shell structures.