A facile strategy for one-step hydrothermal preparation of porous hydroxyapatite microspheres with core–shell structure

Core-shell microspheres have attracted widespread attention in the field of drug delivery due to their special morphology and excellent surface properties. However, the preparation of the core–shell microspheres composed of hydroxyapatite (HA) have been rarely reported. In this paper, porous HA core–shell microspheres were prepared through a one-step hydrothermal method by using sodium trimetaphosphate (STMP) as the phosphorus source. SEM and TEM observations showed that the prepared porous HA core–shell microspheres were composed of a porous shell and a solid core, with a gap between the core and the shell. These microspheres bear uniform size and identical structure. With the increase of the hydrothermal time, the solid microspheres transformed to porous core–shell microspheres with the simultaneous transformation of their phase from amorphous calcium phosphate (ACP) to HA. The possible formation mechanism is proposed, providing inspiration for the design of porous HA core–shell microspheres and their potential biological applications.