Fabrication of Porous Hollow Hydroxyapatite Microspheres with a Facile Gas-Diffusion Method

Porous hollow hydroxyapatite (HA) microspheres were prepared based on a facile gas-diffusion method that used ethylenediaminetetraaceticaciddiso-diumsalt (Na₂EDTA) as a chelating agent. The morphology and structure of the synthesized products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, laser particle size analyzer and Brunauer-Emmett-Teller gas sorptometry analyses. Results showed that the capability of Na₂EDTA to control Ca²⁺ release and distribution in synthesis solution contributed to the formation of porous hollow structure. The diffusing ammonia to gradually increase the solution pH provided the driving force for the formation of HA crystals. The possible formation mechanism of the microspheres based on time-dependent experiments was proposed. The method provides an easy and controllable route to synthesize HA microsphere with hollow structure. Moreover, the porous hollow HA microsphere with high surface area and porosity has great potential applications.