Preparation and characterization of hollow hydroxyapatite microspheres by spray drying method

Hollow hydroxyapatite (Ca10(PO4)6(OH)2) microspheres were prepared using a simple spray drying method. The incorporation of ammonium bicarbonate could produce carbon dioxide and ammonia gas bubbles during the spraying, and thus created a hollow inner structure in the resultant microspheres. The hollow microspheres prepared using different amounts of ammonium bicarbonate were also characterized. These microspheres were composed of nanoparticles with an average crystallite size of 15 nm. A high surface area (80 m2/g) and porosity of the microspheres could be achieved when the concentration of ammonium bicarbonate was about 5 wt.%. Fourier transform infrared results showed that CO32− was incorporated into the HA microspheres. These hollow microspheres have many potential uses such as injectable drug-delivery carriers.