In vitro apatite formation and drug loading/release of porous TiO₂ microspheres prepared by sol-gel processing with different SiO₂ nanoparticle contents

Bioactive titania (TiO₂) microparticles can be used as drug-releasing cement fillers for the chemotherapeutic treatment of metastatic bone tumors. Porous anatase-type TiO₂ microspheres around 15 μm in diameter were obtained through a sol-gel process involving a water-in-oil emulsion with 30:70 SiO₂/H₂O weight ratio and subsequent NaOH solution treatment. The water phase consisted of methanol, titanium tetraisopropoxide, diethanolamine, SiO₂ nanoparticles, and H₂O, while the oil phase consisted of kerosene, Span 80, and Span 60. The resulting microspheres had a high specific surface area of 111.7 m²·g^{- 1}. Apatite with a network-like surface structure formed on the surface of the microspheres within 8 days in simulated body fluid. The good apatite-forming ability of the microspheres is attributed to their porous structure and the negative zeta potential of TiO₂. The release of rhodamine B, a model for a hydrophilic drug, was rapid for the first 6 h of soaking, but diffusion-controlled thereafter. The burst release in the first 6 h is problematic for clinical applications; nonetheless, the present results highlight the potential of porous TiO₂ microspheres as drug-releasing cement fillers able to form apatite.