Controlled synthesis of luminescent F-substituted strontium hydroxyapatite with hierarchical structures for drug delivery

Fluorine substituted strontium hydroxyapatite doped with Tb3+ or Eu3+ ions (SrFHAp:Ln) was successfully synthesized via an efficient and facile hydrothermal process using ethylene diamine tetraacetic acid disodium (Na(2)EDTA) as the chelating ligand. The as-prepared SrFHAp:Ln product was used as a drug carrier to investigate the drug storage and release properties using ibuprofen (IBU) as a model drug. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectrum (EDS), X-ray photoelectron spectra (XPS), fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption/desorption, and photoluminescence spectra were employed to characterize the samples. The results reveal that the as-prepared fluorine substituted hydroxyapatites exhibit a hierarchical double-broccoli-like morphology. By tuning the pH value, Na(2)EDTA content, and the reaction time, SrFHAp microstructures with different morphologies and sizes have been achieved. A possible formation process of these samples based on the crystal splitting growth mechanism has also been proposed in detail. Moreover, the photoluminescence (PL) measurements indicate that the as-prepared SrFHAp:Ln samples exhibit the characteristic emissions of Tb3+ and Eu3+ even after the loading of organic drug molecules, suggesting its feasible possibility to be monitored or tracked during the drug release and disease therapy process.