Influences of Sr dose on the crystal structure parameters and Sr distributions of Sr-incorporated hydroxyapatite

Stoichiometric strontium-incorporated hydroxyapatite (Sr-HA) with different Sr concentrations [Sr/(Sr+Ca)] were synthesized using a wet chemical approach and characterized by X-ray diffraction, Fourier-transformed infrared absorption, X-ray photoelectron spectroscopy, and Rietveld Structure Refinement. The crystal lattice parameter, Sr distribution, chemical state of Sr, and also the relationships between their variations and the Sr concentrations have been intensively studied. The results show that both the crystal lattice parameters and crystal plane space of Sr-HA remarkably increase with the Sr concentration increasing. Whether Sr preferably occupies the Ca(I) site or Ca(II) site after incorporated into apatite lattice depends on the Sr number incorporated into apatite. All the Sr ions completely occupy the Ca(II) sites when the Sr concentration is below 5%. With the exception of partial Sr ions occupying the Ca(II) sites, the other Sr ions start to occupy the Ca(I) sites when the Sr concentration doped in HA is beyond 10%. The ratio of Sr ions occupying the Ca(I) sites increases with the further raising Sr concentration up to 20%. The Sr ions inherit the chemical state and environment of the original Ca(I) or Ca(II) site after incorporated into apatite. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 101B: 1275-1283, 2013.