Structural characterization of sol-gel derived Sr-substituted calcium phosphates with anti-osteoporotic and anti-inflammatory properties

Sol-gel chemistry has been successfully used to prepare un-doped and Sr-doped calcium phosphate ceramics exhibiting a porous structure. The samples composition is very close to the nominal one. All samples present phase mixtures of mainly hydroxyapatite (HAp) and tricalcium phosphate (beta-TCP). Doping with Sr2+ ions has a clear effect on the proportions of the different phases, increasing the amount of beta-TCP. An amorphous phase is also observed incorporating some 40% of the total amount of strontium. Strontium ions also substitute for calcium both in HAp and beta-TCP in specific sites that have been determined from Rietveld refinement on synchrotron powder diffraction data. The soluble amorphous and TCP phases are responsible for a beneficial partial release of strontium ions in solution during interactions between the material and biological fluids. Preliminary in vitro study demonstrates anti-inflammatory effects of strontium for human monocytes cultured in contact with calcium phosphates.