Sr-substituted hydroxyapatites for osteoporotic bone replacement.

Porous apatites, which during resorption can release in situ Sr ions, were prepared to associate an anti-osteoporotic action with the peculiar features of the inorganic phase constituting the bone. Sr-substituted hydroxyapatite (SrHA) powder was directly synthesized using the classical neutralization route, but including Sr ions, and characterized. The higher solubility of SrHA granules of 400-600 microm size, potentially usable as a bone filler, was assessed compared with that of analogous stoichiometric HA granules. The Sr released in synthetic body fluid became constant after 1 week. The Ca release is improved for SrHA compared with stoichiometric HA, due to the higher solubility of the first material. Porous scaffolds with micro-macro interconnected porosity, which mimic the morphology of the spongy bone, were prepared by the impregnation of cellulose sponges with suspensions of the powder and a specific sintering process. A compressive strength of 4.52+/-1.40 MPa was obtained for SrHA scaffolds characterized with 45 vol.% of porosity. Promising biomedical applications, such as resorbable bone filler or bone substitute releasing in situ Sr ions for a prolonged time, can be hypothesized for the SrHA materials when pathologies related with Sr deficiency are present.