Novel biomaterials for bisphosphonate delivery

One type of gem-bisphosphonate (Zoledronate) has been chemically associated onto calcium phosphate (CaP) compounds of various compositions. For that purpose, CaP powders of controlled granulometry have been suspended in aqueous Zoledronate solutions of variable concentrations. Using mainly 31P NMR spectroscopy, two different association modes have been observed, according to the nature of the CaP support and/or the initial concentration of the Zoledronate solution. β-tricalcium phosphate (β-TCP) and mixtures of hydroxyapatite and β-TCP (BCPs) appear to promote Zoledronate-containing crystals formation. On the other hand, at concentrations <0.05 mol l−1 CDAs (calcium deficients apatites) seem to undergo chemisorption of the drug through a surface adsorption process, due to PO3 for PO4 exchange, that is well described by Freundlich equations. At concentrations >0.05 mol l−1, crystalline needles of a Zoledronate complex form onto the CDAs surface. The ability of such materials to release Zoledronate, resulting in the inhibition of osteoclastic activity, was shown using a specific in vitro bone resorption model.