Mimicking bone–metal exchanges with synthetic nanocrystalline apatites

Abstract

Deciphering the mechanisms of metal exchanges between blood plasma and bone requires the reproduction of this complex physicochemical system: bone mineral is a poorly crystalline non-stoichiometric apatite, in equilibrium with blood plasma, a supersaturated calcium phosphate solution. Careful control of synthesis of nanocrystalline apatites possessing similar structural features as bone mineral, followed by preliminary contact with adequate buffered solution enabled the set-up of in vitro experiments that can account for solid/liquid exchange under biomimetic conditions. The interaction between uranium(VI) and bone mineral was studied according to this model, and the results obtained are in full agreement with available biological data, and demonstrate that existing information using crystalline apatites is not relevant. Uranium accumulation in bone is thus not the result of the precipitation of a uranium phosphate phase, but is due to simple diffusion into the surface amorphous layer, which can be described as physical sorption using the Langmuir model.