Hybrid Systems for the Separation (LHYS)
Whatever its entry route into the body, the uranyl cation (UO22+) is sent through the blood to its target organs: kidneys, for rapid elimination, and skeleton, for long term sequestration. The accumulation of uranyl in bones leads to an increased bone resorption and/or and inhibition of bone formation. To limit this accumulation, and favour excretion as a soluble form, several molecules with decorporating properties were evaluated. But today none of these presents a real efficency, and the conception of new molecules deserves a prior understanding of chemical, biochemical and cellular mechanisms which lead to the accumulation of UO22+ into the skeleton.1
Bone is a mineralized composite tissue with 5−10% water, 50−70% apatite [Ca10(PO4)6(OH)2], and 20−40% organic compounds composed mainly of collagen I protein (90%). Throughout the lifetime, bone tissue is continuously remodeled by cycles of events occurring at the same sites, alternating resorption and mineralization, mediated by osteoclasts and osteoblasts respectively. We recently set-up a method to synthetize biomimetic collagen-apatite hybrid materials, into which we can introduce uranium at various levels (Fig. 1).2 These samples are then used as bone cell culture support, and analysed and compared with biological samples using various techniques (XRD, IR, Raman, SEM, XANES, EXAFS, SLRT).
The interaction between uranium and the bone matrix is very complex. At the sole chemical level, several species can be obtained, and the presence of carbonate ions in the medium adds another complexity level. We have already established that low levels of uranium lead to a decrease in the mineralization efficiency, and also to a less crystalline material. Speciation studies at the molecular level are ongoing to establish the nature of the uranium species sorbed at the apatite surface. And further studies will be devoted to the factors governing the chemical equilibria between uranium(VI) and these biomimetic matrixes.