Elaboration and characterization of macroporous carbonated hydroxyapatite for bone tissue engineering

International audienceThe mineral of bone is a biological calcium phosphate material which contains various ions in substitution (magnesium, carbonate, sodium...). Therefore, due to their chemical composition, calcium phosphate based materials such as hydroxyapatite (Ca10(PO4)6(OH)2, HA) or tricalcium phosphate (Ca3(PO4)2, TCP) are currently used to elaborate scaffold for bone grafting applications. These bioceramics allow the creation of a strong bond between the material and the surrounding tissues. However, they present inappropriate in vivo resorption rate especially for bone tissue engineering applications: too slow for HA and too fast for TCP. Ideally, a bone substitute should degrade only after the regenerated tissue has been remodelled at least once in the natural remodelling cycle [1]. One way to modulate the resorption rate of calcium phosphate ceramics would be to substitute carbonate ions (CO32-) for phosphate ones (PO43-) into the HA structure [2]. From this basis, the goal of this work was to elaborate pure carbonated hydroxyapatite (CHA) macroporous scaffold for bone tissue engineering applications. Thereby, granules of CHA were elaborated and their physico-chemical and biochemical properties were studied and compared to pure HA and TCP. To evaluate the biochemical properties of the granules, in vitro assays have been performed to study their dissolution rate. The powders were synthesised by a wet precipitation method. Materials with macroporous architecture were shaped by a replica method. The latter involved the optimisation of the slurry properties. The preparation of the granules was then completed by their sintering under controlled atmosphere and their granulation. To assess the phase composition of the material, X-ray diffraction and Fourier transformed infra-red analysis were performed. The chemical composition of the granules was confirmed by elemental analyses (e.g. inductively coupled plasma atomic emission spectroscopy). The solubility product of the ceramics was then determined through standard experiments and compared to common bioceramics. [1] Evolutionary design of bone scaffolds with reference to material selection, M. K. Heljak et al., Int. J. Numer. Meth. Biomed. Engng. 2012; 28:789-800 [2] Effect of Carbonate Content and Crystallinity on the Metastable Equilibrium Solubility Behavior of Carbonated Apatites, A.A. Baig et al., J. Colloid Interface Sci. 1996; 179:608-61