Non-stoichiometric hydroxyapatite (HAP, Ca10(PO4)6(OH)2) and whitlockite (β-TCP, β-Ca3(PO4)2) enter the human mineral mass. For this reason, phases with a structure of apatite and whitlockite are widely used as biocompatible materials both for the diagnosis of various diseases and for the bone tissue implants.

Many researchers modify the properties of calcium phosphates by introducing various divalent and rare-earth substitution cations [1,2,3,4].

The introduction of rare-earth elements into the crystal lattice has become a very relevant research area for the development of new hybrid materials for sensing, biomedical imaging, drug delivery, etc [5].

Although doped phases based on tricalcium phosphate are actively studied as biomaterials, there is still no reliable data on the influence of the atomic position and distribution of cations on the biological properties of these phases. For this reason, an important task in the study of whitlockite-like (β-TCP) minerals and apatite is their investigation through a multi-methodological approach based on powder X-ray diffraction [6], photoluminescence, Raman and Fourier Transform Infrared (FTIR) spectroscopy, to reveal the various substitutions and understand the onset of properties, especially bioactive ones.

The structural aspects of some whitlockite and hydroxyapatite compounds, doped with different rare-earth cations, will be discussed along with the examination of the occupancies to clarify the location of the respective dopant. This information turn out extremely useful for a physico-chemical characterization aimed at understanding the properties and simulate the biological activity.

References

1. Kannan, S. Pina, J.M.F. Ferreira, Formation of strontium-stabilized β-tricalcium phosphate from calcium deficient apatite, J. Am. Ceram. Soc. 89 (2006) 3277–3280.
2. Mellier, F. Fayon, V. Schnitzler, P. Deniard, M. Allix, S. Quillard, D. Massiot, J.-M. Bouler, B. Bujoli, P. Janvier, Characterization and properties of novel gallium doped calcium phosphate ceramics, Inorg. Chem. 50 (2011) 8252–8260.
3. Quillard, M. Paris, P. Deniard, R. Gildenhaar, G. Berger, L. Obadia, J.-M. Bouler, Structural and spectroscopic characterization of a series of potassium- and/or sodium-substituted β-tricalcium phosphate, Acta Biomater. 7 (2011) 1844–1852.
4. V. Fadeeva, М. R. GafurovГафуров, Ya. Y. Filippov, G. А. DavydovaДавыдова, I. V. Savitzeva, А. S. Fomin, N. V. Petrakova, О. S. Antonova, L. I. Ahmetov, at. all. B. Copper-substituted tricalcium phosphates. Academy of Sciences reports, 2016, 471, p. 1–4.
5. Comby, E.M. Surender, O. Kotova, L.K. Truman, J.K. Molloy, T. Gunnlaugsson, Lanthanide-functionalized nanoparticles as MRI and luminescent probes for sensing and/or imaging applications, Inorg. Chem. 53 (2014) 1867–1879.
6. Altomare, C. Cuocci, C. Giacovazzo, A. Moliterni, R. Rizzi, N. Corriero, A. Falcicchio. J. Appl. Cryst. 2013, 46, 1231.