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Bismuth apatites as the basis of biomaterials for bone tissue regeneration
* 1 , 1 , 1 , 1 , 2 , 2 , 2
1  Lobachevsky University
2  Privolzhsky Research Medical University
Academic Editor: Filippo Rossi


Compounds with apatite structures containing bismuth, of the compositions Ca10-2xBixNax(PO4)6F2 (x = 1, 2, 3, 4), Ca8BiNa(PO4)6O and Ca8BiNa(PO4)5,5(VO4)0,5O, were synthesized by a solid-phase reaction for the first time. The phase identity and crystal structure features of the substances were studied by X-ray diffraction analysis (Rietveld method) and IR spectroscopy. It was found that calcium, bismuth and sodium ions are distributed on cationic positions of the apatite crystal structure, not statistically, but taking into account coordination possibilities. Thus, sodium ions, possessing high values of coordination numbers, are located in the centers of three-caped triangular bipyramids (CN = 9, Wyckoff position 4f), and bismuth ions are located in in the centers of two-caped triangular bipyramids (CN = 8, Wyckoff position 6h). Calcium is distributed uniformly over the positions. Such peculiarity of the crystal structure of substances causes strong binding of bismuth ions, and, therefore, prevents their exit from the structure. The phase stability (stability) of the substances in water, phosphate-salt buffer and trypsin was confirmed by X-ray phase and elemental analyses, which confirmed the prediction of behavior made on the basis of structural data. The absence of cytotoxicity of the materials was confirmed directly in the standard MTT test. For the Ca8BiNa(PO4)6F2 and Ca6Bi2Na2(PO4)6F2 compositions, an increase in cell proliferation was observed. This phenomenon can be explained by the fact that these substances are formed as spheroidal particles during synthesis, which facilitates their penetration through the cell membrane. In addition, it was found that Ca8BiNa(PO4)6O and Ca8BiNa(PO4)5,5(VO4)0,5O do not possess bactericidal activity against S. aureus and E. coli cultures, which also agrees with the previously mentioned conclusions. Thus, new non-cytotoxic materials based on bismuth apatite were obtained.

Keywords: apatite; bismuth; crystal structure; cytotoxicity