Crystal-chemical and morphological interpretation of the biocompatibility of compounds in a Ca–Na–Bi–fluorapatite system

This work is devoted to the study of the features of ismorphism in compounds of the Ca-Na-Bi-P-O-F system, which have a crystalline structure of the mineral apatite, as well as its effect on the biocompatibility of substances in relation to human cells in an in vitro model. The Ca10-2xBixNax(PO4)6F2 system (x = 0,1,2,3,4,5) is characterized by continuous isomorphism, which follows from the minimum deviations of the unit cell parameters from the Vegard and Rotgers rules. The refinement of the crystal structure showed that the cations are unevenly distributed between the 4f and 6h positions of the crystal structure of apatite: bismuth ions are predominantly localized in the 6h position, while sodium ions are concentrated in the 4f position. The standard MTT test showed the biocompatibility of compounds with x = 1,2,3,4, and at x = 1 an anomaly was found in the form of an increased relative cell growth rate. The paper discusses the possible crystal-chemical and morphological reasons for this phenomenon.