Correlation of the Antibacterial Activity and Local Structure in Zn- and Mn-Doped Hydroxyapatites by Rietveld Refinement and the First-Principles Method

Abstract

Zn- and Mn-doped hydroxyapatites were prepared using a sol-gel method at 1, 3, and 5 mol%. The X-ray diffraction results from the Rietveld refinements show that the secondary phases are β-tricalcium phosphate Ca(OH)2, CaCO3, and CaO crystals. A few phases of CaZnO2 and CaMn2O4 are found for Zn and Mn doping, respectively. Moreover, CaZnO2 increases with an increasing Zn concentration. However, CaMn2O4 decreases with an increasing Mn concentration. Interestingly, the XANES results reveal a novel correlation between the local structure of Zn and Mn and the antibacterial activity. The Zn K-edge XANES spectra confirm that Zn2+ is formed into CaZnO2 crystals in all samples. The Mn K-edge XANES spectra indicate that Mn3+ is formed into CaMn2O4 crystals for 1Mn-HAp. For 3Mn-HAp and 5Mn-HAp, Mn2+ is substituted on the Ca5 and Ca4 sites of the β-TCP crystal, and Mn3+ is formed into the CaMn2O4 crystal, which is an important key to inhibiting S. epidermidis.

Keywords: X-ray absorption, XANES, Local structure, Hydroxyapatite