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

In this work, the correlation between the local structure and antibacterial activity of Zn- and Mn-doped hydroxyapatites (HAp) has been studied. 1, 3 and 5 mol% of Zn and Mn were doped into the HAp using a sol-gel method. Their crystal structures have been evaluated by X-ray diffraction (XRD) and Rietveld refinement indicating the hexagonal HAp as a main phase with the secondary phases of beta-tricalcium phosphate (beta-TCP), Ca(OH)(2), CaCO3, and CaO crystals. The quantitative antibacterial activity data were measured on S. epidermis (Gram-positive) and P. aeruginosa (Gram-negative) by disk diffusion method. All doped samples exhibit the inhibition zone of S. epidermis except the 1 mol% of Mn-doped HAp while none of them can inhibit the P. aeruginosa. From the X-ray absorption near edge structure (XANES) results, we found that all Zn-doped HAp prefer to form a new CaZnO2 phase rather than substitute to its original phases. The 1 mol% of Mn-doped HAp also forms a new CaMn2O4 phase while the combination of CaMn2O4 and the Mn substituted-Ca4 and Ca5 sites of the beta-TCP structure has been observed in the 3 and 5 mol% of Mn-doped HAp. These results can be concluded that the CaZnO2 and Mn substitutedCa of the beta-TCP influence the inhibition of S. epidermis. Finally, this report elucidates the insight of antibacterial activity in the metal-doped HAp which could be useful for further biomaterial design.