Toward an efficient antibacterial agent: Zn- and Mg-doped hydroxyapatite nanopowders

The use of synthetic hydroxyapatites (HAps) in biomedical and environmental applications is well warranted given that they have been shown to behave as an excellent bio-compatible material in human teeth and bones. In this paper, a series of HAps doped and co-doped with two metal cations (zinc and magnesium) has been successfully synthesized by means of the precipitation method using CaCl2, Na2HPO4, ZnCl2 and MgCl2 aqueous solutions as reagents. The synthesized samples have been characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). All samples prepared using over 10 mol% of Zn and Mg ions were identified as HAp. However, the presence of metal cations caused a significant increase in their crystallite sizes (30-50 nm) along with the appearance of a second phase (scholzite, whitlockite). The XRF spectra indicated the presence of Ca, P, Zn and Mg in the powders prepared with a high Metal/P ratio (1.7-2). The antimicrobial activity of these nanopowders has been tested in vitro against five bacteria (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa as Gram-negative; Staphylococcus aureus and Bacillus subtilis as Gram-positive) and two fungal strains (Candida albicans and Aspergillus niger). The outcomes revealed that these nanopowders exhibited strong antimicrobial activity, starting at 15 mol% of Zn and/or Mg.