The effects of Fe3+ and Co2+ substitution in Ca10-x-yFexCoy(PO4)6(OH)2 hydroxyapatite nanoparticles: Magnetic, antibacterial, and improved drug release behavior

The mineral constituent of the bone contains non-stoichiometric hydroxyapatite with various substitutional ions. Iron (Fe) and cobalt (Co) are fundamental cofactors, which influence cell respiration and mitosis, respectively. In this study, undoped, Fe3+-, Co2+-, and dually-doped HA nanoparticles (NPs) were synthesized by the hydrothermal method. The molar ratio was varied between 0.02 and 0.2. Samples were analyzed using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), vibrating sample magnetometry (VSM), Fourier-transformed infrared spectroscopy (FT-IR), inductively coupled plasma optical emission spectroscopy (ICP-OES), and biological assessment. XRD results confirmed the formation of the hexagonal HA crystal structure. The crystallite size was reduced from 34.6 nm to 4.4 nm. Also, the c-axis dimension and the degree of crystallinity were reduced in all the doped samples. The FESEM results showed a change of morphology from rod-like in the undoped nHA into a sphere-like morphology in the doped-samples. With the addition of ferromagnetic dopant, the magnetic behavior of samples altered from diamagnetic to paramagnetic-like and ferromagnetic behavior. Bioactivity assessment indicated the formation of the HA particle on the surface of all synthesized materials. The antibacterial test demonstrated antibacterial activity against gram-negative (-) E. coli. Moreover, the antibiotic-impregnated samples had a synergistic effect on both gram (-), E. coli, as well as gram (+), S. aureus, bacteria. The MTT evaluation revealed the enhanced cell viability of osteoblast-like cells in the dually-doped NPs. Based on this survey, we can strongly emphasize the potential for bone bioactivity and antibacterial feature of these newly developed samples.