Hydrothermal synthesis of Cu/Pr doped and Co-doped fluorapatite for biomedical applications: Antibacterial efficiency and cytotoxicity assessment

In this study, Cu2+ and Pr3+doped Fluorapatite (FAP) nanoparticles were successfully synthesized via a hydrothermal method. Their structural, optical, cytotoxic, and antibacterial properties were systematically investigated. X-ray diffraction (XRD) confirmed the preservation of the whole hexagonal fluorapatite structure upon doping and co-doping with Cu2+ and Pr3+ ions, with crystallite sizes estimated using the Scherrer equation as 21.6 nm for pure FAP, 33.7 nm for FAP[sbnd]Cu, 33.0 nm for FAP[sbnd]Pr, and 17.9 nm for co-doped FAP-Pr-Cu. The Williamson–Hall (W[sbnd]H) analysis indicated larger apparent crystallite sizes ranging from 25.2 nm (FAP-Pr-Cu) to 85.5 nm (FAP[sbnd]Cu), suggesting strain-induced peak broadening in the doped samples. Fourier-transform infrared (FTIR) spectroscopy revealed that doping-induced modifications of vibrational modes of fluorapatite matrix and their corresponding intensities, suggesting small structural alterations. By using X-ray photoelectron spectroscopy (XPS), we have confirmed the incorporation of Cu2+ and Pr3+ into the FAP lattice and verified their respective oxidation states. The elemental composition of the prepared powders was investigated by energy dispersive X-ray spectroscopy (EDX). Scanning electron microscopy (SEM) showed agglomerated particles with a sheet-like morphology, while dynamic light scattering (DLS) measurements indicated an increase in the hydrodynamic size upon doping; the average particle sizes ranged from 171.4 nm for pure FAP to 203.0 nm, confirming the impact of dopant incorporation on particle agglomeration. UV–visible absorption spectroscopy revealed a direct bandgap energy of 4.78 eV for pure FAP, whereas the doped samples exhibited bandgap energies ranging between 4.51 eV and 5.40 eV, depending on the doping element. The antibacterial activity was evaluated against clinical bacterial pathogens implicated in oral cavity disease and vagina infection (S1, S2, S3, S4, E1) using the microdilution method. The results demonstrated that Cu[sbnd]Pr co-doped FAP exhibited significantly enhanced antibacterial efficacy against staphylococcus aureus (S1) and Enterococcus faecalis (E1), with minimum inhibitory concentration (MIC) of 0.123 and 1.11 mg/mL, respectively. By contrast, pure FAP was found to have a MIC of 1.11 and 3.33 mg/mL for the same bacteria. Additionally, cytotoxicity assessment on the human osteosarcoma cell line (U2OS) was evaluated using the MTT assay, which indicated that the co-doped sample exhibited lower toxicity.