Synthesis and Characterization of Phosphocalcic Apatites with Phosphite Ions for Biomedical Applications

Phosphocalcic apatites are promising materials for orthopedic and dental surgery, due to their similarity to the mineral phase of bone and their strong affinity to bone tissue. To enhance their physicochemical and biological properties, it is important to prepare apatites with a highly reactive surface. In this work, we synthesized apatites with different amounts of phosphorous acids H3PO3, using a modified double decomposition method. We characterized the synthesized materials by X-ray diffraction, Fourier transform infrared spectrometry, thermogravimetric/differential thermal analysis, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. We also performed a biological study to evaluate the antimicrobial and antifungal activities of the apatites. The results showed that the presence of phosphite ions affected the crystallinity and the structural composition of the apatites. The apatitic phase became less crystallized and more distorted as the phosphite concentration increased and lost its apatitic structure for values above 33% of phosphite ions. The thermal analysis revealed that the phosphite groups stabilized the apatitic structure, as indicated by the shift of the exothermic peaks. The antibacterial activity was tested against four bacterial strains, two Gram-positive (Staphylococcus aureus, Micrococcus luteus) and two Gram-negative (Escherichia coli, Pseudomonas aeruginosa). The results indicated that the addition of phosphite ions improved the antibacterial activity of the apatites, especially against P. aeruginosa. The antifungal activity was evaluated against tow fungal strains, Penicillium digitatum and Aspergillus niger, and a yeast, Candida glabrata. The results suggested that the addition of phosphite ions influenced the antifungal activity of the apatites, but the effect depended on the phosphite concentration, the apatite structure, and the fungal strain. Future research should aim to increase the sample size, optimize the synthesis method, and conduct in vivo tests to confirm the potential of the phosphocalcic apatites with phosphite ions for biomedical applications.