Synthesis, Characterization and In Vitro Bioactivity of Magnetite Nanoparticles Obtained by Co-Precipitation

Magnetite (Fe3O4) nanoparticles have been explored for biomedical applications. Their surface behavior in physiological-like environments has not been fully established. Fe3O4 nanoparticles obtained by chemical co-precipitation were exposed to simulated body fluid (SBF) for up to 28 days, and in vitro bioactivity was examined. Structural and surface changes were investigated using XRD, FTIR-ATR, SEM/EDS and thermal analysis, while pH and electrical conductivity measurements were used to monitor changes at the particle–solution interface. Magnetite was the main crystalline phase, and the main crystalline structure was preserved during SBF exposure within the detection limits. Progressive surface transformations occurred, including hydration/hydroxylation and formation of calcium–phosphate-containing surface deposits. Changes in pH and variations in electrical conductivity were interpreted as complementary indicators of interfacial processes. Cytotoxicity tests on L929 fibroblast cells showed that Fe3O4_14SBF was well tolerated at 25–50 µg/mL, whereas higher concentrations reduced cell viability. These findings suggest that Fe3O4-based magnetic materials may be further considered for biomedical applications, provided that concentration-dependent cytocompatibility is considered.