Impact of structural features of Sr/Fe co-doped HAp on the osteoblast proliferation and osteogenic differentiation for its application as a bone substitute

The potential of external ions doped biomaterials has been extensively explored; however, the co-doped biomaterials remain typically unexplored for their biological properties for precise biomedical applications. The current study was aimed to explore the impact of structural features of Sr/Fe co-doped hydroxyapatite (HAp) bionanomaterial on osteoblastic proliferation and osteogenic differentiation for its application as a bone substitute. A 10 mol% isomorphous co-doping of strontium and iron with respect to calcium was carried into HAp in the solid solution. Raman spectroscopy verified the presence of major functional groups of apatite structure together with the carbonate peaks. The Sr/Fe co-doped HAp bionanomaterials showed slightly negative zeta potential (at neutral pH), versatile DLS particle size (140-205 nm), high BET surface area (186 m²/g), and narrow width pore size (13-19 nm). TG/DTA analysis showed low thermal stability of the Sr/Fe co-doped HAp groups. The nanoparticles showed an initial burst release of amoxicillin for 15 h followed by extended-release up to 81 h and demonstrated an excellent antibacterial activity by producing inhibition zones of 17.6 ± 0.3 mm and 19.5 mm ± 0.4 mm for Escherichia coli and Staphylococcus aureus. Live/dead cell staining and MTT assay confirmed the non-toxic nature of Sr/Fe co-doped HAp bionanomaterial towards MC3T3-E1 cells. Further, an improved ALP activity, increased calcium deposition, enhanced RUNX2 expression, and regulated OPN and OCN expression levels suggest in MC3T3-E1 cells demonstrate the maturation of osteoblasts. This study provides the unique advantages of the co-doping approach for the applications Sr/Fe co-doped HAp bionanomaterials as a bone substitute.