Mesoporous strontium doped nano sized sulphate hydroxyapatite as a novel biomaterial for bone tissue applications

In this study a novel nano-structured hydroxyapatite (HA) incorporated with different fractions of Sr2+ and SO42- ions has been synthesized using the wet precipitation method and characterized. This study explored the potential benefits of dual doping of Sr2+ and SO42- ions for the first time, which would contribute to bone prosthetics' clinical success. The substitution of Sr2+ and SO42- ions into the HA crystal structure was confirmed using XRD, FTIR, Raman spectroscopy, FESEM, BET and XPS techniques. Fetal Bovine Serum (FBS) was used as a model protein for adsorption assay. FBS revealed higher affinity towards Sr-SHA materials rather than pure HA. In vitro bioactivity studies showed that the HA dissolution rate increased with incorporation of Sr2+ and SO42- ions in the HA structure. The highest dissolution rate was recorded on the 1st day of immersion in Simulated Body Fluid (SBF) for SHA and Sr-SHA groups. Intense growth of apatite grains on the surface of Sr-SHA with Ca/P ratio of (1.41-1.64) was observed after 14 days of incubation in SBF. In vitro cytotoxicity studies conducted with Sarcoma Osteogenic (Saos-2) cells showed that Sr-SHA was cytocompatible. It was observed that Sr-SHA promoted cell adhesion, spreading and proliferation of Saos-2 cells compared to pure HA. Saos-2 cells seeded on Sr-SHA had statistically higher alkaline phosphatase (ALP) activity and intracellular calcium deposition compared to HA. Collectively, our results showed that Sr-SHA materials with enhanced bioactivity, cytocompatibility and osteogenic activity hold great potential to be used as materials for bone tissue regeneration.