Objective: Hydroxyapatite nanoparticles have extensively been used in biomedical fields such as drug delivery system, tissue engineering, and bone reparation. Up to now, several methods have been employed for the synthesis of hydroxyapatite nanoparticles such as wet chemical deposition, biomimetic depositional sol-gel route and etc. The aim of this study was to synthesize poly (ethylene glycol)-coated hydroxyapatite (PEG@HAP) nanoparticles by the hydrothermal method and to evaluate their biological effects on osteosarcoma cells. Material and Methods: PEG@HAP nanoparticles were synthesized by the hydrothermal method and characterized by XRD and FT-IR techniques. To detect the cytotoxic effect of nanoparticles on osteosarcoma cells (Saos2), MTT assay was utilized. The cellular morphology of Saos2 cells was observed by phase contrast microscope. Osteogenic differentiation was evaluated by the assessment of alkaline phosphatase activity (ALP). Results: The XRD pattern of nanoparticles showed the formation of single-phase hydroxyapatite, and the spectrum matched well with the JCPDS value (09-0432). The FT-IR spectrum showed the adsorption the band at 604 cm-1 which is related to the bending vibration of phosphate groups and the band at 1044 cm-1 which is attributed to the stretching vibration of phosphate groups. The sharp absorption band at 3570 cm-1 corresponds to the stretching vibration of OH groups. Based on MTT assay and microscopic images, PEG@HAP nanoparticles increased the proliferation of Saos-2 cells at concentrations of 10 and 50 μg/ml while no significant effect was observed at higher concentrations up to 150 μg/ml. Moreover, it was found that PEG@HAP nanoparticles have ability to induce osteogenic differentiation in Saos-2 cells which was quantified by ALP activity. A significant increase was observed in ALP activity in Saos-2 cells as they were treated with PEG@HAP nanoparticles. Conclusion: Based on the obtained results, PEG@HAP nanoparticles possess high potency for the induction of osteogenic differentiation and could be considered as an appropriate biomaterial for cancer therapy.

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