Deep eutectic choline chloride-calcium chloride as all-in-one system for sustainable and one-step synthesis of bioactive fluorapatite nanoparticles

[Display omitted] •Fluorapatite nanoparticles were synthesized in choline chloride-calcium chloride.•The nanoparticles showed 99% crystallinity and mean particle size of 30nm.•XRD and FTIR results revealed 99% crystal purity and fluoride substitution of >97%.•The bio-nontoxicity of the as-synthesized nanoparticles was confirmed by MTT assay. Fluorapatite (FA) nanoparticles were synthesized via an one-step and green pathway by employing the deep eutectic solvent based on choline chloride-CaCl2.6H2O. In an innovative approach, the eutectic solvent was chosen in such a way to act as solvent, reactant and template, simultaneously. The results obtained from characterization of the as-synthesized nanoparticles revealed the formation of FA nanoparticles having average crystal size of 26nm, percent crystallinity of 99%, mean particle size of 30nm, and high crystal, elemental, and structural purity. In vitro study was conducted by immersion of FA nanoparticles in SBF solution. The results obtained by SEM, EDS, FTIR, and Raman analysis confirmed the formation of bioactive apatite layer on surface of the nanoparticles after 7days of immersion. The MTT assay and acridine orange staining test using hMSCs suggested the non-toxicity and osteogenic ability of as-synthesized FA nanoparticles. Based on the proposed synthesis mechanism, the deep eutectic system played a ternary role in synthesis of FA nanoparticles providing the synthesis environment, reactive calcium sites, and steric-electrostatic stabilization by which it can control the growth of as-formed FA particles in the nanometer size-range.