ZnO quantum dots modified bioactive glass nanoparticles with pH-sensitive release of Zn ions, fluorescence, antibacterial and osteogenic properties.

Zinc (Zn)-containing materials have osteogenic and antibacterial activities while bioactive glass nanoparticles (BGN) show bone-bonding ability, as well as osteoconductive and osteoinductive properties. Zn-containing BGN are therefore considered to be promising materials for various biomedical applications, particularly in bone regeneration. In this study, we report a convenient method to prepare Zn-containing BGN by coating ZnO quantum dots (QDs) on BGN via electrostatic interactions. The synthesized ZnO-BGN nanocomposite particles are spherical and highly dispersed, and exhibit a unique fluorescence behavior under UV excitation, emitting three wavelengths in the violet, blue and green range. ZnO-BGN showed apatite-forming ability upon immersion in simulated body fluid, but their apatite formation was delayed compared to BGN. Interestingly, ZnO-BGN showed a rapid release of Zn ions at pH 4 but a far slower release at pH 7.4. ZnO-BGN also exhibited antibacterial effects on both Gram-positive and Gram-negative bacteria at the concentrations of 1, 0.1, and 0.01 mg mL-1. Higher concentrations could lead to stronger antibacterial effects. The LDH and live/dead assays indicated that ZnO-BGN had no significant cytotoxicity towards human mesenchymal stem cells (hMSC) at concentration of 0.1 and 0.01 mg mL-1, but ZnO-BGN inhibited the relative proliferation of hMSC compared to BGN and the control according to the MTT assay. Notably ZnO-BGN improved the osteogenic differentiation of hMSC as indicated by the determination of the alkaline phosphatase activity. In conclusion, coating quantum dots on BGN is a promising strategy to produce Zn-containing BGN. The synthesized ZnO-BGN are potential materials for bone regeneration, considering their apatite-forming ability, unique ion-release behavior, effective antibacterial activity, non-cytotoxicity, and osteogenic potential.