Osteogenic Potential of Zn2+-passivated Carbon Dots for Bone Regeneration in Vivo
Carbon dots is a new kind of nanomaterial which has great potential for biomedical application. Previously, we have synthesized novel Zn2+-passivated carbon dots (Zn-CDs) which showed good osteogenic activity in vitro. In this study, we will further investigate the osteogenic effects of Zn-CDs in vivo which is essential before clinical use. Herein, Zn2+-passivated carbon dots (Zn-CDs) were prepared and characterization as previously. Then, the optimum dose for inducing osteoblasts was evaluated by MTS assay, intracellular reactive oxygen species(ROS), detectionalkaline phosphatase (ALP) activity test and alizarin red staining in vitro. Finally, a 5-mm diameter calvarial bone defect model was created in rat and Zn-CDs were applied for repairing the critical bone defect. It was shown that zinc gluconate (Zn-G) and Zn-CDs promoted the survival of bone marrow stromal cells (BMSCs) when the zinc ion concentration was 10-4 mol/L (Zn-G:45.6µg/mL) and 10-5 mol/L (Zn-CDs:300µg/mL) or below respectively. Turned to the osteogenic capacity, the ALP activity induced by Zn-CDs was significantly higher than Zn-G. Besides, the results of alizarin red staining showed that the area of calcified nodules was increased in a dose-dependent manner in Zn-CDs group. Moreover, there were more calcium nodules in Zn-CDs group than Zn-G group at the same concentration of Zn2+ (10-5 mol/L). Taken together, Zn-CDs achieved highest osteogenic effect at the concentration of 10-5mol/L without affect cell proliferation in long term stimulation. Importantly, the volume of new bone formation in the Zn-CDs group (6.66±1.25mm3) was twice higher than the control group (3.33±0.94mm3) in vivo. Further histological evaluation confirmed the markedly new bone formation at 8 weeks in the Zn-CDs group. The in vitro and in vivo experiments revealed that Zn-CDs could be a new predictable nanomaterial with good biocompatibility and fluorescent property for guiding bone regeneration.