Acceleration of bone repair in critical-size defect using angiopoietin-2 associated with novel carbon nanotubes scaffold via mitophagy-pyroptosis pathway.

To investigate the curative effect of Ang-2 combined with novel carbon nanotubes (CNTs) scaffold critical-size bone defect in rabbits.CNTs with good properties were first prepared by freeze-drying method. The mechanical properties and surface hydrophilicity of scaffolds were improved by adjusting the addition ratio of polylactic acid (LPA) and chitin fibers (CHI). After purification and functionalization of CNTs, CNTs/PLA/CHI three-dimensional porous scaffolds were prepared for animal experiments. Subsequently, the CNTs/PLA/CHI scaffolds were implanted into the rabbit critical-sized radius defect model to evaluate the osteogenic properties in vivo. Adult male New Zealand white rabbits were randomly allocated into three groups. Group A was the control group, and both groups B and C underwent radial bone defect surgery and implanted CNTs/PLA/CHI scaffolds. Animals in group C received a daily local injection of 1 mL of 400 ng/mL Ang-2 dissolved in physiological saline in the bone defect area for up to 14 days after surgery, while group B received the same amount of physiological saline.Scanning electron microscope results showed that the porosity of the CNTs/PLA/CHI three-dimensional porous scaffolds was as high as 80%. The surface contact angle was 35° to 55°, and the hydrophilicity was suitable for cell adhesion and growth. The CNTs/PLA/CHI three-dimensional porous scaffolds had excellent biological properties. The general observation and X-ray imaging after 12 weeks together indicated that the CNTs/PLA/CHI scaffolds could accelerate bone repair with the combination of endogenous angiogenic factor Ang-2. The results of western blotting and histology revealed that the expression of mitophagy proteins LC3, Beclin-1, PINK1 and Parkin was elevated in the new bone, and the expression of pyroptosis proteins Nod-like receptor protein NLRP3, caspase-1 and Gasdermin D (GSDMD) was decreased.Ang-2 associated with CNTs/PLA/CHI scaffolds accelerated bone regeneration through autophagy-pyroptosis pathway.