Abstract: BACKGROUND: Naringin, the active ingredient of Rhizoma Drynariae, has the traditional effect of strengthening the liver and kidney and strengthening the bones and muscles, increasing the thickness of the callus and improving the quality of fracture healing.
OBJECTIVE: To explore the bone conduction and bone induction properties of naringin-chitosan/hydroxyapatite composite scaffolds.  
METHODS: The hydroxyapatite precursor solution with a certain calcium to phosphorus ratio and the chitosan solution containing naringin were crystallized in situ under alkaline conditions and freeze-dried to obtain a naringin-chitosan/hydroxyapatite porous scaffold. A total of 15 SD rats were randomly divided into blank group (n=5), control group (n=5) and experimental group (n=5). The 5 mm-diameter skull bone defect models were established by drilling holes. Biomaterials were not filled in the blank group. Chitosan/hydroxyapatite scaffolds were filled in the control group; and naringin-chitosan/hydroxyapatite scaffolds were filled in the experimental group. At 4 weeks after surgery, CT scans were performed to observe the skull repair. Hematoxylin-eosin staining was used to observe morphological differences. Immunohistochemical staining of bone morphogenetic protein 2 and vascular endothelial growth factor was performed to observe the expression of local osteogenic active factors in the defect areas. 
RESULTS AND CONCLUSION: (1) CT scan showed that no obvious osteogenesis was seen in the skull of rats in the blank group; only a small amount of new bone was seen at the edge of the defect. In the control group, new bone formation could be seen in the defect pores, and there was less new bone. In the experimental group, the bone defect was well repaired; the density of new bone tissue and the skull around the defect pores were similar, and a large area of new bone widely filled the defect pores. (2) Hematoxylin-eosin staining showed that the defect area in the blank group was filled with thin loose reticular fibrous tissue, and a large number of inflammatory response lesions were seen, and only a small amount of new bone was formed at the edge of the defect. In the control group and the experimental group, residual scaffold material, new bone trabecula and osteoblasts were seen in the defect area; osteoblasts were distributed in clusters in the pores of the scaffold and the edges of the defect area, surrounded by a large number of capillaries. Among them, the experimental group showed a stronger ability of new bone growth. (3) Immunohistochemical staining showed that the expression levels of local osteogenic activity factors bone morphogenetic protein 2 and vascular endothelial growth factor in the experimental group were higher than those in the control and blank groups (P < 0.05). (4) The results conclude that naringin-chitosan/hydroxyapatite composite scaffolds can provide necessary carrier for bone defect repair. Naringin can create local osteogenic microenvironment, accelerate the growth and mineralization of new bone tissue, and have good bone repair performance.

Key words: naringin, chitosan, hydroxyapatite, composite scaffold, bone defect, osteogenesis performance