Abstract: BACKGROUND: Composite scaffold has been proven to be effective in treating large segmental bone defects. However, slow bone repair and poor osteogenesis remain to be the main problem. Total flavones of Rhizoma Drynariae can promote osteogenesis and accelerate bone healing, but the route of administration is still confined to intragastric administration and the research about local drug delivery into bone defects is still relatively insufficient.  
OBJECTIVE: To observe the difference between the local and intragastric administration of total flavones of Rhizoma Drynariae for large segmental bone defects by constructing the scaffold composed of total flavones of Rhizoma Drynariae controlled release microsphere-β-tricalcium phosphate. 
METHODS: Three-dimensional printing technology was utilized to construct porous β-tricalcium phosphate scaffold. The ultrasonic emulsification solvent dialysis method was used to prepare total flavones of Rhizoma Drynariae sustained-release microspheres. The total flavones of Rhizoma Drynariae sustained-release microsphere/β-tricalcium phosphate scaffold was prepared by freeze-drying method. A total of forty SD rats were randomly divided into four groups, and a 3 mm long bone defect model of the tibia was constructed using the circular external fixation. No material was implanted in the bone defect of the blank group, and a simple β-tricalcium phosphate scaffold was placed in the blank scaffold group. A β-tricalcium phosphate scaffold was implanted in the gavage group that was combined with intragastric administration of total flavones of Rhizoma Drynariae, whereas the scaffold composed of total flavones of Rhizoma Drynariae controlled release microsphere-β-tricalcium phosphate was implanted in the drug loaded group. At 8 weeks after operation, imaging test, histological staining, and immunohistochemical staining were conducted. 
RESULTS AND CONCLUSION: (1) X-ray films and Micro-CT examination showed that there was almost no callus formation in the defect area of the blank group. The callus generated in the blank scaffold group was connected to the osteotomy end, and the osteotomy line was faintly visible. The osteotomy line in the gavage group basically disappeared, and more new bones could be seen connecting both ends of the osteotomy site. In the drug loaded group, a large amount of callus formation was seen; the osteotomy line disappeared completely; the cortex was reconstructed well; and the medullary cavity was recanned. (2) Hematoxylin-eosin, Masson and Safranin Fast Green staining showed that a small amount of blood vessels and a large amount of connective tissue were seen in the defect area of the blank group. More bone matrix formation was seen in the blank scaffold group, but the maturity was not high. In the gavage group, a large amount of bone matrix was formed and mature. In the drug loaded group, a large amount of bone-like tissue was generated in the gap of the osteotomy defect; the cartilage tissue was highly mature, and the medullary cavity was recanalized. (3) Immunohistochemical staining results showed that compared with the blank scaffold group and blank group, transforming growth factor-β and bone morphogenetic protein 2 expression levels were higher in the gavage group and the drug loaded group (P < 0.05). Furthermore, above expression levels were higher in the drug loaded group than those in the gavage group (P < 0.05). (4) The above results indicated that both local administration and intragastric administration of total flavones of Rhizoma Drynariae could promote the repair of bone defects, but a significant difference was observed between the two methods, of which the local administration of controlled release microspheres of total flavones of Rhizoma Drynariae showed better effects.  

Key words: total flavones of Rhizoma Drynariae, β-tricalcium phosphate, composite scaffold, administration route, large segmental bone defects, bone repair, tissue engineering