Abstract: BACKGROUND: Some studies have shown that basic fibroblast growth factor can promote the proliferation and osteogenic differentiation of mesenchymal stem cells. 
OBJECTIVE: To compare the ability of acellular bone matrix/chitosan scaffold combined with basic fibroblast growth factor in repairing rabbit femoral defect.
METHODS: The acellular bone matrix/chitosan scaffolds were prepared by fusion blending and freeze-drying method, and the acellular bone matrix/chitosan scaffold loaded with basic fibroblast growth factor was prepared by immersion method. Mouse embryonic osteoblasts MC3T3-E1 were seeded on the surface of the two scaffolds for cell proliferation, cell adhesion and osteogenic gene detection. Cells cultured alone served as control. Bone defect models with a diameter of 5 mm were made in bilateral distal femurs using thirty-six 6-month-old New Zealand white rabbits and randomly divided into three groups by drawing lots. The blank group was not intervened. The simple composite scaffold and growth factor + composite scaffold groups were implanted with acellular bone matrix/chitosan scaffold and acellular bone matrix/chitosan scaffold loaded with basic fibroblast growth factor for X-ray and histological examination.
RESULTS AND CONCLUSION: (1) Within 1-11 days of culture, the cell proliferation of basic fibroblast growth factor/acellular bone matrix/chitosan scaffold group was faster than that of the acellular bone matrix/chitosan scaffold group (P < 0.05), and that of the acellular bone matrix/chitosan scaffold group was faster than that of the control group (P < 0.05). (2) After 4 days of co-culture with the scaffold, the mRNA expressions of type I collagen, osteocalcin, osteopontin and Runx2 were higher in the cells in basic fibroblast growth factor/acellular bone matrix/chitosan scaffold group cultured for 4 and 7 days than those of acellular bone matrix/chitosan scaffold group (P < 0.05), and the mRNA expression of alkaline phosphatase was higher than that of acellular bone matrix/chitosan scaffold group after 7 days of culture (P < 0.05). (3) Scanning electron microscopy showed that the scaffolds of the two groups supported the adhesion of MC3T3-E1 cells after 7 days of co-culture. (4) X-ray film of animal experiment showed that there was no obvious bone repair in the blank group at 12 weeks after operation; new bone formation could be seen at 8 weeks after operation in the simple composite scaffold group, and obvious new bone formation could be seen at 12 weeks after operation; new bone formation could be seen at 4 weeks after operation in the cytokine + composite scaffold group, and the bone defect site was almost completely repaired at 12 weeks after operation (5) Hematoxylin staining and Masson staining showed that a large amount of fibrous tissue could be seen in the blank group at 12 weeks after operation; a large amount of new bone formation could be seen in the two scaffold groups, in which the area and maturity of new bone formation in the growth factor + composite scaffold group were higher than those in the simple composite scaffold group. (6) The results showed that the acellular bone matrix/chitosan composite scaffold loaded with basic fibroblast growth factor is an ideal bone tissue repair material, which can promote bone formation.

Key words: basic fibroblast growth factor, chitosan, scaffold, acellular bone matrix, composite scaffold, femoral defect repair