Abstract: BACKGROUND: At present, it is difficult for a single scaffold material to meet the needs of osteogenesis in bone tissue engineering. Microsphere scaffolds combined with a variety of materials can maximize their strengths and avoid their weaknesses, which has great application potential.
OBJECTIVE: To explore the biocompatibility, degradability, and osteoinductivity of a new type of polytrimethylene carbonate/β-tricalcium phosphate in animals. 
METHODS: The β-tricalcium phosphate bone cement and polytrimethylene carbonate/β-tricalcium phosphate microsphere scaffold were prepared. Eighteen male SD rats were randomly divided into three groups (n=6) according to their weight. No material was implanted in the bilateral femoral defects in the blank control group. The β-tricalcium phosphate bone cement was implanted in the bilateral femoral defects in the control group. Polytrimethylene carbonate/β-tricalcium phosphate microsphere scaffold was implanted at bilateral femoral defects in the experimental group. At 4, 8, and 12 weeks after operation, the bilateral femurs were taken out for hematoxylin-eosin staining, Masson staining, and immunohistochemical staining for osteocalcin. 
RESULTS AND CONCLUSION: (1) Hematoxylin-eosin staining and Masson staining: At 4 weeks after operation, the bone defect in the blank control group was surrounded by fibrous tissue and numerous inflammatory cells gathered. In the control group, the material was mostly degraded and surrounded by fibrous tissue, with a small amount of new bone matrix and bone trabecular formation at the edge of the material, which was surrounded by a few inflammatory cells. The material in the experimental group did not degrade remarkably and was surrounded by fibrous tissue. Some new bone matrix and bone trabecular formation were detected at the edge of the material, which was surrounded by a few inflammatory cells. At 12 weeks postoperatively, the blank control group presented regular trabecular bone, which was connected to each other, without inflammatory cells. In the control group, the material was completely degraded and trabecular bone was regular, forming a thick lamellar shape, without inflammatory cells. In the experimental group, materials were partially degraded; bone mass was increased and dense, with the absence of inflammatory cells. (2) Immunohistochemical staining: With prolonged time, the expression of osteocalcin in the bone defect of the control group increased first and then decreased. The expression of osteocalcin in the blank control group and the experimental group showed a gradually increasing trend. The expression of osteocalcin at each time point was higher in the control and experimental groups than that of the blank control group (P < 0.05). The expression of osteocalcin in the experimental group was higher than that of the control group at 12 weeks postoperatively (P < 0.05). (3) These findings exhibit that the polytrimethylene carbonate/β-tricalcium phosphate microsphere scaffold has good biocompatibility, osteoinductivity, and moderate biodegradability. 

Key words: bone tissue engineering, microsphere scaffolds, polytrimethylene carbonate, β-tricalcium phosphate, biocompatibility, degradability, osteoinductivity, osteocalcin