Abstract: BACKGROUND: The development of tissue engineering technology provides new ideas for the repair and reconstruction of bone defects, but the problem of vascularization restricts the clinical application of tissue engineered bone. Platelet-derived growth factor can promote the formation of blood vessels in bone tissue while promoting the formation of bone cells. 
OBJECTIVE: To observe the effects of polycaprolactone /β-tricalcium phosphate/platelet-derived growth factor BB (PCL/β-TCP/PDGF BB) scaffold on osteogenic differentiation of bone marrow mesenchymal stem cells and proliferation and adhesion of human umbilical vein endothelial cells in vitro, as well as the effect of its application in animal bone defects.
METHODS: (1) Polycaprolactone/β-tricalcium phosphate scaffolds were prepared by 3D rapid prototyping machine, and the scaffolds were immersed in platelet-derived growth factor BB solution to prepare PCL/β-TCP/PDGF BB scaffold. (2) In vitro experiment: Bone marrow mesenchymal stem cells and human umbilical vein endothelial cells were inoculated on two kinds of scaffolds, respectively, to detect the osteogenic differentiation of bone marrow mesenchymal stem cells, and to detect the proliferation, adhesion and angiogenic gene expression of human umbilical vein endothelial cells. (3) In vivo experiment: 21 adult rats were taken to establish a bilateral tibial defect model. The experimental group (n=7) was implanted with PCL/β-TCP/PDGF BB scaffolds; the control group (n=7) was implanted with PCL/β-TCP scaffolds; the blank group (n=7) was not implanted with scaffolds. At 12 weeks after operation, micro-CT scanning, bone histomorphological observation, and gene detection of osteogenesis and angiogenesis were performed.
RESULTS AND CONCLUSION: (1) In vitro experiment: Compared with PCL/β-TCP scaffold, PCL/β-TCP/PDGF BB scaffold could promote the osteogenic differentiation of bone marrow mesenchymal stem cells, promote the proliferation and adhesion of human umbilical vein endothelial cells, and promote vascular endothelial growth factor and CD31 mRNA expression in human umbilical vein endothelial cells. (2) In vivo experiments: Micro-CT scans exhibited that bone defects were obvious in the blank group. A large amount of new bone tissue was visible in both control and experimental groups. The repair effect of the experimental group was more clear. Hematoxylin-eosin staining, Masson and safranin fast green staining displayed that there was no obvious bone tissue formation in the blank group. In the control group, a large amount of mature bone matrix and relatively less immature cartilage tissue were detectable. In the experimental group, a large amount of osteoid tissue and mature cartilage tissue were seen, and most of the medullary cavity was recanalized. RT-PCR detection showed that the mRNA expression levels of bone morphogenetic protein 2, basic fibroblast growth factor, alkaline phosphatase, osteocalcin, vascular endothelial growth factor and CD31 in the experimental group were higher than those in the control group (P < 0.05). (3) It is concluded that compared with PCL/β-TCP scaffold, PCL/β-TCP/PDGF BB scaffold promoted the osteogenic differentiation of bone marrow mesenchymal stem cells, the proliferation, adhesion and expression of angiogenic genes of human umbilical vein endothelial cells, and promoted the repair of bone defects.

Key words: bone defect, polycaprolactone, β-tricalcium phosphate, platelet derived growth factor BB, angiogenesis, tissue engineering