骨修复是一个由细胞、信号分子和细胞外基质共同参与的级联响应过程。其中，各种血管诱导因子和成骨因子顺次释放和表达，调控细胞行为、血管发生和新骨生成。因此，体外仿生构建两种生长因子程序释放的骨修复载体，探明生长因子释放与骨组织血管化和成骨规律，有助于解决大段骨修复中的血管化难题。本项目采用热致相分离技术制备PLLA/PCL三维多孔纳米纤维支架；分别制备pH响应性介孔硅纳米粒子（MSNs）和PLGA微球，作为小分子血管诱导因子1-磷酸鞘氨醇（S1P）和成骨因子rhBMP-2的微载体，并复合到纳米纤维支架上。pH响应性MSNs能够响应支架降解引起的pH值变化，实现S1P剂量递减的受控释放，而PLGA微球能够随自身降解缓慢释放rhBMP-2。因而，复合载体可实现两种因子的可控释放。通过揭示生长因子的程序释放在骨的血管化和成骨进程中的作用，为构建具有血管化潜能的组织工程骨提供实验依据。

Bone repair and regeneration is a complex and coordinated cascade of events regulated by the osteogenic cells, signaling molecules and the extracellular matrices. During this process, the sequential release and expression of angiogenic and osteogenic growth factors play central roles in the recruitment of mesenchymal stem cells, angiogenesis and subsequent bone formation. Therefore, the development of bone scaffolds capable of releasing angiogenic and osteogenic growth factors in a sequential fashion is critical for the repair of large bone defects, which remains a major clinical orthopaedic challenge. Since sphingosine 1-phosphate (S1P) has been proved to be a complete angiogenic factor, we hypothesized that sequential delivery of S1P along with bone morphogenic protein-2 (BMP-2) would exert a synergistic effect on bone repair. To demonstrate this hypothesis, composite nanofibrous scaffolds containing both S1P and BMP-2 will be prepared by incorporating S1P-loaded pH-responsive mesoporous silica nanoparticles (MSNs) and BMP-2-loaded poly(lactic-co-glycolic) (PLGA) microspheres into the scaffolds. Poly(L-lactide)/ Polycaprolactone (PLLA/PCL) nanofibrous scaffolds can be prepared by thermally induced phase separation (TIPS) technique. S1P release from MSNs will be triggered by the decreased pH value resulting in the degradation of PLLA/PCL scaffolds, whereas BMP-2 can be released by the degradation of PLGA microspheres. Thus, a tunable dual delivery scaffold will be created which allows the sequential release of S1P and BMP-2 as bone healing under physiological conditions. In this project, we will investigate the S1P and BMP-2 release profiles from the composite scaffolds and their effect on angiogenesis and bone formation by using both in vitro and in vivo studies.