完整的内皮层与平滑肌层是小口径血管再生的关键。传统的体外构建方法受限于细胞来源和培养费时等问题，利用仿生支架诱导血管原位再生成为当前的研究热点。针对小口径血管的结构仿生，我们最近研制出一种具有双相孔径结构的双层纳米纤维血管支架，其内层的微孔结构便于血管内皮细胞的粘附生长，外层的大孔结构利于平滑肌细胞的渗透长入，适合用于小口径血管的原位构建。基质细胞衍生因子-1α（SDF-1α）能够在体内募集血管祖细胞，而血小板衍生生长因子（PDGF-BB）可促进平滑肌细胞的募集和增殖。本项目拟进一步开发具有最佳孔径、力学和降解性能的双层小口径血管支架，并采用肝素固定技术分别在支架内、外层固定SDF-1α和PDGF-BB。通过体内、外实验评价生长因子释放对促进血管祖细胞募集和分化的影响。特别是通过血管原位再生研究，探明生长因子释放对血管内皮层和平滑肌层重建的影响，为小口径血管的原位再生提供新的思路。

To construct the intact endothelial cell (EC) and smooth muscle cell (SMC) layers plays the critical role in the development of small-diameter vascular grafts. The traditional in vitro tissue engineering (TE) approach requires harvest the cells from the patient and extensive culture period, which limits its clinical applicability. To overcome these limitations, an in situ TE approach was proposed and became the research hotspot, in which endogenous progenitor cells are recruited by biomimetic scaffolds for in situ blood vessel regeneration. For mimicking the architecture of a native vessel, we have recently developed a bi-layered tubular scaffold by using a two-step thermally induced phase separation (TIPS) approach. The scaffold incorporates a microporous nanofibrous inner layer which allows ECs adhesion and growth, and a macroporous nanofibrous outer layer to facilitate SMCs infiltration and ingrowth, which may be used as a suitable scaffold to create small diameter vascular grafts in situ. Stromal cell derived factor-1α (SDF-1α) is a potent factor for vascular progenitor cells (VPCs) recruitment in vivo, and platelet-derived growth factor-BB (PDGF-BB) can promote vascular maturity by the recruitment of SMCs and stimulating cell proliferation. In this study, we will fabricate a new bi-layered tubular scaffold with optimal pore size, mechanical and biodegradable properties for in situ blood vessel regeneration, and SDF-1α and PDGF-BB are then immobilized on the inner and outer layers by using heparin as a molecular linker, respectively. We will investigate the effects of the immobilized SDF-1α and PDGF-BB on the recruitment and proliferation of VPCs both in vitro and in vivo, and focus on the roles of the released growth factors in the remodeling of both EC and SMC layers in the vascular grafts. The results of this study may provide new insight into the in situ small-diameter blood vessel regeneration.