快速降解弹性血管支架的结构优化及其体内再生动脉的机理研究

Engineering artificial blood vessel provides important alternative to autologous vascular grafts which has long been limited by donor shortage. However, conventional synthetic vascular grafts or tissue engineering grafts always rely on tough, slowly degrading biomaterials or dense extracellular matrices produced in vitro, which greatly impeded their in vivo remodeling as well as integration with host vessels, thereafter abrogated their clinical success, especially for small caliber vessels. Our project proposed to promote in vivo cell recruiting in grafts, and harness host remodeling ability. We believe fast cell recruitment and appropriate mechanical loading are the critical factors that influence the host remodeling and cell differentiation of tissue engineering grafts, therefore opening structure for cell infiltration, scaffolding materials with adequate degrading rate as well as flexible material which could sense the environmental forces would be essential to graft design. We have fabricated porous tubular scaffolds by using elastomeric polymer poly glycerol-sebacate (PGS), via choosing 25 μm sized salt particles to control the pore size of the scaffold, in addition, the electrospinning polycaprolactone (PCL) fibrous sheath wrapped outside of the grafts significantly stabilized the mechanical strength of the vascular graft. We found large amount of host cells including macrophages infiltrated into the scaffold via opening pores since 3 days after implantation, thereafter, more cells including vascular progenitor cells recruited and aggregated in accordance with the polymer degradation. Arterial matrices become abundant and organized with the pulsation of blood flow, which resulted in compliant arterial regeneration. In our proposals, we will further focus on the problems such as uneven recruitment of vascular cells, uneven distribution of neonatal ECM, and attempted to solve problems via optimization of structural parameters and sheath materials. Furthermore, we will explore the spatiotemporal distribution of recruiting cells, and tissue sources of these cells. Additionally, the relationship between sheath structure and differentiation of recruiting cells will be unraveled. Based on above research experience, vascular grafts with optimized structure and biomaterials will pave the road for their remodeling in situ, which also will crack the bottle neck of the present regenerative medicine.

构建人工血管是解决自体移植血管来源不足的重要途径，然而，为耐受动脉压力而运用坚强性慢降解材料以及组织工程血管致密的组织结构，制约了其在体内的功能性改建以及与宿主的融合，限制了其在小血管修复上的成功率。本项目从促进体内细胞募集、充分利用宿主自身的改建能力出发，构建具有开放性结构及稳定管状形态的双层血管移植体。以Polyglycerol-sebacate 弹性体构建的多孔内层实现了大鼠宿主细胞的快速募集，其快速降解为组织基质沉积创造了空间;而聚己内酯菲薄鞘层稳定了移植体的三维结构，最终再生出具有高度细胞化以及功能性基质的动脉。本项目将针对移植体中出现功能细胞募集不均匀，组织基质合成不均进行移植体的结构优化,并深入研究细胞募集的时空规律以及组织来源，明确细胞分化与移植体结构以及鞘层材料之间的关系。本项目为诱导性动脉再生提供完善的理论依据,并为人工血管的临床转化提供新的技术理念。

我们通过结构优化，体内研究探索材料重塑的过程，研究出细胞募集机理。获得具有优化结构的动脉移植体。证明体内具有改建和生长的潜能。它多孔连通的结构以及快速降解的特性，能够快速动员机体募集单核细胞、SMCs、ECs，而其所具备的柔软、弹性体的力学特性促进了细胞的分化增殖以及细胞外基质的分泌，从而快速补偿材料降解而损失的力学性能。我们的研究结果显示，延长静电纺丝时间，显著增加了PCL纳米纤维鞘层的密度和PGS/PCL双层血管移植体的机械力学强度。另外，随着鞘层密度的改变，机体对PGS/PCL双层血管移植体的肌性改建也发生了很大的变化。本组研究中适中密度的PCL纳米纤维丝鞘层结构能够显著提高机体对移植体肌性改建的能力，使募集的平滑肌细胞持续处于一种稳定的分化状态，机体对移植体的改建持续向着一种稳定的、肌性和功能性的方向发展。另外，外膜的血管化和M2型巨噬细胞的渗入，与鞘层密度和微观结构密切相关，通过调整鞘层密度和微观结构可以调节肌性改建和组织细胞的表型。这些发现证实了对缠绕在PGS管芯外的PCL鞘层合理的设计能够启动高质量的肌性改建，从而保证了新生血管具有更强的压力承受能力，优良的缝合操作性能，以及实现长期在动脉血流动力学环境中与自体血管相当的功能，为进一步的临床转化提供依据。颈动脉重建的体内实验研究表明，用PGS/PCL血管移植体重建颈动脉，与自体静脉重建颈动脉相比，具有更多的优势，突出表现在：1.新生血管在体内长期的改建过程中未出现管壁过度增生、钙化；2.新生血管壁中出现了大量弹性蛋白的沉积； 3.能够形成疏松结缔组织样的外膜结构，不与机体组织发生瘢痕粘连；4.实现了血管壁外膜神经的重建。这个结果暗示了PGS/PCL双层血管移植体可以更好地实现具有收缩性和灵活性并且神经分布比较丰富的肌性颈动脉的重建，为侵犯到颈动脉的头颈部恶性肿瘤的治疗提供一个新的治疗手段。.