基于血管树构建的组织工程血管化基础研究

The fabrication of completed vascular network containing large vessels and capillaries is holding a crucial challenge in building artificial complicated tissues and organs. For instance, liver tissue engineering has become one of the effective treatment for fulminant hepatic failure and end-stage liver disease. However, the size of artificial liver is critically expected to meet the clinical demands. Thereby, a artificial liver construct without vascular network hasn't the capability to grow well or express its functions. Despite the advances in building capillaries have been made approvingly, the fabrication of completed vascular network with both large vessels and capillaries still maintains a big difficulty to date..This study proposes to achieve the vascularization by both the guidance of preformed dendroid vascular network (vessel-tree) and the self-assembly of capillary-islands. Briefly, a dendroid vascular network composed of main blood vessels is designed and developed, based on which a hepatic tissue construct is then fabricated through the cell controlled assembly technology or the direct seeding of cell microcapsules. As to in vivo transplant, the hepatic tissue construct is connected to the blood-supply system of host; while if for the in vivo culture, it is connected to a pumping bioreactor, facilitating the artificial vascular network to connect with the capillaries or the blood islands generated by cell self-assembly towards a engineered hepatic tissue with completed vascular network. The success of this study will present a significant potential of application in, as well as the fabrication of completed vasculature, as well as the ultimate vascularization of complicated tissues or organs.

建立包括大血管及毛细血管网的完整血管网是组织工程技术必须解决的关键问题。以肝组织工程为例，组织工程人工肝是治疗肝衰竭和终末性肝病的理想方法，但组织工程人工肝脏必须具备一定的体积方可满足临床的基本需求。制约大体积肝组织块构建的关键因素就是如何重构可支持组织块功能发挥及生长的血管网。目前人们在毛细血管网成形方面取得了较好的效果，但在成形包含大血管在内的完善的血管网方面却一直难以突破。本项目提出基于血管树重构和诱导毛细血管团（血岛）复合血管化技术路线，其核心是首先设计并成形由主干血管构成的血树，以此为依托利用细胞三维堆积或直接种植由细胞微囊方式构建肝组织块原型。通过体内移植或体外培养将组织块原型与宿主血供相连（或与生物反应器的泵源相连），使人工成形的血树与诱导生成的毛细血管网（血岛）相连通，从而形成包含完整血管网络的肝组织块。本项目在复杂器官血管化及复杂脉管系统的设计成形方面有重要应用。

血管化是组织工程技术必须解决的关键问题之一。毛细血管网络可以通过生长因子调控等方式生成，但骨干血管网却缺乏有效解决手段。如果能成形较为完整的大血管网络，同时辅助以诱导生成毛细血管网，则可将制造成形和生长成形有机结合，则可能为解决大块工程组织血管化问题提供新的技术路线。该路线的核心即首先根据仿生学原理设计、成形多分枝骨干血管网络。该研究成果同样可用于小口径人工血管的设计和制造。.针对学部对提出的修改意见，课题将研究方向和目标进一步明确，主要围绕材料筛选及显微结构优化、血管树成形技术以及血管网三维结构支架设计及优化等方向开展。 .1、完成了血管材料的优化筛选。PCL-MDI-PEG材料（PU改进型）细胞毒性与PLGA材料接近，细胞毒性为0级，具有较好的细胞相容性。溶血试验结果表面血液相容性良好。材料弹性模量仅为12.3MPa，弹性极限高达300%以上，适合作为血管材料。.2、采用基于统计规律的数学建模方法进行多分枝血管的建模设计，并利用数字分析方法对多血管分支出的过渡半径等结构进行优化，以提高多分枝血管的血液运输效率。.3、设计了气动式尖笔直写喷头，并完成了喷头的设计、优化及改进，实验结果表明该喷头适合中等粘度生物材料的喷射成形，可满足RP溶芯-沉积多分枝血管支架成形工艺的要求。设计并搭建了三维成形平台，完成了多分枝血管可溶内芯的成形。对PU材料及PLGA材料的静电纺丝（electrospinning）、浸涂（dip coating）等成形工艺进行了研究，并制备了管壁具有三层结构的仿生小口径人工血管。测试结果表明成形的多层结构人工血管径向顺应性为1.73~1.79%/100mmHg，与天然羊的颈动脉血管相当，良好的缝合强度和爆破压满足使用要求，可满足体内植入测试要求。.4、研发了基于一种交变滞惯力驱动的微滴喷射喷头和喷射系统，研究了驱动频率、驱动电压、喷嘴直径等主要参数对喷射效果的影响规律。结果表明，该技术可有效实现高精度微滴喷射，并可推广到细胞微滴喷射领域。