【作者】 王富军；

【导师】 王璐；

【作者基本信息】 东华大学 ， 纺织工程， 2014， 博士

【摘要】 涉及到分支血管的主动脉瘤及夹层等扩张性疾病,由于其手术危险系数高,是血管外科治疗研究的重点和难点。然而目前用于治疗该类疾病的腔内隔绝术用人工血管在临床应用中的效果并不理想,主要是由于病变部位离心脏较近,手术难度较大,支架释放较难控制；同时由于涉及分支血管,手术方案复杂,容易导致手术操作不成功,造成治疗失败。因此设计并制备手术操作简单的分支人工血管就成为该领域研究的焦点及重点问题,也成为解决涉及分支血管的主动脉疾病的最佳途径。本文针对用于微创治疗的分支人工血管的研究现状和存在的问题,对腔内隔绝术用分支人工血管膜的功能和结构设计、成型以及结构与性能的关系进行了深入研究。通过动物实验、有限元分析和流体力学理论计算,设计了一种具有帽型结构和抛物线曲面形状并且不带金属支架的分支人工血管膜的模型。由在体测量猪主动脉弓和分支动脉血压差的动物实验表明,分支动脉在被封堵前存在着明显的血压差,其数值达到压差均值42.78±5.17mmHg,在腔内隔绝术人工血管的实际释放过程中,其瞬时的压差将远远大于实测的数值。因此根据这个血压差可以设计一种不带金属支架的帽型分支人工血管膜,利用血压差自动突入分支动脉。并利用ANSYS模拟软件,通过有限元方法分析不同曲面函数的应力和形变分布,结果表明,抛物线曲面的结果最优。根据流体力学理论,通过沿程能量损失计算和综合有限元分析,选择了抛物线曲面。因此提出后续分支血管膜设计可采用帽型、无金属支架支撑的、抛物线曲面的制备方案。根据上述确定的最优抛物线曲面函数模型,通过模压成型的方法制备涤纶(PET)机织分支人工血管膜,探索异形分支人工血管膜的表征方法,并研究其几何结构与顶破、径向拉伸、弹性回复等力学性能的关系。选取PET复丝,采用平纹和斜纹两种织物组织通过织造、退浆／致密化过程得到不同密度的织物,利用抛物线曲面的模具制备“帽形”织物再进行热定型即可得PET分支人工血管膜。同时探索了异形分支血管膜的表征体系,测试了模压成型法人工血管膜的几何结构、聚集态结构和力学性能,并对其释放情况进行了体外模拟。由结果可知,经模压法制备的“帽形”分支血管膜试样从帽底至帽顶密度逐步减小,其厚度、克重、结晶度及顶破强度也随之呈现梯度变化；密度较大的斜纹织物试样体现出较好的力学性能；而体外模拟释放试验也表明模压成型的分支人工血管膜在压力作用下,中间区域能够突入分支动脉,保证分支的血供。为了进一步提高分支人工血管膜的力学性能,以及探索新型的加工成型方法,仿真动脉血管的三层结构(内膜、外膜、中膜),内、外膜选用生物相容性较好的多孔聚己内酯(PCL)材料,中膜选用PET网格织物作为增强层,以期提高分支人工血管膜的力学性能。探索了溶液浓度、分子量对多孔膜的影响,SEM结果可知,溶液浓度越小,孔隙率越大：分子量为18万的PCL膜的孔径和孔隙率大于分子量为5万和8万的PCL膜,所有的多孔膜的孔径都在10μm以上,并且是三维贯通的。综合加工工艺,采用了冰乙酸作为PCL材料的溶剂,选择了分子量为18万的PCL作为基材,最大针织网格密度的PET织物作为增强层,用于制备PCL/PET复合分支人工血管膜。采用了压力喷涂和冷冻干燥方法相结合,制备了针织PET网格织物作为中间层以期增强多孔PCL膜的三层分支人工血管膜。同时对成型后PCL分支人工血管膜及PET网格织物增强的复合分支人工血管膜试样进行几何结构,管壁微观结构,顶破强力、径向拉伸、弹性回复、缝合强度等力学性能进行了表征和分析。对比了PCL/PET复合分支人工血管膜与纯PCL分支血管膜的结构与性能,分析了PET网格织物的增强机制,同时比较了单层PET机织分支人工血管膜的研究结果。PCL以及PCL/PET分支人工血管试样的周边区域的管壁厚度值稍大于中央区(帽顶和帽弧)的值,这是由于PCL溶液在重力场的作用下发生微量流延所致,与PET机织分支人工血管膜的结果相似。PCL/PET分支血管膜的SEM照片显示,管壁呈现多孔形貌,并且相互贯穿,孔径10μm以上；同时PCL基体与PET纤维之间相互贯穿,界面相容性较好。由水渗透性实验表明,多孔膜在标准血压下不渗水,因此在植入体内并不发生内漏。人工血管膜材料的力学性能研究结果表明,PCL/PET复合分支人工血管膜的顶破强度、径向拉伸性能、弹性回复性能以及缝合强度均比纯PCL膜材料的性能有明显的提高,网格织物显示了显著的增强作用。同时PCL/PET复合分支人工血管膜的各项力学性能也比单层PET分支人工血管膜有了很大的提高。综上所述,本文利用了腔内隔绝手术过程中主动脉弓与分支之间存在的血压差,设计了无需金属支架支撑的帽状分支人工血管膜,优化了分支人工血管的外形设计,并用两种方法制备了分支血管膜,研究了其结构与性能的关系。该分支血管膜可应用于腔内分支血管的重建,达到一次手术释放,可以降低手术的操作难度。同时丰富了腔内分支人工血管的种类,为临床手术方法提供了更多的选择。更多还原

【Abstract】 There are great challenges to treat the aortic dissection and the aortic arch aneurysm involving its branch vessels. One of those challengeis that it is difficult to design and fabricate a suitable endovascular branched graft. That is because the lesion close to the heart makes the operation more difficult torelease the stent-graft. Meanwhile, the complicated surgical options are easily to lead to unsuccessful surgical operations, resulting in treatment failure. Therefore, the design and preparation of branched graft for simple surgical operation has become the focus and key issues in the field of endovascular graft. It has also become an important branch of the best way to solve the bottlenecks in the clinical application of endovascular graft regarding to the branched vessels.To deal with the existing problems and make a breakthrough of research status in the endovascular grafts with the branched vessels, this paper focuses on the functional design of a suitable endovascular branched graft and its structure molding as well as the their relationship between structure and properties.A hat-like endovascular branched graft model is designed with curved surface, and without metal stent graft,through the results of animal experiments, finite element analysis and computational fluid dynamics. The in vivo measurement of pressure in porcine aortic arch and branched artery have shown that there is a clearly difference in blood pressure before the branched artery was blocked; the value reaches42.78±5.17mmHg. The instantaneous value of the pressure of endovascular branched graft will be far greater than measured in actual release process. Therefore, hat-like endovascular branch graft without metal stent graft can be designed according to the automatic blood pressure difference. The ANSYS simulation software was taken to analyze the stress distribution and displacement of different curve surface by finite element method, and the results showed that the curved arc is optimal. According to the theory of fluid mechanics and the calculation results of energy loss, the parabola curved surface lost the smallest energy. Therefore it is recommended that the hat-like model without metal stents support can be used in the design of endovascular branch graft.The woven polyester (PET) endovascular branch graft was prepared by the compression molding, according to the optimal parabolacurved surface model.The characterization ofcurved shaped endovascular branch graftwas explored.The geometric structure and bursting, tensile strength, elastic recovery and other relationshipsbetween structure and properties were studied. PET multifilament was selected to fabricate two kinds of plain and twill weave fabric with different densities obtained by weaving, desizing and densification process, to form PET endovascular branch graft. Then the PET endovascular branch graft membrane could be obtained after the process of heat-set molded asa hat-like fabric with a parabola curved surface compression mold. After the characterization system of various shaped endovascular branch graft membranes was explored, its geometry compression molding, structure and mechanical properties of aggregation state were tested, as well as the in vitro release of situation. According to the results, the density of hat-like branched vascular membrane samples prepared by molding gradually decreased from the bottom to the crowns, the thickness, weight, degree of crystallinity and bursting strength also show gradient. The density compared with the large twill fabric samples reflected the good mechanical properties. In the in vitro release test of artificial vascular membrane molded under pressures, the resultsshowed the intermediate regions could plunge branched artery and ensure the blood supply to the branch.To further improve the mechanical properties of endovascular branch graft, and to explore the novel molding method and the simulation of the real three-layer structure artery (intima, adventitia, membrane), the porous polycaprolactone (PCL) material was selected for its biocompatibility to form the inner and outer membrane, andthe PET mesh fabric was select as a reinforcing layer in order to improve the mechanical properties of endovascular branch graft. The influences between the concentration, molecular weight and membrane porous structure were conducted by SEM. The results showed the smaller the concentration with the greater the porosity; pore size and porosity of PCL film with a molecular weight of180,000is greater than50000and80000of PCL films. All three-dimensional pore size in the porous membrane is more than10μm. Through the integrated processing technology, using acetic acid as a solvent, choosing180,000molecular weight of PCL for the substrate, the maximum density of the PET mesh knitted fabric as a reinforcing layer to prepare PCL/PET composite film used in endovascular branch graft. A pressure spray and freeze-drying method were used to combine PET knitted fabric mesh as an intermediate layer with PCL membrane. Meanwhile, the specimen geometry, wall microstructure, bursting strength, radial tensile, elastic recovery, strength and other mechanical properties of the suture were conducted to make characterization and analysis of the PCL membrane and PET fabric reinforced composites. Contrast the structure and properties of PCL/PET composite film and pure PCL membranes, the enhancement mechanism of PET fabric mesh was analyzed. The Wall thickness of PCL and PCL/PET endovascular branch graft surrounding the sample area is slightly larger than the central region’s (crowns and caps arc), which is due to occur in trace PCL solution flow under gravity field caused by delay, similar results were found in the PET fabric endovascular branch graft. SEM photographs of PCL/PET composite membrane showed the pore sizewith porouswall is over10μm; the interface compatibility between PCL and PET fiber matrix is good. The water permeability experiment showed that porous membrane is impermeable under the standard pressure, so the leakage will not occur in the in vivo implantation. The result of mechanical properties of the membrane material showed that the bursting strength of PCL/PET composite film branch of artificial blood vessels, radial tensile properties, elastic recovery and suture strength are better than pure PCL membrane materials.The PET fabric mesh showed a significant enhancement to improve the performances. Meanwhile, the mechanical properties of PCL/PET composite endovascular branch graft have also been greatly improved than the monolayer PET film.In summary, the hat-like endovascular branch graftwith stent-less was designed according to the difference of blood pressure between the branch and the aortic arch in the endovascular surgical procedures.The branch graft shape was optimized according to finite element analysis and computational fluid dynamics.Two kinds of endovascular branch graft membrane were prepared and relationship between structure and properties was studied. The hat-like endovascular branch graft can reduce the surgery operational difficulty and provide more choices for clinical surgeon.更多还原