The Study Of The Hemodynamic And Animal Experiment About The Multilayer Stent

The incidence of the aortic aneurysm is increasing year by year,with high mortality and poor prognosis.Although the traditional endovascular aortic repair,which excludes the aneurysm with covered stents,has showed some benefit,not all aortic aneurysms are amenable to endovascular repair because of the anatomic features of the aortic branches.In recent years,a new type of multilayer stents has been developed which could reduce the pressure on the wall of the aneurysm,induce thrombosis forming in the cavity of the aneurysm and therefore shrink the aneurysm due to the organization of the thrombi and prevented the rupture of the aneurysms.In the meantime,it could also maintained the patency of the aortic branches and guide the blood flow into the branch vessels.However,less reports of the clinical application and postoperative follow-up data of this new type of stent can be found overseas,while there is no domestic report.Its therapeutic mechanism is still needed to be investigated.So the aim of this study was to analysis the hemodynamic effects of the multilayer stent on the aneurysms and branches as well as the biocompatibility of this stent through hydrodynamic numerical simulations,experimental researches,and animal experiments which got some beneficial results.The main contents of this study included:(1)Human aortic aneurysms numerical model was established to simulate the implantation of the multilayer stent,and then analyzed the pressure,velocity and other hemodynamic changes in the model of aneurysm and branch vessels.(2)The human aortic aneurysm models were manufactured according to the medical parameters.Measured and recorded the pressure of the cavity of the aneurysm through the steady flow experiments,and then investigated the changes of the pressure after implanting stent.(3)The multilayer stents were tested in the pressure verification experiment and the flow field experiment in order to study the changes of the hemodynamic parameter in the model of the aortic aneurysm.(4)The multilayer stent was implanted into the abdominal aorta of the swine while its bilateral renal arteries were both covered by the stent for 24 weeks or less to evaluate the effectiveness of maintaining the patency of the aorta and branch arteries as well as the biocompatibility of this novel stent.According to the results and conclusions of the numerical simulation,experimental research and animal experiments,the multilayer stent could reduce the impact of blood flow to the aneurysm,changed the status of the blood flow and therefore induced thrombosis,but also ensure the smooth flow of branch vessels and maintained the patency of the branches with favourable biocompatibility.Finally the researches got results as follows:(1)After the implantation of the multilayer stent,the pressure on the wall of the aneurysm had been decreased,as well as the impact of the blood,due to which the risk of expansion or rupture of the aneurysm had been reduced.(2)During the numerical simulations,the implantation of the multilayer stent could reduce the velocity of the blood flow,pressure on the wall of the aneurysm and the wall shear stress to a certain degree.(3)After the implantation of the multilayer stent,many hemodynamic factors in the cavity of the aneurysm had be changed.The flow pattern of the blood flow in the tumor cavity was transformed from a large number of eddy current into laminar flow.(4)In the model of the aneurysm,the multilayer stent was conducive to the formation of thrombi in the cavity of the aneurysm,yet it did not impair the blood supply of the branch vessels significantly.(5)Animal experiments showed that the multilayer stent could maintain the patency of abdominal aorta and branch arteries in a certain period of time without any artery stenosis,thrombosis,blood supply obstruction and other complications,which had nothing to do with the amount of the layer.Furthermore,the stent could be attached securely to the abdominal aortic wall without any shift,bend or break.In addition,the stent could be implanted in vivo safely and reliably with favourable biocompatibility of its material.The series of the study above had manifested that in a certain period of time,multilayer stent could reduce the velocity of the blood flow in the cavity of the aortic aneurysm,pressure of the aneurysm and wall shear stress,and accordingly reduced the possibility of rupture of the aneurysm.Moreover,this new type of stent could change the flow pattern in the cavity of the aneurysm which was conducive to the formation of the thrombi,thus it could shrink the aneurysm due to the organization of the thrombi and reinforce the aneurysm wall as well,which could reduce the risk of expansion or rupture of the aneurysm.Furthermore,the multilayer stent could maintain the patency of the aortic branches and ensure the blood supply to the corresponding organs with satisfactory biocompatibility.Therefore,the multilayer stent was theoretically feasible and safe to treat aortic aneurysm in a certain period of time,yet the long-term effect and clinical manifestations needed to be investigated in the follow-up studies.