Structural Design And Performance Optimization Of Nickel-Titanium "Knickerbocker" Abdominal Aortic Stent-graft

Abdominal aortic aneurysm is one of the most common aortic diseases,which seriously threatens people’s life and health.With the advantages of small trauma and quick recovery,EVAR is gradually replacing open surgery as the main method to treat abdominal aortic aneurysm.Stent graft,as the main medical instrument in EVAR surgery,can restore the normal flow pattern of blood flow by blocking the blood flow into the aneurysm lumen and accelerate the thrombosis in the aneurysm lumen to achieve the therapeutic purpose.Due to the multiple geometric parameters of the stent and the complex working condition in the blood vessels after implantation,the development cycle of the stent is often too long.Finite element analysis technology has been widely used in the research and development of stent due to its advantages of modeling parameter interoperability,intuitive result analysis and data extraction.According to the postoperative complications of abdominal aortic aneurysm,a new type of stent called "Knicherbocker" was innovatively proposed in this study.Its characteristics are as follows:the anchoring area adopts the inverse combined structure stent called "trans-structure stent",further increasing the radial support performance of the stent and reducing the possibility of postoperative endoleaks.The proximal end of the aneurysm was occluded with the extruded structure with variable cross profile to promote the process of aneurysm thrombosis.The treatment effect of the stent was further improved by the above structural characteristics of ni-ti memory alloy stent,so as to reduce the incidence of postoperative complications and the harm of endoleaks.The main parameters of the lesion site were obtained by reverse engineering and the structure of the stent was designed.In this study,the influence of five influencing factors on the radial support performance of the stent was mainly focused on the structure of the stent.When various factors changed,the radial support performance of the new trans-structure stent was better than that of the traditional scaffold called cis-structure stent,but its stability was not as good as that of the cis-structure stent.For the supporting perfomance of the trans-structure stent,increasing wire diameter can improve the supporting performance.Increasing the main peak height,the circumferential length ratio of primary and secondary wave peaks,and the height ratio of primary and secondary wave peaks will reduce the supporting performance.However,as the number of support heads increases,the supporting performance decreases first and then becomes stable.The supporting performance of the trans-structure stent decreased with the increase of wire diameter and head number,but the other 3 factors had no significant effect.The main factors affecting the supporting performance of the trans-structure stent are the wire diameter and the height of the main peak,while the main factor affecting the stability is only the wire diameter.Under the conditions of this experiment,according to the performance requirements,the selected parameters were:wire diameter 0.55mm,main peak height 5mm,number of heads 7,circumferential length ratio of main and secondary wave peaks 0.9,and main and secondary wave peak height ratio 0.8.CFD fluid simulation results showed that the high pressure area at the neck of the aneurysm mainly came from the impact of high-speed blood flow,and the reason for the increase of pressure on the wall of the aneurysm cavity after postoperative endoleak was the cumulative effect of blood.Although the implantation of the new stent did not significantly reduce the wall pressure,it accelerated the process of thrombus in aneurysm lumen.