Analysis Of Arterial Mechanical Response And Hemodynamics After Peripheral Vascular Stent Implantation

Peripheral arterial disease(PAD)mainly refers to the stenosis and occlusion of arterial lumen caused by atherosclerosis,which affects the blood oxygen supply of surrounding tissues and organs,and then leads to ischemia or even necrosis of donor organs or limbs.As a branch of the lower extremity artery,the femoral artery is the most common site of PAD at present.Although the patency of the stenosis femoral artery was improved after interventional therapy,according to the clinical data,the patency rate of the stenosis femoral artery was lower than that of the other arteries,which is attributed to the large-scale mechanical deformation of the limb during exercise,including the unique high dynamics of torsion,bending and compression mechanical environment.For the interaction between stent and blood vessel in interventional therapy of peripheral vascular disease,the current research mainly considers quasi-static environment.While the mechanism of mechanical action of stent and blood vessel in the high dynamic mechanical environment during limb movement and the dynamic action of blood flow on the arterial wall due to the geometric change of arterial cavity during movement flexion may be the key to induce stent restenosis.Therefore,it is of great significance for the improvement of the mechanism of stent restenosis and the selection of clinical treatment strategy to carry out the research on the above problems.The main research work of this paper is as follows:(1)To study the structural mechanics of arteries.A finite element model ofblood vessel and stent was established to calculate and the action mechanism of blood vessel(including residual stress and without residual stress)in different states(health,stenosis,balloon dilatation,combination of stent and balloon dilatation)under the environment of high dynamic mechanics(bending and torsion)of limb uprightness and bending,as well as the condition of balloon pre expansion and post expansion of diseased blood vessel The effect of stent implantation on the stenotic arterial wall.The results showed that under physiological blood pressure,the distribution of circumferential stress between intima and media was more uniform and the stress gradient of adventitia increased with the existence of residual stress.Compared with the diseased artery without residual stress,the intima with residual stress was subjected to circumferential compressive stress,and the maximum principal stress of the plaque at the intersection with the healthy artery increased.The peak stress of the vulnerable site of the plaque increased.Therefore,it was necessary to carry out the research on the artery with residual stress.The maximum principal stress occurred at the ends of both sides of the plaque after balloon angioplasty and the bending area on both sides of the plaque was always in a state of fatigue under cyclic load during movement,which was the most vulnerable site where the plaque damage occurred.Compared with the post-balloon dilatation after stent implantation,the Mises stress of stent released after the pre-balloon dilatation is greater,and it can adapt to the deformation of blood vessel better;The maximum principal stress of the plaque in the bending area increased and distributed widely during the movement,which makes the plaque prone to damage.The maximum principal stress of the plaque was relatively small with the post-balloon dilatation which was located between the mesh of the stent at the bending area.(2)The effect of calcification degree of plaque on stent implantation was studied.In this study,numerical simulation was used to investigate the stress state of the plaque and the artery wall during the upright and movement of the lower extremity after the stent was placed into the diseased arteries with calcified plaques(light,moderate,and heavy)respectively,and to evaluate the effect of the severity of the plaque calcification on treatment outcome.The results showed that the plaque located on the lateral side of the curved artery was in fatigue state after the stent implantation during limb movement,and rupture probably occurs due to structural failure.The maximum plastic equivalent strain of the three kinds of plaques occurred at the narrowest part of the plaque,and the heavy calcified plaque had the highest plastic strain with the lowest stenosis rate in the upright and moving state.The arteries with light and heavy calcified plaques have similar mechanical properties.Arteries with moderate calcified plaques had the highest peak principal stress which located in the narrowest part of the plaque and the junction between the plaque and healthy arteries.This study provides a comprehensive evaluation and elaboration of the mechanism of the location of the lesion artery which prone to rupture with varies calcification degree plaque from the perspective of mechanical biology,providing a guideline for choosing different treatment strategies and prognosis in clinic.(3)A systematic study on hemodynamics of peripheral arteries was carried out.The arterial models in different states(health,stenosis,balloon dilatation,combination of stent and balloon dilatation)were constructed.The hemodynamic of the four kinds of arteries were studied by using computational fluid dynamics(CFD)method and ANSYS CFX during limb upright and movement.The blood flow characteristics and hemodynamic parameters such as blood flow velocity,wall pressure,time average wall shear stress(TAWSS),oscillatory shear index(OSI)of arteries in different states were calculated and analyzed.The results showed that the blood flow velocity and wall pressure were associated with the stenosis rate.The higher the stenosis rate was,the greater the velocity and the pressure difference between the proximal and distal artery stenosis,and the wider the flow separation zone were.When the artery was in a curved state,the pressure gradient between the inside and outside of the curve increased obviously.Low TAWSS and high OSI were located in the area where the stenotic plaque connects to the healthy artery.Accompanied by the movement of the limbs,the dynamic environment of artery changed greatly,and the high OSI is concentrated in the medial region of the curved artery.The stenosis rate of the artery with balloon angioplasty or pre-balloon dilatation after stent implantation decreased.The gradient of TAWSS in the circumferential direction of the artery decreased and the TAWSS was more uniformly distributed.The dynamic environment of the artery was more stable.There existed blood flow stagnation at the stent site,forming a series of discontinuous low tawss distribution areas.Atherogenic factors in blood tend to accumulate,deposit and was easy to develop into atherosclerotic plaques in the inside of arterial curvature with low wall pressure,low TAWSS and high OSI,which is likely to aggravate the further stenosis of the artery.(4)Based on the knowledge of arterial structural mechanics and hemodynamics,the BCS finite element model of braided composite stent was established,and the mechanical properties of BCS and corresponding BMS under the same braided mode were calculated and compared.In this study,an orthogonal experimental design was utilized to quantify the influence of five input factors(number of nitinol wires,braiding angle,diameter of nitinol wire,thickness and stiffness of the PET strip)that govern the material property and geometry of the BCS on the surface coverage,radialstrength,and flexibility.The results showed that the nitinol wire diameter and the braiding angle are two most important factors determining the mechanical performance of the BCS.A larger nitinol wire diameter led to a larger radial strength and less flexibility of the BCS.A larger braiding angle could provide a larger radial strength and better flexibility.In addition,the impact of the braiding angle decreased when the stent underwent a large deformation.Moreover,the number of PET strips played an important role in the surface coverage.In addition,the role of PET strips and the interaction between PET strips and Ni Ti wires were described.This study could help understand the mechanical performance of BCS stent and provides guidance on the optimal design of the stent targeting less complications.In this paper,the structural mechanics and hemodynamics of arteries in different states(health,stenosis,balloon dilatation,combination of stent and balloon dilatation)were studied.The results are helpful to understand the mechanism of atherosclerosis and the biomechanical mechanism of stent restenosis,optimize the design of stent structure,and effectively guide the clinical intervention and improve the prognosis of patients.