Numerical Research On The Biomechanical Performance Evaluation Of Cardiovascular Stents

Cardiovascular disease is a serious threat to human health,and the main cause of its occurrence is atherosclerosis in arteries.As a common method for the treatment of atherosclerosis,stent implantation has the advantages of quick efficacy and few postoperative complications,but stents are usually prone to in-stent restenosis after implantation.The occurrence of in-stent restenosis is not only related to the structure of the implanted stent,but also closely related to the changes of the vascular biomechanical microenvironment after stenting.Basing on the numerical analysis methods of the finite element and computational fluid dynamics,firstly,this research has studied the effects of different plaque shapes and components on stent-plaque-artery interaction after stent implantation.Then,from the perspective of solid mechanics and fluid mechanics,the biomechanical performance of the stent and the changes of the mechanical environment in the artery are analyzed.Finally,based on the patient-specific coronary artery model,the changes of the intravascular mechanical environment caused by stent malapposition are discussed.The main contents are as follows:Ideal plaque models with five different eccentricities and four different components are established,and stent-plaque-artery interaction simulations are performed by finite element analysis method.The influences of plaque eccentricity and component on stent recoil,stent plastic strain,stent foreshortening,stress distributions of artery and plaque,and lumen gain are studied.The results show that due to the existence of fibrous caps or calcified zones,plaque with greater eccentricity and higher mixture of components is more vulnerable during stenting process.Greater plaque eccentricity leads to greater stent recoil and stent foreshortening;thus,a larger expanding pressure should be carefully applied and a slightly longer stent should be used.Basing on the ideal plaque models,six different stent models including three commercially-shaped stent structures and three improved stent structures are established,and the structural analyses of the balloon-stent-plaque-artery interaction are performed respectively.Then,the fluid domain is solved based on the deformed stent,plaque and artery to conduct computational fluid dynamic analyses.Combining structural and fluid dynamic analysis,the performance of six stents is evaluated.The results show that the Palmaz-Schatz-shaped stent exhibits better performance than Cypher-shaped and Xience Prime-shaped stent in both aspects.In particular,compared with the Cypher-shaped stent,the improved C-Rcrown stent has better performance,indicating that the performance of the Cypher-shaped stent can be improved by changing the number of crowns of the stent ring.Different from the above ideal plaque models,a patient-specific coronary plaque model is reconstructed from optical coherence tomography and angiography imaging data,and two finite element analyses are carried out separately to simulate coronary artery stenting and produce a fully adhered stent case and a stent malapposition case.Then,fluid dynamic models are established based on the deformed stent and artery,and two computational fluid dynamic analyses are carried out respectively to compare the differences between fully adhered and stent malapposition cases in hemodynamics,and study the impact of stent malapposition on the hemodynamic environment.The results show the stent malapposition case has a higher flow velocity than the fully adhered case.Compared to the fully adhered case,the stent malapposition case has lower area percentages of adverse WSS(< 0.5 Pa),while higher area percentages of adverse OSI(> 0.1),and adverse WSSG(> 5000 Pa/m).But the differences in OSI and WSSG aspects are relatively small.In this research,three-dimensional plaque models with different eccentricities and components are established.From the perspective of plaque,the effects of plaque shape and composition on stent performance are discussed in detail.Then,the performances of six different stents in the curved artery model are compared and analyzed.Finally,basing on the reconstructed three-dimensional patient-specific coronary artery model,the effects of stent malapposition on the hemodynamic environment are studied.The present study provides some guidance for the simulation of stent implantation,and is helpful to select an appropriate commercial stent according to the patient-specific conditions and guide the design of the stent.