Research On Biomechanical Performance Numerical Simulation And Laser Processing Technology Of Intracranial Vascular Stents

The physiological characteristics of intracranial vascular require the stents should have sufficient flexibility and compressibility.There are great challenges to improve the balloon-expanding stents’ implantation and flexibility by means of structural optimization.This dissertation mainly studies the simulation models of expanding,compressing,bending and implanting of intracranial vascular stents.Based on the simulation results,optimization works about flexibility and compressibility have been conducted.① Seven kinds of stent expansion simulation methods were compared and analyzed.Advantages and disadvantages of various methods have been proposed.② Taking the bending deformation of cantilever beam and simply supported beam as the mechanical models,four kinds of stent bending simulation models have been established and studied;the results show that:a same flexibility index can be obtained from cantilever beam model and simply supported beam model,displacement-loading method is better than moment-loading for simulating the bending deformation of stents.Through the coupling method,a simulation model including the compressing,expanding and bending deformation was established,and the simulation results show that the stiffness of the stent with compressing and expanding deformation is higher.Finally,the influence of structure,number and arrangement of the connection bridges on the stent flexibility were studied.Optimization schemes have been proposed,which can effectively improve the stent flexibility and reduce the flexibility difference in various bending directions.③ A stent compressing simulation model was established,influences of the supporting rings and the connecting bridges on the compressibility were studied,and an optimization scheme has been proposed,which can effectively improve the compressibility.④ A stent implanting simulation model including the compressing,implanting,expanding and recoiling deformation has been established,which can evaluate the implanting performance,the wall-apposition performance and the straightening effect of the stent.Laser cutting is the frequently-used method for manufacturing vascular stents,and the laser cutting technology is a multi-input and multi-output problem,the process parameters have complicated influence on the cutting quality,thereby,optimizing the cutting quality through adjusting the process parameters is a complicated work.The laser cutting technology of Nickel titanium alloy(NiTi)stent and Cobalt chromium(CoCr)stent have been studied by fiber laser cutting experiments;the coupling relationships between the cutting quality and the surface topographies have been studied to explore a rapid optimization method for the stent cutting quality.① Fiber laser cutting experiments were conducted with argon in wet cutting environment,the underlying reason for the mixed topography was discussed,the coupling relationships between the cutting surface topography and the cutting quality were analyzed.The influences of key parameters on the cutting quality were analyzed.Consequently,a guideline for optimizing the cutting quality for manufacturing NiTi vascular stents has been given.② A comparison study of CoCr fiber laser cutting with oxygen and argon was presented,and the differences such as surface topography,chemical composition and kerfs geometry between the oxygen cuts and argon cuts were studied.Three types of topographies were obtained on the oxygen cuts,and the underlying reason for the different topographies was discussed.The influences of key parameters on the cutting quality were analyzed.At last,an optimizing guideline for micro-profiling the CoCr vascular stents has been proposed.This dissertation provides effective numerical simulation models for the expanding,compressing,bending and implanting deformations of intracranial stents,and the stents’flexibility and compressibility have been greatly improved though structure optimizing.In addition,the coupling relationships between the cutting quality and the surface topographies of CoCr vascular stents and NiTi vascular stents have also been obtained;and parameters optimization methods have been proposed,which can optimize the cutting quality quickly.