Effects of design parameters and A_f temperature on superelastic behaviour of Nitinol stent for application in biliary duct:finite element analysis

摘要

For more than a decade, stent implantation has been strategically used for solving gastrointestinal dilemmas such as biliary stenosis. Predicaments like insufficient radial strength, low twisting ability, inappropriate dynamic behaviour and restenosis are expected to be solved by the introduction of new designs. Superelastic Nitinol stent is an interesting alternative for minimising these tight spots. The application of finite element method to predict metallurgical and geometric behaviour of superelastic Nitinol stents for biliary duct dilatation is supported by conventional crimp tests. Model calculations show that all stents encounter the highest stress in their intersegment curvature. Inner curvature can, thus, be considered as the most critical segment with the highest frequency of martensite assessment. Owing to lower chronic outward force, higher radial resistive force and more suitable superelastic behaviour, Nitinol stents with optimal A_f temperature of 24°C and intersegment angle of 65° are shown to have the best mechanical performance for clinical applications. Moreover, model calculations show that a 1° change in stent intersegment and 2°C change in A_f temperature can substantially influence the mechanical performance of the stent.