Mahdi Tavafoghi

Grade:  Master

Thesis Title:

Modeling and Lifetime Prediction of Biodegradable Poly-Lactic Acid Stents with Damage Mechanics Approach

Year: Sept. 2015- Jun. 2018.

Abstract:

Stent is a permanent or temporary structure that keeps the vessel open so that blood can flow. PLLA biodegradable stents are temporary stents which are implanted in arteries and after degradation, they absorb. Cause to PLLA biocompatibility it has no side effect on body. In this research a quasi linear viscoelastic model introduced by fung is considered to analyze the response of stent and artery and a hyperelastic model is used for plaque. Abaqus software ver. 6.14.2 is employed as a finite element solver and a vumat subroutine is used to represent viscoelastic behavior of stent and artery. Plaque hyperelastic model already exist in abaqus library. Tensile and stress relaxation experimental results with different amount of damage are used to verify vumat subroutine and material parameters. By experimental damage results, PLLA damage parameter is calibrated and as a result of PLLA viscoelastic model, hysteresis circle is captured in loading and unloading plots. Two different stents structures, 2B3 and 1Z1, as most significant stent structures are produced in solidwork application and imported to abaqus to model stents. 2B3 and 1Z1 stents with different thicknesses are analyzed in compression and bending and their radial stiffness are compared. 2B3 and 1Z1 stents with 0.1 mm thickness under bending and cyclic loading are simulated and their lifetime are predicted. On final part of this research, 2B3 stent with 0.1 mm thickness is simulated in contact with plaque in an artery. Stress plots for plaque, artery and stent during crimping and balloon inflation are represented and finally stent life-time in artery under cyclic loading is predicted.

Keywords:  Stent, Biodegradable polymer, lifetime prediction, damage mechanics, poly-lactic acid