Finite Element Simulation of Biodegradable Polymer Stent Degradation Caused by Blood Flow Stresses
Year: Sept. 2015- Jun. 2018.
Implantation of stents is one of the most effective and least risky ways to treat cardiovascular diseases. Most of stents remain forever in the human body after the implantation, while investigating the patterns of treatment shows that after a limited period of time after the stent placement, the damaged artery is completely retrieved. Therefore, it is not necessary for a stent to remain permanently in the artery. For this, the use of biodegradable stents has recently been considered as an alternative for the permanent stents. In this thesis, the behavior of a biodegradable polymer stent and its degradation under the influence of blood flow is forecasted. In this study, at first an appropriate model for the stent degradation was developed and its governing equations were surveyed. Then, in order to verify the modeling of the blood flow, an example from the Abaqus software documentation was redone. Then, a model including blood flow, artery and stent was simulated using the finite element software. The hyperelastic material models has been used to model the behavior of stent and the artery. Blood flow was modeled as a Newtonian fluid. In order to model the interaction between the blood flow, the artery and the stent, the CFD ability of the Abaqus software and its FSI capability were used. The USDFLD subroutine of Abaqus/Explicit has been used to evaluate the stent degradation during the time. The degradation rate for two models of stents (2B3 and 1Z1) has been investigated at different input speeds of flow. It was witnessed that the degradation level of the 1Z1 stent is significantly lower than that of the 2B3 stent. Furthermore, the effect of the input speed and the viscosity of the blood on the stent degradation were studied. It was found that the degradation rate is in a direct relation to both, the input speed and viscosity parameters. It was also observed that the degradation along the stent is reduced as the flow gets away from the input region.
Keywords: Biodegradable Polymer Stent, Degradation, Blood flow