Effects of Tensile Stress on Degradation of Poly Lactic Stents

Poly lactic acid (PLA) is widely used for the manufacture of biodegradable stents (BDSs). It was observed and investigated that tensile loads can significantly affect the degradation rate of PLA in our previous study. Additionally, non-uniform degradation can arise from complicated stress distributions in implanted stents under long-term and pulsatile tensile loading. The objective of this work is to develop a model of PLA degradation that is able to predict the degradation rate, thus providing a valuable tool for the design of biodegradable stents. In this study, an innovative method for simulating BDS degradation was developed. The degradation was assumed to be a linear function of the tensile load, based on previous experiments. The model was developed in an FE framework using ABAQUS/Explicit. The evolution law affects the updated stress state in the explicit time integration scheme. The damage evolution is calculated by means of a user subroutine (VUMAT). The developed model can reproduce the behavior of BDSs subjected to long-term tensile loading; stent fracture occurs more rapidly in a high-stress field. This simulation gives new insights into in vivo BDS performance and how stent geometry may affect long-term performance. It was indicated that strengthening the high-stress parts of a BDS is important for achieving uniform degradation over time and for decreasing the risk of fracture.