Evaluation of the stress relaxation behavior of poly (L‐lactic acid) self‐expanding braided stents

Abstract

AbstractStress relaxation of poly (L‐lactic acid) (PLLA) braided stents generated after crimping will significantly influence the radial properties of the stents, due to the viscoelasticity of PLLA. In particular, the environmental temperature and duration in the relaxation process are two vital effects on these radial performances. Thereby, a serious of crimping temperatures and holding durations were adopted in this study to investigate their influence on the radial properties of stents. The radial properties of the stent, including peak compression force, chronic outward force and energy loss, were characterized by radial mechanical tests. Results showed that the stress relaxation rates of PLLA braided stents increased with the increase of the crimp‐holding temperature and time. Specifically, the stress relaxation rates at 25, 37 and 42°C were 22.81%, 28.41% and 36.10% at hold time of 300 s. Moreover, the increase of stress relaxation can reduce chronic outward force of stents, which will furtherly cause complications such as insufficient supporting and the shift of stent and so on. Therefore, decreasing the crimp‐holding temperature and duration of stents is an effective method to reduce the stent stress relaxation. This work provides experimental references for the comprehensive evaluation of mechanical properties of PLLA braided stent in clinical application.