Computational Analysis of the Utilisation of the Shape Memory Effect and Balloon Expansion in Fully Polymeric Stent Deployment.

The desire to overcome the limitations of cardiovascular metal stents is driven by the global clinical need to improve patient outcomes. The opportunity for fully polymeric stents made from materials like Poly-L-lactide Acid (PLLA) is significant. Unfortunately, this potential has not been fully realised due to pressing concerns regarding the radial strength and recoil associated with material stiffness and recoverability. In an effort to achieve effective and reliable performance, it is conceivable that a certain degree of shape memory effect (SME) could be beneficial in order to improve on high recoil associated with fully polymeric stents. In this paper, a computational model is presented to explore this possibility, using a stent geometry based on that of a commercially available polymeric stent (Abbott Absorb). The model predicts improvements in the recoil behaviour if the stent is subjected to temperature changes (introducing the shape memory effect to the material) prior to implantation compared to balloon inflation alone. The analysis indicates that combination of self-expansion and balloon inflation is capable of reducing stent recoil to a desirable level (5%). Additionally, the analysis suggests that the recoil is not strongly related to expansion rate variation. However, the stent expansion rate is critically linked to the maximum stresses in the material, with significantly higher stresses found if the stent was deployed with a higher rate, leading to a significantly higher material failure risk. It is concluded that the model provides new insights that can guide the development of fully polymeric stents towards optimised clinical performance with the potential to improve patient outcomes.