Modeling biodegradable stents and their effect on the arterial wall

Abstract : Today, sent deployment is the most common treatment for symptomatic atherosclerosis. Bioresorbable stents (BRS) are based on the premise that a stent is needed only until arterial wound healing occurs after which it would be desirable for the stent to degrade so that the arterial wall recovers its natural compliance. Deployment of a stent profoundly alters the mechanical environment in the arterial wall, and these alterations play an important role in regulating the incidence of complications such as restenosis and neointimal hyperplasia. In the case of a BRS, the mechanical stresses in both the stent and the arterial wall evolve as the stent degrades. Furthermore, the hydrolysis-driven degradation of the stent can be accelerated by mechanical stresses in the stent, an additional coupling that needs to be taken into account. We are interested in determining the evolution of stresses in both the stent and the arterial wall during the stent deployment and degradation process and in elucidating the effect of these stresses on the stent degradation and on the remodeling process in the wall, which would also be influenced by the loss of endothelial cells and the amount of inflammation induced by the stent deployment and degradation. To this end, we have developed a 3D finite element model of the deployment and degradation of a polylactic acid (PLA) BRS that integrates the coupling between the stent and the artery.This allows one to predict the zones of dismantling of the stent and the evolution of the arterial thickness in response to a BRS stenting procedure. Since the model relies strongly on parameters that need to be determined experimentally, we became interested in developing methods to follow stent degradation. With this aim, we used optical coherence tomography (OCT) to image several BRS that were deployed into tubes and allowed to degrade in a saline solution at 37°C over a period of two years. We subsequently developed a versatile method for automatically detecting stent struts on the OCT images and quantifying the strut gray scale intensity. The results suggest that this automated method of OCT image analysis represents a promising tool to quantitatively assessing BRS degradation states. Lastly, we were interested in establishing the ability of a stented artery to adapt to a modification in its wall shear stress. Studying the in vivo evolution of the lumen of stented mini-swine arteries followed by OCT imaging allowed us to demonstrate that whereas a bare metal stent cages the artery, a BRS, presumably due to its degradation-induced dismantling, frees the vessel and enables it to adapt its lumen diameter in order to decrease its absolute level of shear stress and the compliance mismatch with the unstented portion of the artery. This lumen adaptation allowed by the stent dismantling could be taken into account in future computational models.
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  • HAL Id : tel-01599263, version 2

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Johanne Mensah-Gourmel. Modeling biodegradable stents and their effect on the arterial wall. Biomechanics [physics.med-ph]. Université Paris-Saclay, 2016. English. ⟨NNT : 2016SACLX034⟩. ⟨tel-01599263v2⟩

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