Computational Investigation of the Delamination of Polymer Coatings During Stent Deployment

Abstract

Recent advances in angioplasty have involved the application of polymer coatings to stent surfaces for purposes of drug delivery. Given the high levels of deformation developed in the plastic hinge of a stent during deployment, the achievement of an intact bond between the coating and the stent presents a significant mechanical challenge. Problems with coating delamination have been reported in recent experimental studies. In this paper, a cohesive zone model of the stent-coating interface is implemented in order to investigate coating debonding during stent deployment. Simulations reveal that coatings debond from the stent surface in tensile regions of the plastic hinge during deployment. The critical parameters governing the initiation of delamination include the coating thickness and stiffness, the interface strength between the coating and stent surface, and the curvature of the plastic hinge. The coating is also computed to debond from the stent surface in compressive regions of the plastic hinge by a buckling mechanism. Computed patterns of coating delamination correlate very closely with experimental images. This study provides insight into the critical factors governing coating delamination during stent deployment and offers a predictive framework that can be used to improve the design of coated stents.

Effects of material, coating, design and plaque composition on stent deployment inside a stenotic artery—Finite element simulation

“…The coated stent had a higher residual stress level (793.6MPa) compared to the bare metal stent (778.4MPa). The increase of stress level on the coated stent is due to property mismatch between the stent and the coating, which generally leads to delamination as observed in experiments, particularly in the U-bend regions (Hopkins et al, 2010).…”

“…In addition, the stresses in the plaque-artery system imply that stents with open cell design are less likely to cause plaque rupture, regardless of the plaque composition, due to the lower stress level on the plaque when compared to stents with closed cell design. 30 Table Captions Table 1, Bilinear properties for the phosphorylcholine (PC) polymer coating (Hopkins et al, 2010). Table 2, Coefficients of the Mooney-Rivlin model used to describe the behaviour of the polyurethane balloon (Chua et al, 2004).…”

“…The stress-strain curves in Figure 2a are the tensile test data for stent materials, which were implemented in Abaqus by considering the increase of yield stress as a function of plastic strain (Abaqus, 2013). The stent coating was made of Phosphorylcholine (PC) polymer with bilinear behaviour and the parameter values are given in Table 1 (Hopkins et al, 2010).…”

“…While Hopkins et al (2010) investigated the two-dimensional delamination of the stent coating during deployment, which occurred mainly in the region of hinge with high plastic deformation. The initiation of coating debonding depended on the coating thickness, the coating material and the curvature of the hinge.…”

Potential-based and non-potential-based cohesive zone formulations under mixed-mode separation and over-closure–Part II: Finite element applications

“…While the study of Hopkins et al (2010) simulated delamination and buckling of compliant polymer coatings during deployment, no study to date has modelled the behaviour of stiffer metallic and ceramic coatings on stent surfaces, despite the extensive use of such coatings to improve stent biocompatibility (Babapulle and Eisenberg, 2002;Edelman et al, 2001;Windecker et al, 2001). In this case study the mechanical behaviour of a titanium coating on the compressive region of a stent surface is simulated during stent deployment.…”