A combined computational and experimental methodology to determine the adhesion properties of stent polymer coatings

Reports from recent studies indicate that commercial stent coatings are susceptible to delamination, therefore warranting further research into their adhesion properties. In the present study a robust combined computational–experimental methodology to determine the characteristic interface properties for polyurethane stent coatings bonded to stainless steel is presented. Specifically, delamination of dry and hydrated stent coatings is investigated during 90° peel tests with the force and peel radius being experimentally measured. A comprehensive computational parametric study then establishes the relationship between peel force, peel radius, interface strength and interface characteristic length. Such uniquely determined interface properties are validated for different coating thickness and stiffness. Where accurate measurement of the peeling radius is not possible, it is demonstrated that the slope of the steady state load displacement curve can be used to uniquely characterise the interface. Results suggest that aging does not change the interfacial properties but stiffens the polymer coating. Hydration is found to reduce the interface strength by an order of magnitude, and also decreases the coating stiffness. Such alterations in interface and coating properties are of critical importance in prediction of coating delamination during stent deployment.