Evaluation of drug-eluting stents' coating durability--clinical and regulatory implications

Drug-eluting stents (DES) revolutionized cardiovascular treatment by virtually eliminating in-stent restanosis. However, in the past 3 years the U.S. Food and Drug Administration and published studies have raised several safety issues regarding DES such as late state thrombosis and increased mortality. Recent publications have described DES coating delaminating, cracking, and peeling in commercially available stents. It has been suggested that these properties are responsible for the deleterious effects. The goal of this work is to describe a quantitative in vitro durability tests for DES, referred to as Quantified Defects (QD). The technique was implemented on various stent polymer-coated models to determine its ability to differentiate between coating properties. Stents' coating defects were tested using light microscopy, scanning electron microscopy, and a micro-balance. High-performance liquid chromatography was used for measuring drug release. Stents were incubated at either 37 or 60 degrees C and sampled at 0, 3, and 30 days. Stent coating durability was tested using stainless steel control stents versus stents having increased surface adhesion, both of which were then coated with conventional spray-coating methods. Drug-coated stents tested for defects demonstrated a deteriorating durability profile as reflected by QD indices. Different coating models showed unique QD indices that reflected their superior or inferior coating durability. These results indicated that the methodology was able to differentiate between different models. In conclusion, this simple low-cost testing methodology can be easily used during DES development, with either durable or biodegradable polymers.