Coating irregularities of durable polymer-based drug-eluting stents as assessed by scanning electron microscopy

Aims: To classify and quantify post-expansion irregularities in durable polymer-based coatings of drug-eluting stents (DES). Methods and results: Taxus Liberte (TM), Endeavor Sprint (TM), Endeavor Resolute (TM) and Xience V (TM) DES (three samples of each) were explored by light microscopy and scanning electron microscopy (SEM) following expansion at 14 atm in water. Incidence and size of irregularities were measured during thorough quantitative examinations of a 360 SEM images. DES types examined showed a significant difference in the incidence of irregularities (p<0.0001; 6.6 +/- 4.2/image at 60-fold magnification) with typical patterns specific for each DES. All types showed areas with bare metal-aspects, but incidence, shape, and size differed largely: Sprint showed the largest areas. Cracks were only found in Sprint and Resolute, while wrinkles were seen exclusively in Taxus Liberte and Xience V (p<0.0001). The coating of each DES type showed some inhomogeneity of distribution, but the incidence differed (p<0.0001) and was least in Taxus Liberte, which, on the other hand, was the only DES that showed webbing with large bare-metal exposure. Conclusions: The incidence and size of various coating irregularities on different types of DES varied widely. These data may be considered in ongoing discussions on the differences between DES and may serve as reference to compare novel DES.