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Scanning electron microscopic analysis of defects in polymer coatings of three commercially available stents: comparison of BiodivYsio, Taxus and Cypher stents.

BACKGROUND
Although the use of polymer-based drug-eluting stents appears to markedly reduce the risk of in-stent restenosis, there are concerns about their safety including polymer layer integrity.


OBJECTIVES
The objective of this study was to investigate the morphology of the polymer layer of 3 commercially available polymercoated stents, including the effects of balloon catheter expansion, by scanning electron microscopy (SEM).


METHODS
We assessed discontinuities and other irregularities in the polymer layer of BiodivYsio, Taxus and Cypher stents by SEM after balloon expansion in saline solution at 37 degrees C.


RESULTS
Distinctive polymer layer morphologies were found among the 3 stent types, including responses to balloon expansion and withdrawal. The BiodivYsio stent showed no waving or other irregularities on the outer surface, but excess polymer was present on stent edges and polymer was peeled off from the inner surface. The Taxus stent showed no irregularities on the outer surface, but there were polymer bridgings across strut loops and linear cracking of the bridges, as well as inner surface polymer defects with bare-metal exposure. The Cypher stent showed a rough surface with irregularities and waving on the outer surface. There also appeared to be polymer defects with bare-metal exposure in the loop region and peeling of the top-coated polymer layer in the loop.


CONCLUSIONS
We found several types of defects in the polymer layers on commercially available polymer-coated stents. Some of these indicate potential risks of thrombosis, coronary microembolism of polymer layer pieces and late inflammatory or neointimal reactions.