Complex application of instrumental analytical methods for detection and characteristics of polymer coating defects in drug-eluting stents

Author(s): Dmitry Kapustin, Tatyana Dmitrieva and Alexander Rashkovskiy

Background: The clinical performance of a drug-eluting coronary stent largely depends on the properties of its polymeric coating. While the randomized clinical research is the “gold standard” for the effectiveness and safety evaluation of the coronary stent, the bench top testing of the stent coating may provide valuable insights within the development of new devices. We argue that the combination of the instrumental analytical methods discovers more information of the nature and possible causes of irregularities of the stent coating than scanning electron microscopy conventionally used for this purpose. Methods and findings: We examined bioresorbable coatings of three commercially available DES using scanning electron microscopy (SEM), scanning probe microscopy (SPM), nanoindentation, and X-ray photoelectron spectroscopy (XPS) to evaluate morphology (thickness in particular) and mechanical properties of the coating, as well as the of elemental and chemical composition through the coating thickness. Conclusions: Adding SPM and XPS methods to SEM for analysis of DES surface provides additional value, especially for the development of new polymeric coating. For the coatings being analyzed, the SEM method revealed the difference in the uncoated surface as big as 0.1% and 17% for different models of the stents. The data obtained by XPS method confirmed the results of the SEM-study about the surface uniformity. The depth profiling of the polymer drug-containing layers also showed the difference in thickness of the coatings as well as allowed to determine elemental components of layers. The SPM method allows excluding the heterogenic or difference of elastic properties of the polymer coating as a cause for coating irregularity, that appear to differ only slightly for the stents with the smallest and largest uncoated areas. Further research is needed to find correlation of the properties discovered with analytical methods with characteristics of biological response.

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