Quantitative spatial distribution of sirolimus and polymers in drug-eluting stents using confocal Raman microscopy

Raman spectroscopy was used to differentiate each component found in the CYPHER® Sirolimus‐eluting Coronary Stent. The unique spectral features identified for each component were then used to develop three separate calibration curves to describe the solid phase distribution found on drug‐polymer coated stents. The calibration curves were obtained by analyzing confocal Raman spectral depth profiles from a set of 16 unique formulations of drug‐polymer coatings sprayed onto stents and planar substrates. The sirolimus model was linear from 0 to 100 wt % of drug. The individual polymer calibration curves for poly(ethylene‐co‐vinyl acetate) [PEVA] and poly(n‐butyl methacrylate) [PBMA] were also linear from 0 to 100 wt %. The calibration curves were tested on three independent drug‐polymer coated stents. The sirolimus calibration predicted the drug content within 1 wt % of the laboratory assay value. The polymer calibrations predicted the content within 7 wt % of the formulation solution content. Attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectra from five formulations confirmed a linear response to changes in sirolimus and polymer content. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008