Surface and depth profiling investigation of a drug-loaded copolymer utilized to coat taxus express stents

The surface of a styrene-b-isobutylene-b-styrene triblock copolymer, containing a solid-phase drug, was studied by time-of-flight secondary ion mass spectrometry employing 15-keV Ga⁺ and 20-keV C₆₀ ⁺ ion sources. This polymer/ drug system has direct application in the cardiac stent arena, where it has been used to treat restenosis or renarrowing of arterial walls after stent or angioplasty procedures. Overall, the results illustrate the successful use of a cluster ion beam for greatly enhancing the high-mass fragment ion and molecular ion intensities from the surface and bulk of the polymer system. The use of C₆₀⁺ also established the ability to remove common overlayers like poly(dimethylsiloxane), which was not possible using a Ga⁺ ion source. Furthermore, the use of C60⁺ allowed depth profiles to be obtained using primary ion dose densities in excess of 6 × 10¹⁴ C₆₀⁺/cm². Resultant sputter craters reached depths of ∼2 μm and possessed relatively flat bottoms without the need for sample rotation. AFM and profilometry studies support the relatively gentile removal of surface species via phase contrast and topographic imaging. In addition, the findings suggest that relatively high ion doses do not significantly alter the phase distribution or surface topography of the polymer surface; however, a slight increase in surface roughness was detected.