Surface and Depth Profiling Investigation of a Drug-Loaded Copolymer Utilized To Coat Taxus Express² Stents

Abstract

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 x 1014 C60+/cm2. Resultant sputter craters reached depths of approximately 2 microm 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.

Cluster secondary ion mass spectrometry of polymers and related materials

“…SIMS results are consistent with this (Mahoney, Patwardhan, & McDermott, 2006b). x Yes (Braun, 2006;Gillen, 2006c) …”

“…The results indicated that one could depth profile through most of these films when employing cluster primary ion beams. Braun et al was able to take this a step further and demonstrate C þ 60 depth profiling in Taxus Express 2 stents, comprised of a SIBS coating doped with paclitaxel (Braun et al, 2006). The authors were able to etch through approximately 1.5 mm of material.…”

“…There have been several examples demonstrating that when employing cluster beams for analysis in polymer-based systems, a significant enhancement in the molecular signal of these additives is typically observed. For example Braun et al (2006) published a article on depth profiling in drug-loaded cardiac stents. 2 The stents that were characterized in Braun's work were comprised of poly(styrene-co-isobutylene) (often referred to as SIBS) doped with paclitaxel.…”

Calculation of Effective Penetration Depth in X-Ray Diffraction for Pharmaceutical Solids

“…The study of surface phase transformations is of increasing interest to pharmaceutical scientists because phase transformations induced by interactions with the environment usually occur on the surface 1, 2. A few surface technologies have been applied to study pharmaceutical solids 1–15. Among them is glancing, or grazing, incidence X‐ray diffraction (GIXD).…”

Molecular dynamic‐secondary ion mass spectrometry (D‐SIMS) ionized by co‐sputtering with C60+ and Ar+

“…Throughout the study of these cluster ion sources, buckminsterfullerene (C 60 + ) has received significant attention since it became a commercially available product in 2003 . Using surface analysis techniques and C 60 + ion sputtering, biological/medical and organic electronic materials have been widely studied.…”