Depth profiling of taxol-loaded poly(styrene-b-isobutylene-b-styrene) using Ga + and C 60 + ion beams R.M. Braun a, * , J. Cheng b , E.E. Parsonage c , J. Moeller c , N. Winograd b a Surface Science Laboratory, Bausch & Lomb Inc., Rochester, NY 14609, United States b Department of Chemistry, Penn State University, University Park, PA 16802, United States c Boston Scientific Inc., Maple Grove, MN 55311-1566, United States Received 12 September 2005; accepted 15 February 2006 Available online 2 May 2006 Abstract The surface of a triblock copolymer, containing a solid-phase drug, was investigated using 15 keV Ga + and 20 keV C 60 + ion beams. Overall, the results illustrate the successful use of a cluster ion beam for greatly enhancing the molecular ion and high-mass fragment ion intensities from the surface and bulk of the polymer system. The use of C 60 + also established the ability to see through common overlayers like poly(dimethyl siloxane) which was not possible using atomic ion sources. Moreover, the use of C 60 + allowed depth profiles to be obtained using primary ion dose densities in excess of 6  10 14 C 60 + /cm 2 . Resulting sputter craters possess relatively flat bottoms without the need for sample rotation and reached depths of ca. 2 mm. AFM results illustrate the more gentile removal of surface species using cluster ions. Specifically, phase contrast and topographic images suggest the relatively high ion doses do not significantly alter the phase distribution or surface topography of the polymer. However, a slight increase in rms roughness was noticed. # 2006 Elsevier B.V. All rights reserved. Keywords: TOF–SIMS; AFM; Cluster ion beam; Profiles; Stents 1. Introduction In recent years, the use of polymeric biomaterials for in vivo applications has increased dramatically. Hydrogels and derivatives of poly(lactic acid), poly(glycolic acid) and poly(ethylene glycol) have come to center stage in the development arenas with many applications focusing on drug delivery [1]. Furthermore, the use of polymeric systems as coupling agents and passivation layers has extended the applicability of current materials. Although the applications of polymer coatings and materials are vast, this manuscript will focus on the characterization of a non-degradable polymer coating associated with implantable stent technology. Stents are small, tubular scaffolds used in veins, arteries and ducts within the body to open restrictions. Because of their ability to be expanded and retain their shape, metallic stents have recently become ideal mechanical remedies for a variety of complex chemical problems. However, upon implantation the body’s defense mechanisms respond by encapsulating the stent via enhanced tissue growth around the metal lattice. Consequently, the use of uncoated stents has proven to be short- lived and has lead to more advanced systems [2]. Although the buildup of red/white blood cells as well as plaque within arteries, for example, can be abated using medications, slowing tissue growth around implanted devices presents a challenge which has recently been overcome by incorporating a drug into a biocompatible polymer that is coated onto the stent. Coatings of this nature allow sustained release of drugs that delay or eliminate tissue growth [3]. Of particular interest are the nature of chemical species present on the surface and as a function of depth on the Taxus TM Express TM Paclitaxel- eluting coronary stent. This system consists of paclitaxel (PTx or Taxol) dispersed within a poly(styrene-b-isobutylene-b-styrene) (SIBS) polymer coated onto an Express TM stainless steel stent. We will show that it is possible to characterize the surface and bulk of this drug/polymer system using a C 60 + ion beam. In addition, sputtering artifacts are shown to be minimal and the presence of species like siloxanes do not significantly hinder the detection of molecular ions; a fact that has plagued the use of atomic ion sources (e.g. Ga + ). www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 6615–6618 * Corresponding author. E-mail address: rbraun@bausch.com (R.M. Braun). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2006.02.082