Adhesion between a suspended polymeric film and a metallic substrate: Experiments and models
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Wanliang Shan Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544; and The Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544; and Cordis Corporation, a Johnson & Johnson Company, Spring House, Pennsylvania 19477
Hannah Li, George Papandreou, and Cynthia A. Maryanoff Cordis Corporation, a Johnson & Johnson Company, Spring House, Pennsylvania 19477
Winston O. Soboyejoa) Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey, 08544; and The Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544; and Department of Materials Science and Engineering, The African University of Science and Technology, Abuja, Federal Capital Territory, Nigeria (Received 25 February 2012; accepted 10 May 2012)
This paper presents the results of a combined experimental, theoretical, and computational study of the adhesion between suspended polymeric films and a substrate in a model drug-eluting stent. Atomic force microscope is used to measure the pull-off force between the polymer and the substrate. The adhesion energy was then obtained from the measured pull-off forces and adhesion theories. Subsequently, the adhesion energy was incorporated into interfacial fracture mechanics zone model that was used to determine mode mixity dependence of the interfacial fracture toughness. The mode mixity-dependent fracture toughness conditions were then integrated into finite element models that were used to compute the critical push-out force of the suspended polymeric films. The predicted push-out forces were in good agreement with the results obtained from the experiments. I. INTRODUCTION 1–3
In earlier work, we presented a range of atomic force microscopy and fracture mechanics techniques for the measurement of adhesion and interfacial fracture toughness for the polymeric films on hard substrates. The methods were applied largely to the characterization of adhesion in drugeluting stents (DESs) with thin-film drug coatings on their surfaces. The first generation of such systems had thin conformal coatings in direct contact with the underlying metallic scaffold. For example, the CYPHERÒ Sirolimus-eluting Coronary Stent3 (Cordis, Springhouse, PA) consists of a coating of a Parylene-C primer layer, and a drug-eluting layer of sirolimus, poly(n-butyl methacrylate), and poly (ethylene-co-vinyl acetate) on 316L stainless steel scaffold. In an effort to evaluate adhesion between the layers of the coating, and also between the coating and the substrate, surface pairs were identified to represent both the individual components and the complete chemistry of each a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.178 J. Mater. Res., Vol. 27, No. 14, Jul 28, 2012
layer. Coated atomic force microscope (AFM) tips and two-dimensional coupons, which act as surrogates to the substrate, were prepared and characte
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