Methods to Investigate the Adhesion of Soft Nano‐Coatings on Metal Substrates – Application to Polymer‐Coated Stents

Abstract

Soft coatings are widely used to tailor the surface chemistry of materials without altering their bulk properties. However, the strength of adhesion between the coating and the substrate must be high enough for long‐term applications. This has become a major challenge in the medical field, especially for polymer‐coated stents, mainly due to several coating failures reported after mechanical expansion during clinical implantation. In this work, the applicability of current polymer‐metal adhesion tests to polymer‐coated stents is discussed. The small punch test was proposed as an adhesion test that allows fundamental studies on the adhesion and coating properties. This adhesion test was applied to thin fluorocarbon coatings deposited by plasma on 316L stainless steel.magnified image

On the Growth of Fluorocarbon Thin Films Deposited on Plasma‐Etched 316L Stainless Steel

“…In order to study the coating properties after a stent expansion, a specific deformation device for flat specimens was developed in our laboratory 17, 18. This technique, named small punch test, mimics the stent expansion and the deformed samples are compatible with common characterization tools.…”

On the adhesion of diamond‐like carbon coatings deposited by low‐pressure plasma on 316L stainless steel

“…A 25% biaxial deformation was applied on the coated substrates. 40 If the cohesion strength was to be higher than the adhesion, the coating would delaminate. Otherwise, cracks would appear as the coating absorbs the deformation while it remains attached to the substrate surface.…”

“…37,38 The interface morphology and topography were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the corrosion behavior was evaluated by potentiodynamic tests. 39 The film adhesion on carburized SS316L substrates was assessed by a 25% plastic deformation process using a small-punch test device, 40 and analyzed by SEM after deformation. The long-term stability of DLC on SS316L, essential for coatings commercial use, was assessed on the deformed samples, after 1 year of environmental aging.…”

Adhesion properties of poly(methylmethacrylate‐co‐n‐butylmethacrylate) copolymers in stent coatings

“…The simpler tests to obtain a qualitative evaluation of adhesion after stent deformation are the cyclic crimping/expansion of a coated stent . The small punch test is more quantitative, enabling the replication of stent expansion in flat coated samples, via the biaxial deformation of the specimen with a micro‐indenter.…”