Medical Device Surface Characterization for Optimal Coating Process Control

B. Forsyth
Boston Scientific,
United States

Keywords: coating, characterization, medical device

Summary:

Coating processes are an integral part of manufacturing medical device products within Boston Scientific, such as catheters, guide wires, drug eluting stents (DES), and pacing leads. Coatings can be a combination of hydrophilic, polymeric or pharmaceutical. In order to provide high quality coatings without defects, the specific processes must be able to contend with challenging geometries that can scale to micrometer dimensions. Final coatings must have good substrate adhesion and integrity, be durable and have good consistency (i.e. uniform thickness) for design requirements such as drug release or deliverability. Several product examples will illustrate how specialized characterization equipment, such as Confocal Raman Spectroscopy, High-resolution XPS or Atomic Force Microscopy (AFM) has been used to build scientific understanding in order to explain and complement internal methods for batch release testing. In one example, thermoplastic coatings can be applied to angioplasty balloons in order to change their physical properties like lubricity, impedance and/or pharmaceutical microencapsulation qualities. However when these coatings are applied to certain Pebax balloons, they can demonstrate inadequate adhesion to the balloon material components. Proprietary surface treatment options can cause preferential etching of surface elements which affect its topography relative to its bulk characteristics. To understand this outcome, a novel fixation and cryo-microtoming method was used where balloons were cross-sectioned to expose their bulk properties and material component distribution. Following sample preparation, AFM was employed using sensitive peak force and dynamic modes to measure characteristics such as the topography and roughness of the outer surface, in addition to stiffness and chemical adhesion contrast of the balloon through the bulk. Consequently, optimized surface conditions related to adhesion, coating uniformity, thickness, and component phase orientation were quantified to allow better understanding of unique process and design levers.