Influence of Surface Modification on the Adhesion between Nitinol Wire and Fluoropolymer Films

Abstract

ABSTRACT

YOON, HYOUNIL. Influence of Surface Modification on the Adhesion between Nitinol Wire and Fluoropolymer Films. (Under the direction of Dr. Martin W. King.)

One of the current challenges for the medical device industry is how to manufacture and assemble biomedical implants consisting of a metallic wire component and a fluorocarbon film without the use of an adhesive. There are many devices such as guide wires, stent/grafts and embolic protection devices which rely on these components being bonded together in order to function inside the body. This study has evaluated the effect of modifying the surfaces of metallic wire and fluorocarbon film prior to thermally bonding these two components together. The surface treatments for Nitinol wire included mechanical roughening with sandpaper, treating with atmospheric helium-plasma, and adding a fluorocarbon coating. The surface treatments for fluorinated ethylene-propylene (FEP) film included helium plasma and helium-oxygen plasma under atmospheric conditions. This produced four types of treated and untreated Nitinol and three types of treated and untreated FEP film which were combined together and thermally bonded to prepare 12 different types of pull-out test specimens. A unique pull-out strength test method was developed to assess the level of adhesion between these various candidates. The pull-out force for untreated Nitinol bonded to untreated FEP film was 30.5±2.4N. Significant improvements of up to 14% in this level of adhesion were obtained with the mechanically roughened Nitinol wire bonded to the helium-plasma treated films and up to 6% of increase with the mechanically roughened Nitinol wire bonded to the helium-oxygen-plasma treated FEP films. However, coating the wire with liquid fluorocarbon solution (TG-10) and then passing it through a helium-plasma to cure and polymerize the fluorocarbon coating was not successful. After thermal bonding to FEP film the level of adhesion fell by over 80%. Scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and contact angle measurements were also taken to characterize the appearance and chemistry of the surfaces before and after modification.