This paper is a joint creation between BTG Labs and Teleflex Inc., a prominent provider of medical devices such as medical tubing.
This paper discusses the use of a novel contact angle measurement process to evaluate the surface properties of small diameter medical tubing to confirm the presence of a functional coating.
Understanding and controlling surface properties is vital for creating high-performance medical devices. Materials interact with their environment through their surfaces, and surfaces have properties that are quite distinct from the bulk.
A critical characteristic of a materials’ surface is its excess reactivity: molecules present in a surface are not in chemical equilibrium due to the fact that they have unsatisfied reactive sites presented to the free surface. This excess reactivity represents chemical potential, literally the potential to enter into a chemical reaction (primary or secondary) with another substance.
This chemical potential is referred to as surface energy. This excess energy associated with a surface results in the properties that we associate with surfaces, such as functionalization, adhesion, and contamination.
The existence of a quantitative relationship between wetting and surface energy is demonstrated for a range of treatments.
These measurements uncovered variation in surface energy of both treated and untreated material along the machine direction of the web, suggesting that more precise control of treatment level could result in a more uniform product.
The Surface Analyst™ rapidly obtains contact angles from surfaces via Ballistic Deposition, whereby a small drop of liquid (usually water) is constructed in situ on the surface via a pulsed stream of nanoliter-sized droplets.
The contact angles established in this manner are a sensitive function of surface chemical composition.
In this work, injection molded polypropylene panels were oxidized to various levels via exposure to an atmospheric pressure plasma treatment process. Surface chemical composition was determined via X-ray Photoelectron Spectroscopy (XPS), and the chemical composition was related to the water contact angles determined using a Surface Analyst™.
Surface preparation is a critical manufacturing process that enables sealing, bonding, painting, coating, printing, and cleaning. By utilizing appropriate surface preparation processes medical device manufacturers can speed production, ensure product safety, and decrease the likelihood of recalls.
Despite the critical nature of this process the majority of manufactures are still relying upon outdated surface evaluation methods such as dyne and water break. These current methods lack precision, allow for subjective interpretation, and are often destructive.
BTG Labs sat down with the Generis Group to discuss the challenges of surface preparation and how manufacturers can overcome them.
There are fundamental differences between an NRL-style goniometer and the Surface Analyst, most of which contribute to the value of the measurement for development and control of surface sensitive manufacturing processes.
These include the method of liquid deposition and the method of contact angle calculation once the liquid drop is deposited.
The original motivation for these differences was to allow for a more compact and convenient instrument that could be easily handheld. However, they also significantly improve the speed and accuracy of the measurement as well as the flexibility of the types of surfaces that can be measured.
Solvent wiping and sanding procedures can greatly affect the surface energy of a substrate. To investigate the surface energy differences following different preparation procedures of an epoxy/composite laminate, several different surface conditions were created utilizing different cleaning techniques.
Measurements were obtained using a BTG Labs Surface Analyst™. The Surface Analyst is a fast, easy, accurate and nondestructive instrument that measures the contact angle of water that is applied to the surface in a precise, controlled manner.
This contact angle is determined by how strongly the surface energy of the substrate and the liquid interact with one another. The relationship between this contact angle and surface energy is complex but well understood. More importantly, this relationship correlates with the strength of adhesion of a paint, coating, print or adhesive to the substrate.
- While suitable in some cases for estimating surface energy (and therefore cleanliness or treatment level), the imprecision and subjectivity of wetting tension measurements makes them a poor choice for quality assurance and process control of surface cleaning, surface treatment, bonding, coating, and printing operations.Dyne inks are also destructive to the surface being measured. An alternative method for gauging surface condition and consistency is the Surface Analyst™, which provides a rapid, automated measurement of the water contact angle in a precise, controlled manner.This contact angle is determined by the surface energy of the substrate and the liquid and how strongly they interact with each other. This water contact angle correlates very well with the cleanliness and consistency of a surface.