A medical device manufacturer released a medical instrument that combined glass and plastic components. The plastic component was made of polyether ether ketone (PEEK), which was joined to the glass component using a cured epoxy. The adhesive performed well in product validation testing, with no significant problems observed. However, after the product was released to the market, the company began receiving reports of failures involving the interface between the glass and the plastic. The failures influenced perception of brand reliability and direct costs to repair. The epoxy did not hold up as well as expected under actual use conditions, resulting in separation of the glass and PEEK components. The medical device manufacturer came to Battelle to investigate the failures and develop a solution that would provide better adhesion and reduce the likelihood of failures. A key requirement was that the solution would not require a redesign of the product components or substantial changes to their manufacturing process.
Through Battelle’s Surface Science program we identified an atmospheric plasma treatment as an approach to solve the adhesion problem and avoid changes to the product design or manufacturing process. Battelle’s Surface Science program is focused on development of smart, functional surfaces and coatings tailored to specific client needs. Battelle applies cutting-edge discoveries in material sciences to develop practical, scalable solutions for real-world product problems. For the medical device manufacturer, we first needed to better understand the actual conditions under which the product was being used and the conditions that led to failure of the adhesive. Battelle researchers looked at how the customer uses the product and how variables such as heat, humidity, cycling load and user behaviors interact. Our analysis showed that the initial product validation studies did not fully account for the interaction between all of the variables. We developed a new validation process in order to test alternatives for improving the adhesion between the glass and plastic components.
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Adhesion is influenced by two properties: the topography and microstructure of the surfaces to be joined, and the chemical interactions between the surfaces and the adhesive used to join them. We needed to find a way to change one of these variables in order to improve adhesion without requiring substantial changes to the product design, component materials or manufacturing process. Our solution used an atmospheric plasma treatment to change the surface topography and surface energy of the limiting interface, the PEEK, resulting in better physical wetting between the two parts. Atmospheric plasma treatment, in which surfaces are exposed to a partially ionized gas, or plasma jet, changes the microstructure and surface energy of the treated material. Plasma treatment of the PEEK created a structure that allowed for better surface-to-surface contact between the parts and better bonding with the adhesive.
The new process resulted in better adhesion for the device components, reducing field failures and repair costs and rebuilding brand reliability. Adding the plasma treatment did not require changes to product design or material selection. It was also easy to integrate into their manufacturing process and did not require changing the adhesive application and curing process.
Battelle is continuing to research treatments to improve both mechanical and chemical adhesion. Improving mechanical interlocking through plasma treatments and other methods will provide valuable alternatives for applications where chemical bonding is not an option. Researchers at Battelle are working to advance our understanding of nanostructures for surfaces and coatings in order to solve other difficult adhesion challenges.