Bonding strategies and adhesives for joining medical device components

Implanted medical devices rely on many different and complex joints between dissimilar materials. Adhesives provide one solution for creating such joints. While long-term implants have the advantage of being in a constant-temperature environment, these adhesive joints need to meet the additional challenges of complex loading conditions and ever increasing device-lifetime requirements. The principles of joint design, namely avoiding peel and cleavage-loading conditions, must be scaled down to meet the ever decreasing device sizes. Because the long-term reliability of an adhesive joint under wet fatigue loading conditions generally scales with the adhesion strength between the adhesive and the substrate, surface modification strategies are often employed to improve joint strengths. Any primers or adhesives must meet the biocompatibility requirements which in large part address leachable toxicity. As a result, the use of many fast- or light-cure adhesives is very limited in long-term implant applications. As such, the industry is constrained to relatively few adhesive chemistry options. In this chapter, we review joint design strategies, present methods to test the adhesive strength, discuss methods for improving adhesion strength and provide lessons learned from examples of joints.