They can cure rapidly and have good impact resistance. They also display relatively poor bonding with metals under humid conditions. Some urethane versions will also moisture cure, which has been used as the basis for curing hot-melt urethanes. Newer urethane-adhesive formulations based on carbonate polyols show promise for implantable device bonding. They mechanically adhere to many different surfaces, but their tensile strengths and surface peel strengths are low, suggesting they are more useful as a structural sealant than as a structural adhesive.
Silicones have excellent chemical and electrical resistance.
Fluorinated silicones have shown benefits in bonding to fluoropolymers by virtue both of their low surface energy and the fluorination. Most are acrylic based and cure in less than 1 minute. They often contain leachable materials but are widely used for plastics and metal assemblies outside the body. Many successful device applications take advantage of the inherent rapid assembly time and substrate versatility of UV-curable formulations. Table II summarizes surface-preparation alternatives for many types of materials, shows a comparison chart of the major adhesive types, and provides a selector for combinations of adhesives and surface preparations.