Non-hermetic packaging of biomedical microsystems from a materials perspective: A review

The advancement of reliable encapsulation techniques for long-term implantable biomedical microdevices is of vital importance for the safe and steady operation of implants for chronic applications. Conventional techniques based on titanium or ceramic enclosures, however, cannot meet the packaging requirements of emerging innovations in medical implants due to issues related to scalability, incompatibility with microfabrication processes and challenges with miniaturization. A variety of polymeric materials have been identified for encapsulation of implantable systems, including polyimide, parylene, liquid crystal polymer (LCP), and polydimethylsiloxane (PDMS). These materials are not as hermetic as conventional metal or ceramic packages nor as widely adopted in regulative licensed devices for long-term implantation. However, studies have shown promising results regarding their potential for long-term encapsulation, in particular for devices fabricated on polymeric substrates. This review offers a summary of the encapsulation performance of these emerging polymeric materials with a specific focus on their long-term performance and quantification of their expected lifetime.