Barrier materials for flexible bioelectronic implants with chronic stability—Current approaches and future directions

Flexible, bio-integrated electronic systems have wide-ranging potential for use in biomedical research and clinical medicine, particularly as active implants with the ability to operate in a safe, stable fashion over extended periods of time. Here, the development of a thin, robust biofluid barriers that can simultaneously serve as long-lived sensing and/or actuating interfaces to biological systems represents a significant challenge. Requirements are for defect-free, biocompatible and impermeable materials that can be rendered in thin, flexible forms and integrated with targeted device platforms. This perspective summarizes various material strategies for this purpose, with a focus not only on properties and structures but also on their use in bioelectronic systems. The article begins with an overview of different classes of materials, including means to grow/synthesize/deposit, manipulate, and integrate them into test structures for permeability measurements and into systems for functional bio-interfaces. A comparative discussion of the most widely explored materials follows, with an emphasis on physically transferred layers of SiO2 thermally grown on silicon wafers and on their use in the most sophisticated active, bendable electronic systems for electrophysiological mapping and stimulation. These advances suggest emerging capabilities in flexible bioelectronics implants as chronic implants with diagnostic and therapeutic function across a broad scope of applications in animal model studies and human healthcare.