Functional Hydrogel Interface Materials for Advanced Bioelectronic Devices

A frontier area of modern research focuses on emerging classes of implantable bioelectronic devices with unique modes of operation that are relevant both to research studies and to medical practice. These advanced technologies have the potential to enable revolutionary diagnostic and therapeutic capabilities relevant to a wide spectrum of disorders, where seamless integration onto the surfaces of vital organs allows for accurate sensing, stimulation, or even concurrent sensing and stimulation. Materials for tissue-like interfaces, such as hydrogels, that enable soft mechanical coupling and multifunctional, bidirectional exchange between these technology platforms and living systems are critically important. Functional hydrogels offer significant promise in this context, as illustrated in recent demonstrations of interlayers that support optical, mechanical, electrical, optical, thermal, and biochemical modes of interaction, with chronic biocompatibility and stable function in live animal models. This Account highlights recent progress in hydrogel materials that serve as interfaces between bioelectronics systems and soft tissues to facilitate implantation and to support sensing and stimulation. The content includes materials concepts, compositions, chemistries, and structures that allow for bioelectronic integration. Use as interfacial adhesives and as surface coatings to support mechanical, electrical, optical, thermal, and/or chemical coupling highlight the broad range of options. The Account begins with hydrogels that exploit advanced chemistries to control internal hemorrhage, prevent bacterial infections, and to suppress foreign body responses. Subsequent sections summarize strategies to exploit the mechanics of hydrogels, such as their mechanical, tunable modulus, lubricating surfaces, and interface adhesion properties, to facilitate interactions between bioelectronic and biological systems. Discussions of functional characteristics begin with the electrical conductivity of different types of conductive hydrogels and their long-time stability, with applications in bioelectronic sensing and stimulation. Following sections focus on optical, thermal, and chemical properties, also in the context of device operation. A final passage on chemistry outlines recently developed photocurable and bioresorbable hydrogel adhesives that support multifunctional interfaces to soft biological tissues. The concluding paragraphs highlight remaining challenges and opportunities for research in hydrogel materials science for advanced bioelectronic devices.