Solid Soft Electrolytes for Bioelectronic Devices

Solid-state soft electrolytes are becoming key materials for the development of novel bioelectronic devices thanks to their high electrochemical stability, tunable mechanical properties, and ionic conductivity. So far, hydrogels have mostly dominated the scene, being water-based and highly biocompatible while matching the mechanical properties of tissues. Alternatively, new types of ionic gels with a higher electrochemical stability window and lower volatility than hydrogels are enabling applications that have thus far remained unapproachable with hydrogels, such as recording extended periods of time. Indeed, iongels, based on ionic liquids, and eutectogels, based on deep eutectic solvents, are becoming more prominent for bioelectronics. This review first highlights the electrolyte requirements of bioelectronics devices, then describes advancements in the processing of hydrogels, iongels, and eutectogels, and finally summarizes their recent applications in bioelectronic devices.