Ion-Conducting Hydrogels and Their Applications in Bioelectronics

Bioelectronics focuses on the interface between biological systems and electronics. Most biological systems are soft and wet, while electronics are typically hard and dry. Information in the form of charge is carried by electrons and holes in electronics, while ions and charged molecules are the charge carriers in biological systems. As such, finding the right material for the bioelectronic interface is challenging. Hydrogels are water swollen porous polymer networks and, similarly to biological systems, hydrogels are wet, soft, and ion conducting. These properties make hydrogels an ideal choice for the bioelectronic interface between electronics and biological systems. This review focuses on polyelectrolyte hydrogels, a class of hydrogels that has fixed charges as part of the polymer network. In order to maintain charge neutrality, these charges attract mobile ions of the opposite charge in the water swollen pores. These mobile ions give the hydrogels selective ionic conductivity. Here, it is discussed brief fundamentals of hydrogels, ionic conduction mechanism and optimization of the conductivity, and applications in bioelectronic sensors and mechanical actuators.