Ultrasoft, Elastic, and Ionically Conductive Polyethylene Glycol/Ionic Liquid Bottlebrush Ionogels

Ultrasoft conductors have revolutionized the field of electronics by achieving a level of softness comparable to that of biological tissues. However, the inherent difference in charge carriers between conventional ultrasoft electronics (utilizing electrons) and tissues (utilizing ions) could yield high contact impedance, hindering electronic performance for physiological signal recordings. Although ionic hydrogels exhibit ionic conductivity, their high-water content could limit their practical applications. This study proposes a new type of ultrasoft and ionically conductive bottlebrush ionogels (BBIs), leveraging polyethylene glycol (PEG) bottlebrushes and ionic liquids (ILs). The incorporation of IL into PEG bottlebrushes results in a simultaneous enhancement of compliance and ionic conductivity. Specifically, the PEG/IL BBI achieves a Young's modulus of 1.08 kPa, akin to the softest biological tissues such as the brain. To the best of our knowledge, this is the softest ionic conductor ever reported. The introduction of ionic liquids enables an ionic conductivity of 0.14 S/m, rendering it well-suited for integration into ultrasoft electronics. The PEG/IL BBI was further applied as sensors on silkworms and as electrodes on the Venus flytrap and human body. These applications facilitated electrocardiogram recordings and plant signal monitoring, showcasing the potential of this innovative ionically conductive BBI in various physiological environments.