Ultrasoft, elastic, and ionically conductive polyethylene glycol/ionic liquid bottlebrush ionogels

Abstract

Ultrasoft conductors have advanced 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 lead to high contact impedance, hindering electronic performance for physiological signal recordings. Although ultrasoft hydrogels exhibit ionic conductivity, their high water content could limit their practical applications. This study proposes a type of ultrasoft and ionically conductive bottlebrush ionogel (BBI), leveraging polyethylene glycol (PEG) bottlebrushes and ionic liquids (ILs). The incorporation of ILs into PEG bottlebrushes results in a simultaneous enhancement of mechanical compliance and ionic conductivity. Specifically, the PEG/IL BBI achieves a Young's modulus of 0.52–1.08 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 ionic conductivity of 0.03–0.29 S m⁻¹, rendering it well-suited for integration into ultrasoft electronics. The PEG/IL BBI was further applied as a sensor on silkworms and as an electrode on the human body and venus flytrap. These demonstrations enabled the sensing of subtle deformations, electrocardiogram recordings, and plant signal monitoring, showcasing the potential of this ionically conductive BBI in various physiological environments.