Room-Temperature Viscoelastic Liquid Semiconducting Block Copolymer with Mixed Ionic-Electronic Conduction

Bioelectronic devices benefit from materials that have tissue-like levels of softness and good conductive coupling to biological structures. Conventional conjugated polyelectrolyte complexes such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) have favorable levels of mixed ionic-electronic conductivity, but have high elastic stiffness, typically reflected in Young's moduli in the GPa range. Soft ionic conductors, such as ionogels, offer extreme deformability but generally lack the semiconducting mixed ionic-electronic transport required for signal transduction and amplification. Here, we report the first room-temperature liquid semiconducting block copolymer (L-SBCP) that functions as an organic electrochemical transistor (OECT) and enables solvent-free processing. The synthesis of L-SBCP involves the covalent linkage of two unlike polymers: a π-conjugated block bearing glycol side chains and a PEGMEMA bottlebrush acrylic block. This architecture combines mixed ionic-electronic conductivity with the mechanical properties of a viscoelastic liquid. The result is a phase-stable, free-flowing single-component material with a deformability comparable to that of biological cells (1-100 Pa) and a substrate-limited stretchability of 800%. Its liquid rheology supports direct injection and vacuum filling of microchannels without additives or thermal processing. The L-SBCP exhibits p-type accumulation-mode behavior in an organic electrochemical transistor (OECT), with a threshold voltage of +0.08 V, comparable to that of state-of-the-art soft semiconductors. Importantly, L-SBCP supports robust cell viability (>97%). The cellular compatibility opens opportunities for bioelectronic signal amplification at cell-material interfaces enabled by a semiconducting material with cell-scale softness. By uniting biorelevant softness, extreme deformability, electronic performance, and solvent-free processability, L-SBCP establishes a new material composition and form factor for semiconducting polymers and bioelectronic devices.