Mechanically robust PEDOT:PSS hydrogel via mild liquid metal crosslinking

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) hydrogels are promising for bioelectronic applications but are constrained by the lack of mild processing strategies and limited mechanical robustness. In this work, we report a crosslinking strategy for PEDOT:PSS hydrogels based on eutectic gallium-indium (EGaIn). In aqueous environments, Ga releases Ga³⁺ ions that interact with PSS chains, modifying the electrostatic interactions between the PEDOT chain and the PSS chain to form ionic crosslinks within the polymer network. The resulting Ga-crosslinked PEDOT:PSS hydrogels exhibit a storage modulus (G') of up to 2500 Pa. Microscopic characterization reveals a transition from a porous structure to a more compact, flake-like morphology, which contributes to the improved mechanical stability. Ga crosslinking leads to a reduction in electrical conductivity, reflecting the altered polymer interactions associated with ionic crosslink formation. The combination of mechanical enhancement and preserved ionic-electronic mixed conduction suggests that these hydrogels hold promise for organic electrochemical transistor (OECT) applications, where reduced initial conductivity can be advantageous for device operation.