Fig. 1

Schematic illustration of pure PEDOT:PSS hydrogel preparation. a Chemical structures of PEDOT, PSS, and DMSO. b Typical drying and swelling processes of pristine PEDOT:PSS without DMSO. c Dry-annealing and swelling processes of PEDOT:PSS with DMSO as the additive. Isotropic dry-annealing of PEDOT:PSS aqueous solution with DMSO leads to isotropic swelling of the stable pure PEDOT:PSS hydrogel with extraordinary properties, while anisotropic dry-annealing provides anisotropic swelling in out-of-plane or thickness direction