Fig. 2: Conductive mechanisms and properties of hydrogels.

a Simplified schematic of a hydrogel based on neutral 3D polymer network. The gray areas highlight the ions surrounded by water molecules, forming the hydration sheath that moves freely in an aqueous electrolyte and contributes to the conductivity. b Schematic of an ionic hydrogel based on a polymer having charged functional groups that facilitate the hopping of ions through polymer-electrolyte interaction and enhance the conductivity. c Schematic of the hydrogel based on conjugated polymer with electron transport pathways due to π-π interactions. d Schematic highlighting conductive fillers in electrically conductive hydrogels that facilitate electron transport. e Summary on the documented Young’s modulus and conductivity of ionic hydrogels (blue dots)^{52,54,91,93,118,119,120,121}, electrically conductive hydrogels based on conductive polymers (orange dots)^{32,62,89,98,100}, and electrically conductive hydrogels containing conductive fillers (orange hollows)^{59,69,101,102}.