Anisotropic Conductive Hydrogels with High Water Content

High water content is hard to be achieved in conductive hydrogels because a mass of conductive constituent is needed to form an internal conductive pathway. Here, we developed anisotropic electrically conductive hydrogels with high water content based on bacterial cellulose (BC). Polystyrene sulfonate (PSS) was grafted to the acryloyl chloride-modified BC to provide a template for the subsequent synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT). The BC-g-PSS/PEDOT hydrogels obtained were electrically conductive owing to the immobilization of PEDOT on the surface of cellulose nanofibers. The hydrogels exhibited an electrical conductivity of 0.24 S cm^-1. Further, they demonstrated suppleness in compression (compiled to external compression stress >2.8 MPa and recoverable), inherent high water content (∼95.0 wt %), and anisotropy (anisotropic index of 4.1 in conductivity) from BC. The incorporation of a thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel into the BC-g-PSS/PEDOT hydrogel demonstrated a uniaxial thermoresponsive actuation with resistance change. The expected size and resistance change were only observed in the direction vertical to the cellulose nanofiber layers. These hydrogels could accommodate further developments in novel tissue engineering scaffolds, implantable biosensors, and smart soft electronic devices.