Characterization of conductive hydrogel
Rheological measurements of the shear viscosity of the conductive hydrogel showed that the hydrogel had good shear thinning properties (Figure 2A ), i.e. becomes more liquid when a shear force is applied. This allows for ejection from a needle while still keeping its form after it is extruded from the needle head (Figure 2B ). To evaluate gel formation ability, a solution of 100 mM CaCl2 was added to the extruded hydrogel. The hydrogel exhibited a gelling behavior and after five minutes the hydrogel was able to be lifted using tweezers (Figure 2C ). This indicated that the conductive hydrogel can crosslink with the presence of divalent cations to form a stable gel.
Pure NFC as well as NFC/CNT hydrogel were demonstrated to have well-defined dynamic yield stress (G’=G”; 217 and 106 Pa, respectively) with transition from elastic to viscous behavior. DC conductivity under aqueous conduction was 4.3·10-1 S/cm in the homogeneous dispersion of 20 wt% CNT in NFC hydrogel.