Bio-derived ionic conductive Guar Gum hydrogels as distributed circuit elements for analogue signal processing: the case of Resistor-Capacitor filters

Developing functional electronic materials from renewable resources is a key challenge toward more sustainable electronics. Here, we report on a bio-derived ionic conductive hydrogel based on guar gum and demonstrate its direct integration as a functional circuit element for analogue signal processing. Ionic conductivity is introduced by incorporating sodium chloride into the polysaccharide matrix and systematically tuned through the glycerol and salt contents. Increasing glycerol loading enhances conductivity, while varying NaCl concentration produces a non-monotonic response, with maximum conductivities in the 10-2 S cm-1 range and an optimum salt-loading window. The conductive formulation is subsequently combined with pristine guar gum, used as a dielectric, to fabricate guar gum-based resistor-capacitor elements. Their integration into low-pass and high-pass filters demonstrates frequency-selective operation in the audio range, with cut-off frequencies of 658 and 576 Hz and transition slopes of −17 and +15 dB dec-1, respectively. These results demonstrate that guar gumbased ionic hydrogels can move beyond conventional roles as substrates or electrolytes and directly perform circuit-level functions, providing a simple materials platform for low-frequency analogue electronics.