Application of conductive hydrogel based on polyacrylamide/maleic anhydride modified soy protein isolate in flexible sensor

The popularity of conductive hydrogels in flexible sensor research stems from their excellent strain responsiveness and efficient conduction capability. In this study, maleic anhydride (MA)-modified soy protein isolate (MSPI) crosslinked with acrylamide (AM) to form a hydrogel with a tensile strength of 225 kPa at an MSPI content of 16 %. Furthermore, the incorporation of 15 % of lithium chloride (LiCl) significantly enhanced the electrical conductivity of the hydrogel (namely MSPI0.16Li0.15), mechanical strength (tensile stress similar to 238 kPa with a fracture strain of 241 %) and swelling resistance. MSPI0.16Li0.15 presented a high conductivity of 2.8 S/m, surpassing that of a plethora of bio-based hydrogels. Additionally, MSPI0.16Li0.15 was successfully employed to monitor the movement of fingers, elbows, knees and other joints, and can successfully maintain strain sensing under different pH conditions (pH 1, 3, 5, 9, 11 and 13) and organic solvents. It demonstrated distinct electrical responses to various strains, making it suitable for sensing human motion. This work contributes to the development of hydrogels with enhanced electrical conductivity and mechanical properties, promising applications in the field of flexible sensors.