A conductive hydrogel based on nature polymer agar with self-healing ability and stretchability for flexible sensors

• Agar/Borax/MXene CH was constructed with dynamic borate bond and hydrogen bonds. • The balance of borate bond and hydrogen bond was realized by controlling the pH. • The CH exhibits excellent conductivity, tensile property and self-healing ability. • MXene was used to improve the mechanical properties and ionic conductivity of CH. • The FSS assembled with CH exhibits a wide detection range and high sensitivity. Conductive hydrogels (CHs) have drawn wide attention from the field of flexible sensor for their similarities to tissues, excellent flexibility and good electrical conductivity. However, most of the reported hydrogel-based flexible sensors display the disadvantages of poor tensile strength, low sensitivity and insufficient stability, and most of them are prepared with non-degradable synthetic polymers, which have greatly limited their application. To solve these problems, in this work, we have constructed an agar-based dynamic double cross-linked CH by the dynamic crosslinking between agar and borax via borate bonds and the hydrogen bonds between agar chains. The CH exhibits excellent electrical conductivities, tensile properties and self-healing abilities. A novel two-dimensional material, MXene nanosheet, was introduced to further improve the mechanical properties and ionic conductivity of the CH with its high ionic conductivity and ability to form hydrogen bonds with agar. The obtained Agar/Borax/MXene CH displays the excellent strength and elongation of 129 kPa and 105.1% and the satisfying ionic conductivity of 8.14×10 -2 S/cm. The flexible sensor assembled with Agar/Borax hydrogel with 0.15 wt.% MXene exhibits a wide strain detection range from 0 to 100%, high sensitivity (GF≈1.520) and good stability. Our work has provided a novel strategy for the construction of green flexible sensors with good mechanical properties and high sensitivity.