A flexible piezoresistive strain sensor based on MXene/bacterial cellulose hydrogel with high mechanical strength for real-time monitoring of human motions

A flexible strain sensor for detecting human motion signals has been a research hotspot. However, it is still challenging to achieve a good balance between sensitivity, strain tolerance, and toughness. In this study, we present a piezoresistive strain sensor composed of ductile bacterial cellulose (BC) and highly conductive MXene (Ti3C2Tx) nanosheets by applying simple gel-casting. The hydrogel exhibits excellent mechanical properties owing to the physical crosslinking by hydrogen bonds between the rich hydroxyl groups of BC and the oxygen-containing functional groups on MXene, achieving a breaking strength of 2.52 MPa and a strain of 87%. MXene also exhibits excellent electrical conductivity and sensitivity for detecting strain-induced deformation. The hydrogel can cycle more than 200 times under tensile or compressive strain and has a superior strain detection limit of 0.05% and a response speed of 130 ms. Our sensor shows real-time stress sensing under different amplitudes of human motions, such as fingers, wrists, and elbows, and still maintains its sensing ability underwater. Overall, the hydrogel sensor does not require special instrumentation, modification, or crosslinking agents in preparation; provides high tensile strength and good biocompatibility; and retains response ability underwater. Therefore, the flexible conductive hydrogel has a good application potential in the field of wearable strain-stress sensors. A piezoresistive hydrogel sensor composed of bacterial cellulose and MXene nanosheets shows real-time stress sensing abilities at different amplitudes of human motions and maintains its sensing ability underwater.