Figure 5.

(A) Relative resistance changes and the gauge factor of the hydrogel sensor under different tensile strains (ⅰ); response and recovery time of the sensor under a strain of 50% (ⅱ); relative resistance changes of the hydrogel sensor in the loading–unloading cycles with the fixed strain of 100% (ⅲ); real-time monitoring of human activities (ⅳ). Reproduced with permission from [94]. (B) The applications of the gelatin−PAAc−MXene−Zr⁴⁺ hydrogel sensors. Illustration of the working model of the gel sensor underwater (ⅰ); the relative resistance changes of the gel at different strains underwater (ⅱ); the resistance changes of the gel during loading–unloading cycles at a fixed strain of 200% underwater (ⅲ); a photograph showing the components of the self-powered wireless transmission device (ⅳ); the signals of different Morse codes by controlling the deformation time (ⅴ); message displayed on the screen of the decoder by translating the signals into visible English letters (ⅵ). Reproduced with permission from [95]. (C) The applications of the PEDOT:PSS−PVA hydrogel sensors. Monitoring of human carotid artery pulse (ⅰ); a wearable electronic skin mounted on the back of the hand for gesture recognition and the relative changes in resistance of five channels with different gestures (ⅱ); two-finger pneumatic soft gripper derived by different pressure (ⅲ); soft gripper can detect the grasping process using spherical objects with different radiuses (ⅳ); a constructed robotic system can remotely control an industrial robot to move through a targeted labyrinth (ⅴ). Reproduced with permission from [96].