Relaxation Piezoionic Hydrogel for Self-Powered, Self-Decoupled Monitoring of Finger Rehabilitation

Hand motor dysfunction involves limited finger flexion and impaired release control, making finger flexion angles and active relaxation ability key metrics for rehabilitation assessment. However, existing flexible electronics quantify deformation amplitude, while deformation rate remains difficult to read out directly. Here, we report a mechanically trained poly(vinyl alcohol)-NaCl hydrogel with the relaxation piezoionic effect for self-powered, self-decoupled monitoring of stress magnitude and acceleration. The hydrogel produces a positive piezoionic voltage above 20 mV during compression and a reverse relaxation piezoionic voltage above 18 mV during unloading. Experiments and multiphysics simulations show that the reverse piezoionic voltage correlates with deformation recovery rate, enabling electrical readout of unloading speed. The hydrogel is further integrated into a multichannel platform for real-time finger rehabilitation visualization. This work provides an autonomous strategy for hand rehabilitation monitoring and a design principle for bioelectronic platforms in motion analysis, human-machine interaction, and personalized healthcare.