High-strain sensitive zwitterionic hydrogels with swelling-resistant and controllable rehydration for sustainable wearable sensor.

The irrecoverability of mechanical strength, conductivity and other properties after dehydration, has severely restricted the practical applications of hydrogels. To address this issue, here we report a P(AA-SMA-SBMA) zwitterionic copolymer-based hydrogel with anti-swelling, high mechanical property and reusability after dehydration/hydration process by polymerization of acrylic acid (AA), octadecyl methacrylate (SMA) and sulfobetaine methacrylate (SBMA). The structures of the original hydrogels and that after dehydration/hydration cycles were characterized by SAXS, SEM, Raman, FT-IR, XRD, DSC and rheology, etc. It was proved that both the macroscopic properties and the micro-structures were maintained after several dehydration/hydration cycles, owing to the synergistic effects of hydrophobic and super-hydrophilic interaction in the 3D network structure. Moreover, the fabricated hydrogels possess high strain sensitivity which is applied to monitor both junction motion and subtle movement like breathing and pulse. In addition, such sensitivity of the hydrogel sensors could be maintained after several dehydration/hydration cycles or even sinking in water for over two months. This work provides a type of hydrogel material with stable properties after dehydration process by regulating hydrophobic and hydrophilic interaction, which is beneficial for the life-time and sustainability of hydrogel devises.