Highly stretchable and self-healing double network hydrogel based on polysaccharide and polyzwitterion for wearable electric skin

Hydrogel strain sensor is a robust candidate for electric skin (E-skin). In this paper, a highly stretchable and self-healing chitosan/polysulfobetaine (CS/PSBMA) double network (DN) hydrogel was prepared based on fully physically cross-linking to mimic the function of human skin. The CS network and the PSBMA network in CS/PSBMA DN hydrogel are crosslinked by ion chelation and hydrophobic interaction, respectively. The dynamic cross-linking allows the hydrogel network to reconstruct when damaged, providing the DN hydrogel with a stretchability of 1400% and an excellent self-healing efficiency as high as 91.1% after attaching together naturally at room temperature for 24 h. Moreover, the self-healing behavior of the CS/PSBMA DN hydrogel can repeat at least 7 times at the same incision site. Notably, the resistance of the CS/PSBMA DN hydrogel is sensitive to a wide strain range and the relative resistance exhibits stable and reliable changes during deformation. When used as a strain sensor, the CS/PSBMA DN hydrogel is capable of real-time detecting various human motions such as finger and throat movements. More importantly, the sensitivity and stability of the hydrogel sensor can be maintained after being damaged and self-healing. Therefore, the hydrogel sensor demonstrated here has a promising prospect as E-skin for motions detection and healthcare monitoring.