Tough, anti-drying and thermoplastic hydrogels consisting of biofriendly resources for a wide linear range and fast response strain sensor

Flexible strain sensors have attracted great interest in many fields, including wearable devices, healthcare monitoring, and electronic skin. However, their non-linearity and tardy response time severely influence their sensing precision, and their low toughness, inferior environmental adaptation and non-recyclability are bad for their durability and unfavorable for electronic waste management. Here, we designed and synthesized a wide linear range and fast response strain sensor based on ionic conductive hydrogels (PVA-CS-PA hydrogels) using biodegradable polyvinyl alcohol (PVA) and chitosan (CS) as the polymer backbone, and biogenic phytic acid (PA) as the crosslinker. PVA-CS-PA hydrogels are tough and ductile. The hydrogel with a volume ratio of 3 : 2 for PA : H2O (PVA-CS-3PA-2 hydrogel), had a stretchability of 915 +/- 32.44%, strength of 6.02 +/- 0.18 MPa, and fracture energy of 5.28 +/- 0.24 kJ m(-2). It was also thermoplastic and anti-drying (more than 90% water retention after 30 days). The hydrogel-based strain sensor displayed a wide linear working range up to 900% strain, a fast response time within 50 ms, and reliable stability to detect subtle and large motions. Moreover, its sensing performance is maintained well after a thermoplastic process and long-term storage, suggesting it has reusability and a long lifetime. This tough, wide linear range, fast response, green, and recyclable hydrogel-based strain sensor is expected to pave the way for the development of environmentally friendly and high-performance artificial intelligence in versatile electronic applications.