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

Abstract

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.