Self-healing and transparent ionic conductive PVA/pullulan/borax hydrogels with multi-sensing capabilities for wearable sensors

Conductive hydrogels as wearable sensors have been used for numerous applications in human motion detection, personal healthcare monitoring and other diverse scenarios. However, it remains a challenge to integrate self-healing ability, multiple sensing capabilities, and transparency in one single unit. In this work, multifunctional polyvinyl alcohol (PVA)/Pullulan/Borax conductive hydrogels were fabricated by introducing borate ester bonds and hydrogen bonds. The described hydrogels showed fast self-healing properties, which could autonomously completely recover within 15 s. The hydrogels possessed high optical transparency (92.9%) in the visible light range and had multi-sensing capabilities, such as strain, temperature and humidity sensing. The assembled hydrogel sensor displayed a high strain sensitivity of 2.74 within the strain range of 300%, and it could be used to monitor human motions such as finger and wrist bending. In addition, the hydrogel sensor could sense temperature variations with a temperature coefficient of resistance of -0.914 °C^-1 over 28-46 °C. Besides, the hydrogel sensor demonstrated the humidity sensing ability and can recognize human inhale and exhale. The overall sensing performance of the PVA/Pullulan/Borax hydrogel was satisfactory and repeatable. This conductive hydrogel shows great potential in wearable electronics and personal healthcare and inspires a new generation of multifunctional hydrogel sensors.