Strain sensors enhanced by a flexible, conductive hydrogel with superior transparency, frost resistance, and water retention

Flexible hydrogels have received significant attention for their excellent mechanical properties, fast response and good strain sensitivity. However, relatively little research has been conducted on the investigation of hydrogels that exhibit frost resistance, water retention, and transparency characteristics. In this paper, a new flexible strain sensors material was prepared by introducing calcium chloride (CaCl 2 ) and hydrolysed keratin (HK) into the polyvinyl alcohol (PVA) system through complex chemical bond. The PVA/CaCl 2 /HK hydrogel exhibited excellent mechanical properties, with a tensile strength of 1.578 MPa and a maximum strain of 934 %. Moreover, it showed high transparency, with a transmittance of up to 90 %. The hydrogel demonstrated remarkable water retention properties with about 8 hours of dry resistance under constant temperatures of 40 °C, 60 °C, 80 °C and 100 °C. Additionally, it had excellent frost resistance with a glass transition temperature of −23 °C, making it environmentally tolerant and capable of maintaining long-term stability. Notably, during the experiment, the PVA/CaCl 2 /HK hydrogel exhibited excellent electrical conductivity and self-powered performance, with a power supply capacity of approximately 14.6 mV. The results of this work provide a promising direction for the development of electronic materials for powered hydrogel strain sensors.