Highly sensitive and multifunctional Fe3+ enhanced PVA/gelatin multi-network hydrogels with wide temperature range environmental stability for wearable sensors.

Hydrogels are one of the ideal materials for preparing new flexible sensor devices. In this work, based on the freeze-thaw cycle and Hoffmeister effect to improve the mechanical properties, a low-temperature resistant multifunctional conductive hydrogel with excellent mechanical properties, high transparency, high adhesion, high conductivity, high sensitivity, excellent sensing ability and self-healing ability was prepared by diffusing Fe3+ and ethylene glycol (EG) in the hydrogel network via immersion method. Moreover, wearable sensors assembled from it could accurately monitor the movement of various parts of the human body, and it could accurately identify tiny strain and pressure sensing. In addition, the hydrogel had long-term stability (after 7 days at room temperature, it still maintained 88.03 % of its original weight), strong adhesion (after repeated adhesion for 3 times, the adhesion to 6 materials was more than 72 % of the original value), excellent frost resistance (not freeze under -50 °C), and good self-repairing ability (the cut hydrogel would be self-repaired after 5 min and could be stretched to more than 2 times the original length). The hydrogel's multifunctionality and high sensitivity to small strains will make it show a high application prospect in the field of precision sensing.