Mechanically Robust, Flexible, Fast Responding Temperature Sensor and High-Resolution Array with Ionically Conductive Double Cross-Linked Hydrogel

Abstract

Hydrogel-based sensing devices show potential in wearable electronics. However, most hydrogels are mechanically weak, bringing functional stability problems in real usage environment that may interact with occasionally external forces. There are demands to develop robust hydrogel-based devices with good performances. Here, a highly sensitive temperature sensor with robust, ionic conductive, and double cross-linked polyacrylamide-sodium alginate hydrogel is developed. It is found that ions with larger radius show higher sensitivity to temperature changes (e.g., Ba²⁺) in the hydrogel, because ion movement is dependent with ion sizes. The sensor shows advantages of fast response (2.02 s of 40 °C temperature difference), wide sensing range (22–100 °C), and high robustness (withstanding 2000 cyclic compression and 175 N m⁻¹ for 180° anti-peeling test). The wearable sensor can effectively distinguish the temperatures of various body parts (0.9 °C temperature difference) and monitor respiration (0.5 °C temperature difference) in real-time. A wearable 5×5 sensing array is developed for direct human-body temperature mapping, achieving an optimum resolution of ≈0.15 mm⁻¹ and enabling a clear mapping of superficial vascular pathways at the wrist. This study provides a practical and optimized approach for the implementation of wearable conductive hydrogel-based devices in the field of human health.