PNIPAM-Based Multifunctional Ionic Conductor for Comprehensive Detection of Human Signals

Ionic conductive hydrogels have attracted extensive attention in the field of wearable sensing due to their excellent performance. However, most wearable sensors based on ionic conductive hydrogels focus on the detection of a single form of the human signal such as strain and pressure detection. To realize the comprehensive detection of human signals, the thermosensitive materials N-isopropylacrylamide (NIPAM) and acrylamide (AAm) were chemically cross-linked, and gelatin (GA) and tannic acid (TA) were introduced to construct a double-network structure hydrogel with tensile and temperature-sensing capabilities close to those of human skin. By adjusting the content of hydrophilic and hydrophobic segments of NIPAM and AAm in the first network of the hydrogel, the phase transition temperature could be controlled to realize real-time human temperature monitoring. The introduction of gelatin GA as the second network and TA as the hydrogen bond physical cross-linking center endow the hydrogel skin-like tensile strength (43 kPa) and toughness (33 kJ/m3) to adapt to the external strain changes in wearable sensing applications. Based on the skin-matching mechanical properties and good conductivity, the epidermal electrode assembled by the hydrogel had low interface impedance and excellent stability, which could be used for real-time collection of dynamic electrocardiogram (ECG) and electromyogram (EMG) physiological signals. It is believed that this hydrogel will provide new ideas for the design and manufacture of wearable devices for comprehensive health monitoring and telemedicine.