Preparation of tannic acid/MXene-enhanced hydrogels and their sensing properties

Hydrogels can be used as wearable sensors to detect human motion. However, extant hydrogel sensors generally suffer from poor mechanical properties, insufficient durability, and simple chilling at low temperatures, which significantly influence their applications in the field of wearable devices. Therefore, in this paper, MXene was introduced as a conductive infill in hydrogels and immersed in a tannic acid/water/glycerol binary solvent to obtain the organo-hydrogel AMT. Benzenetriol and catechol groups on the tannic acid molecule formed physical cross-links with the polymer by means of hydrogen bonding, π-π interactions, hydrophobic interactions, etc., which enhanced the mechanical properties of the hydrogel. The results showed that the mechanical properties of the hydrogel were enhanced with the increase of the soaked tannin concentration, and the tensile strain of the hydrogel reached 658.2% with a tension of 172.2 kPa when the tannin-soaked concentration was 200 mg/mL.The presence of the binary solvent allowed the hydrogel to maintain a decent stability even in heated (60℃) and frigid environments (−20℃). In addition, the wearable strain sensor based on this hydrogel shows good sensitivity to both motion and light, and is able to monitor the motion signals of different parts of the human body, such as throat, pulse,fingers, wrists, and arms, in real time, and the sensor is able to indirectly realize the monitoring of light through photothermal conversion under light. This study is expected to extend the application of hydrogel sensors in outdoor light sensing.