Flexible and wearable strain sensors based on conductive hydrogels

In recent years, the field of flexible electronics has been thriving in academic achievements. Among them, the hydrogel-based strain sensors possess some characteristic advantages in stretchability, flexibility, stickiness and regulable modulus of elasticity, thus they are more likely to attach to human skin and the surfaces of objects. Compared to traditional sensors, hydrogels can overcome shortcomings in toughness and elasticity. Therefore, hydrogels are suitable to serve as the core materials of wearable electronics. Hydrogel-based strain sensors, as a typical kind of hydrogel flexible electronics, are in the categories of resistance sensors and capacitive sensors, which are primarily used for real-time monitoring of human motions. This review mainly introduces the up-to-date relative literatures in the field of hydrogel-based strain sensors.