Ultra-stretchable, high conductive, fatigue resistance, and self-healing strain sensor based on mussel-inspired adhesive hydrogel for human motion monitoring

Conductive hydrogels have been widely applied in various electronics, such as artificial skin, flexible devices, and implantable bioelectronics. However, it is still a challenge to develop high-performance hydrogel with high conductivity without compromising the toughness, stretchability, self-healing, and adhesion properties. Herein, inspired by the mussel-adhesion mechanism, an adhesive hydrogel that simultaneously achieves high conductivity (27.0 S·m−1), ultra stretchability (strain ˃ 3700 %), and strong toughness (1930 kJ·m−3) was developed by incorporating polydopamine (PDA)/sodium caseinate (SC) cross-linked network into the poly(acrylamide-co-acrylic acid) (P(AM-co-AA))/Al3+ network. Due to the abundant metal coordination and hydrogen bonds in the network, the obtained hydrogel displayed rapid self-healing capability (healing efficiency, HE > 97 %) and excellent fatigue resistance. Moreover, the introduction of PDA-SC cross-linked network endowed the hydrogels with robust adhesion (36.5 kPa for pigskin) and high conductivity. The conductive hydrogel was assembled into a strain sensor, which demonstrated prominent sensing performance with a wide detection range (∼2500%), high sensitivity (gauge factor (GF) of 23.7), fast response time and reliable repeatability. The hydrogel strain sensor can be attached on human body to distinguish and monitor both large and subtle movement signals. The developed conductive hydrogel strain sensor is expected to have promising applications in wearable devices, human–machine interaction, and electrical skin, and to extend for use in other portable and wearable energy related devices with multifunction.