Melanin-Inspired Conductive Hydrogel Sensors with Ultrahigh Stretchable, Self-Healing, and Photothermal Capacities

Flexible hydrogel strain sensors have received increased attention due to their potential applications in human–machine interfaces, soft robotics, and electronic skin. However, it still remains a challenge to prepare a multifunctional conductive hydrogel integrating high stretchability, strength, and self-healing property. Here, melanin-inspired polydopamine–Fe (PDA–Fe) nanoparticles were successfully incorporated into the hydrogel, with hydrophobic association serving as dynamic physical cross-linking. The hydrogel exhibited ultrahigh stretchability (1900%) and toughness (1.24 MPa), rapid recovery, self-healing property, photothermal effect, and thermal stability. PDA–Fe enhanced the electrical conductivity of the gel, making it potentially useful for application in flexible strain sensors. The PDA–Fe hydrogel strain sensor showed a broad sensing range (350%), high sensitivity (GF = 3.7), a fast response time, and reliable durability, which could enable detection of large (bending of the finger, elbow, and knee) and subtle (pronunciation) human movements. Therefore, the strategy will shed light on preparation of a multifunctional conductive hydrogel for broad applications.