Highly Strong, Stretchable, and Conductive Reduced Graphene Oxide Composite Hydrogel-Based Sensors for Motoring Strain and Pressure

Conductive hydrogels have shown great potential for fabricating flexible and wearable sensors, especially strain/pressure sensors to monitor human motion/health. In practice, the use of conductive hydrogel-based sensors is often limited because of hydrogels' poor mechanical properties and low sensitivity. In the present article, a composite hydrogel comprising acrylamide, N-(3-aminopropyl) methyl acrylamide hydrochloride, and polydopamine-coated reduced graphene oxide is prepared. The dynamic covalent and noncovalent interactions that exist in the hydrogel matrix including C–N bonds, intra-/intermolecular hydrogen bonds and NH3+–π interaction, and π–π interactions rendered the hydrogels with superior fracture stress (496.4 ± 85.9 kPa) and ductility (1156.9 ± 110.1%). Also, prepared hydrogels have excellent cytocompatibility and show appropriate adhesion to the skin, showcasing their potential in fabricating wearable devices. On the basis of these facts, hydrogel-based strain/pressure sensors that cause a change in resistance when strain or pressure is applied are fabricated. The fabricated sensors show a high strain sensitivity in the strain range of 0–800% where, at a subtle strain (100%), the gauge factor reached 5.4. In addition, sensors are also responsive to pressure with a sensitivity of −0.74% kPa–1 in the range from 0 to 10 kPa. The fabricated strain/pressure sensors have the cyclic ability and self-healing property at room temperature. As a proof-of-concept, the sensors are shown to monitor movements of the elbow, knee, fingers, and wrists as well as sense the vocal cord vibration.