Fabrication of highly tough, self-healing sodium alginate/polyacrylamide and copper based nanocomposite hydrogel and its application as strain and pressure sensor for human health monitoring and signature recognition

Conductive hydrogel-based strain and pressure sensors have been extensively employed in various fields such as soft robotics and human-machine interaction. Nonetheless, it still remains challenging to synthesize a conductive hydrogel with exquisite mechanical properties, electrical conductivity and sensitivity. Herein, a novel double network nanocomposite conductive hydrogel was fabricated by using sodium alginate (SA), polyacrylamide (PAm) and copper metal nanoparticles (CuNPs) and further utilized to construct highly sensitive strain and pressure sensors. The optimized SA:PAm/CuNPs-18 hydrogel exhibited a tensile strength of 0.42 MPa, an elongation at break of 1448 %, a toughness of 3.90 MJ m⁻³ and an electrical conductivity of 2.4 S m⁻¹. Furthermore, the SA:PAm/CuNPs-18 hydrogel-based strain sensor was successfully utilized for multi-scale sensing and monitoring of the movements of elbow joint, knee joint, wrist joints, neck muscles, facial expressions and pulse of humans. In addition, the SA:PAm/CuNPs-18 hydrogel-based pressure sensor also showed great potential to detect and differentiate handwritten letters of English even at variable applied pressures and speeds. All these results indicate that the strain and pressure sensors can be integrated in wearable electronic devices, which are useful in medical observation and accurate signature recognition of humans.