Carbon nanotubes reinforced hydrogel as flexible strain sensor with high stretchability and mechanically toughness

Flexible strain sensors have attracted much attention for their applications in human–machine interactions and personal health monitoring. However, fabricating strain sensors based on hydrogels with high stretchability and tensile strength simultaneously still remains a challenge due to the intrinsic brittleness of conventional hydrogel. In this study, a conductive nanocomposite hydrogel comprised of oxidized multi-walled carbon nanotubes (oxCNTs) and polyacrylamide (PAAm) is developed. In the PAAm-oxCNTs hydrogel, the oxCNTs is uniformly dispersed in the presence of gelatin via the hydrogen bonding. The chemical cross-linked PAAm is the main network structure of the hydrogel. Besides, the physical interactions between the oxCNTs, gelatin and PAAm chains contributed to the high performance of the hydrogel as well. The obtained hydrogel integrates satisfactory stretchability (sensing range >700%), high tensile strength (0.71 MPa), good recovery efficiency (90%) and superior sensing abilities. Furthermore, the PAAm-oxCNTs hydrogel exhibits excellent strain sensitivity (Gauge factor = 3.39 at 250–700% strain), fast response (300 ms) and superb durability (over 300 cycles) due to the conductive pathways formed by oxCNTs. The prepared strain sensors could detect both large and subtle human movements (e.g., elbow rotation, wrist bending knee bending, swallowing and phonation) via stable and repeatable electrical signals, indicating their potential applications in human–machine interactions and personal health monitoring.