The composite hydrogel with "2D flexible crosslinking point" of reduced graphene oxide for strain sensor

Intelligent hydrogels with excellent flexibility, biocompatibility, and stimulus responsivity can mimic the functions of the skin to detect human motions. However, the low mechanical strength limits its application in the field of biomimetic materials. In this work, polyacrylamide-reduced graphene oxide (PAM-rGO) composite hydrogels were prepared by the combination of PAM and partially rGO, and their biomimetic strain sensors were studied. The rGO played the role of "2D flexible crosslinking point" in the composite hydrogel. Through the H-bonds between rGO and hydrogels, the toughness and strength of the composite hydrogel were enhanced. The maximum strain of the hydrogel changed from 751% to 1097%, and the maximum stress changed from 0.065 to 0.20 MPa. On the other hand, the interaction between the PAM backbone and the rGO provided a credible resistance response to the stimulation of strain. The better linear relationship between resistance and length was built, with R-2 of 0.992. Furthermore, the composite hydrogels were assembled into wearable devices to monitor human-motion, including fingers bending, elbows bending and walking. The experimental results showed that the PAM-rGO composite hydrogel had great potential in the field of bionic skin.