A fast self-healing and conductive nanocomposite hydrogel as soft strain sensor

Remarkable progress achieved for conductive hydrogels has been witnessed in recent years. However, hydrogels are easily damaged during the course of use, which limits their applications as soft conductors. Here, the nanocomposite hydrogels with fast self-healing property, conductive capability and strain-sensitive performance are successfully obtained via simple synthesis routes. Dynamic diol-borate eater bonds built from polyvinyl alcohol (PVA) and borax mainly allow nanocomposite hydrogels to display decent self-healing behaviors in mechanical (restore 92.89% of original tensile strength within 60 s), electrical (restore 96.7 ± 2% of original resistance within 4.2 s) and rheological recovery experiments without any external stimuli. Meanwhile, hydrogen bonds in prepared networks can endow hydrogels with self-healing property to a certain extent. Graphene oxide (GO) is partially reduced under the oxidative self-polymerization of dopamine (DA), providing conductivity for nanocomposite hydrogels (2.7 mS cm−1). Besides, the mechanical property and conductivity of nanocomposite hydrogels are controlled by the reduction degree of GO. Due to physical interactions formed among oxygen functional groups, the nanocomposite hydrogels show greater behaviors in mechanical, rheological and swelling tests verse pure PVA hydrogels. Furthermore, the acquired hydrogels demonstrate strain sensitivity in the designed LED bulb circuit. In view of no apparent anaphylaxis of nanocomposite hydrogels to human skins, the soft stain sensor prepared by designed hydrogel can be fabricated to detect human activities, such as bending and sitting. Our work offers an effective approach to synthesize a fast self-healing, conductive and strain-sensitive hydrogel applied as soft strain sensor for human movement monitoring.