PVA/gelatin/β-CD-based rapid self-healing supramolecular dual-network conductive hydrogel as bidirectional strain sensor

Hydrogel-based flexible sensors have exhibited great application prospect in the fields of e-skin, movement monitoring and human-computer interaction. Nevertheless, it is still a difficult problem to construct the biomass-based hydrogel sensors with considerable mechanical property, biocompatibility, self-healing property, sensitivity, self-adhesion and fatigue resistance. Herein, a gelatin-based dual-network (DN) hydrogel sensor with multiple dynamic crosslinking was successfully fabricated, in which the dynamic Schiff base bonds between gelatin and an aldehyde-containing supramolecular crosslinker (PCD-Fc-CHO) formed by the host-guest complexing of β-cyclodextrin (β-CD) to ferrocene (Fc) were used to construct the first network of the hydrogel, while the reversible borate ester bonds of PVA with borax were utilized to establish the second network. Meantime, carbon nanotubes (CNTs) were added to endow the gelatin-based DN hydrogel with good conductivity and improved mechanical property. The prepared gelatin-based DN hydrogel possesses favorable ductility (1200%), biocompatibility, double self-healing (HE = 96%), high sensitivity (GF = 6.4), self-adhesion (repeatable adhesion), dual stimuli-responsiveness (pH and oxidation), plasticity and fatigue resistance. The DN hydrogel-based strain sensor can not only monitor various human body (e.g. fingers, knees, speech, etc.) movements and vital signs (pulse), but also monitor in vitro the breathing movements of pig lungs. Interestingly, the self-healed gelatin-based DN hydrogel sensor can also be reused, and its monitoring ability is basically the same as the original hydrogel. This work puts forward a new strategy for the construction of multiple dynamically cross-linked biomass-based self-healing hydrogels as multifunctional wearable flexible sensors.