Natural polymers-enhanced double-network hydrogel as wearable flexible sensor with high mechanical strength and strain sensitivity

Conductive hydrogels have shown great prospects as wearable flexible sensors. Nevertheless, it is still a challenge to construct hydrogel-based sensor with great mechanical strength and high strain sensitivity. Herein, an ion-conducting hydrogel was fabricated by introducing gelatin-dialdehyde β-cyclodextrin (Gel-DACD) into polyvinyl alcohol-borax (PVA-borax) hydrogel network. Natural Gel-DACD network acted as mechanical deformation force through non-covalent cross-linking to endow the polyvinyl alcohol-borax/gelatin-dialdehyde β-cyclodextrin hydrogel (PGBCDH) with excellent mechanical stress (1.35 MPa), stretchability (400%), toughness (1.84 MJ/m3) and great fatigue resistance (200% strain for 100 cycles). Surprisingly, PGBCDH displayed good conductivity of 0.31 S/m after adding DACD to hydrogel network. As sensor, it showed rapid response (168 ms), high strain sensitivity (gage factor (GF) = 8.57 in the strain range of 200%-250%) and reliable sensing stability (100% strain for 200 cycles). Importantly, PGBCDH-based sensor can accurately monitor complex body movements (knee, elbow, wrist and finger joints) and large-scale subtle movements (speech, swallow, breath and facial expressions). Thus, PGBCDH shows great potential for human monitoring with high precision.