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 alcoholborax/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, PGBCDHbased 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.