Green double crosslinked starch-alginate hydrogel regulated by sustained calcium ion-gluconolactone release for human motion monitoring

Ionically conductive hydrogels can be used to produce wearable devices because of their mechanical flexibility and intelligent sensing. However, utilizing petrochemical or synthetic materials via complex procedures remains a challenge to sustainability. Here we report a new simple strategy to fabricate a double network hydrogel from natural ingredients of corn starch and sodium alginate. Starch-alginate hydrogel exhibited porous microstructure and high strength which can be modulated by appropriate calcium ion concentration. Because of the hydrogen bond and ion crosslinking, the starch-alginate hydrogel could be restored to its original shape after being compressed, twisted and stretched. The hydrogel prepared with high amylose starch and sodium alginate with 0.4 % (W/V) calcium ion addition had the highest breaking strength (281.51 kPa) and toughness (61.61 kJ/m3) at 160 % strain. The third harmonic wave revealed the transition process between the formation and destruction of the hydrogel network structure. The conductive hydrogel can adhere to human skin to monitor different motions and vocal cord vibrations. Our research brings new inspiration to the design of environment-friendly wearable electronic devices which can be manufactured in large quantity at extremely low cost.