A fully biobased tough hydrogel derived from guar gum and gelatin as a flexible sensor

Biobased hydrogels have been widely used in drug delivery, tissue engineering and biosensors due to their abundance, non-toxicity and biocompatibility. However, constructing fully biobased hydrogels with good mechanical performance still remains a challenge. Herein, a double network (DN) hydrogel consisting of oxidized hydroxypropyl guar gum (OHPG) and gelatin (Gel) was fabricated via Schiff base reaction. The Gel-OHPG hydrogel had an elongation at break of 497%, a tensile stress of 0.44 MPa and a compressive stress of 25.91 MPa. Then, the mechanical properties of the hydrogel were further enhanced through immersing it in an ammonium sulfate (AMS) solution due to the Hofmeister effect. Its elongation could reach 629% and the corresponding tensile toughness and compressive stress were 3.86 MPa and 59.55 MPa, respectively. The conductivity of the hydrogel was 0.86 S m−1. Furthermore, the Gel-OHPG hydrogel was fabricated as a flexible sensor, and it could accurately monitor human joint motions such as fingers, wrists, knees, elbows, throat and neck. Henceforth, the Gel-OHPG hydrogel prepared using fully natural polymers has promising potential in flexible sensors and tissue engineering.