Tara Tannin-Cross-Linked, Underwater-Adhesive, Super Self-Healing, and Recyclable Gelatin-Based Conductive Hydrogel as a Strain Sensor

Conductive hydrogel strain sensors have triggered extensive research interest in artificial intelligence, human motion detection, electronic skin, and other technical fields. However, it is still challenging work to prepare conductive hydrogels integrated with good biocompatibility, recyclability, self-healing, and strong adhesion properties both in air and underwater. Herein, a novel, ultraexcellent self-healing, adhesive, and multifunctional gelatin composite hydrogel was fabricated through a simple and rapid one-pot method in which gelatin (Gel) and polyvinyl alcohol (PVA) were used as the polymeric skeletons, Tara tannin as the cross-linking agent, and multiwalled carbon nanotubes (CNTs) as the conducting medium. Inspired by the vegetable tanning mechanism in tanning chemistry, the multiple hydrogen bonding and hydrophobic interactions of Tara tannin with Gel were used to build the cross-linking network of the hydrogel. The obtained GTPC (Gel-Tara tannin-PVA-CNTs) hydrogel exhibited considerable stretchability (760%), strong adhesion strength (16 kPa to pigskin), and high conductive sensitivity (gauge factor (GF) = 6.79). In particular, the GTPC hydrogel displayed good repeatable adhesion (≥10 times) and rapid self-healing performance (HE (self-healing efficiency) > 99%) both in air and underwater. The formed GTPC hydrogel strain sensor could accurately detect various motion signals, such as finger bending, ankle bending, and smiling, and it could also sensitively capture sensing signals of body movements underwater. The self-healed hydrogel sensor also exhibited a similar motion sensing ability to the original one. This work affords a new idea and method for the design and fabrication of flexible strain sensors with rapid air and underwater self-healing performance, high sensitivity, and strong adhesion (in air and water) by using vegetable tannin, promoting the underwater application of sensors and the diversified utilization of vegetable tannin.