Tannin-Inspired Hydrogels with Considerable Self-Healing and Adhesive Properties

Hydrogel materials are attracting considerable attention owing to their wide applications such as wound closure, drug delivery, tissue engineering, cell therapy, wrinkle fillers, etc. Considering the unique tannin chemistry including excellent chelating properties to metals, easily oxidability and superior ability to bind proteins, herein, the natural gallol-containing tannic acid (TA), an extract of plant materials such as Chinese gallnuts, cacao, green tea leaves and fruit peels, was used as a natural phenolic crosslinker to fabricate the self-healing and adhesive hydrogels based on the oxidation of polyphenol groups with the aid of NaIO4 under alkaline condition. The properties of the obtained hydrogels were well characterized by rheometer, universal testing machine, thermogravimetry (TG), dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). The feed molar ratio of NaIO4 to TA was found to play an essential role in gelation time (3-15 min), physical properties (MPa range of tensile strength and 50-220% of elongation at break), adhesive strength (up to 36KPa) as well as self-healing efficiency (up to 73%) of the fabricated hydrogels. By using TA and gelatin with complete natural origin, this study opens a new path toward the preparation of biocompatible self-healing and adhesive hydrogel materials with improved properties.