One-pot solvent exchange preparation of non-swellable, thermoplastic, stretchable and adhesive supramolecular hydrogels based on dual synergistic physical crosslinking

Abstract

With their unique properties of self-healing and viscoelasticity, physically crosslinked supramolecular hydrogels are promising materials for soft robotics, wearable electronics and biomedical applications. However, the weak mechanical properties of supramolecular hydrogels, especially those prepared with natural polymers, limit their wide-spread application, and swelling is one of the key factors that contributes to the weakening of hydrogels. Herein, we utilize a simple one-pot solvent exchange method to prepare non-swellable, thermoplastic and tough supramolecular gelatin hydrogels based on two synergistic physical crosslinkings, namely, the self-assembled tri-helix structure of gelatin and the hydrophobic aggregation of gelatin-grafted and free hydrophobic motifs. The obtained hydrogels possess a stable water content above 70% with extended incubation in water. These hydrogels are highly malleable upon heating but are extremely stretchable and tough after cooling to room temperature. Furthermore, the supramolecular gelatin hydrogels exhibit robust adhesion to various material surfaces and minimal cytotoxicity. A method for synthesizing a mechanically robust soft material that can heal itself has been developed by scientists in Hong Kong and China. Self-healing hydrogels are so called because crosslinked polymers can spontaneously form new bonds when old ones break. They are soft and flexible, making them ideal for soft robots and biomedical applications. However, they can swell rapidly when wet, which undermines their mechanical strength. Liming Bian from the Chinese University of Hong Kong and colleagues created a non-swellable, stretchable and tough hydrogel using a simple one-pot technique. They reduced swelling by harnessing two types of crosslinking: the self-assembled tri-helix crosslinking of gelatin and the aggregation of hydrophobic groups on the gelatin molecule. The supramolecular gelatin hydrogel is malleable when heated but extremely stretchable and tough once cooled. A simple one-pot solvent exchange method is developed to prepare non-swellable, thermoplastic and tough supramolecular gelatin hydrogels based on two synergistic physical crosslinking, namely, the self-assembled tri-helix structure of gelatin and hydrophobic aggregation of gelatin-grafted and free hydrophobic motifs. The obtained hydrogels possess stable water content >70% with extended incubation in water and these hydrogels are highly malleable upon heating but are extremely stretchable and tough after cooling to room temperature. Furthermore, the supramolecular gelatin hydrogels exhibit robust adhesion to various material surfaces and minimal cytotoxicity.