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.
Highlights
The dual physical crosslinking of supramolecular gelatin hydrogels Gelatin, a hydrolysis product of natural collagen, is widely used in various biomedical applications due to its good biocompatibility, intrinsic bioactivity, abundance and relatively low antigenicity compared with collagen.[37,38]
We incorporated a second form of supramolecular interaction, hydrophobic interaction, to enhance the toughness of the supramolecular gelatin hydrogels
It should be noted that the presence of an excess amount of unreacted free hydrophobic small molecules is essential to the preparation of such supramolecular hydrogels
Summary
Due to their high water content and tunable physical and biological properties, are extensively used in soft robotics, wearable electronics and biomedical applications.[1,2,3,4,5,6] Supramolecular hydrogels, which are solely stabilized by physical crosslinkings, such as host–guest interactions, electrostatic attraction and hydrophobic aggregation, have recently received increasing attention due to their unique properties, including self-healing, energy dissipation and viscoelasticity.[7,8,9,10,11,12,13] the poor mechanical performance of supramolecular hydrogels, especially hydrogels prepared with natural polymers, which possess superior biocompatibility and bioactivity, remain a major hurdle to the wide-spread application of these hydrogels. One recent study demonstrated very tough physical hydrogels composed of polyampholytes.[23] Another study showed that pre-assembled host and guest monomers via host–guest complexation effectively strengthened the obtained supramolecular hydrogels.[24] Dai et al.[25] recently demonstrated an elegant approach to prepare mechanically strong and highly stable supramolecular hydrogels based on hydrogen bonding. It should be noted that the network structure of supramolecular hydrogels reported by these earlier studies predominantly consists of synthetic polymers, and methods to enhance the mechanical performance of natural polymer-based supramolecular hydrogels remain limited. Our earlier studies showed that pre-organization of host monomers along natural polymers via host–guest interactions before polymerization significantly improved the mechanical robustness of natural polymer-based supramolecular hydrogels, but the toughness of these hydrogels remained low.[26,27] To the best of our knowledge, there has been no prior report on supramolecular hydrogels prepared with pure natural polymers that exhibit outstanding mechanical toughness
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