Ultrahard and Ultraflexible Supramolecular Hydrogel with Superenergy Dissipating Structure for Biomimetic Skin.

How to integrate the "soft" (flexibility and self-healing properties) and "hard" (shape retention) into the supramolecular hydrogel system is an attractive challenge. In this work, a supramolecular hydrogel with an energy dissipation structure is designed and prepared for intelligent biomimetic skin. Lignin molecules with disulfide bonds of fracture and healing activities are introduced into the hydrogel system through covalent bonds. A large number of hydrophobic interactions and ionic bonds constitute the cross-linking structure of this supramolecular hydrogel. These supramolecular cross-linking structures endow the hydrogel with "soft" properties with 1200% of elongation at break and 92.5% of self-healing rate. The disulfide bonds between lignin macromolecules give the hydrogel with "hard" properties and can effectively absorb the work of external forces on the supramolecular hydrogel system, thus maintaining the chemical structure, shape, and resistivity. Furthermore, this supramolecular hydrogel shows good biocompatibility, antibacterial properties, tissue fluid removal properties, wound healing promoting properties, and sensing output characteristics. This covalent binding structure of biomass-based macromolecules and disulfide bonds has an important reference value for the design of supramolecular hydrogels with both "hard" and "soft" properties.