Strong and Tough Hydrogel Enhanced by Aligned Microfibers and Confined Interconnected Polymer

Engineering hydrogels with high strength and toughness are rare and represent an important technological challenge. One conventional way to address this challenge is to use solvents such as salt, deep eutectic solvent, and ionic liquids to improve the strength and fracture tolerance of weak and brittle polymers. The marked changes arise from locally aggregated polymer chain whiles increasing polymer-polymer interactions. Here, we demonstrate a different strategy, where substituting conventional solvent with polar solvents in microfiber channels can produce multiscale hierarchical hydrogels with desirable mechanical properties of both toughness and strength, exhibiting an ultimate stress of 31.2 MPa, strain levels of 3100%, and toughness of 410 MJ/cm³. Molecular simulation and experiment results attribute the multiscale mechanisms to aligned fibrous structures at the microscale, and the strong intermolecular interactions formed in situ and the sliding of molecules with PVA chains in polar solvents. This mechanism is general and could be explored to various hydrogels made of commercially available and natural polymers, important for biomedicine, soft robotics, wearable electronics, and tissue engineering.