Turning Zwitterions into Toughening Agents: Salt-Activated Microdomains in Poly(vinyl alcohol) Double-Network Hydrogels

High Resolution Image Download MS PowerPoint Slide Zwitterionic hydrogels, although highly biocompatible, are widely regarded as mechanically fragile, with typical tensile strengths below 0.1 MPa, which restricts their use in load-bearing applications. Here, we address this limitation by integrating a polyzwitterionic network with a poly(vinyl alcohol) (PVA) network through high-speed pregelation agitation that enhances chain entanglement and induces flow orientation. By exploiting the salt-driven conformational transition of zwitterionic chains, a controlled salting-out step generates uniformly dispersed nanoscale microdomains that act as reversible energy-dissipating units. At the same time, balanced hydrogen bonding between the two networks moderates PVA crystallinity, limiting embrittlement while preserving elasticity. The resulting double-network hydrogel shows an elongation of 890% and a toughness of 18.75 MJ m –3, representing a high combination of stiffness and toughness among zwitterionic–PVA hydrogels reported so far. Beyond materials optimization, this study demonstrates how molecular-scale chain hydration and collapse govern macroscopic mechanical reinforcement. These findings suggest that zwitterionic components can function as effective toughening motifs rather than mechanical liabilities and provide a cross-scale design principle for adaptive, high-strength hydrogels.