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

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.