A Biomimetic "Salting Out - Alignment - Locking" Tactic to Design Strong and Tough Hydrogel.

(Recently, hydrogel-based soft materials have demonstrated huge potential in soft robotics, flexible electronics as well as artificial skins. Although various methods have been developed to prepare tough and strong hydrogels, it is still challenging to simultaneously enhance the strength and toughness of hydrogels, especially for protein-based hydrogels. Herein, we introduce a biomimetic "salting out - alignment - locking" tactic (SALT) for enhancing mechanical properties through the synergy of alignment and the salting out effect. As a typical example, tensile strength and modulus of initially brittle gelatin hydrogels increased 940 folds to 10.12 ± 0.50 MPa and 2830 folds to 34.26 ± 3.94 MPa, respectively, and the toughness increased up to 1785 folds to 14.28 ± 3.13 MJ/m 3 . The obtained strength and toughness hold records for the previously reported gelatin-based hydrogel and are close to the tendons. We further elucidate that the salting out effect engenders hydrophobic domains, while pre-stretching facilitates chain alignment, both synergistically contributing to the outstanding mechanical properties. It is noteworthy that the SALT demonstrates remarkable versatility across different salt types and polymer systems, thus opening up new avenues for engineering strong, tough, and stiff hydrogels.) This article is protected by copyright. All rights reserved.