Design of strong and tough methylcellulose-based hydrogels using kosmotropic Hofmeister salts

Design of strong and tough hydrogels had made significant progress recently. However, most of the cellulose-based hydrogels are soft and brittle. In this work, we fabricate a class of strong and tough hydrogels by simply soaking poly (acrylamide) (PAM)/methylcellulose (MC) hydrogels in kosmotropic solutions. The kosmotropic ions could notably enhance the hydrophobic interactions and chain bundlings of MC. As a consequence, the obtained optimal ammonium sulfate [(NH₄)₂SO₄] treated PAM/MC gel with a water content of approximately 30 wt% exhibit predominant mechanical properties, with the fracture tensile strength of 4.4 MPa, fracture elongation of 690%, elastic modulus of 3.8 MPa, and toughness of 19.3 MJ/m³, superior to that of the most existing cellulose-based hydrogels. The enhancement of mechanical properties could be ascribed to the formation of more hydrophobic associations in methylcellulose network. Additionally, the mechanical properties of the methylcellulose-based hydrogels could be facile and finely tuned by varying the post soaking time and the kind of Hofmeister salts. We expect that this work may enrich the avenue in the preparation and regulation of MC-hydrogels for promising applications in biomedical and load-bearing fields.

The obtained PAM/MC-A_s gels possessed eminent mechanical performances. Additionally, the mechanical properties of MC-based hydrogels could be facile and finely tuned by soaking in different kosmotropic anions solution.