Hofmeister Effect-Assisted One-Pot and Fast Fabrication of Isotropic and Ultra-Tough Hydrogel with Controllable Three-Dimensional Shapes

The soaking method based on the Hofmeister effect has been demonstrated to be an effective approach for improving the strength and toughness of hydrogels. However, the traditional soaking method usually leads to a heterogeneous core-shell structure in the hydrogel and makes it difficult to control the hydrogel's dimensions during processing. Thus, it remains challenging to rapidly fabricate large, size-controlled cylindrical hydrogels with practical applicability by using the Hofmeister effect. In this work, we propose a simple and universal preaddition/soaking strategy to prepare isotropic, ultratough cylindrical hydrogels with tensile strengths exceeding 10 MPa. Specifically, a low concentration of Na₃Cit was preincorporated into the poly(vinyl alcohol) (PVA) hydrogel to induce nanofibril formation. The nanofibril-containing PVA hydrogel was then soaked in a Na₃Cit solution to obtain an isotropic, ultratough PVA hydrogel with precise dimensional control. Compared with conventional direct soaking methods, this approach significantly enhances the mechanical properties of PVA hydrogels in a shorter time. The resulting PVA hydrogel exhibits exceptional mechanical properties, including a tensile strength of 10.59 ± 0.6 MPa, a Young's modulus of 7.27 ± 0.53 MPa, and a toughness of 34.74 ± 1.98 MJ·m^-3. Moreover, its conductivity increases 3-fold to 2.6 mS·cm^-1. This method is also applicable to enhancing the strength of gelatin hydrogels. As far as we know, this is the simplest reported method for preparing isotropic, ultratough hydrogels with controlled dimensions and strengths exceeding 10 MPa.