2D-Planar Decorated 3D-Network Enables Strong Synergistic Mechanics and Programmable Shape Transformations for Alginate-based Hydrogels

Abstract Simultaneously enhancing the strength and toughness of physically crosslinked hydrogels is imperative as structural materials, especially for those from natural sources. Herein, inspired by the principle of synergistic effect, a facile yet effective strategy is developed to construct the two-dimensional planar decorated 3D network (2D-3D) in ionic-crosslinked alginate-based hydrogels, generating the strong synergistic mechanics. The strategy is based on a novel hybrid crosslinker (trivalent/divalent cations, e.g. Fe3+/Ca2+) with very low percentage of Fe3+ (1%), which surprisingly imparts multivalent cations with a balanced complexation competition in the hydrogels and thus co-joints loose 2D and rigid 3D structure units in a tightest matching manner. Using the approach in popular Ca-alginate/polyacrylamide system, the complementary architecture induces a 6-fold increase in yield strength accompanied with improved toughness, breaking its mechanical limitations. By varying the molar percentage of each cation in the primary crosslinker, their association abilities with the hydrogels are precisely tuned, giving architectures and mechanics over a wide range. Additionally, the diverse categories of hybrid crosslinkers become the ideal candidates for the development of programmable stimuli-responsive hydrogels, e.g., interesting reverse and unidirectional shape transformations. The method offers a new path in designing metal–ligand coordinated materials, which will certainly become popular in fabricating new generation of alginate-based hydrogels.