Reversible Assembly of Conductive Supragel Building Blocks by Metallo-Complexes

The design of multicomponent, building block-based assemblies of polymer materials has gained tremendous interest due to the ability to combine functional variety and materials inside one integrated object. One such type of building blocks are polymer hydrogels that assemble into so-called supragels. For that, it is necessary to implement reliable intra- and innerparticle cross-linking methods that ensure mechanical stability and the supragels' adaptiveness over its life cycle, e.g., via selective assembly and disassembly. Here, a facile method for reversible interparticle cross-linking of vinylimidazole-based polymer hydrogel particles is presented. The method is based on supramolecular cross-linking via transition metal complexation. Supragels consisting of four to 27 individual 3 x 3 x 3 mm particles are successfully obtained. By swelling the preassembled hydrogels inside aqueous solutions of Zn2+, Cu2+, and Fe2+ ions, stable interparticle linkage is achieved within 15 min. These supragels resist mechanical forces, but can be quantitatively disassembled into their corresponding building blocks by simple ligand exchange with ethylenediaminetetraacetic acid (EDTA). With this method, it is possible to quickly build hydrogel macrostructures of any shape and complexity, which exemplarily also exhibit electrical conductivity due to the introduction of metal ions for cross-linking. A facile method for reversible interparticle cross-linking of vinylimidazole-based hydrogel cubes based on transition metal complexation is presented. By swelling preassembled hydrogels inside aqueous solutions of Zn2+, Cu2+ or Fe2+ ions, interparticle connectivity-and, exemplarily, electrical conductivity in case of Cu2+ ions-is achieved. These supragels resist mechanical forces, but can be quantitatively disassembled into single building blocks by ligand exchange.image