The successful development of stiff supramolecular gels is an important goal toward their practical application. One approach to stiffen supramolecular gels is to introduce covalent cross-links. The bis-urea dimer 2, having a structure similar to that of the low-molecular-weight gelator 1, was synthesized. Supramolecular hydrogels were formed from mixtures of 1 and 2 in appropriate ratios, with 2 acting as a covalent cross-linker to connect the fibrous aggregates formed by the self-assembly of 1. The introduction of these covalent cross-links greatly influenced the dynamic viscoelasticity of the supramolecular hydrogels. In the supramolecular hydrogel of 1 mixed with 5 % 2, the storage modulus was 1.35 times higher than that of the supramolecular hydrogel of 1 alone, and the crossover strain was extended from 5 % to over 20 %. The supramolecular hydrogel of 1 and 2 was free-standing and supported 13 times its own weight.

Supramolecular hydrogels were formed from mixtures of tris‐urea and a bis‐urea dimer in appropriate ratios, with the bis‐urea dimer acting as a covalent cross‐linker to connect the fibrous aggregates formed by the self‐assembly of tris‐urea. The introduction of these covalent cross‐links greatly influenced the dynamic viscoelasticity of the supramolecular hydrogels. In the supramolecular hydrogel of tris‐urea mixed with 5 % bis‐urea dimer, the storage modulus was 1.35 times higher than that of the supramolecular hydrogel of tris‐urea alone, and the crossover strain was extended from 5 % to over 20 %. More information can be found in the Communication by Hiroki Sawada and Masamichi Yamanaka on page 929 in Issue 8, 2018 (DOI:10.1002/asia.201800217).