Mesoscale Modulation of Supramolecular Ureidopyrimidinone-Based Poly(ethylene glycol) Transient Networks in Water KieltykaRoxanne E. C. H. PapeA. AlbertazziLorenzo NakanoYoko M. C. BastingsMaartje VoetsIlja K. Y. W. DankersPatricia MeijerE. W. 2013 In natural systems, highly synergistic non-covalent interactions among biomolecular components exert mesoscopic control over hierarchical assemblies. We herein present a multicomponent self-assembly strategy to tune hierarchical supramolecular polymer architectures in water using highly affine and directional ureidopyrimidinone-poly­(ethylene glycol)­s (UPy-PEG). Using scattering methods and oscillatory rheology, we observe the structural and mechanical regulation of entangled monofunctional UPy-PEG fibrils by cross-linking bifunctional UPy-PEG fibrils. This supramolecular mixing approach opens the door to a range of subtly distinct materials for chemical and biological applications.