Certain proteins and glycans self-organize in vivo into soft and strongly hydrated, dynamic and gel-like supramolecular assemblies. Among such biomolecular hydrogels are the jelly-like matrix that is formed around the egg during ovulation, mucosal membranes, slimy coats produced by bacteria in biofilms, and the nuclear pore permeability barrier.Even though biomolecular hydrogels play crucial roles in many fundamental biological processes, there is still a very limited understanding about how they function. Our goal is to assess and to understand the relation between the organizational and dynamic features of such supramolecular assemblies, their physicochemical properties, and the resulting biological functions. We will investigate these relationships directly on the supramolecular level, a level that - for this type of assemblies - is hardly accessible with conventional approaches.To this end, we use purpose-designed in vitro model systems that are well-defined in the sense that their composition and supramolecular structure can be controlled and interrogated. These tailor-made models, together with a toolbox of surface-sensitive in situ analysis techniques, permit tightly controlled and quantitative experiments. Combined with polymer physics theory, the experimental data allow us to directly test existing hypotheses and to formulate new hypotheses that can be further tested in complementary molecular and cell-based assays.This project focuses on two types of biomolecular hydrogels: (i) the nuclear pore permeability barrier, a nanoscopic protein meshwork that regulates all macromolecular transport into and out of the nucleus of eukaryotic cells, and (ii) extracellular hydrogel-like matrices that are scaffolded by the polysaccharide hyaluronan and that are of prime importance in a wide range of physiological and pathological processes including inflammation, fertilization and osteoarthritis.