Polyethylenglycol (PEG) hydrogels are widely used as tuneable substrates for biological and technical applications due to their good biocompatibility and their high hydrophilicity. Here we compare the mesh size and diffusion characteristics of PEG hydrogels by analyzing the diffusion of solutes with different, well-defined sizes over long and short time scales. Interestingly, one can tune the mesh size and the density of the gel simply by changing the inital concentrations of the PEG-diacrylate (PEG-DA) polymer, which also enhances the solute uptake in equilibrium through the interaction with the PEG chains. This increased uptake can be characterized by an enhancement factor determined by partition ratio analysis. It increases linearly with the polymer volume fraction, but is not caused by immobilization inside the hydrogel as evident from FRAP measurements, thus rendering these hydrogels ideal materials for i.e. drug delivery applications

The hyaluronan (HA)-rich pericellular coat (PCC) enveloping most mammalian cells plays a vital role in biological processes such as cell adhesion, proliferation, motility and embryogenesis. In particular its presence on chondrocytes, which live in the load-bearing cartilage, has a wide range of implications in diseases such as osteoarthritis, highlighting its mechanical role in living organisms. Despite its significance, the macromolecular organization of the cell coat remains speculative. In order to obtain a more detailed spatial picture of highly hydrated PCCs, we present two independent but complementary non-invasive techniques for the position-resolved analysis of the cell coat's mechanical and structural properties. Position-dependent microrheology provides a micromechanical map of the PCC that reveals a gradient of increasing elastic stiffness towards the plasma membrane on model rat chondrocyte cells (RCJ-P). This gradient can be correlated with the relative distribution of HA, which is inferred using an eGFP-labelled neurocan-binding domain, a small fluorescent molecule that binds to HA. The spatial variation of the HA concentration profile is consistent with the position-dependent elasticity. Combining these approaches sheds light on the molecular architecture of the PCC

We designed bioinspired cross-linkers based on desmosine, the cross-linker in natural elastin, to prepare hydrogels with thiolated hyaluronic acid. These short, rigid cross-linkers are based on pyridinium salts (as in desmosine) and can connect two polymer backbones. Generally, the obtained semi-synthetic hydrogels are form-stable, can withstand repeated stress, have a large linear-elastic range, and show strain stiffening behavior typical for biopolymer networks. In addition, it is possible to introduce a positive charge to the core of the cross-linker without affecting the gelation efficiency, or consequently the network connectivity. However, the mechanical properties strongly depend on the charge of the cross-linker. The properties of the presented hydrogels can thus be tuned in a range important for engineering of soft tissues by controlling the cross-linking density and the charge of the cross-linker.