Charge Matters: Modulating Secondary Interactions in Hyaluronan Hydrogels

Abstract

Hyaluronic acid (HA) is a vital, functional component of the extracellular matrix (ECM). Following a synthetic biology approach, we designed polyelectrolyte hydrogels composed of HA as a polymeric backbone interconnected by short covalent crosslinkers. Utilizing a thiol‐Michael addition, defined network structures are created, which can be modulated by the aromatic core and charge of the crosslinkers. With increasing negative network charge, varied both through the charge of the crosslinker and the degree of functionalization of the HA chain, the Young's modulus of the hydrogels decreases linearly as swelling ratios increase. Interestingly, secondary interactions with aromatic crosslinkers are stronger for elastin inspired crosslinkers with a pyridinium core compared to analogous triazolium crosslinkers. Based on the defined covalent interconnectivity of these HA‐hydrogels, we were able to demonstrate the specific electrostatic and aromatic interactions induced by different short crosslinkers.

Charge-Controlled Synthetic Hyaluronan-Based Cell Matrices

“…In addition to differently charged but structurally similar two-armed short pyridinium-based crosslinkers with acrylamide reactive groups, the charge density of these hydrogels can be varied by different degrees of thiolation on the carboxyl groups of the HA [ 19 ]. Therefore, the negative network charge of the hydrogels can be calculated as the negative charge of the network structure omitting counter ions [ 17 ].…”

“…Generally, the hydrogel properties are regulated by three different types of chemical interactions: (1) covalent linkages within the network, affecting the crosslinker density by variable degrees of thiolation on the HA; (2) electrostatic interactions between crosslinker core and HA backbone mediated by the overall charge of the HA and thus the degree of thiolation as well as the crosslinker charge, and (3) aromatic interactions determined by the different crosslinker core structure. The effects of all three parameters are apparent in different stiffnesses, swelling behavior, and mesh sizes of HA hydrogels with differently thiolated HA and different crosslinkers [ 17 ] ( Figure 2 ). All physicochemical parameters are dependent on the negative network charge of the system, which is calculated from the charge contribution of the thiolated HA and the crosslinker per hydrogel, [ 17 ] and show a distinct linear correlation.…”

“…In this context, the glycosaminoglycan HA, consisting of repeating disaccharides of D-glucuronic acid and N -acetyl- d -glucosamine, is used as a highly negative charged component of the natural ECM. It can be crosslinked with short covalent aromatic crosslinkers mimicking desmosine, a natural positively charged ECM component in a previously established hydrogel system [ 17 ]. This minimal synthetic ECM model offers the opportunity to regulate the network charge of the material.…”

Triazole-based cross-linkers in radical polymerization processes: tuning mechanical properties of poly(acrylamide) and poly(N,N-dimethylacrylamide) hydrogels

“…1) with values for n between 4 and 10 gave hydrogels by thiol-Michael reaction with thiolated hyaluronan in a previous study. 11,12 However, by free-radical cross-linking no hydrogels were obtained with the charged cross-linkers. This behaviour was observed independent of the polymerizable terminal groups and the spacer length of the cross-linkers for both AAm and DMAAm.…”

“…Cross-linking with partially thiolated hyaluronan provided hydrogels, where both the presence of a charged core as well as the spacer length had an impact on E-moduli and equilibrium degrees of swelling. 11,12 While these hydrogels were obtained by Michael additions, the question occurred to us whether such triazole derivatives would be suitable for the cross-linking of acrylamides via radical polymerization. Poly(acrylamide) (PAAm) hydrogels are one of the most commonly used polymer networks.…”