Modulation of kinetic and equilibrium material properties of hyaluronan-based hydrogels for biomaterials

Synthetic extracellular matrix (sECM) hydrogels can be used for three-dimensional (3-D) cell culture, wound repair, and tissue engineering. The mechanical properties of these hydrogels, both transiently during curing and at equilibrium, greatly influence their usefulness in any of these applications. The kinetics of gelation are relevant to the practical usage of these products, particularly when they are cured in situ, while the steady state mechanical properties of these hydrogels have important effects on the behavior of the cells and tissues that come in contact with them. Both of these properties can be modified by changing simple variables in the composition of the hydrogel. To modify the gelation rate, five new homobifunctional cross-linkers have been derived from poly (ethylene glycol) (PEG). These cross-linkers react with free thiol groups covalently bound to hyaluronic acid (HA) to create a hydrogel, each with different reaction kinetics. Thiol reaction rate constants were measured over a pH range of 7.4 to 8.6 at room temperature. The order of reactivity for the functional groups used was determined to be maleimide > iodoacetate > bromoacetate > iodoacetamide > acrylate ^> bromoacetamide, with rates increasing exponentially with increasing pH. The range of gelation times at physiological pH varied from less than 1 min to over 2 h. Modulation of steady state mechanical properties was also achieved by varying the concentrations of sECM components and the concentration of cross-linker. The dynamic shear modulus of these hydrogels was then characterized using oscillatory shear rheology, with storage modulus, G', ranging between 10 Pa and 3.5 kPa.