Real-time in situ rheology of alginate hydrogel photocrosslinking

The reaction dynamics of biodegradable, photocrosslinkable sodium alginate hydrogels are studied by in situ, dynamic rheology. Alginate, chemically-modified with methacrylate groups, crosslinks by ultraviolet (UV) light exposure in the presence of a photoinitiator. The gel formation is monitored during UV irradiation from a light emitting diode (LED) bottom plate fixture on the rheometer. Material properties of the hydrogels, including gel points and relaxation exponent, are evaluated using the Winter-Chambon criteria. We also report a new, complementary empirical method for determining the gel point from the reduction in sample strain at the onset of gelation, via monitoring the strain curve. In addition, the crosslinking dynamics and hydrogel moduli are altered by changing the UV irradiation intensities (3–15 mW cm−2) and degree of methacrylation (5–25%). Dynamic rheological measurements of hydrogels as described in this paper are a potentially powerful tool to elucidate the dynamics of gelation and predict mechanical properties. This technique may aid in the design of polymer formulations with light-reactive chemical species, which have tunable properties that can be matched to a range of applications, including regenerative medicine.