Swelling, Degradation and Rheological Characterization of hydrogels

Alginate hydrogels were prepared as described above with 0, 5, 50 and 500 mU/ml of alginate lyase. Alginate hydrogels were transferred to 12-well plates, each hydrogel was topped with 4 ml of PBS++ and incubated at 37°C. At t= 1 hr, 1, 3, 5, 7, 14 and 21 days hydrogels were removed (n = 3–4), representative images were taken and the hydrogels were weighed to obtain the wet weight (W_s). For swelling and degradation studies, hydrogels were then frozen overnight and lyophilized for 48 hours prior to weighing the hydrogels to obtain the dry weight (W_D). Swelling ratio (Q) was determined by the following equation:

Here ρ_w is the density of water and ρ_P is the density of polymer (1.6 g/ml). Degradation was determined by the percent of the dry weight of the hydrogels at any time divided by the dry weight of the hydrogels at t= 1 hr. For rheological characterization, the hydrogels were removed and placed between parallel plates (axial force set at 0.01 N) in a rheometer (HR3, TA Instruments). The hydrogels were then strained over a range of 0.001–5% at a frequency of 1 Hz and values of storage modulus (G’) were obtained from the linear viscoelastic region. At least a dozen points were used to obtain the average G’ value.