2.4. Swelling Ratio

Swelling ratios of PEG-SN and PEG/PAA-IPN hydrogels were measured at different pH values. The hydrogel films produced via the rheology tests were immersed in buffer solution with pH values of 1, 4, and 7, respectively, for at least one week. Subsequently, the hydrogels were removed from the buffer solution, and their weights were measured after excess solution was removed from their surfaces. The hydrogels were then dried in an oven at 60 °C for 24 h to achieve a fully dried state. The swelling ratio (Q) was calculated using the following equation:

where, w_s and w_d represent the weights of the hydrogel in a fully swollen state and fully dried state, respectively [33]. The swelling tests were conducted in triplicate.