2.10. Swelling

Swelling experiments were conducted to determine the swelling ability and the time required for swelling equilibrium. Kinetic experiments were performed in quadruplicate on hydrogels created from solutions with different pH values and after different curing times. After curing, the hydrogels were placed in a stainless steel grid submerged in a Petri dish containing 50 mL DDW at room temperature. To minimize water evaporation, the Petri dish was covered during the experiment. Each hydrogel was weighed periodically after wiping excess water with Kimwipes^® (Kimberly-Clark™, Roswell, GA, USA) and returned immediately to the Petri dish. The swelling percentage %Q at each time interval was determined gravimetrically and calculated as follows:

where W₀ is the initial weight of the hydrogel, and W_t is the weight of the hydrogel at time t.

The equilibrium swelling was calculated from the swelling vs. time curve, and the initial weight gain rate, r, defined as the slope, was calculated from the linear part of the curve representing the change in %Q with time. Swelling at equilibrium was estimated from the swelling vs. time curve for each type of hydrogel after 24 h of swelling.