2.9. Swelling behavior of the hydrogels

The equilibrium swelling ratio (ESR) of the hydrogel after drying was measured by a conventional gravimetric method. The weight of the dried hydrogel sample was accurately weighed, and then the dry samples were soaked in deionized water (Millipore water) at RT to reach a state of balanced swelling of each angle. Then, the sample was taken out from the water, and the free water on the surface of the hydrogels was wiped out with a tissue paper before the second weighing. ESR could be calculated based on the following equation:

Where ms was the mass (g) of the hydrogel in the equilibrated swollen state; md was the mass (g) of the dried hydrogel before swelling.

In the study of the swell kinetics of the hydrogel, the hydrogel soaked in water was weighed at intervals (t), and the swell rate at the sampling time was calculated.