**3.4. Swelling behavior measurements**

Swelling studies of semi-IPNs were conducted by immersing the dried samples in deionized water at 37± 1°C. The samples were removed from the thermostatic bath at regular intervals of time, their surface was dried with filter paper and then weighed; afterward, they were immersed into the same recipient.

The swelling degree (*SD*) was calculated using Eq. (1):

$$SD = \text{(M\%} - \text{W\%} / \text{W\%} \tag{1}$$

where *Wh* is the weight of swelled hydrogel at a certain time and *Wi* is the weight of initial dried hydrogel. All experiments were performed in triplicate.

#### **3.5. Electron microscopy analyses: SEM and TEM**

ESEM-FEI Quanta 200 (Eindhoven, Netherlands) instrument was used to record SEM images in low vacuum mode with GSED detector. Micrographs were taken in vacuum conditions, operating pressure of 2 torr, 25–30 KV accelerating voltage.

The morphologies of PMAA nanocomposites were obtained by transmission electron microscopy using TEM, Tecnai™ G2 F20 TWIN Cryo-TEM, FEI Company™, at 200 kV acceleration voltages. Powdered samples were deposited on carbon film grids.
