2.5.5. pH Values

The pH values of M1, M2, M3, M4, and CNp-M4 polymer gels was measured through a pH meter. The samples were put into contact with the electrode until a constant value was obtained. The pH meter was previously calibrated against standard solutions to ensure the highest level of accuracy.

#### 2.5.6. Structure and Morphology of M4 and CNp-M4 Membranes

In order to analyze the structure and morphology of the membranes, samples were cut in a circular shape 1 cm in diameter and in a longitudinal section and were analyzed using a scanning electron microscope (Jeol-JCM 6000, MA, USA) at 100× and 220× magnification; then, photographs were taken in four di fferent fields.

The pore diameter and membrane width were measured using a software package (ImageJ, MD, USA), and the average was calculated. Pore number was counted field-by-field, and the average was determined.

In order to evaluate the transparency of M4 and CNp-M4 membranes, samples were cut into a circular shape 3 cm in diameter and these were placed over an image (before swelling); then, they were observed and photographed. Afterward, 1 mL of PBS 1X was added to the samples, and after 20 min (swelling process), photographs were taken of the samples.

#### 2.5.7. In Vitro Release Study of Drug Dispersion, CNp and CNp-M4 Membrane

To evaluate the curcumin release profile from the CNp and CNp-M4 membrane, the direct dispersion method was applied. For the drug and CNp dispersion, a certain amount of curcumin (and the equivalent in nanoparticles) was dissolved into PBS solution (pH 7.4, Pluronic ® F-127 2% *w*/*v*), divided into sets of three tubes each, and placed in a shaker incubator, maintaining this at 37 ◦C. For the CNp-M4 membrane, disks 1 cm in diameter were placed in tubes with the PBS solution under the conditions previously described. At the defined times of 0, 0.25, 0.5, 1, 2, 4, 6, 24, and 48 h, one set of tubes was removed from shaking and centrifuged at 18,514 *g* for 30 min. The curcumin released in the supernatant was quantified by UV-Vis spectrophotometry at 420 nm.

The results of the release tests of CNp and CNp-M4 membrane were analyzed by mathematical models such as zero-order, first-order, the Higuchi model, and the Korsmeyer–Peppas model to predict the drug release mechanism.
