3.2. Characterization of Hydrogels

A Fourier transform infrared spectroscopic analysis (FTIR, PerkinElmer Spectrum Two, OH, USA) was carried out for the study of the chemical structure and functional groups on the material’s surface. Analysis was conducted in a range of 4000–650 cm⁻¹.

Scanning electron microscope (JSM-5910, JEOL, Akishima, Tokyo, Japan) images of the synthesized hydrogels were taken to examine the surface morphology. The operating voltage was 10 kilovolts. The samples were coated with gold using a sputter coater.

A swelling analysis of synthesized gels was carried out in a NaCl saline solution at 37 °C. The three molar (3 M) solution of sodium chloride (NaCl) was prepared in distilled water. A considerable difference in weight between dry (W_d) and wet (W) hydrogels was observed after specified intervals of 0.5, 1, 2, 3, and 24 h [29].

Equation (1) was used to measure the swelling percentage.

A Netzsch TG 209F1 Libra thermogravimetric system was used to check the thermal stability of CS hydrogels incorporating Cp-LE. Samples were heated from 25 to 750 °C under a nitrogen flow of 20 mL/min at a heating rate of 10 °C per minute.

A CAM assay was carried out to determine the healing activity of the prepared hydrogels. At day zero, chick eggs were purchased from the bakery, carefully cleaned with absolute ethanol, and then placed in an incubator at 37 °C in a humid environment. After seven days, on day 8, sterilized hydrogels were implanted on the eggs, cutting off small pieces of each eggshell with a surgical blade. After that, the eggs were sealed with sterilized parafilm or covered by adhesive tape to stop any infection and returned to the incubator. Eggs were reopened on day 14, and their healing response images were captured with a light microscope to examine changes that occurred after implanting hydrogels [29].