4.4. In Vitro Release of Ketorolac from the Hydrogel

The in vitro release assay was conducted using amber glass Franz diffusion cells (Franz Diffusion cells (FDC 400, Crown Glass, Somerville, NY, USA) with an active diffusion area of 1.77 cm² (n = 6). The receptor fluid consisted of 0.06M PBS (pH 7.4), which was continuously stirred with magnetic beads at 500 rpm to keep the contents of the receptor compartment homogeneous throughout the tests. The system was thermostatted at 37 ± 0.5 °C by a circulating water jacket. Sink conditions were held throughout the experiments, and 310 mg ± 10 mg of KT hydrogel was accurately applied to the membranes (mixed ester cellulose 0.45 µm pore size) in the donor compartment. Air bubbles entrapped below the membranes were removed, and the system was allowed to equilibrate for at least 30 min before applying the hydrogel. Parafilm was used to avoid evaporation by sealing the donor compartment and the sampling ports. Samples (300 µL) were collected at specific time intervals for about 20 h (1, 2, 4, 5.5, and 19.75 h), and the same volume was immediately replaced with PBS after the removal of each sample. The ketorolac was determined by High Performance Liquid Chromatography (HPLC) following the norms of a validated method, and the experimental data were fitted to different mathematical models (Zero-order, First-order, and Higuchi) (See Appendix A, Mathematical models fitted to drug release experiments). The best fitting model was chosen according to the correlation coefficient (r²) value.