3.6. In Vitro Release and Release Kinetics Study

In vitro drug release study was carried out using a dialysis bag with a molecular weight cut-off at 12,000 daltons (Cellu Sep^® T4 regenerated cellulose tubular membrane, Membrane Filtration Products, Inc., Seguin, TX, USA). The dialysis bag was activated according to the company method before starting the experiment. The accurate amount of 1 g of the test formulation was placed in the activated dialysis bag without air bubbles, and then the dialysis bag was tightly closed. Artificial saliva prepared according to the previous report [66] was used as a dissolution medium. This whole assembly was kept on a magnetic stirrer and the medium solution was stirred continuously at 100 rpm. The temperature was maintained at 37 °C. The sample was withdrawn at 5, 10, 15, 20, 30, 40, 50, 60, 120, 180, 240, 300, 360, 420, and 480 min and replaced with an equal amount of fresh dissolution medium. The withdrawal samples were subjected to HPLC analysis for the determination of the released CP. The cumulative % drug release was calculated according to Equation (7):

where V_c is the volume of media removed every time (30 mL), V_t is the total volume of release media (50 mL), C_i is the concentration of CP in the media, and C_t is the total CP content in CP-NG. To investigate the release kinetics of CP from the gel formulations, the data obtained from in vitro release study were examined according to several mathematical models, i.e., zero-order kinetics, first-order kinetics, Higuchi model, and Korsmeyer-Peppas model.