4.7. Preparation of Gel

To make the FLU–ACT-coloaded NLC gel applicable for topical use, the NLCs were loaded into Carbopol 934-based gel. A transparent dispersion was obtained by the slow addition of Carbopol 934 (1%) with continuous stirring into distilled water. Complete swelling and hydration were achieved via maintaining the Carbopol 934 dispersion overnight. Two–three drops of triethanolamine were added to neutralize the acidic pH of the Carbopol 934 dispersion. At the end, the prepared optimized FLU–ACT-coloaded NLCs were incorporated with 1 h of continuous stirring [58].

Visual inspection for visible particles, bubbles, lumps, color and transparency was used to determine the homogeneity of the gel [58]. The pH is an important consideration for formulations intended to be applied on the skin to ensure the nonirritant nature of the gel. A digital pH meter was used for the determination of the gel pH [59].

Ethanol and DMF (100 mL) were used to dissolve one gram of FLU–ACT-coloaded NLC gel separately. After that, the prepared solution was sonicated, filtered and the drug content was determined using a UV–visible spectrophotometer [58].

The rheological study of the gel was carried out by using a rheometer (Brookfield). The viscosity was measured at different rpm values. The relation was determined between the viscosity and shear rate to evaluate the gel behavior [60].

The glass slide method was utilized for the evaluation of the spreadability percentage of the FLU–ACT-coloaded NLC gel. A one-centimeter circle was marked on a slide, and 0.5 g gel was placed in the circle. A second slide was placed for covering the gel-containing slide, and a weight of 500 g was maintained over it for 5 min. After the removal of the weight, the increase in the gel diameter was measured, and the spreadability was calculated via the following equation:

where Si is the spreadability index, and d is the diameter (in mm) of the spread area [61].