Scanning electron microscopy (SEM).
The external morphology of the transdermal patches and the dorsal and ventral sides of the skin surface before the in vitro skin permeation study and 50 h after in vitro skin permeation were analyzed with a scanning electron microscope (JSM 6100, JEOL, Tokyo). The experimental samples were
cut into small parts, mounted onto stubs, and coated with gold before SEM analysis (12).
Thickness measurement. The thickness of the backing membrane and of the whole patch (i.e., the adhesive matrix with drug plus backing membrane)
were measured using digital calipers (Digmatic Masschieber, model CD-6 CS, Mitutoyo, Tokyo). The average thicknesses of the
backing membrane and the whole patch were determined. The average thickness of the adhesive matrix containing rosiglitazone
maleate was determined using the following equation:
Area of the patches. The diameter, D, of each patch was measured using a millimeter scale, and the area (π [D/2]2) of each patch was calculated.
The film was weighed and kept in desiccators containing anhydrous calcium chloride for 24 h (12). The film was weighed
repeatedly until it became constant. The percent moisture content was determined with the following equation:
A weighed film kept in a dessicator was exposed to relative humidity of 75% (saturated solution of sodium chloride) in
a dessicator (12). The film was weighed until it showed a constant weight. Percent moisture uptake was determined as follows:
In vitro drug-release study.
An in vitro drug-release study was conducted using a US Pharmacopeia-type V dissolution apparatus (Paddle over disc, Electro-lab, Chennai,
India). The patches were placed between the stainless-steel disks (of which one side was mesh and one side plate stainless-steel
disc meant for transdermal study). The backing membrane side was attached with double-sided adhesive tape (cut same in area
as the patch) to the stainless-steel plate so that release could occur from one side only. The drug-release study was carried
out at 37 ± 0.5 °C and 100 ± 5 rpm in a dissolution jar holding 900 mL of 20% v/v PEG 400 in normal saline; 5 mL samples were
withdrawn at various time intervals and replaced with 5 mL of 20% v/v PEG 400 in normal saline. Samples were analyzed with
a UV–vis spectrophotometer at 318 nm against a blank (20% v/v PEG 400 in normal saline) using a validated method (15). The
quantity of drug released over time was calculated from the calibration curve. The studies were conducted simultaneously by
placing the patch with drug (i.e., the test) and the patch without the drug (i.e., the control) in separate baskets of the
same dissolution apparatus. The difference between the test and control readings was the absorbance caused by the drug. In
each case, the mean cumulative amount of drug released per square centimeter of patch was plotted against time.