Chromeleon 7.2 sr3 systems

The dissolution test was performed in a buffer medium with a pH = 5.5, simulating the physiological acidity of the skin. A sample (corresponding to 0.65 mg budesonide) was placed in a dialysis membrane (MW 10 000 Da) and introduced into a 50 mL acceptor phase tempered at 32 ± 0.5 °C at constant shaking. Aliquot samples were withdrawn at predetermined time intervals and replaced with fresh medium. The released drug amount was evaluated using the HPLC method. The chromatographic procedure was carried out with the HPLC system UltiMate Dionex 3000 SD, Chromeleon 7.2 SR3 Systems (Thermo Fisher Scientific Inc., Waltham, MA, USA). The separation was achieved with Column Luna (Phenomenex, Torrance, CA, USA) C18, 250 × 4.60 mm, particle size 5 μm, and a Diode Array Detector. The chromatographic conditions are as follows: mobile phase acetonitrile:methanol (70:30 v/v), flow rate 1.0 mL/min, and a wavelength of 254 nm. The amount was calculated based on a standard curve prepared in the concentration range of 3.5–10 µg/mL.
The drug release mechanism of the hydrogels was investigated by fitting the release profiles according to different release kinetic equations. Further, regression analysis was performed to evaluate the best fit.

The in vitro release tests were conducted in a phosphate buffer (pH of 7.4) containing 10% ethanol under 32 °C and gentle shaking (IKA Labortechnik HS-B20, Staufen, Germany). Briefly, 2.5 g of the hydrogel (containing 1.16 mg of resveratrol) was placed in 40 mL of the medium. For comparison, an aqueous suspension of resveratrol was introduced into a dialysis membrane and placed in the same medium. At predetermined time intervals, 2 mL of the acceptor phase was taken. Aliquot amounts of fresh medium were returned in order to maintain sink conditions. The concentration of the released drug was determined via high-performance liquid chromatography (HPLC, Thermo Scientific UltiMate Dionex 3000 SD, Chromeleon 7.2 SR3 Systems, Thermo Fisher Scientific, Waltham, MA, USA). Briefly, the system consisted of a Phenomenex C18 Column—Luna (250 mm × 4.60 mm, particle size 5 μm) and an isocratic mobile phase containing methanol:water:anhydrous acetic acid at a ratio of 52:48:0.05 (v/v/v) and a flow rate of 1.0 mL/min [84 (link)]. The detection wavelength was set at 303 nm. The column and the HPLC system were kept at 25 °C ± 1 °C.