2.8. Skin Permeation and In Vitro Drug Release Studies

Both permeation and release studies were performed using modified vertical Franz diffusion cells (Gauer Glas, Püttlingen, Germany) with a receptor volume of 12 mL. For in vitro release studies, synthetic polycarbonate membranes with a pore size diameter of 0.4 µm were used to separate donor and receptor compartments. For permeation studies, pig ears were obtained from the Department of Experimental Medicine of the University Hospital Tuebingen. The live animals were kept at the Department of Experimental Medicine and sacrificed during their experiments, with the approval of the ethics committee of the University Hospital Tuebingen. The ears were delivered directly after the death of the animals. The Department of Pharmaceutical Technology is registered for the use of animal products at the District Office of Tuebingen (registration number: DE 08 416 1052 21). Fresh pig ears were first cleaned with isotonic saline using cotton balls and after postauricular skin excision, they were wrapped in aluminium foil and stored at −30 °C until use. During the day of experiment, the skin samples were thawed at room temperature, skin strips of 3 cm width were made and pinned to a block of Styrofoam precovered with aluminium foil. Thereafter, wounded skin samples were prepared according to [9] by a skin grafting method using a Dermatom (Dermatom GA 630, Aesculap AG & Co. KG, Tüttlingen, Germany). The skin was first “wounded” through removal of the outermost layers of the skin with a thickness of 0.2 mm using Dermatom. Subsequently, the remaining skin was then dermatomed to a thickness of 0.4 mm. From the prepared porcine skin, a specimen was punched to obtain discs of 25 mm in diameter using a circular hole punch (Eduard Gottfried Ferne, Remscheid, Germany) [37].

The synthetic membrane/dermal porcine skin was mounted between the compartments of diffusion cells, and the effective diffusion area was 1.77 cm². For both in vitro release and ex vivo permeation experiments studies, samples of 20 mg fiber mats (F2 and F3), exactly weighed, were used. Consequently, all samples were loaded in the donor compartments and covered with parafilm to prevent solvent evaporation. A mixture of ethanol and water, 50:50 (v/v), was used as the receptor medium and the diffusion cells were maintained at 32 °C under constant magnetic stirring at 500 rpm. At predetermined time intervals, samples of 1 mL were taken from the receptor compartment and replaced with the same volume of fresh prewarmed receptor medium to maintain sink condition. The samples removed were analyzed directly using the HPLC-UV method as described below. The experiments were conducted in triplicate.