2.7.1. Permeation Studies Using Franz Diffusion Cells

Full-thickness skin samples were excised from the dorsal region of a one-month-old pig. Subcutaneous fat, tissues, blood vessels, and epidermal hairs were carefully removed before use. Porcine skin was mounted on the receptor compartment of a Franz cell with the SC side facing upwards into the donor compartment.

Freshly prepared 10% DMSO and 20% ethanol in 0.9% sodium chloride solution was used as the receptor solution for BT, and 0.9% sodium chloride solution was used as the receptor solution for TM. All were maintained at 37 °C under constant stirring. Once the skin temperature had equilibrated to 36 ± 1 °C, 1 mL of the treatment solution or vehicle was applied to the donor compartment. A volume of 1ml of receptor solution was collected at 30 min, 1, 2, 4, 6, and 8 h, and replaced with an equal volume of fresh temperature-equilibrated medium.

At the corresponding sampling time points, skin samples were obtained after receptor solution collection and disassembly of Franz diffusion cells. The skin was trimmed and washed twice with 0.9% sodium chloride, then frozen and stored in a −80 °C freezer. All samples were analyzed using liquid chromatography–mass spectrometry (LC-MS). The number of replicate experiments was n = 6.