Methylene blue

Tofacitinib citrate was purchased from CSN Pharm (Arlington Heights, IL, U.S.A). Phosphate buffered saline, pH 7.4 (PBS, 10X), sodium phosphate dibasic, orthophosphoric acid, and silver wire (0.5 mm diameter, 99.99%) were obtained from Fisher Scientific (Fair Lawn, NJ, U.S.A). HPLC grade acetonitrile and methanol were procured from Pharmco-Aaper (Brookfield, CT, U.S.A). Polyvinyl alcohol (PVA 26-88 EMPROVE® exp Ph Eur, USP, JPE) and carboxymethyl cellulose sodium salt (CMC low viscosity CAS 9004-32-4) were obtained from Sigma Aldrich (St. Louis, MO, U.S.A). Silver chloride electrodes (2 mm x 4mm) were purchased from A-M systems (Sequim, WA, U.S.A.). Staining solutions, namely methylene blue and Fluoresoft (0.35%), were procured from Eastman Kodak Co. (Rochester, NY, U.S.A) and Holles Laboratories Inc. (Cohasset, MA, U.S.A), respectively. Full-thickness human skin tissue was procured from the National Disease Research Interchange (NDRI) with support from NIH grant U42OD11158.

MTX was purchased from Sigma Aldrich (St. Louis, MO, USA). Phosphate buffered saline (PBS) (0.1 M, pH 7.4 ± 0.1) was obtained from Fisher Scientific (Fisher BioReagent, Springfield, NJ, USA). Methylene blue was purchased from Eastman Kodak Co. (Rochester, NY, USA), D-Squame stripping discs from CuDerm (Dallas, TX, USA), while cotton swabs were obtained from Dynarex (Orangeburg, NY, USA). Silver chloride electrodes and silver wire were procured from ALA Scientific Instruments (Farmingdale, NY, USA) and Alfa Aesar (Ward Hill, MA, USA), respectively. Human cadaver skin tissues (0.26 ± 0.04 mm thick, n = 24) were obtained from the New York Fire Fighter skin bank (Presbyterian Hospital, New York, NY, USA).