Penetration Process of a Hydrated Deep Eutectic Solvent Through the Stratum Corneum and its Application as a Protein Penetration Enhancer

The penetration mechanism of choline chloride‐glycerol deep eutectic solvent (DES) through the stratum corneum (SC) as a potential solvent for a novel enhancer of protein penetration into the skin was investigated in a wide and small angle X‐ray diffraction study. We found that DES penetrated through intercellular lipids but not the corneocytes. DES seemed to extract a portion of lipids of the short lamellae in the SC. Hydrated DES with a DES to water weight ratio of 9 to 1 (9DES‐1H(2)O) showed the strongest interaction with the lipids in the SC compared with water, DES, and hydrated DESs with another weight ratio of DES to water (DES : water=8 : 2). In a skin penetration test with a fluorescently labelled lysozyme, 9DES‐1H(2)O increased the amount of penetration through the SC by two‐fold compared with HEPES buffer.