In vivo evaluation of the skin penetration and efficacy of ceramide nanomulsions by confocal Raman spectroscopy

Ceramide NP (Cer-NP) has favorable effects in treating dry skin and barrier damage; nevertheless, their efficacy is hindered by a relatively low skin permeability. The most common used method to evaluate drug permeability in cosmetic filed is Franz diffusion cell, which have limitations in terms of experimental materials and manipulation, making it difficult to reliably quantify drug permeability in vivo on the human skin. In contrast, confocal Raman spectroscopy (CRM) is regarded as a versatile tool for tracking of the penetration of active molecules through the skin, which is non-invasive, non-destructive, and real-time and allows in vivo testing of ceramide permeability and efficacy as well. The goal of this study was to track the skin penetration of Cer-NP nanoemulsions (NEs) into the inner forearm skin, and to assess the short-term effects of Cer-NP on stratum corneum (SC) thickness, hydration, and intercellular lipids (ICL) conformation order using the water content and lateral packing order Slat = I2880/I2850, which were obtained by CRM data. Cer-NP penetrated into the SC and epidermis, and the amount of penetration reduced with depth and increased with duration and finally retained in the SC. The results also uncovered Cer-NP-promoted SC hydration and increased SC thickness and Slat. The research mentioned above demonstrated that Cer-NP NEs successfully penetrated the skin and performed moisturizing and barrier restoration functions. The penetration of ceramide NP nanoemulsions (Cer-NP NEs) in the skin was investigated from a qualitative and semi-quantitative perspective by Raman confocal spectroscopy (CRM) based on the Raman signals of Cer-NP. In addition, based on the changes in Raman signals of lipid and water molecules in the skin, it was demonstrated that the skin treated with Cer-NP NEs has a higher moisture content and a stronger barrier function than the skin treated with free Cer-NP.image