Characterization of skin structure and chemical content in response to topical intervention using coherent Raman scattering imaging (Conference Presentation)

One of the primary functions of human skin is to provide a mechanical barrier and interface with the outside world, owing to its unique structure and composition. Indeed, the most superficial layer of the epidermis, the stratum corneum, is a selectively porous structure composed of thin layers of protein-rich corneocytes joined together by lipids such as ceramides. The overall impermeability of the stratum corneum is crucial for homeostasis, but also hampers the penetration of beneficial topical agents into the skin. Specifically, hydrophilic compounds typically do not permeate through the epidermis, while hydrophobic compounds can readily be delivered through lipid-containing routes such as sebaceous gland ducts or the spacing between corneocytes. A proper understanding of stratum corneum structure and composition is therefore of great benefit for the design of topical formulations in order to properly optimize the delivery of active compounds to the skin. To this aim, coherent Raman scattering imaging techniques including both coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microscopies can be used to study the chemical composition and structure of the stratum corneum, as these modalities are sensitive to unique vibrational modes of specific chemical groups such as lipids, proteins, and water. These metrics can further be used to measure uptake and efficacy of topical compounds in order to optimize formulation design.