In vivo quantitative molecular absorption of glycerol in human skin using coherent anti-Stokes Raman scattering (CARS) and two-photon auto-fluorescence - ScienceDirect
Highlights.?The penetration of small molecules through human skin in vivo is a major issue.?We demonstrate a novel imaging platform using coherent anti-Stokes Raman scattering and two-photon auto-fluorescence to quantify active molecule penetration in skin in vivo.?We exemplify our quantitative imaging platform to study percutaneous penetration in human forearm of glycerol diluted in water and xanthan gel.?We show that contrary to water, xanthan gel vehicle retains glycerol on the skin surface over time enabling its constant release in the long run.Abstract.The penetration of small molecules through the human skin is a major issue for both safety and efficacy issues in cosmetics and pharmaceutic domains. To date, the quantification of active molecular compounds in human skin following a topical application uses ex vivo skin samples mounted on Franz cell diffusion set-up together with appropriate analytical methods. Coherent anti-Stokes Raman scattering (CARS) has also been used to perform active molecule quantification on ex vivo skin samples, but no quantification has been described in human skin in vivo. Here we introduce and validate a framework for imaging and quantifying the active molecule penetration into human skin in vivo. Our approach combines nonlinear imaging microscopy modalities, such as two-photon excited auto-fluorescence (TPEF) and coherent anti-Stokes Raman scattering (CARS), together with the use of deuterated active molecules. The imaging framework was exemplified on topically applied glycerol diluted in various vehicles such as water and xanthan gel. In vivo glycerol quantitative percutaneous penetration over time was demonstrated, showing that, contrary to water, the xanthan gel vehicle acts as a film reservoir that releases glycerol continuously over time. More generally, the proposed imaging framework provides an enabling platform for establishing functional activity of topically applied products in vivo.Graphical abstract. Download high-res image (95KB) .Download full-size image .