466 Characterization of ex vivo human skin for topical delivery studies by confocal Raman microscopy

Protocols to assess the penetration of topically applied products in skin commonly utilize excised skin in a diffusion cell followed by skin segmentation, extraction and quantification of exogenous materials. Chemical analyses via sensitive methods of detection (e.g. HPLC) are applied; however, important information regarding the spatial distribution of exogenous materials in skin and perturbation to skin’s endogenous ultra- and molecular structure are inaccessible. Confocal Raman microscopy (CRM) provides a probe-free, non-destructive approach to examine the spatial distribution (with spatial resolution of ∼1 micron) of multiple components in skin simultaneously. In the current work, confocal Raman images of untreated ex vivo human skin are acquired following typical diffusion cell incubation protocols. Spectral parameters that examine the relative water content and lipid/protein ratio are imaged over an area of 100 x 60 micron2 (width x depth). Consequently, the boundary between the stratum corneum (SC) and viable epidermis (VE) is delineated using the lipid/protein ratio which compares well with the leveling off of the increase in the relative water content profile with depth. Thus, the SC/VE border defined by the lipid/protein ratio in this ex vivo study is qualitatively consistent with the generally accepted SC thickness determination provided by in vivo CRM. In addition, statistical analysis of intra and inter-subject heterogeneity is presented herein. Most importantly, a second spectral parameter to delineate the SC/VE border has been defined and either parameter can be utilized for future ex vivo CRM penetration studies.