Comprehensive investigation of penetration enhancers with complementary analytical techniques.

Transdermal drug delivery system is in the centre of attention in recent years. For efficient dermal drug delivery the drug has to overcome the barrier of the outermost layer of the skin, the stratum corneum. For facilitating dermal drug transport, the barrier properties of the stratum corneum can be varied by applying chemical penetration enhancers. The aim of this work was to characterize various penetration enhancers and investigate their mechanism of action. We combined well established techniques like differential scanning calorimetry (DSC) and infrared spectroscopy (IR) with confocal Raman microscopy (CRM) as an upcoming technique in skin research. CRM offers the possibility of label-free and non- destructive, chemically selective analysis of stratum corneum lipids and proteins. We used isolated human stratum corneum for incubation with the penetration enhancers. As a novel approach, the samples of treated stratum corneum were freeze dried to avoid any discrepancies which might come up with differences in the hydratation state of stratum corneum (SC). Furthermore, the structure of lipids and proteins in the stratum corneum was analyzed. In our study, stratum corneum was treated with dimethyle sulphoxide, propylene glycol, ethylene glycol, ethylene glycol-d4 and oleic acid. We observed that..