Investigating the Nanostructure of the Stratum Corneum Lipid Matrix: A Combined Neutron Diffraction & Molecular Dynamics Simulations Approach

The human skin provides a physiochemical and biological protective barrier to the body due to the unique structure of its outermost layer the stratum corneum. This layer consists of corneocytes and a multi-lamellar lipid matrix forming a composite, which mainly determines the barrier function of the stratum corneum. A substantiated understanding of this barrier is necessary, as controlled breaching or modulation of the same is also essential for many topical drug delivery and personal care applications. In this study, we have discussed the state-of-the-art of neutron diffraction techniques (using specifically deuterated lipids) for stratum corneum lipid analysis and combined it with the information obtained from molecular dynamics simulations, to understand the structure and barrier function of the stratum corneum. As an example, the effect of ceramide concentration on a lipid lamella system consisting of CER[NP]/CER[AP]/Cholesterol/free fatty acid is studied. This study demonstrates the usefulness of the combined approach of neutron diffraction and molecular dynamics simulation for effective analysis of the skin lipid systems. The optimization of force fields by comparison with experimental data is furthermore an important step in the direction of providing a predictive quality.