From the Structure of the Skin Barrier and Dermal Formulations to in vitro Transport Models for Skin Absorption: Skin Research in the Netherlands and in Germany

Abstract

This review presents an overview of German and Dutch research institutions and their studies in the field of skin drug delivery and adjacent topics. In the Netherlands, the involved research groups are mainly localized in Leiden, whereas in Germany the skin research institutions are spread over the whole country. The scientific studies in the Netherlands focus on the in-depth analysis of human skin composition and its individual components as well as on the development and characterization of dermal drug delivery systems ranging from liquid crystalline systems and vesicles up to microneedles with an emphasis on examining the interactions of these drug delivery systems with the human skin in vitro and in vivo. In Germany, the individual areas of research span from in-depth investigations on various drug delivery systems intended for skin application and the development of novel in vitro models for skin absorption testing up to in vivo studies focusing on the biological performance of topically applied actives. Furthermore, sophisticated analytical techniques are applied for the elucidation of skin assembly and transport processes. In addition, experimentally derived data are correlated with advanced computational modelling. Even though the individual research topics in the Netherlands and Germany are quite diverse, the exchange of knowledge and interdisciplinary collaborations between the two neighbouring countries were and are still frequently made. In this context, the review aims at highlighting crosslinks between the different institutions and individual persons to complete the picture. For each institution, the principal investigators and their studies are presented and the upcoming young scientists are introduced as an outlook for the field. This review does not claim completeness, but is rather intended to give a general overview of Dutch and German research in the field of skin drug delivery and adjacent topics.

In vivo Tracking of DNA for Precise Determination of the Stratum Corneum Thickness and Superficial Microbiome Using Confocal Raman Microscopy

“…The skin is composed of three major layers, i.e. epidermis, dermis, and hypodermis [2], and the skin barrier function is mostly ensured by the stratum corneum (SC), the uppermost layer of the epidermis [3][4][5][6]. The SC consists of 10−20 layers of corneocytes, which are enucleated flattened cells embedded in lipid lamellar regions [7][8][9].…”

A depth-dependent profile of the lipid conformation and lateral packing order of the stratum corneum in vivo measured using Raman microscopy

“…The barrier function is one of the main functions of the skin preventing the penetration of exogenous substances into the skin and excessive water loss from the body. 1,2 When the skin is exposed to external stress, the first structural layer of the skin to encounter this stress is the epidermis, which is composed of the stratum corneum (SC), stratum granulosum (SG), stratum spinosum and stratum basale. A skin barrier function prevails in the SC, where the corneocytes and intercellular lipid matrix are densely packed, forming a brick-mortar structure.…”

Analysis of Human and Porcine Skin in vivo/ex vivo for Penetration of Selected Oils by Confocal Raman Microscopy

“…The barrier function of the skin is mostly provided by the lipids of the stratum corneum [1,2,3,4]. External stressors are able to influence the physiology of the human skin's stratum corneum.…”