The dermal application of drugs is promising due to the ease of application. In this context nano-scale carrier systems were already evaluated in several studies with respect to the skin interaction and the impact on drug penetration. At the same time the upcoming production of engineered nano-scale materials requires a thorough safety evaluation. Drug delivery as well as risk assessment depends crucially on the ability of such carriers to overcome the skin barrier and reach deeper tissue layers. Therefore, the interaction of nanoparticles with skin and especially skin models is an intriguing field. However, the data obtained do not show a clear image on the effect of nano-carriers. Especially the penetration of such particles is an open and controversially discussed topic. The literature reports different results mainly on pig or murine skin showing strong penetration (pig and mouse) or the opposite. Looking only at the sizes of the particles also no conclusive picture can be obtained. Nevertheless, size is regarded to play an important role for skin penetration. Furthermore, the state of the skin influences penetration (hydration) and the mechanical stress is of outmost importance. IntroductionAny kind of organism always faced nanoscale environmental compounds interacting with their exterior barrier but a significant interest in these interactions came up not until the broad ascent of artificial nanoparticulate compounds. 1 The great potential for future advanced applications in areas such as energy, electronics, automotive, chemistry and life sciences led to a rapidly growing number of nanoparticulate systems, with respect to material composition, size, shape and formulation. Nanomedicines, incorporating drug delivery, diagnostics, implants, cancer therapy, to name just a few, pose an important and appealing area for beneficial application. Regarding final applicability it is essential to investigate the various biological aspects of nanoparticle exposure to the human organism. On one hand health hazards are to be identified and assessed, on the other hand medical and pharmaceutical potentials may be discovered and exploited. The behavior of nanoparticulate substances in biosystems and their physiological effects can, up to now, neither be extrapolated straightforwardly from bulk properties nor can they be predicted from molecular properties of the constituents. The first step of any interaction between an organism and any compound is the uptake of the compound from the environment. Several pathways of absorption exist for human (and most animal) organisms of which the skin is the most obvious and easiest to reach.The present review focus on skin and its barrier as well as sink function to artificial nanoparticulate compounds. Different classes of nanoparticulate material were studied to gain knowledge on the interaction and possible impact on skin covering bio-resistant particles (e.g., metal oxide, carbon-based) and biodegradable particles (e.g., liposomes, polymeric particles). Furthermore, mainly healthy ...

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