Visualization of the structure of native human pulmonary mucus

Human respiratory mucus lining the airway epithelium forms a challenging barrier to inhalation therapeutics. Therefore, structural elucidation of hydrated mucus is essential for an efficient drug delivery development. The structure of mucus has been primarily investigated by conventional electron microscopy techniques, which operate under vacuum conditions and require sample preparation steps that might alter the structure of mucus. In this study we investigated the impact of dehydration on mucus and analyzed the structure of mucus in its hydrated state. Cryo-scanning electron microscopy (Cryo-SEM) analysis of mucus showed, that during the process of sublimation, non-porous structure of mucus is transformed into a porous network. Similarly, images acquired by environmental scanning electron microscopy (ESEM), revealed a non-porous structure of hydrated mucus, while further observation at decreasing pressure demonstrated the strong influence of dehydration on mucus structure. We could successfully visualize the structural organization of the major gel forming mucin MUC5B in its hydrated state by employing stimulated emission depletion (STED) microscopy, which allowed resolving the nano-scale patterns of mucin macromolecules within the essentially pore-free mucus structure. The general structural organization of mucus components was addressed by confocal laser scanning microscopy (CLSM), which revealed the heterogeneous and composite structure of mucus. These results provide a novel view on the native structure of mucus and will affect drug delivery development.

Interaction of graphene-related materials with human intestinal cells: an in vitro approach

Graphene-related materials (GRM) inherit unique combinations of physicochemical properties which offer a high potential for technological as well as biomedical applications. It is not clear which physicochemical properties are the most relevant factors influencing the behavior of GRM in complex biological environments. In this study we have focused on the interaction of GRM, especially graphene oxide (GO), and Caco-2 cells in vitro. We mimiked stomach transition by acid-treatment of two representative GRM followed by analysis of their physicochemical properties. No significant changes in the material properties or cell viability of exposed Caco-2 cells in respect to untreated GRM could be detected. Furthermore, we explored the interaction of four different GO and Caco-2 cells to identify relevant physicochemical properties for the establishment of a material property-biological response relationship. Despite close interaction with the cell surface and the formation of reactive oxygen species (ROS), no acute toxicity was found for any of the applied GO (concentration range 0-80 μg ml(-1)) after 24 h and 48 h exposure. Graphene nanoplatelet aggregates led to low acute toxicity at high concentrations, indicating that aggregation, the number of layers or the C/O ratio have a more pronounced effect on the cell viability than the lateral size alone.