Abstract
Mucus is the viscous gel that protects mucosal surfaces. It also plays a crucial role in several diseases as well as in mucosal drug delivery. Because of technical limitations, mucus properties have mainly been addressed by in-vitro studies. However, this approach can lead to artifacts as mucus collection can alter its structure. Here we show that by using an implemented atomic force microscope it is possible to measure the interactions between micro-particles and mucus blankets ex-vivo i.e., on fresh excised mucus-covered tissues. By applying this method to study the small intestine, we were able to quantify the stiffness and adhesiveness of its mucus blanket at different pH values. We also demonstrate the ability of mucus blankets to bind and attract particles hundreds of µm away from their surface, and to trap and bury them even if their size is as big as 15 µm.
Highlights
Physico-chemical properties of mucus are drastically dependent on the ambient medium
We show that Atomic Force Microscope (AFM)-based force spectroscopy can be used for this purpose
AFM has been extensively used in the study of biological material such as lipids, proteins, viruses, bacteria and eukaryotic cells[26]
Summary
Physico-chemical properties of mucus are drastically dependent on the ambient medium. Lowering the ambient pH leads to mucin aggregation and, to an increase of mucus viscosity[11, 12] This mechanism might be of physiological and clinical relevance as drops in luminal pH might occur as a consequence of different diseases, physiological states and bacterial fermentation of carbohydrates[13]. Purification protocols usually lead to mucin degradation[14] These problems can be avoided by studying (ex-vivo) freshly excised mucosal samples. It can be used to investigate forces between micro- or nano-meter sized probes and surfaces with a pN resolution This technique, known as force spectroscopy, has been extensively used to study the mechanical properties of mucin films[16,17,18]. The technique was applied to study the interactions between micro-particles and the mucosal surface of the distal part of the small intestine (ileum) collected from adult pigs. We showed that the outer mucus blankets can give rise to bridging interactions that extend several hundreds of μm from their outer steric repulsive surface, and how this outer surface can absorb particles as big as 15 μm i.e., more than one order of magnitude bigger than the values typically reported for mucus mesh size[1]
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