On the structure and mechanical properties of in vitro salivary pellicles

Salivary pellicles display exceptional hydration and lubrication performance. At present, there are still gaps in the understanding of how this is achieved. The aim of this thesis was therefore to increase our knowledge on the mechanisms underlying these properties and deepen the understanding of how they are related to the composition and structure of pellicles, with a focus on those formed under in vitro conditions. This has applications ranging from the development of artificial saliva and lubricating coatings for biomedical applications to methodological approaches for initial testing of oral healthcare products. For this, we also focused on developing suitable methodological approaches for these studies, centering on atomic force microscopy, quartz crystal microbalance with dissipation monitoring, ellipsometry and neutron reflectometry techniques, to investigate in vitro and model salivary pellicles. First, we confirmed a two-layer structure for in vitro salivary pellicles and showed that the outer layer is mainly composed by the oral mucin MUC5B, but that it also contains other salivary components that enhance swelling and hydration. In the presence of bulk saliva, the outer layer also contains a reversibly and loosely bound fraction. This fraction increases the adhesiveness of the pellicle but unexpectedly has no significant effect on its lubrication performance. We also investigated the effect of mechanical confinement on model salivary pellicles by means of Neutron Reflectometry, revealing that at a pressure of 1 bar they are already completely compressed and dehydrated. Finally, with the aim to advance towards better oral healthcare products, we investigated the effect of nonionic and amphoteric surfactants on salivary pellicles, showing that they have a gentler effect on pellicle structure than the commonly employed anionic surfactants.