(112g) Thin-Layer Rheology of Biological Lipid/Lipoprotein Surfactants Using Quartz-Crystal Microbalance with Dissipation

Some biological processes require the formation of a lipid/lipoprotein layer adsorbed on an air-water interface, such as the pulmonary surfactant, which reduces surface tension in the alveoli to facilitate the breathing process; or the tear film lipid layer, which inhibits the evaporation of the aqueous tear film.

Those adsorbed materials are subjected to compression/expansion stresses derived from breathing and blinking, and the integrity of the adsorbed layer thus depends on the viscoelastic properties of the materials. There is an important body of research on the interfacial rheology of the lipids/lipoproteins, which addresses the adsorption/desorption of the materials on the interface when there is the formation of a monolayer. However, the surface active materials usually form multilayers with thickness ranging hundreds of nanometers. In those instances, the materials are better characterized by their bulk rheology. This measurements are challenging, especially due to the minute amounts of materials produced by the body.

We propose a method based on Quartz Crystal Microbalance with Dissipation, using the Kelvin-Voigt model by measuring the shift in frequency and dissipation at different subtones of incremental amounts of material deposited on the surface of the quartz crystal. This procedure require very small amounts of material (approximately 10 micrograms), and is sensible to determine the elasticity and viscosity of several distinct layers/gradients, allowing the possibility of characterizing the surfactants on a patient by patient basis.

This method has the potential to aid in the diagnostic of diseases related to the lipid/lipoproteins deficiencies and the development of novel therapies.