(387b) Rheology of Layered Biological Lipids/Surfactants Using Quartz-Crystal Microbalance with Dissipation

The tear film lipid layer (TFLL) is a 100-200 nm layer covering the tear film on the ocular surface. One of the most important attributed functions of the TFLL is the retardation of the evaporation, and several pathologies affecting these lipids produce dry eye disease (DED) as an outcome.

The inhibition of evaporation by the TFLL depends on the integrity of this layer, which is generally thought as a duplex layer, with a compact layer of polar lipids (phospholipids and glycolipids) assembled on the interface of the aqueous sublayer, and a thin, bulk layer of non-polar lipids (100-200 nm thick). Furthermore, the TFLL it is continuously subjected to compression/expansion stresses during blinking.

The bulk research on the rheology of biological lipids/lipoproteins (such as lung surfactants) addresses the adsorption/desorption of the materials on the interface when a monolayer is formed. However, duplex layers need to be characterized by their bulk rheology. Because of the limited amount of these materials, these bulk measurements are challenging.

One promising technique to characterize this layered materials is the Quartz Crystal Microbalance with Dissipation (QCM-D). This technique allows us to measure very small amount of material (approximately 5-10 micrograms) by quantifying the shift in frequency and dissipation at different subtones while the material is heating until melting. A Kelvin-Voigt model for viscoelastic solids is applied, allowing the possibility of characterizing its elastic (spring) and viscous (damper) elements.

This method has potential to improve diagnostics of DED and the development and testing of novel therapies.