Paper Number
IR8
Session
Interfacial Rheology
Title
Interfacial rheology of crowded phospholipid monolayers as an approach to measure membrane fluidity
Presentation Date and Time
October 10, 2022 (Monday) 1:50
Track / Room
Track 5 / Sheraton 2
Authors
- Renggli, Damian (ETH Zurich, Materials)
- Vermant, Jan (ETH Zürich, Materials)
Author and Affiliation Lines
Damian Renggli and Jan Vermant
Materials, ETH Zürich, Zürich, Switzerland
Speaker / Presenter
Renggli, Damian
Keywords
experimental methods; biomaterials; emulsions; gels; interfacial rheology; rheometry techniques; surfactants; suspensions
Text of Abstract
The fluidity of biological membranes has to be tunable and plays a central role in many biological processes, e.g. cell homeostasis, cell signaling, and the formation of metastatic cancer cells, which represents just one of many diseases related with membrane fluidity dysfunction. The membrane can be enriched with proteins and other molecules which leads to so-called crowded membranes. This raises the question if crowded membranes are still fluid, i.e., if they allow for lateral diffusion of embedded membrane proteins. We approach this question with measuring the interfacial shear rheology of phospholipid monolayers—one leaflet of the lipid bilayer—as a model material for membranes with the interfacial needle stress rheometer (ISR), which is a macroscopic technique.[1] Phospholipid monolayers coat the alveoli in the lung and are used in pulmonary lung surfactant replacements to prevent lung collapse in premature infants (neonatal respiratory distress syndrome) as well as in adults. The lipid mixtures under investigation consist of phosphatidylcholines with saturated (palmitoyl) and unsaturated (oleoyl) fatty acids. At sufficiently high surface pressures, the saturated lipids pack efficiently, and form solid-like liquid condensed (LC) phases in a continuous liquid expanded (LE) matrix. We use the phase separation to mimic crowding of the interface. The phase morphology depends on a balance of attractive and repulsive forces between the lipid molecules, which is carefully explored by changing the bulk phase from water—air to saline buffer—oil. The area fraction of the LE phase is measured simultaneously to the rheology by a custom fluorescent microscope mounted on the ISR. We conclude that the interfacial viscosity of phospholipid monolayers does not diverge with increasing area fraction of the solid-like LC compared to a Brownian hard disk system. Hence the interface maintains its fluidity even if it is very crowded. [1] D. Renggli, A. Alicke, R. H. Ewoldt, and J. Vermant, Journal of Rheology 64, 141 (2020)