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Interactions between a lipid bilayer and its environment : from model systems to living cells - Arnaud HEMMERLÉ

SOLEIL Synchrotron, Gif-sur-Yvette

LPS Moyen Amphi

For more than 50 years physicists have been fascinated by the rich and complex behavior of amphiphilic molecules self-assembling into supramolecular structures, such as lipid bilayers in water. These thin membranes have the particularity of acting as quasi 2D worlds —they are about two molecules thick— evolving in a 3D space, with which the interactions can be complex. Even the seemingly simple case of a floppy bilayer interacting with a flat substrate is hard to describe, since it involves enthalpic contributions from van der Waals and electrostatic interactions, but also entropic ones due to spatial fluctuations of the bilayer. Measuring these interactions at the nanometer scale is challenging, and requires precise experiments on controlled model systems.

I will first describe a system of two bilayers deposited on a solid substrate. The interactions between the membranes are studied via their spacing and their fluctuation spectrum, measured by synchrotron x-ray scattering. We will see in particular how this approach can be used to better understand the effects of electric fields on the mechanical properties of lipid membranes [1].

I will then discuss how membranes can be studied on a larger scale with giant vesicles observed by interferometric optical microscopy (RICM), and how we recently used this non-invasive approach to measure the topography of adherent living cells [2].

Finally, I will describe the beamline SIRIUS at the synchrotron SOLEIL, devoted to the study of surfaces and organized molecular films, with a focus on its potential interest for soft matter systems.

[1] Hemmerle, A. et al., « Reduction in Tension and Stiffening of Lipid Membranes in an Electric Field Revealed by X-Ray Scattering », Phys. Rev. Lett., 116 (2016).

[2] Dejardin, M.-J. et al., « Lamellipod Reconstruction by Three-Dimensional Reflection Interference Contrast Nanoscopy (3D-RICN) », Nano Lett., 18, (2018).


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