Publications by authors named "Arnaud Hemmerle"

9 Publications

  • Page 1 of 1

Measuring and upscaling micromechanical interactions in a cohesive granular material.

Soft Matter 2021 Jun;17(23):5806-5814

School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK.

The mechanical properties of a disordered heterogeneous medium depend, in general, on a complex interplay between multiple length scales. Connecting local interactions to macroscopic observables, such as stiffness or fracture, is thus challenging in this type of material. Here, we study the properties of a cohesive granular material composed of glass beads held together by soft polymer bridges. We characterise the mechanical response of single bridges under traction and shear, using a setup based on the deflection of flexible micropipettes. These measurements, along with information from X-ray microtomograms of the granular packings, then inform large-scale discrete element model (DEM) simulations. Although simple, these simulations are constrained in every way by empirical measurement and accurately predict mechanical responses of the aggregates, including details on their compressive failure, and how the material's stiffness depends on the stiffness and geometry of its parts. By demonstrating how to accurately relate microscopic information to macroscopic properties, these results provide new perspectives for predicting the behaviour of complex disordered materials, such as porous rock, snow, or foam.
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http://dx.doi.org/10.1039/d1sm00458aDOI Listing
June 2021

On the control of dispersion interactions between biological membranes and protein coated biointerfaces.

J Colloid Interface Sci 2021 Sep 11;598:464-473. Epub 2021 Mar 11.

PULS Group, Department of Physics and Interdisciplinary Center for Nanostructured Films, Friedrich-Alexander-Universität Erlangen-Nürnberg, IZNF, Cauerstrasse 3, 91058 Erlangen, Germany; Division of Physical Chemistry, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia. Electronic address:

Hypothesis: Interaction of cellular membranes with biointerfaces is of vital importance for a number of medical devices and implants. Adhesiveness of these surfaces and cells is often regulated by depositing a layer of bovine serum albumin (BSA) or other protein coatings. However, anomalously large separations between phospholipid membranes and the biointerfaces in various conditions and buffers have been observed, which could not be understood using available theoretical arguments.

Methods: Using the Lifshitz theory, we here evaluate the distance-dependent Hamaker coefficient describing the dispersion interaction between a biointerface and a membrane to understand the relative positioning of two surfaces. Our theoretical modeling is supported by experiments where the biointerface is represented by a glass substrate with deposited BSA and protein layers. These biointerfaces are allowed to interact with giant unilamellar vesicles decorated with polyethylene glycol (PEG) using PEG lipids to mimic cellular membranes and their pericellular coat.

Results: We demonstrate that careful treatment of the van der Waals interactions is critical for explaining the lack of adhesiveness of the membranes with protein-decorated biointerfaces. We show that BSA alone indeed passivates the glass, but depositing an additional protein layer on the surface BSA, or producing multiple layers of proteins and BSA results in repulsive dispersion forces responsible for 100 nm large equilibrium separations between the two surfaces.
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http://dx.doi.org/10.1016/j.jcis.2021.02.078DOI Listing
September 2021

Insertion and activation of functional Bacteriorhodopsin in a floating bilayer.

J Colloid Interface Sci 2021 Sep 31;597:370-382. Epub 2021 Mar 31.

Institut Laue-Langevin, 71 av.des Martyrs, BP 156, 38042 Grenoble Cedex, France.

The proton pump transmembrane protein bacteriorhodopsin was successfully incorporated into planar floating lipid bilayers in gel and fluid phases, by applying a detergent-mediated incorporation method. The method was optimized on single supported bilayers by using quartz crystal microbalance, atomic force and fluorescence microscopy techniques. Neutron and X-ray reflectometry were used on both single and floating bilayers with the aim of determining the structure and composition of this membrane-protein system before and after protein reconstitution at sub-nanometer resolution. Lipid bilayer integrity and protein activity were preserved upon the reconstitution process. Reversible structural modifications of the membrane, induced by the bacteriorhodopsin functional activity triggered by visible light, were observed and characterized at the nanoscale.
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http://dx.doi.org/10.1016/j.jcis.2021.03.155DOI Listing
September 2021

Attractive Interaction between Fully Charged Lipid Bilayers in a Strongly Confined Geometry.

J Phys Chem Lett 2019 Nov 11;10(22):7195-7199. Epub 2019 Nov 11.

UPR 22/CNRS, Institut Charles Sadron , Université de Strasbourg , 23 rue du Loess, BP 84047 , 67034 Strasbourg Cedex 2, France.

We investigate the interaction between highly charged lipid bilayers in the presence of monovalent counterions. Neutron and X-ray reflectivity experiments show that the water layer between like-charged bilayers is thinner than for zwitterionic lipids, demonstrating the existence of counterintuitive electrostatic attractive interaction between them. Such attraction can be explained by taking into account the correlations between counterions within the Strong Coupling limit, which falls beyond the classical Poisson-Boltzmann theory of electrostatics. Our results show the limit of the Strong Coupling continuous theory in a highly confined geometry and are in agreement with a decrease in the water dielectric constant due to a surface charge-induced orientation of water molecules.
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http://dx.doi.org/10.1021/acs.jpclett.9b02804DOI Listing
November 2019

Lamellipod Reconstruction by Three-Dimensional Reflection Interference Contrast Nanoscopy (3D-RICN).

Nano Lett 2018 10 6;18(10):6544-6550. Epub 2018 Sep 6.

Aix Marseille Univ , CNRS, INSERM, LAI , Marseille 13288 , France.

There are very few techniques to reconstruct the shape of a cell at nanometric resolution, and those that exist are almost exclusively based on fluorescence, implying limitations due to staining constraints and artifacts. Reflection interference contrast microscopy (RICM), a label-free technique, permits the measurement of nanometric distances between refractive objects. However, its quantitative application to cells has been largely limited due to the complex interferometric pattern caused by multiple reflections on internal or thin structures like lamellipodia. Here we introduce 3D reflection interference contrast nanoscopy, 3D-RICN, which combines information from multiple illumination wavelengths and aperture angles to characterize the lamellipodial region of an adherent cell in terms of its distance from the surface and its thickness. We validate this new method by comparing data obtained on fixed cells imaged with atomic force microscopy and quantitative phase imaging. We show that as expected, cells adhering to micropatterns exhibit a radial symmetry for the lamellipodial thickness. We demonstrate that the substrate-lamellipod distance may be as high as 100 nm. We also show how the method applies to living cells, opening the way for label-free dynamical study of cell structures with nanometric resolution.
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http://dx.doi.org/10.1021/acs.nanolett.8b03134DOI Listing
October 2018

Fracture of a model cohesive granular material.

Soft Matter 2017 Feb 13;13(5):1040-1047. Epub 2017 Jan 13.

Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Göttingen, Germany.

We study experimentally the fracture mechanisms of a model cohesive granular medium consisting of glass beads held together by solidified polymer bridges. The elastic response of this material can be controlled by changing the cross-linking of the polymer phase, for example. Here we show that its fracture toughness can be tuned over an order of magnitude by adjusting the stiffness and size of the polymer bridges. We extract a well-defined fracture energy from fracture testing under a range of material preparations. This energy is found to scale linearly with the cross-sectional area of the bridges. Finally, X-ray microcomputed tomography shows that crack propagation is driven by adhesive failure of about one polymer bridge per bead located at the interface, along with microcracks in the vicinity of the failure plane. Our findings provide insight into the fracture mechanisms of this model material, and the mechanical properties of disordered cohesive granular media in general.
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http://dx.doi.org/10.1039/c6sm02600aDOI Listing
February 2017

A cohesive granular material with tunable elasticity.

Sci Rep 2016 10 24;6:35650. Epub 2016 Oct 24.

Max Planck Institute for Dynamics and Self-Organization (MPIDS), Göttingen, 37077, Germany.

By mixing glass beads with a curable polymer we create a well-defined cohesive granular medium, held together by solidified, and hence elastic, capillary bridges. This material has a geometry similar to a wet packing of beads, but with an additional control over the elasticity of the bonds holding the particles together. We show that its mechanical response can be varied over several orders of magnitude by adjusting the size and stiffness of the bridges, and the size of the particles. We also investigate its mechanism of failure under unconfined uniaxial compression in combination with in situ x-ray microtomography. We show that a broad linear-elastic regime ends at a limiting strain of about 8%, whatever the stiffness of the agglomerate, which corresponds to the beginning of shear failure. The possibility to finely tune the stiffness, size and shape of this simple material makes it an ideal model system for investigations on, for example, fracturing of porous rocks, seismology, or root growth in cohesive porous media.
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http://dx.doi.org/10.1038/srep35650DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5075937PMC
October 2016

Reduction in Tension and Stiffening of Lipid Membranes in an Electric Field Revealed by X-Ray Scattering.

Phys Rev Lett 2016 Jun 2;116(22):228101. Epub 2016 Jun 2.

UPR 22/CNRS, Institut Charles Sadron, Université de Strasbourg, 23 rue du Loess, BP 84047 67034 Strasbourg Cedex 2, France.

The effect of ac electric fields on the elasticity of supported lipid bilayers is investigated at the microscopic level using grazing incidence synchrotron x-ray scattering. A strong decrease in the membrane tension up to 1  mN/m and a dramatic increase of its effective rigidity up to 300  k_{B}T are observed for local electric potentials seen by the membrane ≲1  V. The experimental results are analyzed using detailed electrokinetic modeling and nonlinear Poisson-Boltzmann theory. Based on a modeling of the electromagnetic stress, which provides an accurate description of the bilayer separation versus pressure curves, we show that the decrease in tension results from the amplification of charge fluctuations on the membrane surface whereas the increase in bending rigidity results from the direct interaction between charges in the electric double layer. These effects eventually lead to a destabilization of the bilayer and vesicle formation. Similar effects are expected at the tens of nanometers length scale in cell membranes with lower tension, and could explain a number of electrically driven processes.
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http://dx.doi.org/10.1103/PhysRevLett.116.228101DOI Listing
June 2016

Controlling interactions in supported bilayers from weak electrostatic repulsion to high osmotic pressure.

Proc Natl Acad Sci U S A 2012 Dec 19;109(49):19938-42. Epub 2012 Nov 19.

Université de Strasbourg, Institut Charles Sadron, Unité Propre de Recherche 22, Centre National de la Recherche Scientifique, 67034 Strasbourg Cedex 2, France.

Understanding interactions between membranes requires measurements on well-controlled systems close to natural conditions, in which fluctuations play an important role. We have determined, by grazing incidence X-ray scattering, the interaction potential between two lipid bilayers, one adsorbed on a solid surface and the other floating close by. We find that interactions in this highly hydrated model system are two orders of magnitude softer than in previously reported work on multilayer stacks. This is attributed to the weak electrostatic repulsion due to the small fraction of ionized lipids in supported bilayers with a lower number of defects. Our data are consistent with the Poisson-Boltzmann theory, in the regime where repulsion is dominated by the entropy of counter ions. We also have unique access to very weak entropic repulsion potentials, which allowed us to discriminate between the various models proposed in the literature. We further demonstrate that the interaction potential between supported bilayers can be tuned at will by applying osmotic pressure, providing a way to manipulate these model membranes, thus considerably enlarging the range of biological or physical problems that can be addressed.
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http://dx.doi.org/10.1073/pnas.1211669109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3523853PMC
December 2012