Blanc SIMI 4 - Blanc - SIMI 4 - Physique des milieux condensés et dilués

Biolubrication from phospholipid membranes – Biolub

Submission summary

The mechanism of boundary lubrication of articulating cartilage, which leads to exceptionally low friction coefficients, is still poorly understood. The extreme lubricant properties of the articulating cartilages are even more surprising if one realizes that cartilage is rough and the joint filled with a complex synovial fluid. Using a biotribometer mimicking the articular contact, two partners in this project (LPMCN and LaMCoS) have shown that the stacking of phospholipid bilayers is a serious candidate for explaining these exceptional properties. Friction coefficients close to the ones of joints were measured with surfaces covered with supported phospholipid bilayers (SPB) in the gel state (DPPC). Values were larger in the presence of fluid bilayers (DOPC), due to bilayer degradation under mechanical stress during sliding.

The general objective of the BioLub project is to understand better the lubricant role of phospholipid bilayers from complementary theoretical, numerical and experimental approaches. The consortium is highly pluridisciplinary as it associates laboratories from condensed, bio-, nano- and soft matter physics (LPMCN), but also nano- and molecular physics (LASIM), biomaterials and tribology (LaMCoS).

On the experimental side, SPB will be used and deposited on different substrates, in presence of various buffers in order to understand the biolubrication of healthy joints (influence of lipid phase and ions): smooth model substrates, rough substrates, substrates separated with a vesicular solution with or without biopolymers. A second biotribometer will be developed during the project in order to detect small changes in friction coefficients by these parameters. Complementary experiments at a molecular scale will be performed: FRAP (Fluorescence Recovery After PhotoBleaching) to measure the diffusion of lipids in SPB, in particular in presence of roughness, ions or biopolymers, and AFM (Atomic Force Microscopy) in both imaging and force spectroscopy modes, to measure the bilayer structure, in particular on rough or patterned substrates.

The dynamics of fluid membranes in the complex structure of synovial joints are intrinsically a multiscale phenomenon. In order to interpret the experimental results at different scales, theoretical modeling is essential, but it requires a full hierarchy of models, ranging from molecular dynamics at small scale to continuum theories at large scales. These models will be calibrated using experimental results. Mainly three approaches will be used in this project. At small scale molecular dynamics will be used to investigate the internal structure of the membranes, their phase behavior and their friction properties for various lipid molecules (DPPC, DMPC, DOPC). But these approaches (all-atoms models) are restricted to nanometric scales and coarse-grained molecular dynamics will be used to describe the larger scale behavior, including hydrodynamic flows. A continuum description at the largest scales will be used as well to investigate the hydrodynamic instabilities and the collective behavior of membranes or vesicles in a flow, based on analytical approaches or on numerical techniques such as the Boundary Integral formulation. Each model will benefit from the data of smaller scale models, and a wide variety of physical phenomena such as phase transitions, equilibrium and non-equilibrium fluctuations as well as destabilization or topological changes will be investigated and compared to experimental findings.

Project coordination

Jean Paul RIEU (Laboratoire de physique de la matiere condensee et nanostructures) – jean-paul.rieu@univ-lyon1.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LASIM Laboratoire de Spectroscopie Ionique et Moléculaire
LPMCN Laboratoire de physique de la matiere condensee et nanostructures
Insa de Lyon - LaMCoS Institut National des Sciences Appliquées de Lyon - Laboratoire de Mécanique des Contacts et des Structures

Help of the ANR 474,728 euros
Beginning and duration of the scientific project: October 2012 - 36 Months

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