L.BUREAU – 24 AVRIL

Interactions between circulating cells and blood vessel walls are central to many physiological processes such as the early stages of the immune or inflammatory response, gas exchanges with tissues, or vascular remodeling. Among these interactions, hydrodynamic forces play a key role, as they control the radial migration of the circulating cells towards or away from the vascular walls. A point that has been largely overlooked so far is the contribution of the wall deformability to such hydrodynamic forces, and in particular the role of the endothelial glycocalyx, a compliant meshwork of polysaccharides lining the lumen of blood vessels. In this context, we have developed an experimental setup allowing for the study of microparticles flowing past a surface bearing a macromolecular layer mimicking the nature, thickness and elastic properties of the endothelial surface layer. Combining parallel plate flow assays and 3D particle tracking based on interference microscopy, we show that:
(i) non-deformable spherical microbeads traveling close to the macromolecular layer are repelled and lift away from the surface under strong enough (yet physiological) shear rates,
(ii) the bead/surface distance increases with increasing shear rate and/or layer compliance,
(iii) our experimental results can be quantitatively described in the theoretical framework of elastohydrodynamics accounting for the effect of substrate deformations.
This work underlines the important mechanical role that the soft endothelial glycocalyx is likely to play in regulating cell/wall interactions in blood flow.