Morphology and Rheology of Biological Complex Fluids in Confined Geometry

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Soft interfaces on solid surfaces mimeticking typical physical properties and functions of glycocalices of cell surfaces are designed and studied by various surface sensitive techniques including neutron and X-ray reflextivity, micro-interferometry and colloidal probe microscopy. Artificial glycocalices are designed: 1. by reconstitution of lipopolymers (phospholipids with PEO-headgroups of various size) and glycosilated lipids (gangliosides and lipid-coupled Lewis X factors) in supported membranes, 2. by surface grafting of polysaccharides (heparan sulfate and hyaluronic acid) and coupling of lectins (as model of selectins) to polymer chains. One major objective of the project is to understand the control of cell-cell adhesion and the binding of biofunctionalized (nano- to micrometer) colloidal particles (acting as phagosomes) by the grafting density, the structure and dynamics of the glycocalix. One approac to this problem is the measurement of the binding kinetics of macromolecular ligands to receptors (e.g. lipid coupled selectins or lectins) buried within the surface grafted glycocalix models (e.g. by application of neutron reflectivity). A second strategy is to measure adhesion forces by a newly developed colloidal force microscopy based on magnetic tweezers. The time evolution of the interaction potential of magnetic beads functionalized by attachment of various ligands (RGDligands, Lewis X factor od adsorbed fibronectin) is measured by application of magnetic force pulse sequences and analysis of the force-deflection curves through microinterferometry. These studies are closely related to a project on the regulation of vesicle uptake by cells through functionalization with RGD-ligands or Lewis factors by the group of Valérie MarchiArtzner.