Kinetics of membrane adhesion mediated by ligand-receptor interaction studied with a biomimetic system

We report the first measurement of the kinetics of adhesion of a single gia nt vesicle controlled by the competition between membrane-substrate interac tion mediated by ligand-receptor interaction, gravitation, and Helfrich rep ulsion. To model the cell-tissue interaction, we doped the vesicles with li pid-coupled polymers (mimicking the glycocalix) and the reconstituted ligan ds selectively recognized by alpha (IIb)beta (3) integrin-mediating specifi c attraction forces. The integrin was grafted on glass substrates to act as a target cell. The adhesion of the vesicle membrane to the integrin-covere d surface starts with the spontaneous formation of a small (similar to 200 nm) domain of tight adhesion, which then gradually grows until the whole ad hesion area is in the state of tight adhesion. The time of adhesion varies from few tens of seconds to about one hour depending on the ligand and lipo polymer concentration. At small ligand concentrations, we observed the disp lacement of the front of tight adhesion following the square root law xi si milar to t(1/2), whereas, at high concentrations, we found a linear law xi similar to t. We show both experimentally and theoretically that the t(1/2) -regime is dominated by diffusion of ligands, and the t-regime by the kinet ics of ligands-receptors association.