ADHESION OF LATEX SPHERES TO GIANT PHOSPHOLIPID-VESICLES - STATICS AND DYNAMICS

We studied the sequence of phenomena which occur when a solid microsph ere is brought in contact with an isolated giant lipid vesicle. We use d Latex beads, a few microns in diameter, which were manipulated indiv idually by means of a long-working-distance optical trap. The evolutio n of the bead/vesicle system was characterized in time, from similar t o 1 ms to similar to 100 s. In this time range, we identified differen t steps, namely adhesion, ingestion, expulsion and recapture. In the a dhesion step the sphere moves quickly in direction to the vesicle inte rior and the surface of the particle becomes wetted by lipids. We prop ose a simple model, based on the counter-balance between adhesion and stretching of the lipid lamella, which explains the experimental equil ibrium configuration. The bead/vesicle configuration after the adhesio n step pertains to partial or complete wetting, depending on the initi al vesicle state. Partial wetting can be followed by a second step, wh ich we named ''particle ingestion'', and which leads to complete (or n early complete) wetting of the particle surface. Ingestion is characte rized by a further penetration of the particle across the vesicle cont our, in concomitance with a decrease of the vesicle size. The phenomen on is attributed to the occurrence of a dynamically stabilized pore ac ross the membrane, which allows part of the water initially inside the vesicle to how out. Ingestion can be followed by a back and forth mov ement (expulsion and re-capture) of the particle. In the ultimate conf iguration, the solid surface is totally wetted by lipids, however with a finite contact angle between the membrane and the solid surface.