Intact vesicle adsorption and supported biomembrane formation from vesicles in solution:: Influence of surface chemistry, vesicle size, temperature, and osmotic pressure

The adsorption kinetics of small unilamellar egg-yolk phosphatidylcholine vesicles was investigated by the quartz crystal microbalance-dissipation (QCM-D) technique, as a function of surface chemistry (on SiO2, Si3N4, Au, TiO2, and Pt), temperature (273-303 K), vesicle size (25-200 nm), and osmotic pressure. On SiO2 and Si3N4, the vesicles adsorb intact at low coverage, followed by transformation to a bilayer at a critical coverage. On TiO2, oxidized Pt, and oxidized Au, the vesicles adsorb intact at all coverages and all studied temperatures. Variation of vesicle size does not change the qualitative behavior on any of the surfaces, but the quantitative differences provide important information about surface-induced vesicle deformation. In the low-coverage regime (where vesicles adsorb intact on all surfaces), the deformation is much larger on SiO2 than on the surfaces where bilayer formation does not occur. This is attributed to stronger vesicle-surface interaction on SiO2. The bilayer formation is thermally activated with an apparent activation energy of 63-78 kJ/mol. Osmotic pressure promotes bilayer formation, especially when the external salt concentration is higher than the internal one. Depending on preparation conditions, a varying amount of nonruptured vesicles are trapped in the saturated bilayer on SiO2, but the fraction can be efficiently reduced to below the detection level using elevated temperature and/or high osmotic stress.