ABSTRACT
The adhesion of lipid vesicles (liposomes) having controlled chemical and physical structure to polymer supported human serum albumin (HSA) thin layers was investigated by a spectrofluorimetric technique. The vesicle lipid bilayer was labeled with a small amount of an apolar fluorescent probe (diphenylexathriene) and the vesicle suspension was set in contact with the protein film. After washing and drying, the adhering vesicles containing sample was dissolved in chloroform and the homogeneous solution was analyzed by standard spectrofluorimetric techniques. Different parameters of the lipid bilayer, suspending solution, and protein film were varied and their influence on the liposome binding was investigated. Concerning the lipid bilayer, we studied the effect of liposome surface charge by using different mixtures of neutral (dipalmitoyl-phosphatidylcholine) and charged (dipalmitoyl-phosphatidic acid) phospholipids and the fluid or gel nature of the lipid bilayer (switched on and off by temperature variation). Variations of the local environment involve Ca(2+) and H(+) changes in the millimolar range as well as different hydrodynamical flows (in the range 0.1-10 cm/s). Preliminary measurements using different protein layers were also performed. Results show: (a) negligible adhesion without the protein layer, (b) the presence of a maximum for the liposome adhesion vs ion concentration (depending on the liposome composition and kind of the adsorbed ions), (c) a much stronger adhesion for vesicles in the fluid phase (overcoming the entropy-driven desorption increase with temperature), and (d) a dramatic lowering of the adhesion capability under hydrodynamic flow. Points a-c have been interpreted on the basis of a simple mechanoelectrical model. Copyright 2000 Academic Press.
