Binding of lipid vesicles to protein-coated solid polymer surfaces: A model for cell adhesion to artificial biocompatible materials

The adhesion of lipid vesicles (liposomes) having controlled chemical and p hysical structure to polymer supported human serum albumin (HSA) thin layer s was investigated by a spectrofluorimetric technique. The vesicle lipid bi layer was labeled with a small amount of an apolar fluorescent probe (diphe nylexathriene) and the vesicle suspension was set in contact with the prote in film. After washing and drying, the adhering vesicles containing sample was dissolved in chloroform and the homogeneous solution was analyzed by st andard spectrofluorimetric techniques. Different parameters of the lipid bi layer, suspending solution, and protein film were varied and their influenc e on the liposome binding was investigated. Concerning the lipid bilayer, w e studied the effect of liposome surface charge by using different mixtures of neutral (dipalmitoyl-phosphatidylcholine) and charged (dipalmitoyl-phos phatidic acid) phospholipids and the fluid or gel nature of the lipid bilay er (switched on and off by temperature variation). Variations of the local environment involve Ca2+ and H+ changes in the millimolar range as well as different hydrodynamical flows (in the range 0.1-10 cm/s). Preliminary meas urements using different protein layers were also performed. Results show: (a) negligible adhesion without the protein layer, (b) the presence of a ma ximum for the liposome adhesion vs ion concentration (depending on the lipo some composition and kind of the adsorbed ions), (c) a much stronger adhesi on for vesicles in the fluid phase (overcoming the entropy-driven desorptio n increase with temperature), and (d) a dramatic lowering of the adhesion c apability under hydrodynamic flow. Points a-e have been interpreted on the basis of a simple mechanoelectrical model. (C) 2000 Academic Press.