Lipid coating on polyelectrolyte surface modified colloidal particles and polyelectrolyte capsules

Dipalmitoyldiphosphatidic acid (DPPA), dipalmitoyldiphosphatidylcholine (DP PC), and sphingosine were adsorbed onto polyelectrolyte coated colloids and capsules forming composite lipid-polyelectrolyte layers. The stepwise coat ing was performed either by adsorption of preformed vesicles onto the capsu le surface or by a solvent exchange protocol. The lipid assembly was monito red by zeta-potential measurements. Single particle light scattering, flow cytometry, and fluorescence studies of Forster energy transfer have been us ed to quantify the lipid coating. Confocal microscopy images of capsules co ated with fluorescent lipids demonstrated a homogeneous coverage of the cap sule surface. Differential scanning calorimetry shows a phase transition te mperature characteristic for lipid layer structures. It was concluded that the adsorbed DPPA form bilayers while DPPC may form multilayers. It was fur ther shown that on top of the lipid layers further polyelectrolyte layers c ould be assembled. The permeability of B-carboxyfluorescein (6-CF) through the composite layer structure was studied by means of confocal laser scanni ng microscopy. The permeation time through the composite layer was of the o rder of 10(1)-10(2) min, while in the absence of lipids 6-CF equilibrated f aster than the time resolution of the technique.