Solid supported vesicles for bactericide delivery

Cationic and anionic liposomes have been prepared by extrusion from dipalmitoylphosphatidylcholine (DPPC) and its mixtures with cholesterol and dimethyldioctadecyltrimethylammonium bromide (DDAB) and with phosphatidylinositol (PI) respectively covering a range of composition from 0 to 19 mole % DDAB and PI. The adsorption of liposomal lipid from the liposome dispersion onto particles of silica and titanium dioxide in suspension has been studied as a function of liposome composition and concentration. The adsorption isotherms have been fitted using a Langmuir equation from which the binding constants and maximum surface coverage were obtained. The Gibbs energies of adsorption for the cationic liposomes were on average -61.0 +/- 2.1 kJ mol(-1) (on silica) and -50.6 +/- 2.9 kJ mol(-1) (on titanium dioxide). On average saturation adsorption is equivalent to 3 to 10 lipid monolayers on silica and 3 to 7 on titanium dioxide. Using liposomes encapsulating D-glucose it is demonstrated that there is almost no release of glucose on adsorption of the lipid, indicating that the liposomes are adsorbed intact to form a liposome monolayer on the particle surfaces. Adsorption of intact liposomes to form a close-packed liposome monolayer of solid supported vesicles (SSV) is shown to be equivalent to on average 7.0 +/- 0.2 phospholipid monolayers. The SSVs are shown to have increased stability to disruption by surfactants and when carrying the oil-soluble bactericide, Triclosan(TM), to be capable of inhibiting the growth of oral bacteria from immobilised biofilms.