The effect of grafted poly(ethylene glycol) on the electrophoretic properties of phospholipid liposomes and their adsorption to bacterial biofilms

Liposomes have been prepared from the phospholipids, dimyristoyl, dipalmitoyl and distearoyl phosphatidylcholine (DMPC, DPPC, DSPC, respectively) containing dimethyldioctadecylammonium bromide (DDAB) or phosphatidylinositol (PI) and variable amounts (0–9 mole%) of dipalmitoylphosphatidylethanolamine bonded to poly(ethylene glycol) [PEG] of molecular mass 2000 (DPPE-PEG-2000). The electrophoretic mobilities of the liposomes and corresponding zeta potentials were found to decrease in magnitude for both cationic (DDAB) and anionic (PI) liposomes with increasing DPPE-PEG-2000 incorporation. The chain length of the major lipids in the liposomes (DMPC, DPPC and DSPC) did not significantly affect the zeta potentials of cationic liposomes but had a small effect on anionic liposomes. The zeta potentials were larger for DMPC–PI liposomes where the acyl chains were in the lamellar liquid crystalline phase. The adsorption of the liposomes to immobilised biofilms of Staphylococcus aureus was found to be represented satisfactorily by the Langmuir isotherm. The affinity of the liposomes for the biofilms was inhibited by pegylation suggesting that the ‘stealth’ property of pegylated liposomes applies to bacterial biofilms. Both the surface coverage and the magnitude of the Gibbs energy of adsorption decrease with the extent of pegylation.