Abstract
We investigated the effect of surface grafted polyethylene glycol (PEG) in the presence of free PEG on leakage and fusion of small unilamellar vesicles. High concentrations of free PEG (MW 2000) caused leakage and fusion of small unilamellar vesicles. Addition of distearoyl phosphatidylethanolamine-polyethylene glycol (DSPE-PEG), a lipid containing a covalently bonded PEG at the headgroup, to the membrane forming solution reduced leakage and fusion induced by free PEG drastically. The inhibitory effect of this surface grafted PEG was a function of the concentration of DSPE-PEG in the lipid mixtures and increased continuously up to 10 mol%, at which leakage or fusion almost vanished. From our studies we concluded that surface grafted PEG acts as a steric barrier inhibiting the close approach of liposomes which is necessary for fusion.
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