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Phosphatidyl-choline liposomes can be PEGylated by post-insertion technique.It avoids the hindrance of the aqueous compartments elicited by the PEG moieties.The concentration of cholesterol is proportional to the retention of PEG-derivative.A plateau of insertion is obtained at a concentration of PEG-derivative ≥10% w/w.The insertion of specific derivatives into pre-formed colloidal systems has been shown to be a useful method for modifying their pharmacokinetic characteristics and biodistribution profiles.In this experimental work the effect of the post-insertion of different PEG-derivatives into pre-formed 100-nm liposomes made up of various lipid mixtures (DMPC, DPPC, DOPC, DSPC and cholesterol at different molar ratios) was investigated. The vesicles were incubated with increasing amounts of DSPE-mPEG2000 as sterically stabilized micelles (5, 10 and 15% w/w with respect to the liposomal lipid mixture) in order to favour the insertion of the PEG-lipid into the liposomal bilayer. The colloidal formulations were characterized by photo-correlation spectroscopy; the DSPE-mPEG2000 integrated into the pre-formed liposomes was demonstrated by means of field flow fractionation while the amount of post-inserted compound was quantified using a suitable spectrophotometric assay (I2 assay). Similar investigations have been performed using PEG-derivatives characterized by a different molecular weight.The physico-chemical properties of the various liposomal formulations were influenced by the post-insertion of PEG-derivatives. The lipid mixture made up of saturated phospholipids and cholesterol proved to be the best, post-insertion (P.I.E.).The post-insertion technique may be a suitable approach to be used in personalized (nano)medicine.