Effect of lipopolymer (DSPE-PEG750) on phospholipid monolayers and bilayers differing in the structure of the polar head group

Abstract

Phospholipid liposomes are the most popular kind of vesicles used in drug delivery due to their high biocompatibility with biomembranes. However, this type of liposomes show some limitations related with their short half-life in bloodstream. This problem can be resolved by the coating of their surface with the application of PEG molecules which form steric and entropic barrier, avoiding recognition of encapsulated liposomes by the reticuloendothelial system (RES). Such modification of liposomes significantly affects the physicochemical characteristics of PEGylated liposomes, which is related to the intermolecular interactions between the lipopolymer molecules and the phospholipid that builds the liposome membrane. In our work we investigated the influence of the PEG-ylated lipid (DSPE-PEG750) on physicochemical properties of phospholipid monolayers and bilayers with different structure of the polar group (DPPC, DPPE, DPPS). The phospholipid monolayers were examined with the application of Langmuir monolayer technique and Brewster angle microscopy (BAM) as well as grazing incidence x-ray diffraction (GIXD). The studies performed on phospholipid bilayer systems were related to dynamic light scattering and zeta potential measurements and the experiments with the calcein release and steady-state fluorescence anisotropy of DPH. The obtained results showed that the type of polar group of phospholipid as well as the addition of PEG-ylated lipid significantly changes the molecular organization of phospholipid monolayers. Moreover, these parameters also influence the properties of phospholipid bilayers such as size, surface charge, stability and permeability.