The metastable phases as modulators of biophysical behavior of liposomal membranes
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In this work, we investigate the alterations of the physicochemical, morphological, and thermotropic characteristics of conventional, stealth, and chimeric DPPC (dipalmitoylphosphatidylcholine) liposomes, caused by the incorporation of PEGylated lipid and block copolymers with different architectures and compositions. 1,2-Dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[Methoxy(Polyethylene glycol)-3000] (DPPE-PEG 3000) is the PEGylated lipid, poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) is the block copolymer, and poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline) (MPOx) is the gradient block copolymer, which are selected for preparing the liposomal systems. Light scattering techniques and differential scanning calorimetry (DSC) were used in order to extract information on the physicochemical/thermodynamic balance of the prepared liposomal systems. The physicochemical characteristics and the morphology via fractal analysis of these chimeric nanoassemblies were found to depend on the composition of the polymeric component, while DPPC liposomes were used for comparison reasons (reference system). The incorporation of polymeric components into liposomes promotes a structural rearrangement of lipid bilayers and affects their behavior, as DSC experiments indicated. The fluidity, the intervesicle interactions and the cooperativity of structural elements of liposomes were also changed significantly by polymer addition. It could be concluded that the different macromolecular architectures of the polymeric guest affect the thermotropic behavior of liposomal membrane by producing new metastable phases, and consequently promote new insights in the field of biophysical concept for designing and developing chimeric advanced drug delivery nano systems (aDDnSs).
KeywordsBlock copolymers Gradient copolymers Chimeric liposomes Differential scanning calorimetry Interdigitation Metastable phase
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