Membrane fluidity properties of lipid-coated polylactic acid nanoparticles.

Lipid coating is considered a versatile strategy to equip nanoparticles (NPs) with a biomimetic surface coating, but the membrane properties of these nanoassemblies remain in many cases insufficiently understood. In this work, we apply C-Laurdan generalized polarization (GP) measurements to probe the temperature-dependent polarity of hybrid membranes consisting of a lipid monolayer adsorbed onto a polylactic acid (PLA) polymer core as function of lipid composition and compare the behavior of the lipid coated NPs (LNPs) with that of liposomes assembled from identical lipid mixtures. The LNPs were generated by nanoprecipitation of the polymer in aqueous solutions containing two types of lipid mixtures: (i) cholesterol, dipalmitoylphosphatidylcholine (DPPC), and the ganglioside GM3, as well as (ii) dioleoylphosphatidylcholine (DOPC), DPPC and GM3. LNPs were found to exhibit more distinct and narrower phase transitions than corresponding liposomes and to retain detectable phase transitions even for cholesterol or DOPC concentrations that yielded no detectable transitions in liposomes. These findings together with higher GP values in the case of the LNPs for temperatures above the phase transition temperature indicate a stabilization of the membrane through the polymer core. LNP binding studies to GM3-recognizing cells indicate that differences in the membrane fluidity affect binding avidity in the investigated model system.