Interactions of Engineered Silica Nanoparticles with Lipid Monolayers and Bilayers

Abstract

The widespread use of engineered nanomaterials has led to significant interest in studying their interactions with the cell plasma membrane. Mechanistic studies of nanoparticle-membrane interactions have generally used lipid monolayers and lipid vesicles as membrane models. However, it is unclear whether differences in membrane models might affect their interactions with nanoparticles. The current study aimed to elucidate the interactions of engineered silica nanoparticles (105 nm) with lipid monolayers and vesicles in order to provide information on the potential differences between these commonly used models in their interactions with nanomaterials. Lipid monolayers and vesicles, both comprised of equimolar concentrations of sphingomyelin, cholesterol, and dioleoylphosphatidylcholine, were used as membrane models. Silica nanoparticles, surface-modified with hydroxyl, amine, and polyethylene glycol (PEG) with molecular weights of 2K, 5K, and 20K Da, were used as particle model. A Langmuir-Wilhelmy apparatus was used to study nanoparticle effects on lipid monolayer interfacial properties. Atomic force microscopy (AFM) was used to examine nanoparticle effects on lipid topography. Nanoparticle effects on vesicle integrity were monitored using a vesicle leakage assay with carboxylfluorescein (CF) as the fluorescent probe. Nanoparticle effects on lipid monolayers were dependent on particle surface properties. Hydroxyl- and amine-modified nanoparticles did not affect the interfacial properties of lipid monolayers while PEGylated nanoparticles induced a reduction in surface tension. AFM experiments demonstrated that only PEGylated nanoparticles penetrated into the lipid monolayer. Nanoparticles effects on lipid bilayers were different from monolayers. Hydroxyl-, amine-, and PEG 20K-modified nanoparticles disrupted the vesicles, causing significant CF leakage, while PEG 2K- and PEG 5K-modified nanoparticles did not cause vesicle disruption. These results demonstrate that lipid monolayers and vesicles interact differently with engineered nanoparticles, suggesting that it might not be possible to translate the results from one model to another.