Effect of Glucose on the Mobility of Membrane-Adhering Liposomes

Abstract

Enclosed lipid bilayer structures, referred to as liposomes or lipid vesicles, have a wide range of biological functions, such as cellular signaling and membrane trafficking. The efficiency of cellular uptake of liposomes, a key step in many of these functions, is strongly dependent on the contact area between a liposome and a cell membrane, which is governed by the adhesion force w, the membrane bending energy κ, and the osmotic pressure Δp. Herein, we investigate the relationship between these forces and the physicochemical properties of the solvent, namely, the presence of glucose (a nonionic osmolyte). Using fluorescence microscopy, we measure the diffusivity D of small (∼50 nm radius), fluorescently labeled liposomes adhering to a supported lipid bilayer or to the freestanding membrane of a giant (∼10 μm radius) liposome. It is observed that glucose in solution reduces D on the supported membrane, while having negligible effect on D on the freestanding membrane. Using well-known hydrodynamic theory for the diffusivity of membrane inclusions, these observations suggest that glucose enhances the contact area between the small liposomes and the underlying membrane, while not affecting the viscosity of the underlying membrane. In addition, quartz crystal microbalance experiments showed no significant change in the hydrodynamic height of the adsorbed liposomes, upon adding glucose. This observation suggests that instead of osmotic deflation, glucose enhances the contact area via adhesion forces, presumably due to the depletion of the glucose molecules from the intermembrane hydration layer.

Improved Atomic Force Microscopy Stiffness Measurements of Nanoscale Liposomes by Cantilever Tip Shape Evaluation

“…The effect of substrate interaction on lipid membrane stiffness has recently been observed in AFM measurement for supported DPPC lipid bilayers, but not liposomes . Therefore, in the case of liposome flattening being pronounced, the stiffness of a liposome measured by AFM could be different to that of the free-standing analogue owing to the increase in the membrane curvature of the liposome on the substrate as discussed . However, such variations induced by solid substrates were not seen in our AFM measurement (Figure B).…”

“…44 Therefore, in the case of liposome flattening being pronounced, the stiffness of a liposome measured by AFM could be different to that of the free-standing analogue owing to the increase in the membrane curvature of the liposome on the substrate as discussed. 33 However, such variations induced by solid substrates were not seen in our AFM measurement (Figure 2B). To the best of our knowledge, there has been no direct evidence to show the effect of the solid substrate on the stiffness of liposomes measured by AFM.…”

“…Liposome stiffness was determined in 5% w/w aqueous glucose solution (pH 5.3) via the QI mode of the JPK microscope, as described previously. 32 A recent study indicated that glucose molecules contribute to the immobilization of liposomes on a solid substrate, 33 which is conducive to AFM measurement. All the measurements were performed at 25 ± 1 °C, unless noted otherwise.…”

Nanoarchitectonic‐Based Material Platforms for Environmental and Bioprocessing Applications

“…By determining which osmotic pressure condition induced the onset of vesicle deformation, it was possible to determine the membrane bending energy of adsorbed vesicles and the results agreed with literature values (Figure ). The measurement approach was further utilized to understand how glucose affects vesicle‐membrane interactions by increasing the intermembrane contact area while not affecting the height of adsorbed vesicles . Specifically, it was reasoned that there is depletion of glucose molecules from the intermembrane hydration layer, which increases the corresponding adhesion force.…”

Anisotropic Particle Deposition Kinetics from Quartz Crystal Microbalance Measurements: Beyond the Sphere Paradigm

“…In comparison to these techniques, the widely used quartz crystal microbalance (QCM) method exhibits pronounced advantages, enabling sensitive, in situ measurements of deposition/desorption kinetics under flow conditions for particle size ranging from nanometers − to a few micrometers. , However, these investigations were mainly focused on spherical particles, with only a few studies performed for anisotropic particles. In refs − , the deposition of liposomes was investigated and theoretically interpreted in terms of lattice Boltzmann numerical modeling. It was predicted that the absolute value of the negative frequency shift decreased with the coverage and axis ratio of the liposomes modeled as oblate spheroids with the size of 78 nm.…”