Binding of Lipopolysaccharide and Cholesterol-Modified Gelatin on Supported Lipid Bilayers: Effect of Bilayer Area Confinement and Bilayer Edge Tension

Domain Sorting in Giant Unilamellar Vesicles Adsorbed on Glass

Giant unilamellar vesicles (GUVs) adsorb to a solid surface and rupture to form a planar bilayer patch. These bilayer patches are used to investigate the properties and functions of biological membranes. Therefore, it is crucial to understand the mechanisms of GUV adsorption. In this study, we investigate the adsorption of phase-separated GUVs on glass using fluorescence microscopy. GUVs containing liquid-ordered (L_o) and liquid-disordered (L_d) phases underwent domain sorting after adsorption. The L_d domain in the unbound region migrated to the highly curved region near the edge of the adsorbed region. Additionally, the L_o phase grew linearly along the edge of the adsorbed region, creating a thin ring-like domain. After the domain sorting event, the GUV ruptured to form a planar bilayer patch with circular-patterned domains in the initially adsorbed area. We found that domain sorting was promoted by increasing the extent of GUV deformation. These results suggest that both the L_d and L_o domains are reorganized for stabilizing the curved bilayer region in adsorbed GUVs.

Mechanochemical Regulation of Cell Adhesion by Incorporation of Synthetic Polymers to Plasma Membranes

Chemical control of cell-cell interactions using synthetic materials is useful for a wide range of biomedical applications. Herein, we report a method to regulate cell adhesion and dispersion by introducing repulsive forces to live cell membranes. To induce repulsion, we tethered amphiphilic polymers, such as cholesterol-modified poly(ethylene glycol) (PEG-CLS), to cell membranes. We found that the repulsive forces introduced by these tethered polymers induced cell detachment from a substrate and allowed cell dispersion in a suspension, modulated the speed of cell migration, and improved the separation of cells from tissues. Our analyses showed that coating the cells with tethered polymers most likely generated two distinct repulsive forces, lateral tension and steric repulsion, on the surface, which were tuned by altering the polymer size and density. We modeled how these two forces are generated in kinetically distinctive manners to explain the various responses of cells to the coating. Collectively, our observations demonstrate mechanochemical regulation of cell adhesion and dispersion by simply adding polymers to cells without genetic manipulation or chemical synthesis in the cells, which may contribute to the optimization of chemical coating strategies to regulate various types of cell-cell interacting systems.

Structure, Formation, and Biological Interactions of Supported Lipid Bilayers (SLB) Incorporating Lipopolysaccharide

Biomimetic membrane systems play a crucial role in the field of biosensor engineering. Over the years, significant progress has been achieved creating artificial membranes by various strategies from vesicle fusion to Langmuir transfer approaches to meet an ever-growing demand for supported lipid bilayers on various substrates such as glass, mica, gold, polymer cushions, and many more. This paper reviews the diversity seen in the preparation of biologically relevant model lipid membranes which includes monolayers and bilayers of phospholipid and other crucial components such as proteins, characterization techniques, changes in the physical properties of the membranes during molecular interactions and the dynamics of the lipid membrane with biologically active molecules with special emphasis on lipopolysaccharides (LPS).

Effect of tetracaine on dynamic reorganization of lipid membranes

To understand the intrinsic influence of a drug on lipid membranes is of critical importance in pharmacological science. Herein, we report fluorescence microscopy analysis of the interaction between the local anesthetic tetracaine (TTC) and planar supported lipid bilayers (SLBs), as model membranes. Our results show that TTC increases lipid chain mobility, destabilizes the SLBs and remarkably induces membrane disruption and solubilization. Upon TTC binding, a local curvature change in the bilayer was observed, which led to the subsequent formation of up to 20-μm-long flexible lipid tubules as well as the formation of micron-size holes. Quantitative analysis revealed that membrane solubilization process can be divided into two distinct different stages as a function of TTC concentration. In the first stage (<800 μM), the bilayer disruption profiles fit well to a Langmuir isotherm, while in the second stage (800 μM-25 mM), TTC solubilizes the membrane in a detergent-like manner. Notably, the onset of membrane solubilization occurred below the critical micelle concentration (cmc) of TTC, indicating a local accumulation of the drug in the membrane. Additionally, cholesterol increases the insertion of TTC into the membrane and thus promotes the solubilization effect of TTC on lipid bilayers. These findings may help to elucidate the possible mechanisms of TTC interaction with lipid membranes, the dose dependent toxicity attributed to local anesthetics, as well as provide valuable information for drug development and modification.

Interaction Mechanisms of Giant Unilamellar Vesicles with Hydrophobic Glass Surfaces and Silicone Oil-Water Interfaces: Adsorption, Deformation, Rupture, Dynamic Shape Changes, Internal Vesicle Formation, and Desorption

Phospholipid monolayers at oil-water interfaces are often obtained via vesicle adsorption. However, the interaction mechanisms of vesicles with these oil-water interfaces remain unclear. Herein, we studied the adsorption of giant unilamellar vesicles (GUVs) of approximately 2-5 μm diameter onto silicone oil-water interfaces and glass surfaces modified with hexamethyldisilazane (HMDS) and octadecyltrimethoxysilane (ODTMS) using fluorescence microscopy. The GUVs exhibited various modes of interaction, adsorbing on the silanized glass surfaces without sizable deformation, whereas GUVs bound to the silicone oil-water interface exhibited large deformation. After adsorption, GUV rupture occurred within 350, 110, and 3 ms on HMDS-modified glass, ODTMS-modified glass, and silicone oil-water interface, respectively. On glass surfaces, GUV rupture was often initiated and proceeded with pore formation near the surface. The monolayer patches formed by GUV rupture on HMDS-modified glass remained for at least 1 h over an area approximately twice of that estimated from the original GUV. On the ODTMS-modified glass and silicone oil surfaces, the monolayer patch structures disappeared in milliseconds owing to lipid diffusion across the interface. When adsorbed on the oil-water interface, the GUVs spontaneously underwent dynamic shape changes, internal vesicle formation, and desorption without rupture. Thus, it can be concluded that these different pathways arose from different lipid-surface affinities.