Hydrophobic droplets in amphiphilic bilayers: a coarse-grained mean-field theory study

Abstract

Hydrophobic molecules such as oils and certain drugs can be encapsulated between the two leaflets of an amphiphilic bilayer in both lipid and polymer systems. We investigate the case where the hydrophobic molecules are incompatible with the amphiphile tails and so form droplets. Using a coarse-grained mean-field model (self-consistent field theory, or SCFT), we find that droplets of a wide range of sizes have the same characteristic lens shape, and explain this result in terms of simple capillarity arguments, consistent with the measured variations of surface concentrations of amphiphile in the bilayer and in the monolayers that cover the droplet. We study the effect of the strength χ BO of the repulsion between the hydrophobic liquid and the amphiphile tails on the droplet shape, and find a gradual flattening of the droplet as χ BO is reduced. The droplet remains at least metastable even at very low values of χ BO . This is in contrast to the behavior as the length of the hydrophobic molecules is varied. Specifically, if these molecules are at least as long as the amphiphile tails, increasing their length further is found to have little effect on the droplet shape, while reducing their length below this value quickly causes the droplet to become unstable.

Penetration of polymer-grafted nanoparticles through a lipid bilayer

“…In recent years, SCFT has been extended to study the microphase separation of lipids or the lipid bilayer, the fusion of the lipid bilayer, and the interactions between nanoparticles and lipid bilayers, etc. [36][37][38][39][40][41][42][43][44][45][46][47][48] Although the lipids are described by completely exible Gaussian chains in SCFT, the effective molecular shape and the amphiphilicity of the lipids can be properly considered, and the theoretical results of SCFT agreed well with the experimental results. [36][37][38][39] Here, we will systematically examine the morphological deformation of the polymer-graed nanoparticles and the lipid bilayer as well as the free energy of the system during the penetration of the nanoparticles through a lipid bilayer by varying the chain length and the graing density of the polymers.…”

Lipid Droplets Embedded in a Model Cell Membrane Create a Phospholipid Diffusion Barrier

“…[3,4] Numerical modeling suggests that such lenses could exist in the ER membrane with a size of tens of nanometers. [3,5,6] Upon the continuous production of neutral lipids, they accumulate into the reservoir which leads to a lipid lens growth. Above a certain size, this lipid lens becomes unstable and can lead to a spontaneous budding of the oily reservoir.…”

Can adding oil control domain formation in binary amphiphile bilayers?

“…We have two main reasons for choosing this problem, which also builds on our earlier work on oil droplets in bilayers composed of a single amphiphile species. 25 First, from a practical point of view, we wish to nd whether adding oil could prove to be a viable technique for controlling domain formation and the properties of the bilayer. Our second motivation is more theoretical.…”

“…Domain formation can be controlled by a variety of factors, including the difference in chain length between the two amphiphile species [4,9,16,17], the lateral tension in the bilayer [11,18] and the presence of a third species, such as a protein or peptide [1,[19][20][21][22], cholesterol [4,10,12,20], ionised calcium [23] or a ceramide [24].In this paper, we focus on a system in which two of these factors interact, and use a coarse-grained mean-field model to investigate how adding oil to a bilayer composed of two amphiphiles of different chain lengths affects the structure of the membrane around the boundary between two liquid domains. We have two main reasons for choosing this problem, which also builds on our earlier work on oil droplets in bilayers composed of a single amphiphile species [25]. First, from a practical point of view, we wish to find whether adding oil could prove to be a viable technique for controlling domain formation and the properties of the bilayer.…”

“…In this paper, we focus on a system in which two of these factors interact, and use a coarse-grained mean-field model to investigate how adding oil to a bilayer composed of two amphiphiles of different chain lengths affects the structure of the membrane around the boundary between two liquid domains. We have two main reasons for choosing this problem, which also builds on our earlier work on oil droplets in bilayers composed of a single amphiphile species [25]. First, from a practical point of view, we wish to find whether adding oil could prove to be a viable technique for controlling domain formation and the properties of the bilayer.…”