Hydrophilic nanoparticles stabilising mesophase curvature at low concentration but disrupting mesophase order at higher concentrations

Abstract

Using high pressure small angle X-ray scattering (HP-SAXS), we have studied monoolein (MO) mesophases at 18 wt% hydration in the presence of 10 nm silica nanoparticles (NPs) at NP-lipid number ratios (ν) of 1 × 10(-6), 1 × 10(-5) and 1 × 10(-4) over the pressure range 1-2700 bar and temperature range 20-60 °C. In the absence of the silica NPs, the pressure-temperature (p-T) phase diagram of monoolein exhibited inverse bicontinuous cubic gyroid (Q), lamellar alpha (Lα), and lamellar crystalline (Lc) phases. The addition of the NPs significantly altered the p-T phase diagram, changing the pressure (p) and the temperature (T) at which the transitions between these mesophases occurred. In particular, a strong NP concentration effect on the mesophase behaviour was observed. At low NP concentration, the p-T region pervaded by the Q phase and the Lα-Q mixture increased, and we attribute this behaviour to the NPs forming clusters at the mesophase domain boundaries, encouraging transition to the mesophase with a higher curvature. At high NP concentrations, the Q phase was no longer observed in the p-T phase diagram. Instead, it was dominated by the lamellar (L) phases until the transition to a fluid isotropic (FI) phase at 60 °C at low pressure. We speculate that NPs formed aggregates with a "chain of pearls" structure at the mesophase domain boundaries, hindering transitions to the mesophases with higher curvatures. These observations were supported by small angle neutron scattering (SANS) and scanning electron microscopy (SEM). Our results have implications to nanocomposite materials and nanoparticle cellular entry where the interactions between NPs and organised lipid structures are an important consideration.

Interactions between Mutant Bacterial Lipopolysaccharide (LPS-Ra) Surface Layers: Surface Vesicles, Membrane Fusion, and Effect of Ca2+and Temperature

“…Although the chain-melting effect has been induced by temperature elevation in this study, one could envisage alternative routes to impart similar effects, e.g. by inserting nano-objects of certain size and surface chemistry into the membrane to induce structural disorders [69][70][71][72] .…”

Supported lipid bilayers with encapsulated quantum dots (QDs) via liposome fusion: effect of QD size on bilayer formation and structure

“…High pressure small angle X-ray scattering (HP-SAXS) experiments showed that 10 nm hydrophobic SiO 2 NPs promoted lamellar to inverted hexagonal transitions in phospholipid dioleoyl phosphatidylethanolamine (DOPE) mesophases, 41 whilst 10 nm hydrophilic SiO 2 NPs stabilized monoolein (MO) mesophase curvature at low NP concentrations, but disrupted mesophase order at high NP concentrations. 42 However, our knowledge remains limited regarding the influence of hydrophobic nanoparticles on the formation of SLBs via liposome (or vesicle) fusion. In particular, it is not well understood how the presence of NPs might influence the reorganization and evolution of the structure and morphology of SLBs.…”

“…First, it is comparable to the upper range of those investigated in a number of previous studies, where the strongest effects on NP-membrane interactions number ratios have been observed. 41,42 Secondly, this QD concentration was optimized to give the highest fluorescence intensity. For higher QD concentrations, it became more difficult for extruding liposomes through polycarbonate membranes and QD residues were also observed on the extrusion membranes.…”

Inorganic nanoparticles modify the phase behavior and viscoelastic properties of non-lamellar lipid mesophases

“…This is the case for fatty acids [15,16], photo-switchable molecules [17][18][19], and proteins [20] that can be even crystallized within the lyotropic phase [21,22]. Recently, Briscoe et al [23,24] investigated the effects of hydrophobic silica NPs on dioleoyl-phopshatidylethanolamine mesophases, highlighting a temperature and pressure-dependent lamellar to hexagonal phase transition. Mezzenga and coauthors studied the inclusion of hydrophilic SPIONs in monolinolein assemblies, observing the structural responsiveness of the lipid-SPION hybrids to static magnetic fields [25,26].…”