Coverage and Disruption of Phospholipid Membranes by Oxide Nanoparticles

Abstract

We studied the interactions of silica and titanium dioxide nanoparticles with phospholipid membranes and show how electrostatics plays an important role. For this, we systematically varied the charge density of both the membranes by changing their lipid composition and the oxide particles by changing the pH. For the silica nanoparticles, results from our recently presented fluorescence vesicle leakage assay are combined with data on particle adsorption onto supported lipid bilayers obtained by optical reflectometry. Because of the strong tendency of the TiO2 nanoparticles to aggregate, the interaction of these particles with the bilayer was studied only in the leakage assay. Self-consistent field (SCF) modeling was applied to interpret the results on a molecular level. At low charge densities of either the silica nanoparticles or the lipid bilayers, no electrostatic barrier to adsorption exists. However, the adsorption rate and adsorbed amounts drop with increasing (negative) charge densities on particles and membranes because of electric double-layer repulsion, which is confirmed by the effect of the ionic strength. SCF calculations show that charged particles change the structure of lipid bilayers by a reorientation of a fraction of the zwitterionic phosphatidylcholine (PC) headgroups. This explains the affinity of the silica particles for pure PC lipid layers, even at relatively high particle charge densities. Particle adsorption does not always lead to the disruption of the membrane integrity, as is clear from a comparison of the leakage and adsorption data for the silica particles. The attraction should be strong enough, and in line with this, we found that for positively charged TiO2 particles vesicle disruption increases with increasing negative charge density on the membranes. Our results may be extrapolated to a broader range of oxide nanoparticles and ultimately may be used for establishing more accurate nanoparticle toxicity assessments and drug-delivery systems.

Self-limiting aggregation of phospholipid vesicles

“…Vesicle preparation was performed similarly to previous work. 42,43 In short, we mixed phospholipids together in the desired ratio in a round bottom flask, evaporated the chloroform under a stream of nitrogen and dried the lipid film under vacuum for at least 2 h. After drying, the lipids were resuspended in the appropriate buffer to a final lipid concentration (C l E 2.0 Â 10 À2 M) and hydrated for about 1 h in a rotary evaporator (no vacuum, 323 K, 100 rpm). This resulted in multilamellar vesicles.…”

Biophysicochemical Interaction of a Clinical Pulmonary Surfactant with Nanoalumina

“…[11][12] To evaluate the risks of exposure to inhaled nanomaterials, recent studies have been focusing on the interaction of particles with membranes, more specifically on model systems made of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) or DOPC (1,2-dioleoyl-sn-glycero-3phosphocholine) unilamellar vesicles. [13][14][15][16][17][18][19][20] The review of the different interaction potentials between particles and membranes revealed the importance of the interplay between particle/vesicle attraction and bilayer bending energy. 17 For diameters lower than a critical size (order of 10 nm for silica), the particles decorate the outer surface of the membrane, and induce aggregation.…”

Modeling nanoparticle wrapping or translocation in bilayer membranes

“…[9,10,11,12,13,14,15,16]. The levels of detail used to represent the molecules in these models fall roughly in two main categories: high-resolution and low-resolution.…”