Emeritus Professor Hans J. Lyklema and staff member Dr.ir. Mieke Kleijn will be giving talks in the International Conference on Interfaces against Pollution (IAP) in Leeuwarden with the titles "Colloidal models and model colloids" and "Coverage and disruption of phospholipid membranes by oxide nanoparticles".
Abstract for the talk "Coverage and disruption of phospholipid membranes by oxide nanoparticles":
The interaction between nanoparticles and biological membranes has been subject of much research over the past decades, mainly for two reasons. On the one hand, engineered nanoparticles are used in many products, for example cosmetics, tires, coatings and anti-bacterial substances. Since a large part of these particles ends up in the environment, concerns have raised with respect to their possible (cyto)toxicity. On the other hand, nanoparticles may be used as vehicles for drug delivery into cells. In both cases an important question is whether they can enter a living cell, i.e., how do they interact with the cell membrane and can they cross it?
In our studies we focus on the interaction of oxide nanoparticles, in particular silica and titanium dioxide with phospholipid membranes. We show how electrostatics plays an important role in this interaction. For this we systematically varied the charge density of both the lipid membranes by changing their composition, and the oxide particles by changing the pH. Results from our fluorescence vesicle leakage assay  are combined with recent data on particle adsorption onto supported lipid bilayers obtained by optical reflectometry and AFM imaging. Self-consistent field (SCF) modelling  has been applied to interpret the results on a molecular level.
At low particle charge density no barrier for adsorption exists and the adsorption rate is determined by transport kinetics only. Both the adsorption rate and adsorbed amounts drop with increasing (negative) charge densities on particles and membranes (see e.g. Figure 1) due to electric double layer repulsion. This is confirmed by the effect of the ionic strength. SCF calculations show that charged nanoparticles change the structure and dynamics of lipid bilayers by a reorientation of the zwitterionic phosphatidylcholine (PC) head groups. This explains the affinity of the silica particles for PC lipid layers, even at relatively high particle charge densities.
Particle adsorption does not always lead to disruption of the membrane integrity as is clear from comparison of the leakage and adsorption data. Using AFM we can distinguish between particles that penetrated into the bilayer and particles that resided on top of the bilayer, depending on physicochemical conditions.
Our results may be extrapolated to a broader range of oxide nanoparticles and ultimately be used for establishing more accurate nanoparticle toxicity assessments.
- H. Pera, J.M. Kleijn, F.A.M. Leermakers, “Interaction of Silica Nanoparticles with Phospholipid Membranes”, Chem. Lett. 41 (2012) 1322 - 1324.
- H. Pera, J.M. Kleijn, F.A.M. Leermakers, “Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling”, J. Chem. Phys. 2014, accepted.