Free energy of adhesion of lipid bilayers on titania surfaces.

M Schneemilch,N Quirke

doi:10.1063/1.5120810

Abstract

The adhesion strength between a flexible membrane and a solid substrate (formally the free energy of adhesion per unit area) is difficult to determine experimentally, yet is a key parameter in determining the extent of the wrapping of a particle by the membrane. Here, we present molecular dynamics simulations designed to estimate this quantity between dimyristoylphosphatidylcholine (DMPC) bilayers and a range of low-energy titanium dioxide cleavage planes for both anatase and rutile polymorphs. The average adhesion strength across the cleavage planes for rutile and anatase is relatively weak ∼-2.0 ± 0.4 mN m-1. However, rutile has two surfaces (100 and 101) displaying relatively strong adhesion (-4 mN m-1), while anatase has only one (110). This suggests a slightly greater tendency for bilayers to wrap rutile particles compared to anatase particles but both would wrap less than amorphous silica. We also estimate the adsorption free energies of isolated DMPC lipids and find that only the rutile 101 surface shows significant adsorption. In addition, we estimate the adhesion enthalpies and infer that the entropic contribution to the adhesion free energy drives adhesion on the rutile surfaces and opposes adhesion on the anatase surfaces.

Highlights

The interaction of inorganic surfaces with biological tissue is of interest in medicine and in toxicology
There has been a rapid increase in the number and variety of engineered nanoparticles in the environment,6 for example, those arising from the use of batteries, catalysts, chemical coatings and paints, packaging, electronic devices, implants, biomedicines, food additives, and cosmetics
All titania surfaces exhibited a large degree of hydrophilicity as reflected in the uniformly exothermic heats of immersion, which were an order of magnitude greater than the silica surfaces studied previously

Summary

Introduction

The interaction of inorganic surfaces with biological tissue is of interest in medicine and in toxicology. The effects of exposure to finely divided inorganic materials in the form of nanoparticles are of great concern as their toxicological properties are uncertain, even for naturally occurring minerals such as silica and titania. There has been a rapid increase in the number and variety of engineered nanoparticles in the environment, for example, those arising from the use of batteries, catalysts, chemical coatings and paints, packaging, electronic devices, implants, biomedicines, food additives, and cosmetics.. Our research is focused on the interaction of nanoparticles with cytoplasmic membranes with a view to assessing the likely damage due to nanoparticles at the cellular level.. To help identify the essential features of such interactions, we first study much simpler “model” membranes such as lipid vesicles. Our research is focused on the interaction of nanoparticles with cytoplasmic membranes with a view to assessing the likely damage due to nanoparticles at the cellular level. To help identify the essential features of such interactions, we first study much simpler “model” membranes such as lipid vesicles.

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Conclusion