Free energy of adhesion of lipid bilayers on silica surfaces

M Schneemilch,N Quirke

doi:10.1063/1.5028557

Abstract

The free energy of adhesion per unit area (hereafter referred to as the adhesion strength) of lipid arrays on surfaces is a key parameter that determines the nature of the interaction between materials and biological systems. Here we report classical molecular simulations of water and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayers at model silica surfaces with a range of silanol densities and structures. We employ a novel technique that enables us to estimate the adhesion strength of supported lipid bilayers in the presence of water. We find that silanols on the silica surface form hydrogen bonds with water molecules and that the water immersion enthalpy for all surfaces varies linearly with the surface density of these hydrogen bonds. The adhesion strength of lipid bilayers is a linear function of the surface density of hydrogen bonds formed between silanols and the lipid molecules on crystalline surfaces. Approximately 20% of isolated silanols form such bonds but more than 99% of mutually interacting geminal silanols do not engage in hydrogen bonding with water. On amorphous silica, the bilayer displays much stronger adhesion than expected from the crystalline surface data. We discuss the implications of these results for nanoparticle toxicity.

Highlights

The interaction of cell membranes with inorganic surfaces is of interest in medicine and in toxicology
We introduced a method for determining the adhesion strength of lipid bilayers on surfaces in the presence of water from molecular simulation21 and demonstrated its application with a study of DMPC bilayer adhesion to a model gold surface
This paper details the study of four model silica surfaces: (1) a fully hydroxylated crystalline α-quartz (100) surface (Q2) featuring geminal silanols, (2) a fully hydroxylated crystalline α-cristobalite (101 ̄) surface (Q3) featuring isolated silanols, (3) a fully hydroxylated amorphous α-cristobalite (101 ̄) surface (Q3a) featuring a mixture of isolated and vicinal silanols, and (4) a fully dehydroxylated amorphous α-cristobalite (101 ̄) surface (Q4) without silanols

Summary

Introduction

The interaction of cell membranes with inorganic surfaces is of interest in medicine and in toxicology. Inorganic materials are used in implants and in finely divided form (nanoparticles) as nanomedicines or magnetic resonance imaging (MRI) contrast agents.. Inorganic engineered nanoparticles (ENMs) are increasingly found in the environment. They are present in batteries, catalysts, chemical coatings, packaging, electronic devices, and cosmetics.. The expanding production of ENMs has led to serious concerns regarding their impact on human health and the environment in general.. Most recently the focus of research has been on the interaction of nanoparticles with cytoplasmic membranes with a view to assessing likely damage due to nanoparticles at the cellular level.. They are present in batteries, catalysts, chemical coatings, packaging, electronic devices, and cosmetics. The expanding production of ENMs has led to serious concerns regarding their impact on human health and the environment in general. Most recently the focus of research has been on the interaction of nanoparticles with cytoplasmic membranes with a view to assessing likely damage due to nanoparticles at the cellular level. At the same time, there is interest in experiments on model membranes comprising lipid vesicles with the goal of understanding the factors that control particle uptake in these much simpler systems.

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