The Interaction of Nanoparticles with Biomimetic Bilayers using Molecular Dynamics Simulations

The self-assembly of nanoparticles (NPs) and amphiphilic macromolecules offers a powerful route to generate functional soft materials with controllable structure and properties. Furthermore, synthetic model membranes can serve as a platform to investigate the passage of NPs across biological membranes (e.g. lung, skin and cell membranes) which will help to address issues of nanotoxicology and assist in the design of functionalised NPs for use in the diagnosis and treatment of disease. The problem is that the relationship between the physiochemical properties of NPs and their interaction with and transport across membranes remains poorly understood. To address this challenge we have investigated the mechanisms by which NPs of varying size and hydrophobicity interact with and cross biomimetic polymer membranes. We have developed a model NP-bilayer system which comprised a coarse-grained poly(ethylene)6-block-poly(ethylene oxide)2 (C12E2) bilayer in water and a generic NP of 1.0, 1.5 or 2.0 nm radii with hydrophilic, hydrophobic or intermediate character (nine different systems in total). In addition, we have carried out free energy studies on each of these trajectories and simulated two-component bilayers with hydrophobic nanoparticles. We show that the hydrophobic nanoparticle can induce a local ordering of amphiphilic structures, and show that it can act as a lineactant between the interfaces of the phase-separated domains. Throughout the study of the surfactant system, we have compared the two free energy methods - the Umbrella Sampling (US) method and Steered Molecular Dynamics (SMD) method with NP/bilayer systems, and compare their accuracy and efficiency