In targeted drug delivery systems, nanoparticle carriers are often functionalized with polyethylene glycol (PEG) polymers to improve solubility and in-vivo stability in biological media. Gold nanoparticles decorated with ligands are excellent candidates in particular for delivery of therapeutic agents. This is due to their distinctive physical and chemical characteristics, which include the ability to be synthesized in a wide range of shapes and ease of functionalization of the nanoparticle surface. In this study, we have carried out a series of coarse-grained molecular dynamics simulations to investigate the permeation of polyethylene oxide (methyl-terminated PEG or PEO) functionalized gold spherical nanoparticles and nanorods across a protein free phospholipid bilayer membrane. Investigation of permeation of functionalized nanoparticles under various conditions is important because it can aid in developing strategies for using nanoparticle as drug carriers while suppressing cytotoxic effects as they permeate cell membranes in-vivo. Previously we have shown that ligand-coated gold nanoparticle permeation across lipid bilayer membranes induces water and ion penetration as well as incidence of lipid flip flop and lipid displacement.
In our studies we have studied the effect of ion concentration gradients, nanoparticle shapes, nanoparticle permeation velocities, length of PEO ligands, and chain density of grafted PEO ligands on water and ion leakage, lipid flip-flop, and lipid loss from the lipid bilayer membrane. Additionally, the mechanism of penetration of the PEO functionalized nanorods and spherical nanoparticles into the bilayer and the nature of the interactions between the PEO ligands and the lipids of the bilayer are discussed. The results of this work will be of interest to experimentalists who engineer nanoparticles with surface modifications for biomedical applications.