Molecular Dynamics study of the effect of graphene on lipid bilayers

Abstract

The interaction of graphene-based materials with cells has recently become an important field of study. Its relevance lies on the demonstrated graphene toxicity for the human beings. In this project, the graphene effect on lipid vesicles (the simplest model of cell membrane) is studied by means of coarse-grained Molecular Dynamics. Different simulations have been performed in order to track the evolution path between both graphene and graphene oxide with an interacting vesicle. Moreover, POPC and cholesterol are chosen to compose the vesicle. Three different variables have been taken into account: oxidation degree, size, and relative orientation of the graphene sheet. First, two different graphene oxidation states have been considered (0% and 20%). For each of those, both large and small graphene sheet sizes have been built. These four specific graphene sheets have been placed in four relative orientations with respect to the lipid vesicle, labelled as corner, edge, face, and inside initial positions. This set of initial conditions appears to affect the system evolution path, registering 6 different outcomes out of 16 simulations. Analysis of the MD results reveals useful information about the effects of graphene size,oxidation and orientation and it also helps to register some synergies between them. For example, the relative orientation effect appears to determine the final system configuration in larger graphene sheets. In turn, it does not appear to be relevant in the small-sized cases. On the other hand, the relative oxidation seems affect in the evolution path independently of the size. Moreover, the vesicle curvature effect has been also noticed by comparing the lasting final state of some graphene-lipid vesicle simulations with respect to considering a planar lipid bilayer. Finally, a graphene-mediated vesicle fusion is registered on placing two identical vesicles in direct contact with a large graphene sheet.