Charged nanoparticle induced pattern formation and dynamic re-organisation on model biomembranes

Nanoparticles-both natural and engineered-are ubiquitous in their interactions with cells and especially their membranes. Beneficial aspects of such interactions range from targeted drug delivery to imaging applications while the major concern in terms of the potential hazards of such interactions is to understand their cytotoxic effects. It is well documented that of the various classes of nanoparticles, charged nanoparticles, especially cationic, have a significantly higher penetrating capability of cell membranes and in most cases also lead to enhanced cytotoxicity. However, a microscopic physical understanding of the mechanism of interaction, membrane re-organization and penetration by such charged nanoparticles is absent. Recently, we have initiated a concerted effort towards achieving this goal by studying various classes of charged nanoparticles interacting with model lipid bilayer membranes of varied composition using various real and reciprocal space high-resolution techniques as well as atomistic molecular dynamics simulations. In this article, we describe the process of membrane re-organization and pattern formation due to interaction of charged polymer capped quantum dots and dendrimers with single component lipid bilayer membranes. The size of the nanoparticles, as well as their concentration, determines the nature of membrane re-organization and shape of these patterns formed. Depending on the nanoparticle size, smaller particles generate membrane-bound disc like complexes whereas comparatively larger particles drive the formation of loosely bound aggregates ranging from discs to tubules. Diffusion studies on these structures suggest the presence of fluidized aggregates in the former case whereas fluidized membrane surround these structures in case of the latter. A consequence of this membrane re-organization is reflected through calcein leakage experiments. Understanding of these processes would go a long way in delineating the pathways for cytotoxicity or their efficacy in drug delivery and imaging applications.