Polyelectrolyte brushes affect the adsorption kinetics of nanoparticles onto lipid membranes

Abstract

This article explores the adsorption kinetics of positively charged hard and soft silica nanoparticles (NPs) on supported lipid bilayers (SLBs) with an anionic surface charge. The softness of the NPs is adjusted by varying the grafting density of covalently bound Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes. The adsorption process, which is irreversible, can be described by a Langmuir-like adsorption model, where the desorption term is replaced by a term representing repulsive interactions, while the adsorption term is the classical one governed by its rate constant that quantifies how quickly a particle becomes bound to the SLBs. This occurs because further NP adsorption leads to a surface charge conversion that prevents additional particles from covering the SLB interface. NP adsorption is favored by electrostatic attraction and increases the adsorption kinetics. However, the latter decreases with increasing grafting density of the polyelectrolyte layer, ultimately preventing adsorption at a critical grafting density. This results from the interaction between the brush-grafted particle and the supported lipid bilayer depends on the counterion density in the contact area. This reduces the polymer flexibility in the brush, preventing it from making direct contact. Overall, the NP adsorption is favored, but counterions limit the extent of adsorption on a molecular scale, reaching the osmotic limit regime.