Penetration of polymer-grafted nanoparticles through a lipid bilayer

Surface functionalization is an efficient method to modify the properties of nanoparticles for nanomedical and other applications. Here, we investigate the penetration of polymer-grafted nanoparticles through a lipid bilayer using self-consistent field theory. We examine the morphological deformation of the polymer-grafted nanoparticles and the lipid bilayer and the variation of the free energy of the system during the penetration of the nanoparticles grafted by polymers with different chain lengths and densities. It is found that the nanoparticles grafted by long polymers can penetrate through the lipid bilayer more easily. Additionally, with varying the grafting density, we find two different penetration pathways of the polymer-grafted nanoparticles. For the nanoparticle grafted by polymers with low density, the lipid bilayer is curved by the nanoparticle when the nanoparticle is inserted into the bilayer shallowly and then a pore is formed when the nanoparticle is inserted into the bilayer deeply enough; whereas, for the nanoparticle grafted by polymers with high density, the lipid bilayer is not curved before and after the pore formation. We further reveal the underlying mechanism of these two different penetration pathways. The results may yield some theoretical insights into the applications of nanoparticles in nanomedicine.