Molecular insights into the uptake of SiO2 nanoparticles on phospholipid membrane: Effect of surface properties and particle size.

Silica (SiO2) nanoparticles (NPs) have attracted much attention due to the potential for a wide range of applications and they have been confirmed to be hazardous to humans. Partitioning to phospholipid bilayers is an important way for their bioaccumulation. However, the detailed mechanism of SiO2 NPs uptake by membrane phospholipids remains uncertain. In this work, molecular dynamics (MD) simulations were employed to study the uptake process of SiO2 NPs into DPPC bilayers. Results show that these SiO2 NPs uptake onto DPPC bilayer surface is favorable from the viewpoint of thermodynamics. During the uptake process, the SiO2 NP needed to adjust the angle of interaction with the DPPC surface until the most stable adsorption configuration was reached. After incorporating into DPPC bilayers, the interaction between PO4- group and SiO2 particle is stronger than -N+(CH3)3 group and SiO2. Small SiO2 NP was found to adsorb to the surface of DPPC bilayer without disturbing the morphology or membrane. In contract, bioaccumulation of large SiO2 NP to DPPC induced a strong local membrane deformation. In addition, the effect of SiO2 NP surface functionalization on its interaction with DPPC was also investigated. This molecular-level study reports a complete description of the interaction between SiO2 NPs and DPPC bilayer, aiming to provide some insights for the further work on the bioaccumulation and hemolytic activity of SiO2 NPs.