Lipid Membrane-Nanoparticles Interactions

The interactions between lipid membrane and nanosized particles are associated with the issues of nanoparticle toxicity, targeted drug delivery, endocytosis/ exocytosis and more. The charge-dipole interaction between nanoparticles and the zwitterionic headgroups of lipids is found to drive charged nanoparticles to adsorb onto liposome membrane surface and stabilize the liposomes against fusion. In this study, I found that the geometry of the P--N+ dipolar headgroup determines that cationic nanoparticles interact with lipid membrane more weakly than anionic ones, which is crucial to stabilize liposomes at the concentrations approaching their close random packing density. In the case when nanoparticles are only encapsulated inside liposomes, cationic nanoparticles induce large membrane fluctuation and gradual shape instability of an originally spherical giant unilamellar liposome, while anionic ones do not.

Heterogeneous Dynamics of Liposomes in Dense Suspensions

In this study, we investigate the dynamics of fluorescently labeled liposomes or hard-sphere particles embedded in a unique soft glassy material: dense liposome suspension. Liposomes are formed by self-assembly of amphiphilic lipid molecules in aqueous solution. The dense suspension is a mixture of liposomes with zero net charge and positively charged small nanoparticles adsorbed on the liposome surfaces due to the charge-dipole attraction between the nanoparticles and lipids’ dipolar headgroups. Our previous studies have suggested that it is a system with long-range electrostatic repulsion and short-range attraction due to small nanoparticle “bridging”. Using fluorescence microscopy and single-particle tracking, we found that both liposomes and hard-sphere nanoparticles show heterogeneous dynamics possibly due to the percolating formation of clusters.