Adhesion and Dimerization of Spherocylindrical Nanoparticles on Tensionless Lipid Bilayers

We present a numerical investigation of the interaction of sphero-cylindrical nanoparticles (SCNPs) with tensionless planar lipid bilayers, using molecular dynamics simulations of an implicit-solvent model. The investigation is performed systematically with respect to the adhesion energy density, ξ, SCNP's diameter D, and aspect ratio α. A single SCNP adheres to the membrane through a parallel mode at weak ξ and through a normal mode at large ξ. The value of ξ, at the transition from the parallel to the normal mode, decreases with increasing D or α, in agreement with theoretical arguments based on the Helfrich Hamiltonian. As ξ is further increased, the SCNP undergoes endocytosis. The value of ξ, at the transition from the normal mode to endocytosis, is independent of α but decreases with increasing D. Similarly, we investigated the modes of adhesion of two SCNPs on tensionless lipid bilayers and found that, when the NPs are placed relatively close to each other initially, the SCNPs dimerize into a sequence of modes including in-plane dimers, V-shape dimers, and tubular dimers, as ξ is increased. Importantly, α is found to play a greater role in the endocytosis of two NPs than a single NP. The stabilities of the different modes are inferred from free energy calculations based on the weighted histogram analysis method and from free energy calculations based on the Helfrich Hamiltonian.