In the framework of a recently developed scheme for a hybrid particle-field simulation technique where self-consistent field theory (SCF) and molecular dynamics (MD) are combined [ J. Chem. Phys. 2009 , 130 , 214106 ], specific coarse-grained models for phospholipids and water have been developed. We optimized the model parameters, which are necessary in evaluating the interactions between the particles and the density fields, so that the coarse-grained model can reproduce the structural properties of the reference particle-particle simulations. The development of these specific coarse-grained models suitable for hybrid particle-field simulations opens the way toward simulations of large-scale systems employing models with chemical specificity, especially for biological systems.

The parallel implementation of a recently developed hybrid scheme for molecular dynamics (MD) simulations (Milano and Kawakatsu, J Chem Phys 2009, 130, 214106) where selfconsistent field theory (SCF) and particle models are combined is described. Because of the peculiar formulation of the hybrid method, considering single particles interacting with density fields, the most computationally expensive part of the hybrid particle-field MD simulation can be efficiently parallelized using a straightforward particle decomposition algorithm. Benchmarks of simulations, including comparisons of serial MD and MD-SCF program profiles, serial MD-SCF and parallel MD-SCF program profiles, and parallel benchmarks compared with efficient MD program GROMACS 4.5.4 are tested and reported. The results of benchmarks indicate that the proposed parallelization scheme is very efficient and opens the way to molecular simulations of large scale systems with reasonable computational costs.

In this paper, we present a computational model of the adsorption and percolation mechanism of poloxamers (poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymers) across a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayer. A coarse-grained model was used to cope with the long time scale of the percolation process. The simulations have provided details of the interaction mechanism of Pluronics with lipid bilayer. In particular, the results have shown that polymer chains containing a PPO block with a length comparable to the DMPC bilayer thickness, such as P85, tends to percolate across the lipid bilayer. On the contrary, Pluronics with a shorter PPO chain, such as L64 and F38, insert partially into the membrane with the PPO block part while the PEO blocks remain in water on one side of the lipid bilayer. The percolation of the polymers into the lipid tail groups reduces the membrane thickness and increases the area per lipid. These effects are more evident for P85 than L64 or F38. Our findings are qualitatively in good agreement with published small-angle X-ray scattering experiments that have evidenced a thinning effect of Pluronics on the lipid bilayer as well as the role of the length of the PPO block on the permeation process of the polymer through the lipid bilayer. Our theoretical results complement the experimental data with a detailed structural and dynamic model of poloxamers at the interface and inside the lipid bilayer.

5Pluronics based formulations are among the most successful nanomedicines and block-copolymer micelles including drugs are undergoing phase I/II studies as anticancer agents. Using coarse-grained models, molecular dynamics simulations of large-scale systems, modeling Pluronic micelles interacting with DPPC lipid bilayers, on the µs timescale have been performed. Simulations show, in agreement with experiments, a release of Pluronic chains from the micelle to the bilayer. This release changes the size of 10 the micelle. Moreover, the presence of drug molecules inside the core of the micelle has a strong influence on this process. The picture emerging from the simulations is that the micelle stability is a result of an interplay between drug/micelle core and block-copolymer/bilayer interactions. The equilibrium size of the drug vector shows a strong dependency on the hydrophobicity of the drug molecules embedded into the core of the micelle. In particular, the radius of the micelle shows an abrupt increase in a very 15 narrow range of drug molecule hydrophobicity.