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We demonstrate the adsorption of nanoparticles (NPs) with charged patches onto a binary vesicle encompassing polar neutral and polar zwitterionic lipids via an implicit solvent coarse-grained model and molecular dynamics simulations. Our investigations on the interactions between NPs and a binary vesicle demonstrate that the adsorption of charged NPs onto a binary vesicle surface can induce structural reorganization of the lipid bilayer. The approach of the NP to the vesicle surface is accompanied by spatial reorganization of the zwitterionic lipids, and the degree of reorganization is found to depend on the NP patch size. Interfacial adsorption of the NP is observed to promote a group of zwitterionic lipids to cluster at the adsorption site. Spatial reorganization of the zwitterionic lipids is activated by favorable electrostatic interactions with the NP and not between the lipids. The favorable electrostatic interaction between oppositely charged lipid headgroup moieties increases and assists the clustering process as the NP approaches the vesicle surface. In addition, the availability of zwitterionic lipids in the vesicle affects the adsorption dynamics of multiple NPs. Our results can be used for the design of reconfigurable biomaterials for applications in drug delivery, sensing, and imaging. [ABSTRACT FROM AUTHOR]

The dissipative particle dynamics (DPD) simulation technique is a coarse-grained (CG) molecular dynamics-based approach that can effectively capture the hydrodynamics of complex systems while retaining essential information about the structural properties of the molecular species. An advantageous feature of DPD is that it utilizes soft repulsive interactions between the beads, which are CG representation of groups of atoms or molecules. In this study, we used the DPD simulation technique to study the aggregation characteristics of ABA triblock copolymers in aqueous medium. Pluronic polymers (PEG-PPO-PEG) were modeled as two segments of hydrophilic beads and one segment of hydrophobic beads. Tyrosine-derived PEG5K-b-oligo(desaminotyrosyl tyrosine octyl ester-suberate)-b-PEG5K (PEG5K-oligo(DTO-SA)-PEG5K) block copolymers possess alternate rigid and flexible components along the hydrophobic oligo(DTO-SA) chain, and were modeled as two segments of hydrophilic beads and one segment of hydrophobic, alternate soft and hard beads. The formation, structure, and morphology of the initial aggregation of the polymer molecules in aqueous medium were investigated by following the aggregation dynamics. The dimensions of the aggregates predicted by the computational approach were in good agreement with corresponding results from experiments, for the Pluronic and PEG5K-oligo(DTO-SA)-PEG5K block copolymers. In addition, DPD simulations were utilized to determine the critical aggregation concentration (CAC), which was compared with corresponding results from an experimental approach. For Pluronic polymers F68, F88, F108, and F127, the computational results agreed well with experimental measurements of the CAC measurements. For PEG5K-b-oligo(DTO-SA)-b-PEG5K block polymers, the complexity in polymer structure made it difficult to directly determine their CAC values via the CG scheme. Therefore, we determined CAC values of a series of triblock copolymers with 3-8 DTO-SA units using DPD simulations, and used these results to predict the CAC values of triblock copolymers with higher molecular weights by extrapolation. In parallel, a PEG5K-b-oligo(DTO-SA)-b-PEG5K block copolymer was synthesized, and the CAC value was determined experimentally using the pyrene method. The experimental CAC value agreed well with the CAC value predicted by simulation. These results validate our CG models, and demonstrate an avenue to simulate and predict aggregation characteristics of ABA amphiphilic triblock copolymers with complex structures. [ABSTRACT FROM AUTHOR]

Viaimplicit solvent molecular dynamics simulations, we demonstrate theself-assembly of stable single and binary vesicles composed of two-tailphospholipid molecules. The amphiphilic lipid molecules are composedof a hydrophilic headgroup and two hydrophobic tails and are representedby a reduced coarse-grained model which effectively captures the keychemical and geometric attributes of phospholipid molecules. We reportour measurements of the bilayer thickness to be consistent with experimentalvalues reported in the literature. We have probed the role of temperatureon the physical properties of single component lipid vesicles andfound our results to concur with experimental results. Our investigationson the phase segregation in binary vesicles demonstrate that the degreeof distinction between the tail groups of the lipid species can beused to tune their phase segregation in the vesicle bilayer. Finally,our measurements of the scaling exponents for macroscopically phase-segregatedsystems have been found to be in good agreement with theoretical andsimulation studies. Our results can be used for the design of responsivebiomaterials for applications in drug delivery, sensing, and imaging. [ABSTRACT FROM AUTHOR]

We design sterically stable biocompatible vehicles with tunable shapes through the self-assembly of a binary mixture composed of amphiphilic molecular species, such as PEGylated lipids, and phospholipids under volumetric confinement. We use a molecular dynamics-based mesoscopic simulation technique called dissipative particle dynamics to resolve the aggregation dynamics, structure, and morphology of the hybrid aggregate. We examine the effect of confinement on the growth dynamics and shape of the hybrid aggregate, and demonstrate the formation of different morphologies, such as oblate and prolate shaped vesicles and bicelles. We perform these investigations by varying the degree of nanoscale confinement, for different relative concentrations of the species and the length of the functional groups. Results from our investigations can be used for the design and prediction of novel hybrid soft materials for applications requiring the encapsulation of therapeutic agents in micro- or nanofluidic channels.