Dissipative Particle Dynamics Simulations Research Articles

Stabilization mechanism of different emulsifiers using dissipative particle dynamic simulation

Understanding the effects of the emulsifiers hydrophobic structure on the interfacial properties and dynamic processes of emulsions is critical for the formation of stable emulsions. In this study, three emulsifiers (OSA-modified starch, Tween 80/Span 80 and lecithin) with different numbers of hydrophobic beads were selected to construct nanoemulsions, and their effects on emulsion properties and oil–water interface behavior were studied by experiment combined dissipative particle dynamics (DPD) simulation method. Experimental results such as particle size, potential, interfacial tension and emulsification index showed significant stability differences among the three nanoemulsions. Using formation process and interfacial tension analyses obtained by DPD simulation, we found that the interfacial characteristics of different emulsifiers were different. The cross-sectional graph and isodensity profiles revealed that of the three emulsifiers, lecithin provided the best protection against curcumin. Based on density and root-mean-square (RMS) analysis, we posit that the number of hydrophobic beads in the emulsifier is the main factor affecting the interfacial behavior of the emulsifier, resulting in stability differences among the three emulsions.

The formation and temperature stability of microemulsion emulsified by polyoxyethylene ether surfactant

The effect of polyoxyethylene chain length on the formation and temperature stability of W/O microemulsion emulsified by polyoxyethylene ether surfactant is investigated by dissipative particle dynamics simulation (DPD) on the mesoscopic level. The results show that W/O microemulsions can be formed by three polyoxyethylene chain length ether nonionic surfactants with decreasing the water-oil ratio equal to increasing the oil phase content. However, W/O microemulsion is most easily formed by diethylene glycol monododecyl ether (H1T2) with the smallest oxyethylene base.The results of temperature stability show that W/O microemulsion emulsified by H1T2 has better stability resistant to high or low temperature. In addition, the interfacial tension of the W/O microemulsion system is the lowest, the end-to-end distance of the surfactant molecule is smallest, and the molecular chain is the most curved at the water-oil interface. The theoretical simulation results can guide the formation of the W/O microemulsion induced by polyoxyethylene ether nonionic surfactant, and provide the guidance for its practical application.

Relationship Between The Co-Continuous Morphology of Immiscible Polymer Blends and the Structure of An In Situ Formed Graft Copolymer.

Suitable compatibilizers are essential to prepare immiscible polymer blends with stable co-continuous morphologies. From the thermodynamic point of view, such compatibilizer should not only reduce the interfacial tension, but also promote the formation of flat interface between different phases. Meanwhile, it must not hinder the coalescence of dispersed phase. Therefore, asymmetric structures are required for those block or graft copolymer compatibilizers. However, from the kinetic point of view, copolymers with asymmetric structures are prone to be dragged out from the interface and form micelles in one phase under the processing conditions, which will lose their compatibilization effects. The balance between such thermodynamic and kinetic factors remains unclear. In this paper, the relationship between the morphology of the compatibilized polystyrene/nylon 6/styrene-maleic anhydride copolymers (PS/PA6/SMA) immiscible polymer blends and the structures of the in-situ formed SMA-g-PA6 graft copolymers as well as the processing conditions are studied. Two kinds of SMA are used as compatibilizers: SMA28 (Mw = 110,000g/mol, MAH content 28wt.%) and SMA11 (Mw = 110,000g/mol, MAH content 11wt.%). After melt blending with PA6 into an internal mixer, the in-situ formed copolymer SMA28-g-PA6 has an average four PA6 side chains grafted on one SMA backbone, while that of SMA11-g-PA6 has only one PA6 side chain. Dissipative particle dynamics (DPD) simulation results indicate that both SMA28-g-PA6 copolymer and PS/PA6/SMA28 blends tend to form co-continuous structure, while SMA11-g-PA6 copolymer and PS/PA6/SMA11 blends form sea-island morphologies. However, these results are confirmed experimentally only at relatively low rotor speed of the internal mixer (60rpm). When the rotor speed of the mixer is higher (105rpm), sea-island morphologies are obtained in PS/PA6/SMA28 blends and co-continuous ones are found in PS/PA6/SMA11 systems. These results indicate that higher shear stress will favor to elongate the minor phase domains and form flat interfaces, which is benefit for the formation of co-continuous morphologies; meanwhile, high shear stress may pull the graft copolymers with asymmetric structures (SMA28-g-PA6) out from the interface of PS and PA6 and induce the formation of sea island morphologies. This article is protected by copyright. All rights reserved.

Ultra/loose nano-filtration polyarylene ether sulfone membranes with reversibly tunable pore size enabled via amine oxide units

Developing a new generation of polymer membranes with switchable pores for multiple separation processes remains challenging due to the lack of materials with reversible and adjustable chemical structures. Herein, amine oxide units were introduced in the chains of poly (arylene ether sulfone) via oxidizing the tertiary amine (TA) in poly (arylene ether sulfone)/amide tertiary amine (PAES/ATA) copolymer, and then served as switches to tune the pores of the prepared membranes. The smart membranes could be reversibly tuned between loose nanofiltration mode with water permeance of 178 L m−2 h−1 bar−1 and dye (e.g., Rhodamine B) rejection of 95%, and ultrafiltration mode, with water permeance of 650 L m−2 h−1 bar−1 and dye rejection of 55%, by cyclic acid-alkali treatment. The mechanism of the switchable pore size was elucidated by dissipative particle dynamics (DPD) simulations, and the results were in good agreement with experimental results. This study provides a novel and facile route to fabricate functional membranes with reversibly tunable and highly efficient filtration performance, which could be applicable to multiple separations.

Hydrodynamic and transport behavior of solid nanoparticles simulated with dissipative particle dynamics

Inertial migration of micro- and nanoparticles flowing through microchannels is commonly used for particle separation, sorting, and focusing on many lab-on-a-chip devices. Computer simulations of inertial migration of nanoparticles by mesoscale simulation methods, such as Dissipative Particle Dynamics (DPD) would be helpful to future experimental development of these lab-on-a-chip devices. However, the conventional DPD approach has a low Schmidt number and its ability to model inertial migration is questioned. In this work, we examine the ability of DPD simulations to investigate the inertial migration of rigid nanoparticles flowing through a slit channel. By varying the exponent and cutoff distance in the weight function of the random and dissipative forces, DPD models with Schmidt number varying between 1 and 370 were examined. We show that solvent penetration into nanoparticles and solvent-induced attraction between nanoparticles can be controlled by choosing appropriate interaction coefficients of the DPD conservative force and that these properties are not influenced by the Schmidt number of the DPD model. On the other hand, hydrodynamic properties and transport behaviour of rigid nanoparticles are influenced by the Schmidt number. With the conventional DPD model, nanoparticles tend to be evenly distributed across the channel and do not remain in steady-state positions during flow. At high Schmidt numbers, the particles migrate to long-lasting steady-state positions located between the channel center and walls, in agreement with known experimental observations. We conclude that to properly simulate inertial migration, modifications to the conventional DPD model that yield a high Schmidt number are required.

Phase separation kinetics of block copolymer melts confined under moving parallel walls: A DPD study

We use dissipative particle dynamics (DPD) simulations to study the effect of shear on domain morphology and kinetics of microphase separating critical diblock copolymer (BCP) bulk melts. The melt is confined within two parallel amorphous solid walls at the top and bottom of the simulation box. The shear is induced by allowing the walls to move in a direction with a specific velocity. We explore the following cases: (i) walls are fixed, (ii) only the top wall moves, (iii) both walls move in the same direction, and (iv) both walls move in opposite directions. After the temperature quench from an uniformly mixed state, we monitor the effect of shear on evolution morphology, scaling behavior, characteristic length scale and growth laws of the evolving system. The characteristic length scale follows typical power-law behavior at early times and saturates at late times when both walls are fixed. The length scale changes significantly with shear rates caused by wall velocities. The usual lamellar morphology, which is not achieved for case 1 within the considered simulation time steps, is noticed much earlier for the nonzero wall velocity cases. Specifically, it is seen much before in case 4 than in the other cases. We find that the shear viscosity decreases (shear-thinning) with shear rate for all the cases at a given coarsening time. Overall, we report the influence rule of shear rates on microphase separation kinetics of BCP melts. This study can provide a scheme to anticipate and design anisotropic microstructures under the application of externally controlled wall shear that may further guide in producing the various composite materials with superior mechanical and physical properties.

Effect of surfactant hydrophobic chain equivalence on the oil-water interface and emulsion stability: A dissipative particle dynamics and experimental study

Gemini surfactants have shown great potential and have become a popular topic of research and are considered a novel alternative to conventional surfactants because of their extraordinary physical and chemical properties. In this study, a series of surfactants with similar structures but different numbers of hydrophobic chains were constructed, and their effects on an oil–water interface were systematically investigated using dissipative particle dynamics (DPD) simulations. The effects of these surfactants on the behavior of the oil–water interface were further analyzed when the surfactant concentrations in the system were the same and when the numbers of hydrophobic chains in the system were the same. The effects of surfactant structure on the stability of the emulsion were further investigated on the basis of an analysis of the effects of the surfactants on the behavior of the oil–water interface. The results showed that Gemini and tri-cationic surfactants transitioned the oil–water interface from a lamellar structure to an emulsion form at lower concentrations compared to conventional single-chain surfactants, (e.g., 39.0% for SC-21, 33.0% for DC-21, and 15.0% for TC-21), but this superiority may be due to the absolute advantage of concentration rather than structural properties. The use of Gemini and tri-cationic surfactants have a positive effect on emulsion stabilization when the surfactant concentrations are the same. However, the use of Gemini and tri-cationic surfactants, which have more complex synthetic routes, is not necessary. The present work provides a theoretical basis for the rational selection of surfactants for emulsion applications.

Dissipative particle dynamics to study asphaltenes and surfactants interactions at the oil–water interface

Heavy oil is an important unconventional oil resource, but its high viscosity and complex composition make them difficult to transport. Heavy oil-in-water emulsion transportation is considered to be one of the most effective methods. Asphaltenes in crude oil is a natural surfactant that is responsible for the stability of the emulsions. It is necessary to better understand the influence of asphaltenes and surfactants on the stability of the oil–water interface during the transportation of heavy oil. Although several studies have been carried out on the properties of asphaltenes at the oil–water interface, the scientific understanding of asphaltenes in reducing the interfacial tension (IFT) is still limited in terms of simulation studies. In this paper, asphaltenes were extracted and characterized, and the molecular structure of asphaltenes was constructed. Dissipative particle dynamics (DPD) simulations are employed to study the distributions and interfacial behaviors of asphaltenes and surfactants in oil–water systems. The coarse-grained model of asphaltenes is constructed from basic structural fragments in the simulations, which is based on the inferred average molecular structure of asphaltenes. The results show that asphaltenes diffuse to the oil–water interface spontaneously and adsorb at the interface to form an interfacial film, which could reduce the IFT. However, the IFT is not controlled by the volume concentration of asphaltenes, but is directly related to the interfacial concentration. The IFT value of the oil–water system decreases by up to approximately 8 mN/m at an asphaltene concentration of 133 mM. In addition, the interfacial film formed by the synergistic adsorption of surfactants and asphaltenes has a tighter configuration, which further reduces the IFT and enhances the stability of emulsions. Moreover, the effect of surfactant head length on IFT of the oil–water interface was investigated in this study. The outcomes from this paper can help for a better understanding of asphaltenes and surfactants in stabilizing the oil–water interface and provide useful information for heavy oil transportation.

The formation and stability of microemulsions formed with organic solvent as inner/outer phases: Insight from DPD simulation

Organic solvents are selected as the inner/outer phases to construct the microemulsion systems can open new areas of application in providing a reaction medium for various organic conversions. O/W and reverse W/O microemulsions are prepared, using four different organic solvents of Benzene, Cyclohexane, Octane and Dodecane and nonionic surfactant Dodecylhexaglycol (C12E6) as a stabilizer by using Dissipative particle dynamics (DPD) simulation method. The oil–water ratio is applied to control the topology of the microemulsions and more importantly achieve the transformation of O/W and reverse W/O microemulsions. For cyclic hydrocarbons, Cyclohexane needs the same ratio to form O/W microemulsions and reverse W/O microemulsions with Benzene though possessing the special π chemical bond. However, the liner hydrocarbon with a short molecular chain of Octane is conducive to form O/W microemulsions and the longer chain of Dodecane is easier to create reverse W/O microemulsions. The interfacial tension and end-to-end distance values are lowest when O/W and reverse W/O microemulsions are formed in the system. The temperature-induced stability results show that O/W microemulsions have the same stability for four organic solvents, but Cyclohexane and Octane present superior strength than Benzene and Dodecane for reverse W/O microemulsions. In addition, the more substantial hydrophobic effect of Cyclohexane and Dodecane promotes better salt-induced stability for O/W microemulsions, interestingly, reverse W/O microemulsions present the same stability for four systems. Our findings are instructive in providing the physical understanding necessary for future progress in research and applications of microemulsions, especially for organic solvents as the oil phase in the field of microreactors.

The effect of changing the molecular structure of the surfactant on the dissolution of lamellar phases

Dissolution processes of surfactants, especially when in the lamellar phase, into water are important for product formulation. Understanding this process at a molecular level will help to enhance product design and control surfactant processes. The main goal of this study is to examine the effect of different lengths of surfactants and the hydrophobic to hydrophilic ratio on the dissolution process of surfactants. To achieve this goal dissipative particle dynamic (DPD) simulations were used. Lamellar equilibrium simulations were carried out for different surfactant chain lengths at 80 vol% with water. The surfactant chains were each run in a simulation box of dimensions 20 × 20 × 20 until equilibrium was reached. The lamellar phase formed for all different surfactant chain lengths and, after the initial equilibrium the surfactant systems were then simulated with a water box for dissolution. The dissolution process was tracked by visual analysis, local concentration analysis, micelle size, and a zonal model to calculate the diffusion parameter.Results show that as the surfactant chain length increased by adding more of the hydrophobic beads, the dissolution process slowed down. Increasing the hydrophilic part of the surfactant speeds up the dissolution process, but the effect of adding more of the hydrophobic part is greater than the effect of adding more of the hydrophilic part on the dissolution process.

Properties of Pluronic F68 and F127 micelles interacting furosemide from coarse-grained molecular simulations as validated by experiments

Understanding properties of the drug delivery nanoparticles is of utmost importance to investigate the properties of the currently used systems and/or to design new drug delivery materials. Therefore, in this work we strive to study particular FDA approved drug delivery materials, namely Pluronics, to understand micellization properties and drug encapsulation behaviour at the molecular-level. Our main approach is to employ molecular simulations, which are confirmed by experiments performed within the scope of this work. To that aim, dissipative particle dynamics (DPD) simulations are employed. We quantify the encapsulation efficiency properties of Pluronics, namely F68 and F127, where furosemide as the drug. The DPD simulations predict the encapsulation efficiency of the F68 system higher than F127 system due to a shorter hydrophobic section. Moreover, the micelle properties of Pluronics are quantified by means of the number of micelles, aggregation number, surface area to volume ratio, micelle sizes; and polymer chain properties such as, chain end-to-end distance, radius of gyration properties. We observe similar number of micelles for both systems and the aggregation numbers are rather higher for the F127 system. Moreover, both systems adopt alike end-to-end distance and radius-of-gyration values, and the micelle sizes agree with the experimental data in literature. Furthermore, the interactions of hydrophilic and hydrophobic groups with furosemide and water are analysed by computing the radial distribution functions. Long-range hydrophobic-furosemide interactions indicate that furosemide beads are mainly located near core/corona interface. In all, our manuscript can be viewed as an attempt to provide insights on the structural and micellization properties of Pluronics by molecular simulations, where the findings can be utilized to guide attempts in designing prospective drug carrier nanoparticles.

A combined experimental and computational study on the interfacial distribution behavior in colloidal particle-surfactant co-stabilized Pickering emulsions

Recently, co-stabilized Pickering emulsion (CPE) that stabilized by colloidal particles and surfactant has received increased research attention, owing to its improved stability and fluid properties comparing with conventional emulsions stabilized by particles or surfactants alone. Herein, the dynamic distribution behavior at multi-scale and the synergistic-competitive interfacial absorption in CPE co-stabilized by Tween20 (Tw20) and zein particles (Zp) were studied by experiment combined simulation method. The experimental studies identified the delicate synergistic-competitive stabilization phenomenon tuned by the molar ratio of Zp and Tw20. Meanwhile, dissipative particle dynamic (DPD) simulation was utilized to reveal the distribution and kinetic motion. Based on the two- and three-dimensional simulation on the formation of CPE, simulation revealed that Zp - Tw20 aggregates were formed when anchoring at the interface. The interfacial adsorption efficiency of Zp was improved at low Tw 20 concentration (0–1.0%wt), Tw20 inhibited the Brownian motion of Zp at the interface and competed them out at high concentrations (1.5–2.0%wt). Zp was departured from the interface 4.5 Å to 10 Å, as Tw20 increased from 1.06% to 5%. The study offers a novel approach to reveal the dynamic distribution behavior of surface active substances during the dynamic formation process of CEP, which will expand our current strategies for interface engineering of emulsions.

Novel multiscale simulations on the membrane formation via hybrid induced phase separation process based on dissipative particle dynamics

A novel simulation methodology, that was based on dissipative particle dynamics (DPD) combined with information from molecular dynamics (MD) and calculations of an extended Maxwell-Stefan (MS) equations, was established to obtain multiscale analysis on the dynamics of hybrid induced phase separation (HIPS), taking polyvinylidene fluoride-diphenyl carbonate/water–ethanol (PVDF-DPC/water–ethanol) system as an example. Firstly, MS equations were derived to describe the heat transfer across the interface between the casting solution and coagulation to get the temperature profiles of the casting solution. Secondly, MD simulations for the PVDF-DPC solution were conducted to acquire bond and angle distributions of the PVDF chains. And compared to the DPD particle distributions, a novel DPD force field to describe the real flexibility of PVDF chains and a coarse-graining mapping between the MD and DPD were developed. Thirdly, based on the quenching time calculated by the MS equations and the DPD time scale, DPD simulations were carried out to demonstrate the dynamics of phase separation and membrane formation for different parts of the polymer solution via HIPS and compared to that via thermally induced phase separation (TIPS). The simulation results indicated that the mass transfer had a decisive effect on the phase separation of polymer solution near the interface and resulted in a highly asymmetric structure with a denser polymer top layer and porous sublayer, and this effect was together decided by the quenching rate and polymer solidification. For the inner parts of the polymer solution, a mainly isotropic structure was formed due to heat transfer. Based on experimental verification and simulation results, it can be known that the multiscale simulation was much closer to reality and can provide deep insights into the membrane formation prepared via the HIPS process.

Tuning the Microstructure of Protein Corona by Nanoparticle Hydrophobicity: A Dissipative Particle Dynamics Study

Although multiple experimental methods have been used to investigate protein corona, however, the microstructure of protein corona on nanoparticles is still unknown. By using dissipative particle dynamics (DPD) simulation, we found that hydrophobic nanoparticles adsorbed more proteins than hydrophilic ones. The distance between hydrophobic nanoparticles and proteins was closer than that between hydrophilic nanoparticles and proteins. Moreover, the distribution of different-sized proteins around nanoparticles was also systematically investigated. These findings provide detailed structural information of protein corona at microscopic level.

Incorporating tertiary amine and thioether in polyarylene sulfide sulfone membranes for multiple separations

Polymers have been widely applied for membrane separations; however, most polymer membranes lack adjustable pores and cannot serve in multiple separations once fabricated. Here, a novel block copolymer, polyarylene sulfide sulfone/amide tertiary amine (PASS/ATA), containing tertiary amine and thioether groups was designed for membrane fabrication as it can be self-assembled into a well-defined, uniform, and continuous pores. Via a facile oxidization procedure, the tertiary amine and thioether groups in the membrane molecular chains were converted into amine oxide and sulfone groups, respectively, which dramatically narrows down the pores of the membranes and greatly improves dye rejection, altering the application of the membranes from ultrafiltration (UF) to nanofiltration (NF). Furthermore, after the thioether units were oxidized into sulfone groups, the solvent resistance of the membranes was greatly increased, ensuring the application of the oxidized membranes in organic solvent nanofiltration (OSN). Dissipative particle dynamics (DPD) simulation was applied to shed insight on the formation mechanisms and transformation processes, as well as to explain the decrease of pore size combined with the enhancement of solvent resistance. As a result, combing tertiary amines with thioether groups in polymer chains endows the membrane with multiple functionalities, allowing for multiple separations including UF, NF, and OSN.

Controlling self-assembling co-polymer coatings of hydrophilic polysaccharide substrates via co-polymer block length ratio

HypothesisThe degree of polymerization of amphiphilic di-block co-polymers, which can be varied with ease in computer simulations, provides a means to control self-assembling di-block co-polymer coatings on hydrophilic substrates. SimulationsWe examine self-assembly of linear amphiphilic di-block co-polymers on hydrophilic surface via dissipative particle dynamics simulations. The system models a glucose based polysaccharide surface on which random co-polymers of styrene and n-butyl acrylate, as the hydrophobic block, and starch, as the hydrophilic block, forms a film. Such setups are common in e.g. hygiene, pharmaceutical, and paper product applications. FindingsVariation of the block length ratio (35 monomers in total) reveals that all examined compositions readily coat the substrate. However, strongly asymmetric block co-polymers with short hydrophobic segments are best in wetting the surface, whereas approximately symmetric composition leads to most stable films with highest internal order and well-defined internal stratification. At intermediate asymmetries, isolated hydrophobic domains form. We map the sensitivity and stability of the assembly response for a large variety of interaction parameters. The reported response persists for a wide polymer mixing interactions range, providing general means to tune surface coating films and their internal structure, including compartmentalization.

Notes on molecular fragmentation and parameter settings for a dissipative particle dynamics study of a C10E4/water mixture with lamellar bilayer formation

The influence of molecular fragmentation and parameter settings on a mesoscopic dissipative particle dynamics (DPD) simulation of lamellar bilayer formation for a C10E4/water mixture is studied. A “bottom-up” decomposition of C10E4 into the smallest fragment molecules (particles) that satisfy chemical intuition leads to convincing simulation results which agree with experimental findings for bilayer formation and thickness. For integration of the equations of motion Shardlow’s S1 scheme proves to be a favorable choice with best overall performance. Increasing the integration time steps above the common setting of 0.04 DPD units leads to increasingly unphysical temperature drifts, but also to increasingly rapid formation of bilayer superstructures without significantly distorted particle distributions up to an integration time step of 0.12. A scaling of the mutual particle–particle repulsions that guide the dynamics has negligible influence within a considerable range of values but exhibits apparent lower thresholds beyond which a simulation fails. Repulsion parameter scaling and molecular particle decomposition show a mutual dependence. For mapping of concentrations to molecule numbers in the simulation box particle volume scaling should be taken into account. A repulsion parameter morphing investigation suggests to not overstretch repulsion parameter accuracy considerations.

Tunable Ordered Nanostructured Phases by Co-assembly of Amphiphilic Polyoxometalates and Pluronic Block Copolymers.

The assembly of polyoxometalate (POM) metal-oxygen clusters into ordered nanostructures is attracting a growing interest for catalytic and sensing applications. However, assembly of ordered nanostructured POMs from solution can be impaired by aggregation, and the structural diversity is poorly understood. Here, we present a time-resolved small-angle X-ray scattering (SAXS) study of the co-assembly in aqueous solutions of amphiphilic organo-functionalized Wells-Dawson-type POMs with a Pluronic block copolymer over a wide concentration range in levitating droplets. SAXS analysis revealed the formation and subsequent transformation with increasing concentration of large vesicles, a lamellar phase, a mixture of two cubic phases that evolved into one dominating cubic phase, and eventually a hexagonal phase formed at concentrations above 110 mM. The structural versatility of co-assembled amphiphilic POMs and Pluronic block copolymers was supported by dissipative particle dynamics simulations and cryo-TEM.

Rheology of Pseudomonas fluorescens biofilms: From experiments to predictive DPD mesoscopic modeling.

Bacterial biofilms mechanically behave as viscoelastic media consisting of micron-sized bacteria cross-linked to a self-produced network of extracellular polymeric substances (EPSs) embedded in water. Structural principles for numerical modeling aim at describing mesoscopic viscoelasticity without losing details on the underlying interactions existing in wide regimes of deformation under hydrodynamic stress. Here, we approach the computational challenge to model bacterial biofilms for predictive mechanics in silico under variable stress conditions. Up-to-date models are not entirely satisfactory due to the plethora of parameters required to make them functioning under the effects of stress. As guided by the structural depiction gained in a previous work with Pseudomonas fluorescens [Jara et al., Front. Microbiol. 11, 588884 (2021)], we propose a mechanical modeling by means of Dissipative Particle Dynamics (DPD), which captures the essentials of topological and compositional interactions between bacterial particles and cross-linked EPS-embedding under imposed shear. The P. fluorescens biofilms have been modeled under mechanical stress mimicking shear stresses as undergone in vitro. The predictive capacity for mechanical features in DPD-simulated biofilms has been investigated by varying the externally imposed field of shear strain at variable amplitude and frequency. The parametric map of essential biofilm ingredients has been explored by making the rheological responses to emerge among conservative mesoscopic interactions and frictional dissipation in the underlying microscale. The proposed coarse grained DPD simulation qualitatively catches the rheology of the P. fluorescens biofilm over several decades of dynamic scaling.

Tuning the Endocytosis of Hybrid Micelles through Spatial Regulation of Cationic Groups.

The ability of nanocarriers to enter tumor cells can be enhanced by positive surface charge. Nonetheless, the relationship between the spatial distributions of cationic groups and the endocytosis and tumor penetration of nanocarriers remains largely elusive. Here, using quaternary ammonium salt (QAS) as a model cationic group, a series of hybrid micelles (HMs) bearing QAS with different spatial distributions were prepared from star-shaped polymers with well-defined molecular architectures. The structural characteristics of HM, such as spatial location of QAS and local poly(ethylene glycol) (PEG) density near QAS, were investigated by both experimental techniques and dissipative particle dynamics (DPD) simulation. We show that the drug carriers with QAS extending to the micellar outer space allows QAS to facilitate cell surface binding with minimized hindrance, resulting in greatly enhanced endocytosis compared with nanocarriers with QAS attached onto the micellar surface or shielded by a PEG corona. This study offers cues for future development of tumor-penetrating drug delivery systems.