Pickering emulsion transport in skeletal muscle tissue:A dissipative particle dynamics simulation approach

Lymph node targeting is a commonly used strategy for particulate vaccines,particularly for Pickering emulsions.However,extensive research on the internal delivery mechanisms of these emulsions,especially the complex intercellular interactions of deformable Pickering emulsions,has been surprisingly sparse.This gap in knowledge holds significant potential for enhancing vaccine efficacy.This study aims to address this by summarizing the process of lymph-node-targeting transport and introducing a dissipative particle dynamics simulation method to evaluate the dynamic processes within cell tissue.The transport of Pickering emulsions in skeletal muscle tissue is specifically investigated as a case study.Various factors impacting the transport process are explored,including local cellular tissue environmental factors and the properties of the Pickering emulsion itself.The simulation results primarily demonstrate that an increase in radial repulsive interaction between emulsion particles can decrease the transport efficiency.Additionally,larger intercellular gaps also diminish the transport efficiency of emulsion droplet particles due to the increased motion complexity within the intricate transport space compared to a single channel.This study sheds light on the nuanced interplay between engineered and biological systems influencing the transport dynamics of Pickering emulsions.Such insights hold valuable potential for optimizing transport processes in practical biomedical applications such as drug delivery.Importantly,the desired transport efficiency varies depending on the specific application.For instance,while a more rapid transport might be crucial for lymph-node-targeted drug delivery,certain applications requiring a slower release of active components could benefit from the reduced transport efficiency observed with increased particle repulsion or larger intercellular gaps.

Simulation of nanofluid natural convection based on single-particle hydrodynamics in energy-conserving dissipative particle dynamics(eDPD)

In the present study,the nanofliud natural convection is investigated by the energy-conserving dissipative particle dynamics(eDPD)method,where the nanoparticles are considered at the single-particle level.The thermal expansion coefficientβand the viscosityμof the simulated system containing nanoparticles are calculated and found to be in close alignment with the previous simulation results.The single-particle hydrodynamics in e DPD enables simulations of nanofluid natural convection with higher Rayleigh numbers and greater nanoparticle volume fractions.Additionally,this approach is utilized to simulate the nanoparticle distribution during the enhanced heat transfer process in the nanofluid natural convection.The localized aggregation of nanoparticles enhances the heat transfer performance of the nanofluid under specific Rayleigh numbers and nanoparticles volume fractions.

Charging Properties and Particle Dynamics of Chang’e-5 Lunar Sample in an External Electric Field

Facing the challenges of in-situ utilization of lunar regolith resources,applying an external electric field to manipulate lunar particles has become a promising method for space particle control,which mainly depends on the particle charging properties in the applied electric field.Using the surficial lunar regolith samples brought back from the Moon by the Chang’e-5 mission(CE5 LS),this work successively studied their charging properties,particle dynamics,and their collision damages to aerospace materials under the action of an external electric field in high-vacuum conditions.The results indicated that the charging pro-cess and electrostatic projection of lunar regolith particles under high-vacuum conditions were different from those under atmosphere conditions.The particle diameter range of CE5 LS used in the experiment is 27.7-139.0 lm.For electric field strength of 3-12 kV·cm^(-1),the charge obtained by CE5 LS is 4.8×10^(-15)-4.7×10^(-13) C and the charge-to-mass ratio is 1.2×10^(-5)-6.8×10^(-4) C·kg^(-1).The CE5 LS is easier to be negatively charged in an external electric field.Furthermore,significant damages were observed on the target impact surfaces,indicating severe influences of lunar regolith particles on aerospace materials.Our work contributes to a more comprehensive understanding of physical mechanisms controlling the lunar regolith shielding and utilization,and will inspire broad efforts to develop the lunar in-situ engi-neering solutions.

The Paraffin Crystallization in Emulsified Waxy Crude Oil by Dissipative Particle Dynamics

With the advancement of oilfield extraction technology,since oil-water emulsions in waxy crude oil are prone to be deposited on the pipe wall,increasing the difficulty of crude oil extraction.In this paper,the mesoscopic dissipative particle dynamics method is used to study themechanism of the crystallization and deposition adsorbed on thewall.The results show that in the absence of water molecules,the paraffin molecules near the substrate are deposited on themetallic surface with a horizontalmorphology,while the paraffin molecules close to the fluid side are arranged in a vertical column morphology.In the emulsified system,more water molecules will be absorbed on the metallic substrate than paraffin molecules,which obstructed the direct interaction between paraffin molecules and solid surface.Therefore,the addition of watermolecules hinders the crystallization of wax near the substrate.Perversely,on the fluid side,water molecules promote the formation of paraffin crystallization.The research in this paper reveals the crystallization mechanism of paraffin wax in oil-water emulsions in the pipeline from the microscopic scale,which provides theoretical support for improving the recovery of wax-containing crude oil and enhancing the transport efficiency.

Dissipative Particle Dynamics Simulation of Microscopic Properties in Diblock Copolymer Films

Mean-square bond length, root-mean-square end-to-end distance and gyration radius in diblock copolymer films have been studied by dissipative particle dynamics simulations. Results show evident linear trends of any property separately with the thickness of film, the interaction between particles of different types, the repulsion between particle and boundary, except for the dependence of the variations of mean-square bond length on the thickness of film, which exhibits as a wave trend. What＇s more, the varying trends of mean-square bond length and root-mean-square end-to-end distance can correspond to each other. The density distribution of either component in diblock copolymer film can be controlled and adjusted effectively through its interaction with boundary.

Microphase Separation of Star-diblock Copolymer Films： a Dissipative Particle Dynamics Simulation

The microphase-separating behaviors of two types of star-diblock copolymers （Ax）4（By）4 and （A^Bg）4 in thin films are studied using the simulation technique of dissipative particle dynamics. A variety of ordered mesostructures have been observed and the simulated phase diagrams show obvious symmetries for the （Ax）4（By）a films and asymmetries for the （AxBy）4 films, besides, it is easier for the （Ax）4（By）4 than for the （A^By）4 to carry out microphase separation under the same conditions, which has been recognized in bulk and can be ascribed to the structural difference between the two types of star copolymers. There are some correspondences between the mesostructures formed in the film and those formed in bulk at the same composition fraction. Decreasing the thickness of film and strengthening the A-B repulsion both help the mesostructures enhance the degree of order. Composition fraction dependences of the mean-square radius of gyration in the two types of star copolymer films are almost contrary, which can be attributed to the differences in their respective structures. These findings can provide a guide to designing novel microstructures involving star-diblock copolymers via geometrical confinement.

Two-dimensional non-selfsimilar initial value problem for adhesion particle dynamics

A two-dimensional non-selfsimilar initial value problem for adhesion particle dynamics with two pieces of constant states separated by a circular ring is considered. By using the generalized characteristic method and the generalized Rankine-Hugoniot relation, which is a system of ordinary equations, the global solution which includes delta-shock waves and vacuum is constructed.

Dissipative particle dynamics simulation of flow through periodic arrays of circular micropillar

Flow through arrays of micropillar embedded inside microfluidic chip systems is important for various microfluidic devices. It is critical to accurately predict the mass flow rate through pillar arrays based on the pillar design. This work presents a dissipative particle dynamics （DPD） model to simulate a problem of flow across periodic arrays of circular micropillar and investigates the permeability of two types of micropillar arrays. The flow fields including horizontal and vertical velocity fields, the number density field, and the streamline of the flow are analyzed. The predicted solid volumes by the presented DPD simulation of both types of arrays are quite close to the actual counterparts. These quantitative agreements show usefulness and effectiveness of the DPD model in simulating arrays of micropillar. By comparing two types of micropillar arrangement patterns, we find that the arrangement pattern of micropillar does not have significant influence on the permeability of the array.

Particle dynamics revealed by^(210)Po/^(210)Pb disequilibria around Prydz Bay,the Southern Ocean in summer

Seawater samples were collected around Prydz Bay in summer of 2014,dissolved and particulate^(210)Po and^(210)Pb were measured to reveal the disequilibrium characteristics and particle dynamics.Our results show that the distribution of^(210)Po and^(210)Po/^(210)Pb activity ratio in the upper water is mainly affected by biological absorption or particle adsorption.An abnormal excess of^(210)Po relative to^(210)Pb was observed in the surface water at stations P1-2 and P2-2,which is likely to be the horizontal transport of water mass with high DPo/DPb)_(A.R.)and TPo/TPb)_(A.R.).In this study,the removal of particulate^(210)Po is mainly controlled by the scavenging of dissolved^(210)Po and the two have a linear positive correlation with the salinity,a negative linear correlation with the content of dissolved oxygen and a reciprocal relationship with the content of POC.The export flux of POC at 100 m is estimated to be 1.8-4.4 mmol·m^(−2)·d^(−1)(avg.2.9 mmol·m^(−2)·d^(−1))based on^(210)Po/^(210)Pb disequilibria,with the highest value in the shelf,which is consistent with the distribution of biological productivity.

A note on hydrodynamics from dissipative particle dynamics

We calculate current correlation functions （CCFs） of dissipative particle dy- namics （DPD） and compare them with results of molecular dynamics （MD） and solutions of linearized hydrodynamic equations. In particular, we consider three versions of DPD, the empirical/classical DPD, coarse-grained （CG） DPD with radial-direction interactions only and full （radial, transversal, and rotational） interactions between particles. To fa- cilitate quantitative discussions, we consider specifically a star-polymer melt system at a moderate density. For bonded molecules, it is straightforward to define the CG variables and to further derive CG force fields for DPD within the framework of the Mori-Zwanzig formalism. For both transversal and longitudinal current correlation functions （TCCFs and LCCFs）, we observe that results of MD, DPD, and hydrodynamic solutions agree with each other at the continuum limit. Below the continuum limit to certain length scales, results of MD deviate significantly from hydrodynamic solutions, whereas results of both empirical and CG DPD resemble those of MD. This indicates that the DPD method with Markovian force laws possibly has a larger applicability than the continuum description of a Newtonian fluid. This is worth being explored further to represent gen- eralized hydrodynamics.

A new model for dissipative particle dynamics boundary condition of walls with different wettabilities

The implementation of solid-fluid boundary condition has been a major challenge for dissipative particle dynamics(DPD)method.Current implementations of boundary conditions usually try to approach a uniform density distribution and a velocity profile close to analytical solution.The density oscillations and slip velocity are intentionally eliminated,and different wall properties disappear in the same analytical solution.This paper develops a new wall model that combines image and frozen particles and a new strategy to emphasize different wall properties especially wettabilities.The strategy first studies the realistic wall-fluid system by molecular dynamics(MD)simulation depending on physical parameters.Then,a DPD simulation is used to match the density and velocity profiles with the new wall model.The obtained DPD parameters can simulate the systems with the same wall and fluid materials.With this method,a simulation of the Poiseuille flow of liquid argon with copper walls is presented.Other walls with super-hydrophilic,hydrophilic,and hydrophobic wettabilities are also simulated.The limitations of the analytical solution and the effect of the wall-fluid interaction are discussed.The results show that the method suggested in this paper can simulate the mesoscale behavior of the microchannel flow related to realistic systems.

Effect of shear on the symmetric diblock copolymer/nanorod mixture:A dissipative particle dynamics study

The phase behaviours of a lamellar diblock copolymer/nanorod composite under steady shear are investigated using dissipative particle dynamics. We consider a wide range of nanorod concentrations, where the nanorods each have a preferential affinity to one of the blocks. Our results suggest that shear not only aligns the orientations of the diblock eopolymer templates and nanorods towards flow direction, but also regulates the distribution of the nanorods within the polymer matrix. Meanwhile, the shear-induced reorientation and morphology transitions of the systems also significantly depend on the nanorod concentration. At certain nanorod concentrations, the competitions between shearinduced polymer thinning and nanorods dispersion behaviours determine the phase behaviours of the composites. For high nanorod concentrations, no morphology transition is observed, but reorientation is present, in which the sheared nanorods are arranged into hexagonal packing arrays. Additionally, the orientation behaviour of nanorods is determined directly by the applied shear, also interfered with by the shear-stretched copolymer molecules.

Utilizing ^(234)Th/^(238)U disequilibrium to constrain particle dynamics in hydrothermal plumes in the Southwest Indian Ocean

Metal-enriched minerals have been widely observed near hydrothermal vent fields.However,the dynamics of particulate metals influenced by hydrothermal activities is poorly constrained.Here,radioactive 234Th in both dissolved and particulate phases were used to examine the kinetics of particle-reactive metal adsorption,removal,and residence in a newly found hydrothermal plume over the Southwest Indian Ridge.The results showed a relatively low value on ^(234)Th/^(238)U ratios(i.e.,0.73-0.88)compared to the deep oceans,indicating an enhanced adsorption of particle-reactive metals onto particulate matter in the plume.Based on the 234Th-238U disequilibria,the adsorption and sinking rate constants of 234Th averaged(0.009±0.001)d^(-1) and(0.113±0.024)d^(-1) in the hydrothermal plume,corresponding to the residence times of(115±19)d and(16±5)d for dissolved and particulate 234Th,respectively.This timescale allows vent-discharged particle-reactive metals to disperse hundreds to thousands of miles away.Thus,hydrothermal activities might influence the metal distribution in deep ocean over a very large scope.Also,a high sinking flux of(36.2±5.4)B q/(m^(2)·d)for 234Th was observed for the plume,suggesting an enrichment of metal in particles deposited close to the vent.The enhancement of particle sinking could also benefit the transport of organic carbon and nitrogen and fuel the benthic ecosystems under the plume regimes.Thus,hydrothermal plumes may have an impact on both the elemental geochemistry and/or ecosystem to the deep oceans interior than previous expectation.

Many-body dissipative particle dynamics with energy conservation:temperature-dependent long-term attractive interaction

Heat and mass transfer during the process of liquid droplet dynamic behaviors has attracted much attention in decades.At mesoscopic scale,numerical simulations of liquid droplets motion,such as impacting,sliding,and coalescence,have been widely studied by using the particle-based method named many-body dissipative particle dynamics(MDPD).However,the detailed information on heat transfer needs further description.This paper develops a modified MDPD with energy conservation(MDPDE)by introducing a temperature-dependent long-term attractive interaction.By fitting or deriving the expressions of the strength of the attractive force,the exponent of the weight function in the dissipative force,and the mesoscopic heat friction coefficient about temperature,we calculate the viscosity,self-diffusivity,thermal conductivity,and surface tension,and obtain the Schmidt number Sc,the Prandtl number P r,and the Ohnesorge number Oh for 273 K to 373 K.The simulation data of MDPDE coincide well with the experimental data of water,indicating that our model can be used to simulate the dynamic behaviors of liquid water.Furthermore,we compare the equilibrium contact angle of droplets wetting on solid surfaces with that calculated from three interfacial tensions by MDPDE simulations.The coincident results not only stand for the validation of Young’s equation at mesoscale,but manifest the reliability of our MDPDE model and applicability to the cases with free surfaces.Our model can be extended to study the multiphase flow withcomplex heat and mass transfer.

Dissipative Particle Dynamics Simulations of Domain Growth and Phase Separation in Binary Immiscible Fluids

It was investigated that the domain growth processes of spinodal decomposition with different quenching depth in two and three dimensional binary immiscible fluids by using parallel dissipative particle dynamics simulations. In two dimensions, the dynamic scaling exponent 1/2 for coalescence and 2/3 for inertial regimes in the shallow quench and strong finite size effects in the cases of deep quenching were obtained. In three dimensions, it was used that the diffusive regime with exponent n=l/3 in the shallow quench and the inertial hydrodynamic regime with n=2/3 for different quenches. The viscous effects are not clearly reflected, showing n=1/2 in both shallow and deep quenches in this time period, due to the soft nature of interaction potential adopted in dissipative particle dynamics.

Polymer translocation through nanopore under external electric field:dissipative particle dynamics study

The DNA sequencing technology has achieved a leapfrog development in recent years. As a new generation of the DNA sequencing technology, nanopore sequenc- ing has shown a broad application prospect and attracted vast research interests since it was proposed. In the present study, the dynamics of the electric-driven translocation of a homopolymer through a nanopore is investigated by the dissipative particle dynam- ics （DPD）, in which the homopolymer is modeled as a worm-like chain （WLC）. The DPD simulations show that the polymer chain undergoes conformation changes during the translocation process. The different structures of the polymer in the translocation process, i.e., single-file, double folded, and partially folded, and the induced current block- ades are analyzed. It is found that the current blockades have different magnitudes due to the polymer molecules traversing the pore with different folding conformations. The nanoscale vortices caused by the concentration polarization layers （CPLs） in the vicinity of the sheet are also studied. The results indicate that the translocation of the polymer has the effect of eliminating the vortices in the polyelectrolyte solution. These findings are expected to provide the theoretical guide for improving the nanopore sequencing tech- nique.

Discussions on the correspondence of dissipative particle dynamics and Langevin dynamics at small scales

We investigate the behavior of dissipative particle dynamics （DPD） within different scaling regimes by numerical simulations. The paper extends earlier analytical findings of Ripoll, M., Ernst, M. H., and Espafiol, P. （Large scale and mesoscopic hy- drodynamics for dissipative particle dynamics. Journal of Chemical Physics, 115（15）, 7271-7281 （2001）） by evaluation of numerical data for the particle and collective scaling regimes and the four different subregimes. DPD simulations are performed for a range of dynamic overlapping parameters. Based on analyses of the current auto-correlation functions （CACFs）, we demonstrate that within the particle regime at scales smaller than its force cut-off radius, DPD follows Langevin dynamics. For the collective regime, we show that the small-scale behavior of DPD differs from Langevin dynamics. For the wavenumber-dependent effective shear viscosity, universal scaling regimes are observed in the microscopic and mesoscopic wavenumber ranges over the considered range of dynamic overlapping parameters.

Temperature dependence of microscopic properties in diblock copolymer films:A dissipative particle dynamics simulation

Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length （MSBL） and system temperature can be described as a quadratic curve. The root-mean-square radius of gyration （RMSGR） and end-end distance （RMSED） increase gradually as the temperature rises and composition fraction changes from 0.1 to 0.5, in which the effect of the former is primary. Especially, the relation between RMSGR and temperature is nearly linear in the confinement-introduced direction. Density distribution of each component in the films can be controlled and adjusted effectively by its interaction with other components and boundaries. Moreover, the changes of system temperature and composition fraction can both affect the density distributions to a certain extent.

Stable and accurate schemes for smoothed dissipative particle dynamics

Smoothed dissipative particle dynamics （SDPD） is a mesoscopic particle method that allows to select the level of resolution at which a fluid is simulated. The numerical integration of its equations of motion still suffers from the lack of numerical schemes satisfying all the desired properties such as energy conservation and stability. Similarities between SDPD and dissipative particle dynamics with energy （DPDE） con- servation, which is another coarse-grained model, enable adaptation of recent numerical schemes developed for DPDE to the SDPD setting. In this article, a Metropolis step in the integration of the fluctuation/dissipation part of SDPD is introduced to improve its stability.

Establishing an Initial Electron Beam Model with Monte Carlo Simulation for a Single 6 MV X-ray Medical Linac Based on Particle Dynamics Characteristics

Objective:In this study,we try to establish an initial electron beam model by combining Monte Carlo simulation method with particle dynamic calculation(TRSV)for the single 6 MV X-ray accelerating waveguide of BJ-6 medical linac.Methods and Materials:1.We adapted the treatment head configuration of BJ-6 medical linac made by Beijing Medical Equipment Institute(BMEI)as the radiation system for this study.2.Use particle dynamics calculation code called TRSV to drive out the initial electron beam parameters of the energy spectrum,the spatial intensity distribution,and the beam incidence angle.3.Analyze the 6 MV X-ray beam characteristics of PDDc,OARc in a water phantom by using Monte Carlo simulation(BEAMnrc,DOSXYZnrc)for a preset of the initial electron beam parameters which have been determined by TRSV,do the comparisons of the measured results of PDDm,OARm in a real water phantom,and then use the deviations of calculated and measured results to slightly modify the initial electron beam model back and forth until the deviations meet the error less than 2%.Results:The deviations between the Monte Carlo simulation results of percentage depth doses at PDDc and off-axis ratios OARc and the measured results of PDDm and OARm in a water phantom were within 2%.Conclusion:When doing the Monte Carlo simulation to determine the parameters of an initial electron beam for a particular medical linac like BJ-6,modifying some parameters based on the particle dynamics calculation code would give some more reasonable and more acceptable results.