Dissipative Particle Dynamics Simulation Results Research Articles

Cell-scale hemolysis evaluation of intervenient ventricular assist device based on dissipative particle dynamics.

Most of the existing hemolysis mechanism studies are carried out on the macro flow scale. They assume that the erythrocyte membranes with different loads will suffer the same damage, which obviously has limitations. Thus, exploring the hemolysis mechanism through the macroscopic flow field information is a tough challenge. In order to further understand the non-physiological shear hemolysis phenomenon at the cell scale, this study used the coarse-grained erythrocytes damage model at the mesoscopic scale based on the transport dissipative particle dynamics (tDPD) method. Combined with computational fluid dynamics the hemolysis of scalarized shear stress () in the clearance of "Impella 5.0" was evaluated under the Lagrange perspective and Euler perspective. The results from the Lagrange perspective showed that the change rate of scaled shear stress () was the most critical factor in damaging RBCs in the rotor region of "Impella 5.0"and other transvalvular micro-axial blood pumps. Then, we propose a dimensionless number with time integration based on to evaluate hemolysis. The Dissipative particle dynamics simulation results are consistent with the evaluation results, so may be an important factor in the hemolysis of VADs. Finally, we tested the hemolysis of 30% hematocrit whole blood in the "Impella 5.0" shroud clearance from the Euler perspective. Relevant results indicate that because of the wall effect, the RBCs near the impeller side are more prone to damage, and most of the cytoplasm is also gathered at the rotor side.

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.

Linear polymer chain diffusion in semi-flexible polymer network: A dissipative particle dynamics study

Linear polymer chains transport in the crowded biological environment is profoundly important to biomedical engineering and nanotechnology. Cytoskeleton, which can be modeled as a semi-flexible polymer network, acts as a barrier when linear polymers diffuse inside the cell. The diffusion of linear polymers with length N in this polymer network is investigated by the dissipative particle dynamics (DPD) in the present study. Rouse theory is applied to analyze the conformational dynamics of the linear polymers based on the numerical results. It is found that the geometric constraint length Na is a crucial parameter to describe the role of the network of the polymer diffusion. Analyses on Rouse modes show that, in a short wavelength regime, the relaxation time obtained in numerical simulation follows the prediction of the Rouse theory. With the increasing wavelength, the linear polymer exhibits a transition from reptation behavior to the spatially homogeneous behavior at critical length scale Na, which is illustrated by different scaling laws dependent on wavelength. Based on the analyses on the Rouse modes and mean square displacements of the linear polymer, we present a non-dimensional conformational dynamics function dependent on time, with which a scaling law is proposed to predict the long time diffusivity of the linear polymer in a semi-flexible polymer network with different mesh sizes. It is shown that the prediction is well consistent with our DPD simulation results.

Additives-directed lyotropic liquid crystals architecture: Simulations and experiments

In this study, alkanes and sucrose esters are employed to investigate the influence of additives on lyotropic liquid crystal architecture. After molecular dynamic simulations and experiment characterization, we showed how the additives control the structure of LLCs. By controlling the polarity of additives, the phase behavior of LLCs can be engineered to form the required structure. Dissipative particle dynamics (DPD) is introduced for simulating the self-assembly of phytantriol (PT), providing intuitionistic images and structure information, which shows that additives with low-polarity complicate the internal structure of liquid crystal systems. Then the ternary phase diagrams of additives, PT, and water are constructed to systematically study the effects of additives on the phase behavior of LLCs. Consistent with DPD simulation results, there is a certain regularity in the effects of additives on the structure of liquid crystals. The difference in the structure of LLCs is due to the variability in the critical packing parameter (CPP) obtained by changing the polarity of additives. Our findings demonstrate that additives polarity is a key factor in LLCs structure, and may pave a promising avenue for novel LLCs development and translation, determining the self-assembly process and the resulting phase of LLCs.

Multiple Particle Manipulation under Dielectrophoresis Effect: Modeling and Experiments.

The dissipative particle dynamics (DPD) technique was employed to design multiple microfluidic devices for investigating the motion of bioparticles at low Reynolds numbers. A DPD in-house FORTRAN code was developed to simulate the trajectories of two microparticles in the presence of hydrodynamic and transverse deflecting force fields via considering interparticle interaction forces. The particle-particle interactions were described by using a simplified version of the Morse potential. The transverse deflecting force considered in this microfluidic application was the dielectrophoresis (DEP) force. Multiple microfluidic devices with different configurations of microelectrodes were numerically designed to investigate the dielectrophoretic behavior of bioparticles for their trajectories and the focusing of bioparticles into a single stream in the middle of the microchannel. The DPD simulation results were verified and validated against previously reported numerical and experimental works in the literature. The computationally designed microdevices were fabricated by employing standard lithographic techniques, and experiments were conducted via taking red blood cells as the representative bioparticles. The experimental results for the trajectories and focusing showed good agreement with the numerical results.

Dissipative particle dynamics simulation of magnetorheological fluids in shear flow

In the present study, the behavior of a magnetorheological fluid (MRF) in shear flow is investigated using dissipative particle dynamics (DPD), a particle-based method. The solid particles in the MRF are modeled by a magnetization model, and Lennard-Jones potential is used to simulate the interaction between the solid and the liquid phases. The columnar structure (chain) of the solid particles along the applied magnetic field direction is modeled that is similar to previous experimental observations. Subsequently, this complex fluid is simulated under shear flow and the velocity profiles depict the “plug region”. The effect of shear rate and area fraction on the rheological properties is investigated by Irving–Kirkwood model. The DPD simulation results indicate a shear-thinning and viscoplastic behavior of MRF which is similar to experimental reports. Following, the effect of magnetization of solid particles is also studied and it is shown that the MR effect is significantly dependent to the solid particle magnetism. Furthermore, the results show that the viscosity of base fluid has a considerable effect on the dynamic range of this smart fluid.

Stearic acid crystals stabilization in aqueous polymeric dispersions

In wet granulation processes, coatings or binders generally consist of mixtures of various raw materials that confer or enhance specific properties to the final product. Typically, a coating solution is composed of water, film forming polymer (such as hydroxypropyl-methylcellulose, HPMC) and filler (such as stearic acid, SA).One of the important issues in wet granulation processes is the stability of the aqueous coating (or binder) dispersion. An unstable dispersion results in the agglomeration of the colloidal particles, thereby affecting the film coating properties and eventually the coating process.In this study, we use dissipative particle dynamics (DPD) to elucidate the structure of aqueous colloidal formulations. DPD is a coarse-grained molecular dynamics simulation method where the materials are described as a set of soft beads interacting according to the Flory–Huggins (1942) model. The DPD simulation results are compared to experimental results obtained by Cryogenic-SEM and particle size distribution analysis.It is shown from the DPD simulation results that the HPMC polymer is able to form a layer that covers SA particles and thus produces stable colloids. Microcrystalline cellulose (MCC) also covers SA agglomerate but it is not able to diffuse inside its inner core. The agglomerate structure is characterized via the density distribution and the polymer chain end-to-end distance.Experimental results show similar trends; particle size distribution analysis shows that in the presence of HPMC, the majority of SA particles are below 1μm in diameter, also MCC is able to prevent the formation of big SA agglomerates and may be a better stabilizing agent than HPMC. SEM images reveal that HPMC surrounds SA agglomerates with a hatching textured film and anchors on their surface.

A polymer microgel at a liquid-liquid interface: theory vs. computer simulations.

We propose a mean-field theory and dissipative particle dynamics (DPD) simulations of swelling and collapse of a polymer microgel adsorbed at the interface of two immiscible liquids (A and B). The microgel reveals surface activity and lowers A-B interfacial tension. Attempting to occupy as large an interfacial area as possible, the microgel undergoes anisotropic deformation and adopts a flattened shape. Spreading over the interface is restricted by polymer subchain elasticity. The equilibrium shape of the microgel at the interface depends on its size. Small microgels are shown to be more oblate than the larger microgels. Increasing microgel cross-link density results in stronger reduction of the surface tension and weaker flattening. As the degree of immiscibility of A and B liquids increases, the microgel volume changes in a non-monotonous fashion: the microgel contraction at moderate immiscibility of A and B liquids is followed by its swelling at high incompatibility of the liquids. The segregation regime of the liquids within and outside the microgel is different. Being segregated outside the microgel, the liquids can be fully (homogeneously) mixed or weakly segregated within it. The density profiles of the liquids and the polymer were plotted under different conditions. The theoretical and the DPD simulation results are in good agreement. We hope that our findings will be useful for the design of stimuli responsive emulsions, which are stabilized by the microgel particles, as well as for their practical applications, for instance, in biocatalysis.

Structure of aqueous colloidal formulations used in coating and agglomeration processes: Mesoscale model and experiments

In coating and agglomeration processes, the properties of the final product, such as solubility, size distribution, permeability and mechanical resistance, depend on the process parameters and the binder (or coating) solution properties. These properties include the type of solvent used, the binder composition and the affinity between its constituents.In this study, we used mesoscale simulations to investigate the structure of agglomerates formed in aqueous colloidal formulations used in coating and granulation processes. The formulations include water, a film forming polymer (Hydroxypropyl-methylcellulose, HPMC), a hydrophobic filler (Stearic acid, SA) and a plasticizer (Polyethylene glycol, PEG). For the simulations, dissipative particle dynamics (DPD) and a coarse-grained approach were used. In the DPD method, the materials are described as a set of soft beads interacting according to the Flory–Huggins model. The repulsive interactions between the beads were evaluated using the solubility parameter (δ) as input, where δ was calculated by all-atom molecular dynamics. The DPD simulation results were compared to experimental results obtained by cryogenic-SEM and particle size distribution analysis.DPD simulation results showed that the HPMC polymer is able to adsorb in depth into the inner core of SA particle and covers it with a thick layer. We also observed that the structure of HPMC-SA mixture varies under different amounts of SA. For high amounts of SA, HPMC is unable to fully stabilize SA. Affinity between the binder materials was deduced from the DPD simulations and compared with Jarray et al. (2014) theoretical affinity model.Experimental results presented similar trends; particle size distribution analysis showed that for low percentage of SA (below 10% w/w) and in the presence of HPMC, the majority of SA particles are below 1μm in diameter. Cryogenic-SEM images reveal that SA crystals are covered and surrounded by HPMC polymer. SA crystals remain dispersed and small in size for low percentages of SA.

Mechanism analysis of poly(lactic acid) particles formation by mesoscale simulation

AbstractIn this work, the mechanism analysis of Poly(DL‐lactic acid) (PLA) particles formation is investigated by dissipative particle dynamics (DPD) simulations. The polymer PLA is usually as a carrier at the drug deliver system (DDS), first, the mechanism analysis of PLA particles formation was preceded on the basis of the blank PLA particles. At the same time, the formation of PLA particles for drug delivery systems has been investigated. The results of DPD simulations indicate that the formation of PLA particles with drug or not, consists of three steps: (1) aggregation‐individual PLA chains got aggregated with each other in solution; (2) formation and disruption of PLA particles; (3) solidification of PLA particles. At the same time, the effects of PLA, drug content on the aggregation morphology are investigated, which indicates the PLA particles with drug or not aggregated and formed is spherical particles, drug molecules are amorphously and homogeneously distributed inside the PLA matrix, the size of PLA particles increases with increasing the initial PLA content and drug content in the solution. The content of DMF is gotten when PLA chains and drug molecules begin to aggregate and form the particles. These could be used to guide the experimental preparation of PLA blank particles and DDS with desired properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Dissipative particle dynamics study on the multicompartment micelles self-assembled from the mixture of diblock copolymer poly(ethyl ethylene)-block-poly(ethylene oxide) and homopolymer poly(propylene oxide) in aqueous solution

Dissipative particle dynamics (DPD) method is applied to model the self-assembly of diblock copolymer poly(ethyl ethylene)-block-poly(ethylene oxide) (PEE-b-PEO) and homopolymer poly(propylene oxide) (PPO) in aqueous solution. In this study, several segments are coarse-grained into a single simulation bead based on the experimental density. For the self-assembly of pure diblock copolymer PEE-b-PEO in dilute solution, the DPD simulation results are in good agreement with experimental data of micelle morphologies and sizes. The chain lengths of the block copolymers and the volume ratios between PPO and PEE-b-PEO are varied to find the conditions of forming multicompartment micelles. The micelles with core–shell–corona structure and the micelles with two compartments are both formed from the mixture of PEE-b-PEO and PPO in aqueous solution.

Dissipative particle dynamics simulation of gold nanoparticles stabilization by PEO–PPO–PEO block copolymer micelles

Dissipative particle dynamics (DPD) was used to simulate the formation and stabilization of gold nanoparticles in poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer micelles. Primary gold clusters that were experimentally observed in the early stage of gold nanoparticle formation were modeled as gold bead in DPD simulation. It showed that gold beads were wrapped by the block copolymer and aggregated into spherical particles inside the micelles and forming stable Pluronic–gold colloids with two-layer structures. Increasing Pluronic concentration, molecular weight, and PPO block length led to the formation of more uniform and more stable gold nanoparticles. Density profiles of water beads suggested that the micelles, especially the hydrophobicity of the micellar cores, played an important role in stabilizing gold nanoparticles. Dynamic process indicated that the formation of gold nanoparticles was controlled by the competition between aggregation of primary gold clusters and the stabilization by micelles of block copolymers.. The DPD simulation results of gold–copolymer–water system agree well with previous experiments, while more structure information on microscopic level could be provided.

Micro powder injection molding: process characterization and modeling

The development of a new simulation tool for micro powder injection molding (MicroPIM) needs experimental material data and verification experiments to describe the process correctly. A new and innovative approach is to use dissipative particle dynamics (DPD) to describe the form filling process with respect to the interactions on a mesoscopic scale (Hoogerbrugge and Koelman in Europhys Lett 19(1):155–160, 1992). The individual parameters that enter DPD modeling of this process have to be adjusted using specially designed experiments for the injection molding process. The material properties in the standard injection molding process are primarily determined by the bulk material. In micro dimensions surface effects begin to dominate because of the large surface to volume ratio. Therefore, the surface interactions between feedstock and mold insert were studied. Finally, first observations of the injection molding experiments are shown and qualitatively compared to DPD simulation results.

Studies on the interaction between tetradecyl dimethyl betaine and sodium carboxymethyl cellulose by DPD simulations

The dissipative particle dynamics (DPD) simulation method has been used to investigate the effect of pH value on the interaction between tetradecyl dimethyl betaine (C 14BE) and sodium carboxymethyl cellulose (Na-CMC) in aqueous solution. The simulation results indicate that C 14BE/Na-CMC aggregate does not form at pH = 7 (the isoelectric point p I of C 14BE is 5), but at pH = 2 typical C 14BE/Na-CMC aggregate is observed, which means the interactions between them get stronger. Furthermore, at pH = 2 the curve of the end-to-end distance of Na-CMC chain as a function of C 14BE volume fraction initially increases, then reduce and finally increase; while at pH = 7 its end-to-end distance remains constant. The results of surface tension measurements are consistent with DPD simulation results. It is concluded that DPD simulation method can provide some important information on surfactants and macromolecules at the molecular level.