Particle Deformability Research Articles

Fire-Shaped Nozzles to Produce a Stress Peak for Deformability Studies.

Fire-shaped nozzles can be used to study the deformability of microcapsules, particles, or cells traveling in a flow. Though their geometry depends on the dimensions of the original glass capillary and the heating conditions, they all produce a strain rate peak approximately at the section where the diameter is 1.5 times the minimum. The intensity of this peak and the time from its position to the neck can be easily estimated from the flow rate and three geometrical parameters, without the need for any simulation. In the convergent region of these nozzles, it is possible to observe the evolution of the deformation. It is necessary to use a sufficiently long nozzle to produce the maximum deformation before the neck.

Erratum: Bridging particle deformability and collective response in soft solids [Phys. Rev. Materials 5 , 055605 (2021)

Erratum: Bridging particle deformability and collective response in soft solids [Phys. Rev. Materials <b>5</b> , 055605 (2021)

Viscous resuspension of droplets

Shear-induced migration is ubiquitous in a suspension of solid and soft particles. The contribution to particle deformability and frictional contacts between particles needs to be clarified. By measuring normal forces with viscous resuspension experiments of frictionless droplets, we show droplet deformation does not play a significant role, contrary to frictional contacts, as the normal force is much weaker for droplets than for solid particles at high volume fractions.

Designing, Optimization and Characterization of Trifluralin Transfersomal Gel to Passively Target Cutaneous Leishmaniasis

Herein, Trifluralin (TFL) laden transfersomes (TFS) were investigated against Cutaneous Leishmaniasis (CL), via localized and targeted dermal delivery of TFL. Designed TFL-TFS were optimized utilizing 23 full factorial design on the basis of desired response factors including Particle size (P.S), Polydispersity index (PDI), TFL entrapment (%EE) and deformability index (DI). Optimized formulation was found to display P.S of 140.3 ± 2.3, PDI of 0.006 ± 0.002, %EE of 86 ± 0.5 and 43.5 ± 1.0 DI. Results of TEM and XRD analysis have shown intact spherical structure of TFL-TFS and alteration in TFL crystallinity, respectively. Moreover, the optimized TFL-TFS were loaded in Carbopol-940 gel to attain protracted skin retention. TFL-TFS were found to exhibit sustain TFL release profile for up to 24 h. Ameliorated skin permeation of TFL-TFS, even in absence of permeation enhancers, has shown its suitability for cutaneous application. Macrophage uptake assay demonstrated higher intracellular penetration, evidenced by intense reddish fluorescence of rhodamine loaded TFS in comparison to rhodamine-solution. In vitro anti-leishmanial assessment was showing 2.86-folds and 3.07-folds decrement in IC50-value of TFL-TFS against L. tropica KWH23 amastigotes and promastigotes, respectively. Percent inhibition assay against intra-macrophage amastigotes demonstrated that 90.87% amastigotes were assassinated at 50 μg/ml concentration of TFL-TFS, in comparison to the plain TFL-solution, exhibiting 54% parasitic killing.

Drying rate of latex coating affected by the deformability of resin particles in convection drying.

Latex paints are widely used, and many researchers pointed out that the film formation process depends on the deformability of dispersed polymer particles. However, the relationship between the film formation process and drying rate has not been totally understood due to the lack of accurate data on drying rate throughout the drying process. In the present study, we measured the drying rate of latex coating by the temperature change method proposed by Imakoma in convective drying. We revealed that the drying process significantly depends on particle deformability, especially in the former stage of the falling drying rate period. At a low drying temperature, the close-packed structure of polymer particles is formed throughout the film at the end of the constant drying rate period. On the other hand, partially deformed soft particles due to wet sintering inhibit the drying rate even under high moisture content at high drying temperatures. In either case, after forming the closest-packed structure, the shrinkage of the gap space between particles due to capillary deformation decreases the drying rate, proportional to the moisture content.

Effects of rheological properties of the fluids on migration behavior of double emulsions

Particle migration in microfluidic devices has received considerable attention because of its applications in medicine, chemistry, and engineering, including diagnostics, particle separation, and cell sorting. In this study, we observe inertial migration of soft particles in a straight tube at Re ranging from 100 to 1000. Uniform double emulsions as soft particles are produced by a flow focusing technique in a micro fluidic device. Mechanical properties of the double emulsions were measured prior to migration experiments. Equilibrium radial positions of the double emulsions were measured at several Re. Re affected the distance from the tube center and numbers of the equilibrium radial position. In Re < 250 range, a single equilibrium radial position was observed, which gradually shifted toward the channel wall. Two equilibrium positions were observed at Re ranging from 300 to 500. In Re > 500 range, a single equilibrium radial position closer to the center was observed. These different flow regimes and transitions were influenced by particle deformability.

Deformable hard particles confined in a disordered porous matrix.

With suitably designed Monte Carlo simulations, we have investigated the properties of mobile, impenetrable, yet deformable particles that are immersed into a porous matrix, the latter one realized by a frozen configuration of spherical particles. By virtue of a model put forward by Batista and Miller [Phys. Rev. Lett. 105, 088305 (2010)], the fluid particles can change in their surroundings, formed by other fluid particles or the matrix particles, their shape within the class of ellipsoids of revolution; such a change in shape is related to a change in energy, which is fed into suitably defined selection rules in the deformation "moves" of the Monte Carlo simulations. This concept represents a simple yet powerful model of realistic, deformable molecules with complex internal structures (such as dendrimers or polymers). For the evaluation of the properties of the system, we have used the well-known quenched-annealed protocol (with its characteristic double average prescription) and have analyzed the simulation data in terms of static properties (the radial distribution function and aspect ratio distribution of the ellipsoids) and dynamic features (notably the mean squared displacement). Our data provide evidence that the degree of deformability of the fluid particles has a distinct impact on the aforementioned properties of the system.

Preparation of anisotropic multiscale micro-hydrogels via two-photon continuous flow lithography

HypothesisPolymeric anisotropic soft microparticles show interesting behavior in biological environments and hold promise for drug delivery and biomedical applications. However, self-assembly and substrate-based lithographic techniques are limited by low resolution, batch operation or specific particle geometry and deformability. Two-photon polymerization in microfluidic channels may offer the required resolution to continuously fabricate anisotropic micro-hydrogels in sub-10 µm size-range. ExperimentsHere, a pulsed laser source is used to perform two-photon polymerization under microfluidic flow of a poly(ethylene glycol) diacrylate (PEGDA) solution with the objective of realizing anisotropic micro-hydrogels carrying payloads of various nature, including small molecules and nanoparticles. The fabrication process is described via a reactive-convective-diffusion system of equations, whose solution under proper auxiliary conditions is used to corroborate the experimental observations and sample the configuration space. FindingsBy tuning the flow velocity, exposure time and pre-polymer composition, anisotropic PEGDA micro-hydrogels are obtained in the 1–10 μm size-range and exhibit an aspect ratio varying from 1 to 5. Furthermore, 200 nm curcumin-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles and 100 nm ssRNA-encapsulating lipid nanoparticles were entrapped within square PEGDA micro-hydrogels. The proposed approach could support the fabrication of micro-hydrogels of well-defined morphology, stiffness, and surface properties for the sustained release of therapeutic agents.

Assembly of Defect-Free Microgel Nanomembranes for CO2 Separation.

The development of robust and thin CO2 separation membranes that allow fast and selective permeation of CO2 will be crucial for rebalancing the global carbon cycle. Hydrogels are attractive membrane materials because of their tunable chemical properties and exceptionally high diffusion coefficients for solutes. However, their fragility prevents the fabrication of thin defect-free membranes suitable for gas separation. Here, we report the assembly of defect-free hydrogel nanomembranes for CO2 separation. Such membranes can be prepared by coating an aqueous suspension of colloidal hydrogel microparticles (microgels) onto a flat, rough, or micropatterned porous support as long as the pores are hydrophilic and the pore size is smaller than the diameter of the microgels. The deformability of the microgel particles enables the autonomous assembly of defect-free 30-50 nm-thick membrane layers from deformed ∼15 nm-thick discoidal particles. Microscopic analysis established that the penetration of water into the pores driven by capillary force assists the assembly of a defect-free dense hydrogel layer on the pores. Although the dried films did not show significant CO2 permeance even in the presence of amine groups, the permeance dramatically increased when the membranes are adequately hydrated to form a hydrogel. This result indicated the importance of free water in the membranes to achieve fast diffusion of bicarbonate ions. The hydrogel nanomembranes consisting of amine-containing microgel particles show selective CO2 permeation (850 GPU, αCO2/N2 = 25) against post-combustion gases. Acid-containing microgel membranes doped with amines show highly selective CO2 permeation against post-combustion gases (1010 GPU, αCO2/N2 = 216) and direct air capture (1270 GPU, αCO2/N2 = 2380). The membrane formation mechanism reported in this paper will provide insights into the self-assembly of soft matters. Furthermore, the versatile strategy of fabricating hydrogel nanomembranes by the autonomous assembly of deformable microgels will enable the large-scale manufacturing of high-performance separation membranes, allowing low-cost carbon capture from post-combustion gases and atmospheric air.

Bridging particle deformability and collective response in soft solids

Soft, amorphous solids such as tissues, foams, and emulsions are composed of deformable particles. However, the effect of single-particle deformability on the collective behavior of soft solids is still poorly understood. We perform numerical simulations of two-dimensional jammed packings of explicitly deformable particles to study the mechanical response of model soft solids. We find that jammed packings of deformable particles with excess shape degrees of freedom possess low-frequency quartic vibrational modes that stabilize the packings even though they possess fewer interparticle contacts than the nominal isostatic value. Adding intra-particle constraints can rigidify the particles, but these particles undergo a buckling transition and gain an effective shape degree of freedom when their preferred perimeter is above a threshold value. We find that the mechanical response of jammed packings of deformable particles with shape degrees of freedom differs significantly from that of jammed packings of rigid-shape particles, which emphasizes the importance of particle deformability in modelling soft solids.

3D formulation of the deformable discrete element method

AbstractThis work presents a 3D extension of the deformable discrete element method (DDEM) developed previously for 2D problems. The 3D formulation employs spherical particles. The particle deformation is made up of a global and local deformation mode. The global mode is assumed to be produced by uniform stress due to the contact forces. Particle deformability yields a nonlocal contact model, in which one contact between particles is influenced by contacts with other particles. It also leads to the formation of new contacts in the particle assembly. The DDEM affects the behavior of the granular material at the macroscopic level and gives new possibilities in material modeling by the discrete element method (DEM). The new algorithm is verified on a unconfined uniaxial compression test of a cuboid specimen discretized with equal‐size bonded particles aligned in a simple cubic pattern using an analytical solution. Enhanced modeling capabilities are presented by simulating cylindrical specimens discretized with a nonuniform size of bonded particles. The micro–macro relationships for elastic parameters are obtained. It is shown that the DDEM extends the range of the Poisson's ratio achievable with the DEM. Additional simulations are performed to determine the stability limits of the DDEM.

Study on the binding focusing state of particles in inertial migration

In this paper, the inertial migration of particles in a periodic straight channel is studied numerically based on the immersed boundary-lattice Boltzmann method in two-dimensional and three-dimensional Poiseuille flow. In the model, on considering the inertial migration of particles, the interaction of a soft particle and a hard particle that are similar in size is studied. We observe an interesting particle interaction phenomenon named the binding focusing state (BFS). That is, when the focused soft particle gets close to the hard particle, both particles will switch their original runways, and then run together on a new equilibrium position. To investigate the characteristics of the BFS, the effects of the soft particle deformability, the Reynolds numbers and the initial particle positions on the BFS are studied in detail. The soft particle deformability and Reynolds numbers can affect the formation of the BFS. Moreover, the streamline and pressure around the particles are analyzed to show the formation laws of the BFS; this is more intuitive and aids in understanding the BFS.

A permeable on-chip microvasculature for assessing the transport of macromolecules and polymeric nanoconstructs

HypothesisThe selective permeation of molecules and nanomedicines across the diseased vasculature dictates the success of a therapeutic intervention. Yet, in vitro assays cannot recapitulate relevant differences between the physiological and pathological microvasculature. Here, a double-channel microfluidic device was engineered to comprise vascular and extravascular compartments connected through a micropillar membrane with tunable permeability. ExperimentsThe vascular compartment was coated by endothelial cells to achieve permeability values ranging from ~0.1 μm/sec, following a cyclic adenosine monophosphate (cAMP) pre-treatment (25 μg/mL), up to ~2 μm/sec, upon exposure to Mannitol, Lexiscan or in the absence of cells. Fluorescent microscopy was used to monitor the vascular behavior of 250 kDa Dextran molecules, 200 nm polystyrene nanoparticles (PB), and 1,000 × 400 nm discoidal polymeric nanoconstructs (DPN), under different permeability and flow conditions. FindingsIn the proposed on-chip microvasculature, it was confirmed that permeation enhancers could favor the perivascular accumulation of ~200 nm, in a dose and time dependent fashion, while have no effect on larger particles. Moreover, the microfluidic device was used to interrogate the role of particle deformability in vascular dynamics. In the presence of a continuous endothelium, soft DPN attached to the vasculature more avidly at sub-physiological flows (100 μm/sec) than rigid DPN, whose deposition was larger at higher flow rates (1 mm/sec). The proposed double-channel microfluidic device can be efficiently used to systematically analyze the vascular behavior of drug delivery systems to enhance their tissue specific accumulation.

Macrophage targeting with the novel carbopol-based miltefosine-loaded transfersomal gel for the treatment of cutaneous leishmaniasis: in vitro and in vivo analyses

Objective The purpose of this study was to develop novel carbopol-based miltefosine-loaded transfersomal gel (HePCTG) for the treatment of cutaneous leishmaniasis (CL) via efficient targeting of leishmania infected macrophages. Methods Miltefosine-loaded transfersomes (HePCT) were prepared by ethanol injection method followed by their incorporation into carbopol gel to form HePCTG. The prepared HePCT were assessed for physicochemical properties including mean particle size, polydispersity index, zeta potential, entrapment efficiency, morphology, and deformability. Similarly, HePCTG was evaluated for physiochemical and rheological attributes. The in vitro release, skin permeation, skin irritation, anti-leishmanial activity, and in vivo efficacy in BALB/c mice against infected macrophages were also performed for HePCT. Results The optimized HePCT displayed a particle size of 168 nm with entrapment efficiency of 92%. HePCTG showed suitable viscosity, pH, and sustained release of the incorporated drug. Furthermore, HePCT and HePCTG demonstrated higher skin permeation than drug solution. The results of macrophage uptake study indicated improved drug intake by passive diffusion. The lower half maximal inhibitory concentration value, selectivity index and higher 50% cytotoxic concentration value of HePCT compared to that of HePC solution demonstrated the improved anti-leishmanial efficacy and non-toxicity of the formulation. This was further confirmed by the notable reduction in parasite load and lesion size observed in in vivo anti-leishmanial study. Conclusion It can be stated that the formulated HePCTG can effectively be used for the treatment of CL.

Suspensions of deformable particles in Poiseuille flows at finite inertia

We analyze a suspension of deformable particles in a pressure-driven flow. The suspension is composed of neutrally buoyant initially spherical particles and a Newtonian carrier fluid, and the flow is solved by means of direct numerical simulations, using a fully Eulerian method based on a one-continuum formulation. The solid phase is modeled with an incompressible viscous hyperelastic constitutive relation, and the flow is characterized by three main dimensionless parameters, namely the solid volume fraction, the Reynolds and capillary numbers. The dependency of the effective viscosity on these three quantities is investigated to study the inertial effects on a suspension of deformable particles. It can be observed that the suspension has a shear-thinning behavior, and the reduction in effective viscosity for high shear rates is emphasized in denser configurations. The separate analysis of the Reynolds and capillary numbers reveal that the effective viscosity depends more on the capillary than on the Reynolds number. In addition, our simulations exhibit a consistent tendency for deformable particles to move toward the center of the channel, where the shear rate is low. This phenomenon is particularly marked for very dilute suspensions, where a whole region near the wall is empty of particles. Furthermore, when the volume fraction is increased this near-wall region is gradually occupied, because of higher mutual particle interactions. Deformability also plays an important role in the process. Indeed, at high capillary numbers, particles are more sensitive to shear rate variations and can modify their shape more easily to accommodate a greater number of particles in the central region of the channel. Finally, the total stress budgets show that the relative particle-induced stress contribution increases with the volume fraction and Reynolds number, and decreases with the particle deformability.

Filler Particle Size and Packaging and Compositions of Filled Polymer Composites with Different Types of Structures and Properties

Questions of the influence of the particle size of solid fillers on the packing density and the maximum filler fraction (φm) in dispersion-filled polymer composite materials (DFPCMs) are studied. The dependence of the parameter φm from the diameter of solid particles of fillers is given. It is shown that, for large particles (over 50 μm), φm in DFPCMs can reach ~0.64 vol/vol and, for nanoparticles (1–100 nm), it can reach no more than ~0.255 vol/vol. For deformable-under-pressure and gaseous particles, as well as for dense compositions of fillers, the value of parameter φm in DFPCMs can reach ~0.90–0.94 vol/vol. The relationship between the size of particles and their packing and the generalized parameter of the dispersed structure Θ has been established, which makes it possible to classify the type of materials under consideration with different particle sizes according to the structural principle and establish their type of structural organization (dilute, low-filled, medium-filled, highly filled, and ultra-high-filled systems), which determines the properties of composites. An algorithm is proposed for calculating the content of filler and compositions of DFPCMs with different particle sizes, natures, and deformability of particles for the design of various types of composite structures and technological and operational properties.

Particle flattening during cold spray: Mechanistic regimes revealed by single particle impact tests

The flattening ratio, ε, is an important diagnostic measurement of particle deformability and coating quality assessment in cold spray. However, the experimental determination of ε and correlation of it to experimental parameters (particle size, velocity) is not straightforward from observations of cold-sprayed coatings. Here we present a series of direct site-specific measurements of ε for well-known particle sizes and velocities, without the many complications involved in a full cold spray experiment. This approach permits us to identify mechanistic transitions separating three apparent regimes of behavior. In regime I, at lower velocities just high enough to cause bonding, an impacting particle flattens largely unhindered. In regime II, at somewhat higher velocities, the substrate develops a significant crater, which in turn constrains lateral particle flattening as the particle burrows more deeply into the substrate. In regime III, at very high velocities, hydrodynamic particle penetration is observed, distinguished by deep burrowing of the particle, which adopts a concave-saucer shape, with large petals of substrate ejected backwards out of the surface. While direct measurements in regimes I and II show that deformed particles can be reasonably modeled as oblate spheroids, that assumption fails in regime III. To the extent that particle flattening is deemed desirable, this analysis suggests a more nuanced view of the velocities used in cold spray.

Discrete element modeling of switchgrass particles under compression and rotational shear

Switchgrass is a perennial herbaceous plant regarded as a biomass energy crop in the United States for its high adaptability and yield potential. Processing and handling of switchgrass particles are challenging due to the erratic mechanical and flow behavior originating from their intrinsic particulate properties. In this work, we present a bonded-sphere discrete element model designed specifically for switchgrass particles. The model simultaneously captures three key particulate features, i.e., fibrous particle shapes, a wide range of particle sizes, and particle deformability. Realistic yet computationally efficient particle shape templates are created based on the image analysis data of switchgrass specimens. A fitting procedure is proposed to ensure both the particle width and length distributions are captured, a unique requirement for fibrous particles. Two full-scale numerical models, i.e., a uniaxial compression model and a Schulze ring shear model, are developed using information from physical experiments. The model is calibrated using experimental data of chopped-small switchgrass specimens, and then, is validated using data of chopped-large specimens in both compression and ring-shear tests. Numerical results show that the numerical models capture bulk densities accurately (with an error of 3%) while slightly underestimate the bulk friction angle. Furthermore, an extensive sensitivity analysis reveals that (1) switchgrass particles with rougher edges (due to different processing techniques) exhibit a higher shear strength and a lower flowability; (2) stiffer particles yield a lower bulk density (up to 21% lower) compared to more deformable particles, indicating particle deformability should be incorporated when modeling biomass flow in a preprocessing system.

Limitation of spiral microchannels for particle separation in heterogeneous mixtures: Impact of particles' size and deformability.

Spiral microchannels have shown promising results for separation applications. Hydrodynamic particle-particle interactions are a known factor strongly influencing focusing behaviors in inertial devices, with recent work highlighting how the performance of bidisperse mixtures is altered when compared with pure components in square channels. This phenomenon has not been previously investigated in detail for spiral channels. Here, we demonstrate that, in spiral channels, both the proportion and deformability of larger particles (13 μm diameter) impact upon the recovery (up to 47% decrease) of small rigid particles (4 μm). The effect, observed at low concentrations (volume fraction <0.0012), is attributed to the hydrodynamic capture of beads by larger cells. These changes in particles focusing behavior directly impede the efficiency of the separation-diverting beads from locations expected from measurements with pure populations to co-collection with larger cells-and could hamper deployment of technology for certain applications. Similar focusing behavior alterations were noted when working with purification of stem cell end products.

Path planning of the viscoelastic micro biological particle to minimize path length and particle's deformation using genetic algorithm.

Manipulation of biological particles including pulling, and holding-and-indenting them, using the atomic force microscope (AFM) has attracted enormous interests. High deformability and vulnerability of biological particles, especially cells, make moving toward the target point inside complex biological environments with the least invasion the most critical factor. In this article, the optimal path of the particle movement is determined by considering the mechanical and morphological properties of the biological cell. Furthermore, the shortest path with the least amount of cell deformation is determined by using the equations of 3D manipulation of spherical viscoelastic particles and genetic algorithm (GA). Eventually, the final path is determined considering the mechanical properties of breast cancer cells by applying different constraints such as folding factor and the particle's roughness.Results reveal that increasing the number of constraints raise the needed time to find the optimal path. Additionally, the maximum time belongs to the spherical particle in the presence of folding. As a result, the total path planning times for the smooth, rough, and folded spherical particle are 59.386, 129.578, and 214.404s, respectively. Various optimal pathfinders are used, to reduce calculations and speed up the process, as well as obtaining the correct answer with high certainty. Comparing the error files founded for three methods including cellular learning Automata, Dijkstra, and GA, the third method has the best performance in the lowest error rate. Using the GA, the error rate can be reduced by 40%, compared to the cellular learning Automata method. Furthermore, comparing the cellular learning Automata method used in previous studies, it can be seen that not only the results are correct, but also less time spent, at the practically identical situation, on finding the optimal path for this algorithm.