Particle Deformability Research Articles

Micro-Superplastic Behavior of Copper Oxide in AgCuO Composites

In the investigation of AgCuO composites, we have found a type of copper oxide particles with a superplastic deformability behavior, which is similar to that of metals. To find the reason of the deformability of the copper oxide particles. SCM, STEM and TEM were used to analyze their crystal structures in AgCuO composites, The results show that the copper oxide particles with micro-superplasticity in the composites have cubic crystal structure, and their maximum elongation can be up to 300%, The copper oxide particles with no micro-superplasticity in the composites have monoclinic crystal structure. But the micro-superplastic behavior and mechanism of the copper oxides with the cubic crystal structure are not clear for the time being, the further investigation could be needed.

Dynamics of a deformable active particle under shear flow

The motion of a deformable active particle in linear shear flow is explored theoretically. Based on symmetry considerations, we propose coupled nonlinear dynamical equations for the particle position, velocity, deformation, and rotation. In our model, both, passive rotations induced by the shear flow as well as active spinning motions, are taken into account. Our equations reduce to known models in the two limits of vanishing shear flow and vanishing particle deformability. For varied shear rate and particle propulsion speed, we solve the equations numerically in two spatial dimensions and obtain a manifold of different dynamical modes including active straight motion, periodic motions, motions on undulated cycloids, winding motions, as well as quasi-periodic and chaotic motions induced at high shear rates. The types of motion are distinguished by different characteristics in the real-space trajectories and in the dynamical behavior of the particle orientation and its deformation. Our predictions can be verified in experiments on self-propelled droplets exposed to a linear shear flow.

Influence of the polymer size on depletion attraction—induced gel and glass transitions of microgel colloids

In previous work of our group on the re-entrant melting of colloidal glasses we observed an unexpectedly huge re-entry region for a binary system of 1:50 crosslinked polystyrene (PS) microgel spheres when a depletion attraction range ξ=Rg,polymer/Rcolloid=0.08 was induced by non-adsorbing (free) PS chains. To investigate whether this fluid region can even be increased by reducing polymer size and therefore the attraction range as predicted by mode coupling theory (MCT), we studied an almost identical system. It consists of a binary 1:50 PS microgel mixture (Rh,L=105.8nm, Rh,S=82.9nm; Γ=Rh,S/Rh,L=0.85) with a reduced attraction range of ξ=0.059 by use of an appropriate free PS polymer (Mw=79,600g/mol, Rg,polymer=9.18nm). Here the glass transition is shifted from ϕg=0.577 to higher values, allowing for fluid states up to volume fractions of ϕ=0.715. This is significantly higher than the maximum fluid state of ϕ=0.69 reached for ξ=0.08. Tentatively correcting for osmotic deswelling these volume fractions reduce to 0.673 and 0.66, respectively. This is in qualitative agreement with MCT, but in quantitative disagreement because the theory predicts a shift of only a few percent. Such fluid states beyond the maximum amorphous packing of hard spheres (ϕrcp∼0.64) do not occur for PMMA colloids and 1:10 crosslinked PS microgel spheres that can both be considered as hard spheres. Thus, we tentatively attribute the observation of fluid states at such high volume fractions to a combination of the slight softness of the 1:50 microgels, leading to osmotic deswelling and particle deformability. In addition, polydispersity and polymer non-ideality effects should be taken into account.

Statistical modelling of the coupled effect of mix design and rebar spacing on restricted flow characteristics of SCC

Self-consolidating concrete (SCC) is designed to exhibit high deformability and stability to maintain homogenous suspension of coarse aggregate particles in the mortar during flow to ensure adequate passing ability of the concrete through restricted areas and the filling of the formwork without any consolidation. Proper deformability and uniform suspension of coarse aggregate particles in the matrix are key parameters to ensure successful casting and adequate in situ performance. The required flow properties of concrete are affected by the rheological properties of the mixture and the characteristics of the cast element, including the level of reinforcement.The mixture proportioning of SCC involves tailoring several mixture parameters to achieve adequate stability and reduce the risk of arching of solid particles and blockage at the vicinity of closely spaced obstacles which is required to ensure proper passing ability and flow characteristics. The objective of this study is to evaluate the coupled effect of mixture parameters and density of reinforcement on flow characteristics of SCC using a statistical design approach. This study seeks to model the coupled effect of the content of supplementary cementitious materials (SCMs), coarse aggregate volume (CA), and density of reinforcement on flowability, passing ability, and filling capacity of SCC. The comparison between predicted and measured responses determined on eight mixtures indicates the accuracy of the established models to describe the effect of the independent variables on the flow behavior of SCC through restricted sections. The derived models show that the flow rate of SCC in the presence of reinforcement is dominated by the content of SCM and clear spacing between the reinforcement. On the other hand, the SCM content is shown to have a three-time greater effect on plastic viscosity than the relative volume of coarse aggregate. Trade-offs between rheological parameters, clear spacing, and flow of SCC in the presence of obstacles showed that for a given clear spacing, higher viscosity and lower yield stress values resulted in higher flow time of concrete. For clear spacing between obstacles of 30mm, SCC mixtures with plastic viscosity lower than 50Pas and yield stress of 45Pa are shown to ensure proper passing ability.

Isoquercitrin의 세포 보호 작용과 피부 흡수 증진을 위한 리포좀 제형 연구

In this study, the cellular protective effect of isoquercitrin against H2O2 and rose bengal-indued HaCaT cell damage was investigated. The ethosome and elastic liposome for enhanced transdermal delivery were prepared. Particle size, loading efficiency and cumulative permeated amounts of them were evaluated. Isoquercitrin didn't show any characteristic cytotoxicity at 50 μM. When HaCaT cells were treated with 5 mM H2O2 and 25 μM rose bengal, isoquercitrin protected the cells against the oxidative damage in a concentration dependent manner (6.25 ~ 50 μM). The size of 0.03 % isoquercitrin loaded ethosome was 222.85 nm and the loading efficiency was 82.26 %. The ethosome loaded with 0.03 % isoquercitrin was stable and maintained the constant particle size for 2 weeks after being prepared. The ethosome exhibited more enhanced skin permeability than general liposome and ethanol solution. The optimal ratio of lipid to surfactant of 0.1 % isoquercitrin loaded elastic liposomes was observed to be 89 : 5 through evaluating particle size (341.2 nm), deformability index (59.89), loading efficiency (54.3 %), and skin permeability (54.4 %).

The effect of particle size on the biodistribution of low-modulus hydrogel PRINT particles

There is a growing recognition that the deformability of particles used for drug delivery plays a significant role on their biodistribution and circulation profile. Understanding these effects would provide a crucial tool for the rational design of drug delivery systems. While particles resembling red blood cells (RBCs) in size, shape and deformability have extended circulation times and altered biodistribution profiles compared to rigid, but otherwise similar particles, the in vivo behavior of such highly deformable particles of varied size has not been explored. We report the fabrication of a series of discoid, monodisperse, low-modulus hydrogel particles with diameters ranging from 0.8 to 8.9μm, spanning sizes smaller than and larger than RBCs. We injected these particles into healthy mice, and tracked their concentration in the blood and their distribution into major organs. These deformable particles all demonstrated some hold up in filtration tissues like the lungs and spleen, followed by release back into the circulation, characterized by decreases in particles in these tissues with concomitant increases in particle concentration in blood. Particles similar to red blood cells in size demonstrated longer circulation times, suggesting that this size and shape of deformable particle is uniquely suited to avoid clearance.

Effect of Aspect Ratio and Deformability on Nanoparticle Extravasation through Nanopores

We describe the fabrication of filamentous hydrogel nanoparticles using a unique soft lithography based particle molding process referred to as PRINT (particle replication in nonwetting templates). The nanoparticles possess a constant width of 80 nm, and we varied their lengths ranging from 180 to 5000 nm. In addition to varying the aspect ratio of the particles, the deformability of the particles was tuned by varying the cross-link density within the particle matrix. Size characteristics such as hydrodynamic diameter and persistence length of the particles were analyzed using dynamic light scattering and electron microscopy techniques, respectively, while particle deformability was assessed by atomic force microscopy. Additionally, the ability of the particles to pass through membranes containing 0.2 μm pores was assessed by means of a simple filtration technique, and particle recovery was determined using fluorescence spectroscopy. The results show that particle recovery is mostly independent of aspect ratio at all cross-linker concentrations utilized, with the exception of 96 wt % PEG diacrylate 80 × 5000 nm particles, which showed the lowest percent recovery.

Self-assembly of amphiphilic patchy particles with different cross-linking densities

The influence of deformability of two-patch particles on their self-assembly behavior is studied via computer simulations. The softness and the deformability of the patchy particles can be controlled by varying the cross-linking densities in different parts of the particles. The patchy particles in a solvent that is bad for patches but good for the matrix form linear thread-like structures when cross-linking densities are low, whereas they form three-dimensional network structures at relatively high cross-linking densities. For patchy particles in a solvent that is good for patches but bad for the matrix, inter-connected membrane structures are obtained at relatively low cross-linking densities, and some cluster structures emerge when cross-linking densities are high. Bicontinuous membranes with better morphologies can be observed by tuning the cross-linking densities of different parts of the patchy particles.

Deformability-selective particle entrainment and separation in a rectangular microchannel using medium viscoelasticity

We report a new phenomenon that particles are selectively entrained along the corners of a straight rectangular microchannel according to their deformabilities under viscoelastic flows of a polymer solution. The mechanism behind this phenomenon is elucidated by the competition between the wall lift force induced by the particle deformability and the elastic force of the medium at the corners. On the basis of these findings, we devise a novel label-free deformability-selective cell-separation method, which achieves the high-purity separation of rigid particles and rigidified red blood cells (RBCs) from fresh RBCs in a single step, without any active components such as an electric force or sophisticated channel design. Furthermore, our novel method can be used directly to isolate white blood cells (WBCs) from diluted whole blood with a high enrichment ratio (>300) by utilizing difference in cell deformability.

Flow-induced size distribution and anisotropy of the minor phase droplets in a polypropylene/poly (ethylene-octene) copolymer blend: Interplay between break-up and coalescence

The morphology of an immiscible blend of polypropylene and (ethylene-octene) copolymer has been studied for different flow conditions. Samples were taken and quenched at the exit of a slit die attached to an extruder. For a statistical analysis of the minor phase droplets, scanning electron images of cryo-fractured samples were used. The size distribution and anisotropy of the minority phase droplets were determined for different positions within the flow profile in the slit die. The distribution functions are discussed in terms of micro-structure of the droplets of the minority phase in the melt which develops due to the interplay of break-up and coalescence. The coexistence of two statistical ensembles for some flow conditions gives evidence for the existence of two regimes (or two length scales) of structure formation: break-up and coalescence. The deformed particles were found to be elongated in the flow direction, which results in a so-called skin/core morphology. From a quantitative analysis of the particle deformation, it was found that the deformability of particles is determined by their size rather than by the shear stress.

The rheology and microstructure of concentrated non-colloidal suspensions of deformable capsules

AbstractA detailed study into the rheology and microstructure of dense suspensions of initially spherical capsules is presented, where capsules are composed of a fluid-filled interior surrounded by an elastic membrane. This study couples a lattice-Boltzmann fluid solver to a finite-element membrane model creating a robust and scalable method for the simulation of these suspensions. A Lees–Edwards boundary condition is used to simulate periodic simple shear to obtain bulk rheological properties, and three-dimensional results are presented for capsules in the regime of negligible inertia, Brownian motion and colloidal interparticle forces. The simulation results focus on describing the suspension rheology as a function of the particle concentration and deformability, and relating these macroscopic rheological findings to changes at the particle level, i.e. the suspension microstructure. Several important findings are made: suspensions of deformable capsules are found to be shear thinning, and the initially compressive normal stresses associated with rigid spherical suspensions undergo rapid changes with moderate levels of particle deformation. These normal stress changes are particularly evident in the first normal stress difference, which undergoes a sign change at fairly minor levels of deformation, and the particle pressure, which decreases rapidly with increasing particle deformability. Changes in the microstructure as quantified by the single-body microstructure and the pair distribution function are reported. Also, results calculating particle self-diffusion are presented and related to changes in the normal stresses.

Separation of deformable particles in deterministic lateral displacement devices

Using numerical simulations, we study the separation of deformable bodies, such as capsules, vesicles, and cells, in deterministic lateral displacement devices, also known as bump arrays. These arrays comprise regular rows of obstacles such as micropillars whose arrangements are shifted between adjacent rows by a fixed amount. We show that, in addition to the zigzag and laterally displaced trajectories that have been observed experimentally, there exists a third type of trajectory which we call dispersive, characterized by seemingly random bumpings off the micropillars. These dispersive trajectories are observed only for large and rigid particles whose diameters are approximately more than half the gap size between micropillars and whose stiffness exceeds approximately 500 MPa. We then map out the regions in phase space, spanned by the row shift, row separation, particle diameter, and particle deformability, in which the different types of trajectories are expected. We also show that, in this phase space, it is possible to transition from zigzag to dispersive trajectories, bypassing lateral displacement. Experimentally, this is undesirable because it limits the ability of the device to sort particles according to size. Finally, we discuss how our numerical simulations may be of use in device prototyping and optimization.

Comparing colloidal phase separation induced by linear polymer and by microgel particles

Depletion interactions give rise to phase separation in colloid-polymer mixtures at sufficiently high concentrations of both species. Similarly a fluid-solid phase separation is expected for binary hard sphere (BHS) mixtures, however in practice it appears such mixtures are very prone to form metastable (jammed) states. Here pNIPAM microgel particles are used to induce depletion attractions between polystyrene latex spheres. Such microgels can be modelled as hard spheres with a polymer brush-like outer layer. Mixtures with a microgel/polystyrene size ratio of 0.11 showed a fluid-solid phase separation, in good agreement with predictions for BHS. Gel states were obtained on further increase of concentration, around the position of the predicted metastable BHS fluid-fluid binodal, echoing previous claims of the significance of a hidden fluid-fluid phase boundary as the precursor to gelation. It thus appears that the slight deformability of the microgel particles reduces the tendency for mixtures to remain in jammed states relative to binary hard sphere systems. Nevertheless the mixtures did tend to form gels more easily than mixtures of the same polystyrene spheres with linear polymer coils at a similar polymer/colloid size ratio.

Effects of Membrane Rheology on Leuko-polymersome Adhesion to Inflammatory Ligands.

A strategy for treating inflammatory disease is to create micro-particles with the adhesive properties of leukocytes. The underlying rheology of deformable adhesive microspheres would be an important factor in the adhesive performance of such particles. In this work the effect of particle deformability on the selectin-mediated rolling of polymer vesicles (polymersomes) is evaluated. The rheology of the polymersome membrane was modulated by cross-linking unsaturated side-chains within the hydrophobic core of the membrane. Increased membrane rigidity resulted in decreased rates of particle recruitment rather than decreased average rolling velocities. Reflective interference contrast microscopy of rolling vesicles confirmed that neither flaccid nor rigid vesicles sustained close contacts with the substrate during rolling adhesion. A variable-shear rate parallel-plate flow chamber was employed to evaluate individual vesicles rolling on substrates under different flow conditions. Analysis of the trajectories of single flaccid vesicles revealed several distinct populations of rolling vesicles; however, some of these populations disappear when the vesicle membranes are made rigid. This work shows that membrane mechanics affects the capture, but not the rolling dynamics, of adherent leuko-polymersomes.

Soft microgels as Pickering emulsion stabilisers: role of particle deformability

We synthesised soft uncharged microgels made of poly(N-isopropylacrylamide) of variable cross-linking degrees and we probed their efficiency as stabilisers to fabricate oil-in-water emulsions. Interestingly, such particles undergo a swollen-to-collapsed transition above a critical temperature. By combining several microscopy methods and by exploiting the limited coalescence process, we were able to determine both the particle concentration and structure at the interface, as a function of the cross-linking density. Being deformable, the initially spherical microgels adopt a “fried egg-like” structure when adsorbed at the oil/water interface. As expected, the interfacial deformation is increasingly pronounced as the cross-linking degree decreases. The most deformable microgels tend to form 2D connected networks characterised by significant overlapping of the peripheral parts. When the deformability is lost, by increasing the cross-linking density or the temperature, the stabilisation efficiency is considerably reduced. Our results strongly suggest that emulsion stability is mainly determined by the microgels' deformability and we discuss the origin of that empirical link in terms of lateral overlapping and interfacial elasticity.

Effects of Soft Particle Deformability and Particle/Pore Size Ratio on the Blocking Mechanism in Dead‐End Microfiltration

AbstractMicrofiltrations of Saccharomyces cerevisiae yeast particles of various deformabilities were conducted to examine the blocking mechanism due to particle deposition during the initial stage of the microfiltration process. The S. cerevisiae particles were treated with glutaraldehyde to form particles of various deformabilities. To compare differences in the blocking mechanisms among the different particles during microfiltration, a blocking model was adopted to estimate the filtrate flux, which accounts for initial blocking due to pore obstruction and subsequent blocking due to the growth of a cake over these initially blocked regions. The surface morphology of the cake layer on the membrane surface and the blockage by particles in membrane pores was examined by scanning electron microscopy (SEM). Analysis of the blocking mechanism of particles of varying deformability during microfiltration based on the blocking model indicated that softer particles resulted in more severe pore blocking problems and greater flux decline. A comparison of the theoretical results with experimental observations by SEM showed good qualitative agreement.

Retinyl palmitate flexible polymeric nanocapsules: Characterization and permeation studies

Polymeric nanocapsules with elastic characteristics were prepared by the pre-formed polymer interfacial deposition method. The system consists of an oily core of retinyl palmitate with Span 60 and a polymeric wall of poly( d, l-lactide) (PLA). A narrow size distribution (215 nm, P.D.I. 0.10) was showed by dynamic light scattering (DLS) analyses. Particle deformability was observed by transmission electron microscopy (TEM) images and permeation of the particles through two superposed membranes of smaller pore diameters. Permeation studies were achieved using plastic surgery abdominal human skin by Franz diffusion cell. Retinyl palmitate permeates into deep skin layers. Besides, a PLA fluorescent derivative conjugated with Nile blue dye by an amide covalent bound was additionally obtained. Permeation profile of the nanocapsules with the fluorescent polymer was evaluated by confocal laser scanning microscopy (CLSM). The CLSM showed that nanocapsules were distributed uniformly, suggesting that the permeation mechanism through skin is intercellular. Thus, the use of these nanocapsules may be a feasible strategy to enhance the permeation of actives into the skin when delivery to deep layers is aimed.

Liposomal formulations of prilocaine: effect of complexation with hydroxypropyl-ß-cyclodextrin on drug anesthetic efficacy

A combined strategy, based on cyclodextrin complexation and loading in liposomes, has been investigated to develop a new delivery system with improved therapeutic activity of the local anesthetic, prilocaine (PRL). In order to evaluate the actual effectiveness and advantages of this approach compared to the traditional drug-in-liposome one, four different liposomal formulations were prepared: (1) liposomes loaded with PRL base as complex with hydroxypropyl-β-cyclodextrin (HP CD) in the aqueous phase; (2) liposomes loaded with PRL hydrochloride in the aqueous phase; (3) liposomes loaded with PRL base in the lipophilic phase; and (4) “double-loaded” liposomes, containing free PRL base in the membrane bilayer and its HP CD complex in the aqueous compartment. All batches were characterized for particle size, charge, deformability, and entrapment efficiency from using, respectively, light scattering, extrusion, and dialysis techniques, while the anesthetic effect was evaluated in vivo on Guinea pigs, according to the test of dorsal muscle contraction. All drug liposomal dispersions showed enhanced analgesic duration with respect to the corresponding aqueous solutions, but significant differences were observed between the different formulations. In particular, cyclodextrin complexation not only allowed an efficient encapsulation of PRL base in the aqueous vesicle core, but also increased the anesthetic effect duration and reduced the initial lag time, in comparison with the corresponding formulations containing, respectively, free PRL in the lipophilic phase or PRL hydrochloride in the aqueous vesicle core. The technique of double loading was the most effective, giving rise to the shortest onset time and longest duration of anesthetic effect.

Deformability and adhesive force of artificial platelets measured by atomic force microscopy

Platelet glycoprotein GPIaIIa is an adhesive protein that recognizes collagen. We have investigated polymerized albumin particles conjugated with recombinant GPIaIIa (rGPIaIIa-poly Alb) for their platelet-like function. To evaluate the feasibility of these particles to achieve the hemostatic process, we measured the deformability (Young’s modulus and spring constant) and the adhesive force of the particles using atomic force microscopy, which can measure the mechanical properties of individual cells. Our results showed that the Young’s modulus of these particles was 2.3-fold larger than that of natural platelets and 12-fold larger than that of human red blood cells. The Young’s modulus of the particles may have been determined by the properties of the polymerized albumin particle, although the glycoprotein of the platelet surface also contributed to the higher modulus. Our results also showed that the adhesive force of the rGPIaIIa-poly Alb with the collagen ligand was 52% of that of natural platelets. These two mechanical properties (deformability and adhesive force) of cells or particles, such as rGPIaIIa-poly Alb, are important specifications for the optimum design of platelet substitutes.

A comparison of viscosity–concentration relationships for emulsions

Differential effective medium theory (D-EMT) has been used by a number of investigators to derive expressions for the shear viscosity of a colloidal suspension or an emulsion as a function of the volume fraction of the dispersed phase. Pal and Rhodes [R. Pal, E. Rhodes, J. Rheol. 33 (7) (1989) 1021–1045] used D-EMT to derive a viscosity–concentration expression for non-Newtonian emulsions, in which variations among different oil–water emulsions were accommodated by fitting the value of an empirical solvation factor by matching the volume fraction at which the ratio of each emulsion was experimentally observed to have a viscosity 100 times greater than that of the pure solvent. When the particles in suspension have occluded volume due to solvation or flocculation, we show that the application of D-EMT to the problem becomes more ambiguous than these investigators have indicated. In addition, the resulting equations either do not account for the limiting behavior near the critical concentration, that is, the concentration at which the viscosity diverges, or they incorporate this critical behavior in an ad hoc way. We suggest an alternative viscosity–concentration equation for emulsions, based on work by Bicerano and coworkers [J. Bicerano, J.F. Douglas, D.A. Brune, J. Macromol. Sci., Rev. Macromol. Chem. Phys. C 39 (4) (1999) 561–642]. This alternative equation has the advantages that (1) its parameters are more closely related to physical properties of the suspension and (2) it recovers the correct limiting behavior both in the dilute limit and near the critical concentration for rigid particles. In addition, the equation can account for the deformability of flexible particles in the semidilute regime. The proposed equation is compared to the equation proposed by Pal and Rhodes.