Behavior Of Magnetic Particles Research Articles

Three-Dimensional Patterning of the ECM Microenvironment Using Magnetic Nanoparticle Self Assembly.

This protocol describes a way to introduce topography to three-dimensional (3D) biomaterials. The self-assembling behavior of magnetic particles can be exploited to form nanoscale to microscale fibers, such that one can dissect the contribution of topography on cell behavior, which is independent of other physical properties of the biomaterial (e.g., stiffness). The magnetic particles are chemically cross-linked with several extracellular matrix (ECM) proteins and then using magnetic force-mediated assembly, one can program aligned nanofibers in a 3D hydrogel. This process allows the creation of diverse topographic patterns in 3D, including isotropic, anisotropic (fibril), or interfaced architectures, without changing the bulk stiffness of the scaffold material. This anisotropic architecture guides the dendritic protrusions of cells, which can be compared to cells grown in an isotropic architecture lacking spatial guidance cues. Several cell types, such as fibroblasts and neurons, have been cultured in this engineered 3D matrix. This technology provides an easy way to construct nano-bio interfaces for various biomedical engineering applications as well as dissect the role of topography in various cell behaviors. © 2016 by John Wiley & Sons, Inc.

ＭＲ流体単純せん断流れ中強磁性微粒子挙動の可視化

ＭＲ流体単純せん断流れ中強磁性微粒子挙動の可視化

<italic>In Situ</italic> Observation of Behavior of Magnetic Particle Clusters During Torque Transfer Between Textured Magnetic Poles

The viscosity of a magnetorheological fluid (MRF) changes with the magnetic field; however, the behavior of magnetic particles in an MRF under the application of a magnetic field has not been fully clarified. In our previous work, we proposed a real-time observation system in which the torque is simultaneously measured. Textured poles concentrated on a magnetic field, increasing the transfer of torque. In this paper, the behavior of magnetic particles, such as the formation, fracture, and sliding of clusters, in the presence of textured poles as well as the transfer of torque was investigated by in situ observation using our torque measurement system. With increasing depth of the pole texture, the magnetic-field gradient increased, the magnetic field at the edges of the texture increased, the clusters became concentrated in a narrower region, and the maximum torque increased. These results are expected to lead to the design of more efficient torque transfer devices using MRFs.

Optimization of the capture element for an OGMS based on the 3D computation of the magnetic particle behavior

Optimization of the capture element for an OGMS based on the 3D computation of the magnetic particle behavior

Tailored mechanical behavior of magnetic particles loaded carbon nanotube foam in presence of magnetic field

The compressive behavior of carbon nanotube (CNT) foam with an entangled microstructure has become an important research area due to its excellent energy absorption capability. This report presents a tailored mechanical behavior of CNT foam under an applied magnetic field when all CNTs in the foam are coated with magnetic nanoparticles. The presence of nanoparticles not only enhanced the stiffness of the foam to four times but also revealed a nonlinear variation in both the stress and energy absorption capability with the gradual increase of the magnetic field. Magnetization of both CNT and attached nanoparticles along the magnetic field direction are shown to play a crucial role in determining the dominant deformation mechanism.

Condensation, demixing, and orientational ordering of magnetic colloidal suspensions.

In this work we study the phase behavior of magnetic particles suspended in a simple nonmagnetic solvent. Magnetic particles are modelled as spherical particles carrying a three-dimensional, classical Heisenberg spin, whereas solvent molecules are treated as spherically symmetric Lennard-Jones particles. The binary mixture of magnetic particles and solvent is studied within the framework of classical density functional theory (DFT). Within DFT pair correlations are treated at the modified mean-field level at which they are approximated by orientation dependent Mayer f functions. In the absence of an external magnetic field four generic types of phase diagrams are observed depending on the concentration of magnetic particles. In this case we observe liquid-liquid phase coexistence between an orientationally ordered (polarized) and a disordered phase characterized by slightly different concentrations of magnetic particles. Liquid-liquid phase coexistence is suppressed by an external field and vanishes completely if the strength of the field is sufficiently large.

Microscopic observation of behavior of magnetic particle clusters during torque transfer between magnetic poles

The behavior of magnetic particles during the formation, fracture, and sliding of clusters was investigated. A setup, in which particles can be visualized and the torque between poles is measured simultaneously, was designed and built. In the case of flat poles, clusters were inclined in both the fracture and sliding mode areas. In the case of textured poles, the torque increased and varied with the cycle corresponding to the pitch of the texture. These clusters inclined by an angle less than that in the case of flat poles. The magnetic field distribution calculated by a finite element method supported this result, in which the field was concentrated at the concaves and their edges. These results will lead to the design of more efficient torque transfer devices using magnetorheological fluids.

MR流体単純せん断流れにおける強磁性微粒子挙動の数値解析

Behavior of micrometer-size magnetic particles in a simple shear flow of magnetorheological fluids is investigated by using numerical simulation. Hybrid simulation method which combined both HSMAC method and discrete particle method based on the simplified Stokes dynamics is performed. Behaviors of magnetic particles in shear flows between two parallel plates are simulated. Chain-like clusters appear and they are combined each other to form wall structure in the presence of magnetic field in the static state. In the weak shear flow, such clusters move with flow, however, magnetic particles are rearranged as layered sheet-like structure in the rather strong shear flow.

Investigation of the motion of particles in magnetorheological elastomers by X-μCT

The behavior of magnetic particles inside elastomeric matrices is a complex issue and can be influenced in many ways, e.g. by applying a magnetic field or external mechanical stimuli. It is of fundamental interest for theoretical descriptions and technological applications to study processes like structure formation of these particles in a magnetic field. For a better understanding of the microstructure and the motion of particles in magnetorheological elastomers (MRE), x-ray micro-computed tomography (Xμ-CT) investigations were carried out. A MRE with a quantity of 2 wt.% of iron powder and an isotropic allocation of the particles inside the matrix was prepared. By means of quantitative analysis with image processing software, information regarding the geometrical properties of the particles and their individual motion under the influence of a magnetic field was obtained. Therefore a set of three tomograms—a reference taken without magnetic field, a second tomogram in presence of an applied field and third one again taken at B = 0 mT—has been taken and compared. It is shown that the combination of Xμ-CT and digital image processing provides a tool for a quantitative analysis of single particle motion in a MRE forced by external stimuli.

The Behavior of Nano- and Micro-Magnetic Particles Under a High Magnetic Field Using a Superconducting Magnet

Magnetic force has been used for drug delivery, magnetic separation, and other kinds of micro- and nano-particle handling. As fundamental studies of these applications, we have investigated the visualization of the motion of micro-magnetic particles under a dynamic magnetic field. We have also studied the contactless grasp of a micro-magnetic particle suspended in a fluid by using coil currents. In the study, we have developed a method for quantitatively estimating the influencing forces. However, these experiments have limitations in the magnetic field strength of normal conducting electromagnets or permanent magnets. Therefore, much higher magnetic force is needed for the application to drug delivery or cell/DNA manipulation. High magnetic field generating high magnetic force saturates the magnetization of magnetic particles during the particle control, and the magnetic saturation influences the particle behavior. However, such behavior of magnetic particles has not been sufficiently studied yet. In this paper, the behavior of the particles nearly or fully saturated under the high magnetic field of a superconducting magnet was visualized successfully, and ferrite and feeble magnetic particles were introduced in order to gain insight into their behavior.

Surface finishing of cobalt chromium alloy femoral knee components

This paper describes the modification of surface roughness and lay of cobalt chromium alloy femoral knee components by magnetic abrasive finishing (MAF), including clarification of the MAF surface-processing mechanisms. The MAF process creates characteristic surfaces by micro-cutting of abrasive pressed by magnetic particles that nearly conform to the surface, removing large asperities and creating microasperities compared to hand-buffed surfaces. The process enables smoothing the surface on the nanometer scale with critical control of surface lay (e.g., crosshatch angle), altering the contact angle of water by a combination of kinematic behavior of magnetic particles over the freeform condyle surface.

Behavior of magnetic particles under fluctuating fields considering hysteresis characteristics

Simulations of magnetic particles are mostly carried out under spatially and temporally static magnetic fields. It is well known that chain-like clusters are formed under these constant fields. However the hysteresis characteristics of particles are therefore often neglected. In this paper, methods to analyze behavior of magnetic particles with hysteresis characteristics under fluctuating fields are proposed. Consideration of hysteresis characteristics and fluctuating fields brings nonlinearity and driving forces to the system in addition to the energy dissipation caused by particle collisions. This research aims to find the foothold of chaotic behavior, which is often found in these systems, among particle clustering. The proposed methods start from the discretization of fields. Collisions and clustering are modeled by treating mechanical contacts, namely, by solving Hertz's contact problem. A symplectic integrator is used for time integration. For the simulation, behavior of 200 magnetic particles under spatially and temporally fluctuating fields were examined. The results imply hysteresis characteristics have a great effect on clustering patterns.

Lattice Boltzmann simulation of the two-dimensional flow of a magnetic suspension between two parallel walls under a non-uniform magnetic field

We have developed a lattice Boltzmann method based on fluctuation hydrodynamics that is applicable to the flow problem of a particle suspension. In this method, we have introduced the viscosity-modifying method, rather than the velocity-scaling method, in which a modified viscosity is used for generating random forces in lattice Boltzmann simulations. The viscosity-modifying method is found to be applicable to the simulation of a magnetic particle suspension. We have applied this method to the two-dimensional Poiseuille flow of a magnetic suspension between two parallel walls in order to investigate the behavior of magnetic particles in a non-uniform applied magnetic field. From the results of the snapshots, the pair correlation function between the magnetic pole and the magnetic particles and the averaged local particle velocity and magnetization distributions, it was observed that the behavior of the magnetic particles changes significantly depending upon which factor dominates the phenomenon in the balance between the magnetic particle–particle interaction, the non-uniform applied magnetic field and the translational and rotational Brownian motion.

Lattice Boltzmann Simulation of a Two-Dimensional Flow of a Magnetic Suspension between the Two Parallel Walls under a Non-Uniform Magnetic Field

First we have developed the Lattice Boltzmann method based on the fluctuation hydrodynamics which is applicable to a flow problem of a particle suspension. In this method, we have introduced the viscosity-modifying method, instead of the velocity-scaling method, in which the modified viscosity is used for generating the random forces in the lattice Boltzmann simulation. This viscosity-modifying method has been seen to be available for a magnetic particle suspension. Then we have applied this method to a two-dimensional Poiseuille flow of a magnetic suspension between the two parallel walls in order to investigate the behavior of magnetic particles in a non-uniform applied magnetic field situation. From the results of the snapshots, the pair correlation function between the magnetic pole and the magnetic particles and the averaged local particle velocity and magnetization distributions, it is seen that the behavior of magnetic particles drastically changes due to which factor dominates the phenomenon much more significantly among the magnetic particle-particle interaction, the non-uniform applied magnetic field strength and the translational and rotational Brownian motion.

The behaviors of ferromagnetic nano-particles in and around blood vessels under applied magnetic fields

In magnetic drug delivery, therapeutic magnetizable particles are typically injected into the blood stream and magnets are then used to concentrate them to disease locations. The behavior of such particles in-vivo is complex and is governed by blood convection, diffusion (in blood and in tissue), extravasation, and the applied magnetic fields. Using physical first-principles and a sophisticated vessel-membrane-tissue (VMT) numerical solver, we comprehensively analyze in detail the behavior of magnetic particles in blood vessels and surrounding tissue. For any blood vessel (of any size, depth, and blood velocity) and tissue properties, particle size and applied magnetic fields, we consider a Krogh tissue cylinder geometry and solve for the resulting spatial distribution of particles. We find that there are three prototypical behaviors (blood velocity dominated, magnetic force dominated, and boundary-layer formation) and that the type of behavior observed is uniquely determined by three non-dimensional numbers (the magnetic-Richardson number, mass Péclet number, and Renkin reduced diffusion coefficient). Plots and equations are provided to easily read out which behavior is found under which circumstances (Figs. 5–8). We compare our results to previously published in-vitro and in-vivo magnetic drug delivery experiments. Not only do we find excellent agreement between our predictions and prior experimental observations, but we are also able to qualitatively and quantitatively explain behavior that was previously not understood.

Behaviour of magnetic particles in a liquid under a non-uniform magnetic field and gravity

Behaviour of magnetic particles in a liquid under a non-uniform magnetic field and gravity

In vitro investigation of the behaviour of magnetic particles by a circulating artery model

Magnetic drug targeting is the use of coated magnetic nanoparticles as carriers for cytostatic drugs. After intraarterial application of these carriers, they are attracted with an external magnetic field to, for example, an experimental VX2 tumour. The biological compatibility of this system depends on several physiological and physical parameters. We established an in vitro model to simulate in vivo conditions in a circulating system consisting of a circuit with an intact bovine femoral artery close to an external magnetic field. Nanoparticle suspensions were applied by a side inlet. After the magnetisation procedure particle size, concentration and distribution was examined.

Dynamic Consideration of Crowded Magnetic Particle Behavior in Magnetic Field Assisted Finishing Process

Magnetic force acting on each particle based on magnetic field data is analyzed in this report, by thinking of structure of brush-like cohering magnetic particles as a machining tool of magnetic assisted finishing process. The resultant explanation is that horizontal magnetic force in centripetal direction introduces downward force to workpiece surface in upward magnetic field, and that the force transmission formation made of crowded magnetic particles generates strong pressing force when machining resistance affects the move of magnetic particles on the occasion of machining. Knowledge on difference of magnetic particle behavior, whether resistant force transmission mode occurs or not, will materialize to select hard removing or fine finishing.

Dynamic Consideration of Crowded Magnetic Particle Behavior in Magnetic Field Assisted Finishing Process

Dynamic Consideration of Crowded Magnetic Particle Behavior in Magnetic Field Assisted Finishing Process

The investigation of capture behaviors of different shape magnetic sources in the high-gradient magnetic field

In this paper, we simulate the capture behavior and the advection–diffusion behavior of magnetic particles in the cross-section of different curvature magnetic sources which bring the high-gradient magnetic field with the time evolution. The results show that the capture behavior is affected not only by the fluid velocities, dynamic viscosity, particle size, and susceptibility, but also affected by the shape of magnetic sources. Although the curvature of magnetic source dominates the gradient of the magnetic field, enough large area facing the incoming fluid is still the main factor which affects the capture efficiency. The distribution of concentration in the cross-section area and source surface are both affected by the surface curvature, especially under the relatively stronger interaction of magnetic source. The influence by surface curvature becomes much more evident, larger curvature costs shorter time for particles accumulation than the smaller one. The magnetic force competing with the fluid drag force and the body force exerted on the fluid medium could both decide the concentration distribution.