Chains Of Magnetic Particles Research Articles

Effects of magnetic fields on fibrin polymerization and fibrinolysis

The authors' study first focuses on the role of ferromagnetic particles in the magnetic orientation of fibrin polymers. Rod-like magnetic particles were mixed into a solution of fibrinogen. The fibrin polymerization process was exposed to a magnetic field of 8 T. Magnetic particles agglomerated to form chains of clusters which were oriented parallel to magnetic fields. Magnetic orientation of fibrin polymers did not occur near the chains of magnetic particles. In a study of the possible effects of magnetic fields on the fibrinolytic process, dissolution of fibrin formed due to magnetic fields was observed. The fibrinolytic activities were evaluated by the absorbance changes at 500 nm and by a fibrin plate method. A distinguishable difference was observed in the dissolution of fibrin between fibrin gel formed with a magnetic field at 8 T and that formed without a field.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

フィブリンの磁場配向における磁性微粒子の影響

Fibrin polymers are diamagnetic materials that are Oriented in a magnetic field. Fibrinogen is changed to fibrin monomer by the action of protease thrombin, and fibrin monomers are polymerized. When a strong magnetic field is applied to the polymerization process of fibrin, the fibrin fibers are oriented parallel to the magnetic fields. The present study focuses on the role of ferromagnetic particles in the magnetic orientation of fibrin polymers. Fine magnetic particles were mixed into a solution of fibrinogen. The polymerization process of fibrin was exposed to magnetic fields up to 8.0 T created by using a superconducting magnet. Magnetic particles were agglomerated to form chains of clusters oriented parallel to the magnetic fields. The chains of magnetic particles themselves agglomerated and polymerized to a large fiber. We observed no oriented fibrin near the chains. In contrast, oriented fibrins were observed in the large fibers of chains.

Yield stress of a magnetic fluid in a magnetic field

The yield stressτ0 of a magnetic fluid in a plane channel and the shape of the chains restraining the motion of the fluid are determined. The equilibrium problem for a magnetic fluid in a plane channel in the presence of an external magnetic field perpendicular to the plane of the channel and a pressure difference between the channel ends is solved within the framework of the structured fluid model. It is shown that equilibrium is possible only when the pressure difference does not exceed a certain limit Δpcr at which the shear stress on the channel wall has a maximum. In weak fields Δpcr and the correspondingτ0 depend quadratically on the field and in strong fields tend to saturation. The phenomenological parameters of the model are estimated for the case in which the microstructure is a system of chains of magnetic particles. The results obtained are found to be in qualitative agreement with the experimentally observed dependence of Δpcr andτ0 on the field and the magnetic phase concentration.

The aggregation mechanism of small magnetic particle chains

The aggregation mechanism of small ferromagnetic particle chains in viscous media is discussed. If we describe such chains as infinite uniformly magnetized cylinders, there will be no interchain interaction. It is shown that in the next approximation - chains of identical (i.e. spherical) particle - the interaction force decreases exponentially with the interchain distance ( f≈exp(− r/ a), where a is the particle diameter), and hence this model cannot explain the strong aggregation of chains. However, the distribution of particle magnetic moments (resulting from size, shape etc. distributions) leads to an interaction, decreasing only as f≈ r −6 which can probably explain the observed phenomena.

Dissociation–association equilibrium of magnetic particle chains in homogeneous magnetic fields

An idealized statistical theory of chaining in a dilute suspension of macroscopic magnetic particles in a rarefied gas is presented when an external homogeneous magnetic field is present. The primary colloidal particles are assumed to be spherical, of the same size, and to have saturated magnetic moments. The magnetochemical potentials and the association–dissociation equations are derived for chains consisting of v≥1 magnetic grains, in dependence of the temperature T, the density Nv of chains, and the homogeneous magnetic field B0. High field intensities B0 are shown to shift the chain length distribution F=F(v) in favor of long chains, v≫1, whereas increasing temperatures T move the maximum of this statistical distribution to smaller chain lengths, v→1. The theory appears to be in qualitative agreement with oven experiments using an external magnetic field for the alignment and stabilization of the chains.