Biomedical subjects

Tsunehisa Kimura

Publications and source records attributed to Tsunehisa Kimura.

7 recordsLinked to original sources

PubMed2006

Simultaneous Alignment and Micropatterning of Organic Crystallites under a Modulated Magnetic Field.

In a previous paper, we reported the micropatterning of magnetically isotropic particles using a microscopically modulated magnetic field. In this paper, we report that the alignment occurs simultaneously if the particles have magnetic anisotropy. An oil-in-water emulsion of p-terphenyl or anthracene was subjected to the modulated magnetic field and allowed to evaporate the solvent to obtain a line pattern consisting of the crystallites with alignment. The patterned samples exhibited an emission strongly polarized in the direction of the applied magnetic field that is perpendicular to the patterning lines.

Anisotropy↗

PubMed2006

Magnetic alteration of crystallite alignment converting powder to a pseudo single crystal.

The powder crystallites of L-alanine, selected for demonstration purposes, suspended in a photocurable resin were subjected to a frequency-modulated rotating magnetic field, and the achieved three-dimensional alignment was fixed by photopolymerization of the resin. The obtained sample exhibited the X-ray diffraction pattern that was comparable to the pattern of an equivalent actual original single crystal. This was achieved for the first time by the simultaneous alignment of the two magnetic axes, i.e., the easy and hard magnetization axes with respect to the space coordinates. A theoretical estimation indicates that a better alignment of the sample can be obtained if the sample preparation conditions are improved.

Journal Article↗

PubMed2005

Three-dimensional crystal alignment using a time-dependent elliptic magnetic field.

A theoretical study has been presented to show that it is possible to align three different diamagnetic susceptibility axes (chi(3) < chi(2) < chi(1) < 0) of a crystallite with respect to the laboratory coordinate system (x, y, z). The time-dependent magnetic field that periodically changes in direction and intensity on the xy plane in an elliptic manner (the intensity stronger in the x direction) at a rate quicker than the intrinsic rate of magnetic response causes the three-dimensional alignment, that is, chi(1) parallel x, chi(2) parallel y, and chi(3) parallel z. The fluctuation of the three susceptibility axes around the corresponding laboratory coordinates is estimated in terms of the fluctuation around the minimum of the time-averaged magnetic potential. This technique enables the three-dimensional alignment of the crystallographic axes.

Journal Article↗

PubMed2005

Magnetic alignment of the chiral nematic phase of a cellulose microfibril suspension.

Stable suspensions of tunicate cellulose microfibrils were prepared by acid hydrolysis of the cellulosic mantles of tunicin. They formed a chiral nematic phase above a critical concentration. External magnetic fields were applied to the chiral nematic phase in two different manners to control its phase structure. (i) Static magnetic fields ranging 1-28 T were used to align the chiral nematic axis (helical axis) in the field direction. (ii) A rotating magnetic field (5 T, 10 rpm) was applied to unwind the helices and to form a nematic phase. These phenomena were interpreted in terms of the anisotropic diamagnetic susceptibility of the cellulose microfibril. The diamagnetic susceptibility of the microfibril is smaller in the direction parallel (chi( parallel)) to the fiber axis than in the direction perpendicular (chi( perpendicular)) to the fiber axis, that is, chi( parallel) < chi( perpendicular) < 0. Because the helical axis coincides with the direction normal ( perpendicular) to the fiber axis, the helical axis aligned parallel to the applied field. On the other hand, the rotating magnetic field induced the uniaxial alignment of the smallest susceptibility axis, that is, chi( parallel) in the present case, and brought about unwinding of the helices.

Animals↗

PubMed2005

Micropatterning of cells using modulated magnetic fields.

A new technique of cell micropatterning was presented. Mouse osteoblast cells (MC3T3-E1) were seeded on a substrate whose surface was exposed to a periodically modulated magnetic field (a line pattern with a 200- or 600-microm pitch) produced by a field modulator inserted into a homogeneous magnetic field of 1 T generated by an electromagnet. The cells were trapped consistent with the line profile of the modulated field. The trapping efficiency was enhanced by adding Mn(II)EDTA (paramagnetic) to the cultivation medium. The cells were subsequently incubated in the magnetic field. The same technique was applied to whole blood to pattern red blood cells.

3T3 Cells↗

PubMed2004

Uniaxial alignment of the smallest diamagnetic susceptibility axis using time-dependent magnetic fields.

A diamagnetic particle with magnetic susceptibilities chi3 < chi2 = chi1 < 0 was subjected to a rotating magnetic field to obtain an alignment of the chi3 axis (the smallest susceptibility axis) in the direction perpendicular to the plane of the rotating magnetic field. A polymer short fiber, whose fiber axis coincides with the chi3 axis, was suspended in a fluid with the same density, and then a rotating magnetic field generated by a rotation of a pair of permanent magnets was applied. The fiber axis, rotating following the applied field, finally ended up with an alignment perpendicular to the plane of the rotating magnetic field. The experimental data on the time course of the alignment was in good agreement with the numerical calculation based on the equation of rotation.

Journal Article↗

PubMed2004

Particle trapping and undulation of a liquid surface using a microscopically modulated magnetic field.

An aluminum/iron-layered block (periodicity of 300 microm) was placed in a homogeneous magnetic field (ca. 1 T) to produce a periodic modulation of the magnetic field over the block surface. This modulation caused an undulation of the surface of a thin liquid layer spread over the block. The same modulated field was used to trap polystyrene spheres (20 microm in diameter suspended in a liquid) in a periodic line pattern. The spheres were trapped above the iron layers of the block where the field strength is lower in the present experimental setup. Upon drying, the trapped spheres formed self-organized packing.

Letter↗