Low gravity on earth by magnetic levitation of biological material

The use of a magnetic field gradient levitation apparatus as a tool for investigating gravisensing mechanisms in biological systems and as a low gravity simulator for biological systems is described. The basic principles are described. Differences between its application to pure materials and the heterogeneous materials of biological materials are emphasized.     

Static magnetic field with a strong magnetic field gradient (41.7 T/m) induces c-Jun expression in HL-60 cells

We investigated the effects of 6- and 10-T static magnetic fields (SMFs) on the expression of protooncogenes using Western blot immunohybridization methods. We used a SMF exposure system, which can expose cells to a spatially inhomogeneous 6 T with a strong magnetic field (MF) gradient (41.7 T/m) and a spatially homogeneous 10 T of the highest magnetic flux density in this experiment. HL-60 cells exposed to either 6- or 10-T SMF for periods of 1 to 48 h did not exhibit remarkable differences in levels of c-Myc and c-Fos protein expression, as compared with sham-exposed cells. In contrast, c-Jun protein expression increased in HL-60 cells after exposure to 6-T SMF for 24, 36, 48, and 72 h. These results suggest that a homogeneous 10-T SMF does not alter the expression of the c-jun, c-fos, and c-myc protooncogenes. However, our observation that exposure to a strong MF gradient induced c-Jun expression suggests that a strong MF gradient may have significant biological effects, particularly regarding processes related to an elevation of c-jun gene expression.     

Cleavage and survival of Xenopus embryos exposed to 8 T static magnetic fields in a rotating clinostat

In this study, we examined cleavage and survival of fertilized Xenopus embryos exposed to 8 T static magnetic fields (SMFs). We investigated fertilized Xenopus embryos exposed to magnetic field either in static chamber or in a rotating culture system. Our results showed that the exposure to the strong magnetic field of 8 T changed the third cleavage furrow from the usual horizontal one to a perpendicular one; however, when the direction of gravity was randomized by exposing embryos to magnetic field in a rotating culture system, the third cleavage furrow were formed horizontally, a finding which suggests that the observed distortion of the third cleavage furrow in magnetism-exposed embryos was accomplished by altering gravity effects which were elicited by diamagnetic force due to high gradient magnetic field. Our results also showed that the exposure to the strong magnetic field did not damage survival. These results demonstrate that SMF and altering gravity cause distortion of the third cleavage furrow and show that effects of exposing cleavage embryos to magnetic field were transient and did not affect the post-cleavage development. We also showed that strong magnetic field is not hazardous to the cleavage and blastula-gastrula transition of developing embryonic cells.     

Magnetic field is the dominant factor to induce the response of Streptomyces avermitilis in altered gravity simulated by diamagnetic levitation

Background

Diamagnetic levitation is a technique that uses a strong, spatially varying magnetic field to simulate an altered gravity environment, as in space. In this study, using Streptomyces avermitilis as the test organism, we investigate whether changes in magnetic field and altered gravity induce changes in morphology and secondary metabolism. We find that a strong magnetic field (12T) inhibit the morphological development of S. avermitilis in solid culture, and increase the production of secondary metabolites.

Methodology/Principal Findings

S. avermitilis on solid medium was levitated at 0 g*, 1 g* and 2 g* in an altered gravity environment simulated by diamagnetic levitation and under a strong magnetic field, denoted by the asterix. The morphology was obtained by electromicroscopy. The production of the secondary metabolite, avermectin, was determined by OD_{245 nm}. The results showed that diamagnetic levitation could induce a physiological response in S. avermitilis. The difference between 1 g* and the control group grown without the strong magnetic field (1 g), showed that the magnetic field was a more dominant factor influencing changes in morphology and secondary metabolite production, than altered gravity.

Conclusion/Significance

We have discovered that magnetic field, rather than altered gravity, is the dominant factor in altered gravity simulated by diamagnetic levitation, therefore care should to be taken in the interpretation of results when using diamagnetic levitation as a technique to simulate altered gravity. Hence, these results are significant, and timely to researchers considering the use of diamagnetic levitation to explore effects of weightlessness on living organisms and on physical phenomena.     

Induction of primary root curvature in radish seedlings in a static magnetic field

Primary roots of radish (Raphanus sativus L.) seedlings were exposed to an inhomogeneous static magnetic field generated by a permanent magnet, during continuous rotation on a 0.06 rpm clinostat, thereby reducing the unilateral influence of gravity. The roots responded tropically to the static magnetic field with the tropism appearing to be negative. These roots responded significantly (P < 0.05) to the south pole of the magnet. The significant tropic response was found for a magnetic flux density of 13-68 mT, for a field gradient of 1.8-14.7 T/m, and for the product of magnetic field and field gradient of 0.023-1.0 T(2)/m. A small, but insignificant, response of the roots to the north pole has also been found.     

Effect of static magnetic fields on the budding of yeast cells

The effect of static magnetic fields on the budding of single yeast cells was investigated using a magnetic circuit that was capable of generating a strong magnetic field (2.93 T) and gradient (6100 T² m^?1). Saccharomyces cerevisiae yeast cells were grown in an aqueous YPD agar in a silica capillary under either a homogeneous or inhomogeneous static magnetic field. Although the size of budding yeast cells was only slightly affected by the magnetic fields after 4 h, the budding angle was clearly affected by the direction of the homogeneous and inhomogeneous magnetic fields. In the homogeneous magnetic field, the budding direction of daughter yeast cells was mainly oriented in the direction of magnetic field B. However, when subjected to the inhomogeneous magnetic field, the daughter yeast cells tended to bud along the axis of capillary flow in regions where the magnetic gradient, estimated by B(dB/dx), were high. Based on the present experimental results, the possible mechanism for the magnetic effect on the budding direction of daughter yeast cells is theoretically discussed. Bioelectromagnetics 31:622–629, 2010. © 2010 Wiley‐Liss, Inc.     

Retardation of embryogenesis by extremely low frequency 60 Hz electromagnetic fields

Fertilized Medaka fish eggs were used to determine if electromagnetic fields, designed to simulate those beneath a high voltage power line, have biological effects on vertebrate embryo development. The newly fertilized eggs were exposed to a 60 Hz electrical field of 300 mA/m2 current density, a 60 Hz magnetic field of 1.0 gauss RMS, or to the combined electric plus magnetic fields for 48 hours. No gross abnormalities were observed in any of the embryos as they developed, but significant development delays were seen in those embryos exposed to either the magnetic or to the combined electromagnetic fields; delays were not seen in the embryos exposed to the electrical field. Thus, a 60 Hz magnetic field like that encountered in a man made powerline environment was shown to retard development of fish embryos.     

Effects of strong static magnetic fields used in magnetic resonance imaging on insulin-secreting cells

The magnetic flux density of MRI for clinical diagnosis has been steadily increasing. However, there remains very little biological data regarding the effect of strong static magnetic fields (SMFs) on human health. To evaluate the effects of strong SMFs on biological systems, we cultured insulin-secreting cells under exposure to sham and SMF conditions (3-10 T of magnetic flux density, and 0-41.7 T/m of magnetic field gradient) for 0.5 or 1 h, and analyzed insulin secretion, mRNA expression, glucose-stimulated insulin secretion, insulin content, cell proliferation and cell number. Exposure to SMF with a high magnetic field gradient for 1 h significantly increased insulin secretion and insulin 1 mRNA expression. Exposure to SMF with a high magnetic flux density for 0.5 h significantly enhanced responsiveness to glucose stimulation. Exposure to SMF did not affect the insulin content, cell proliferation or cell number. Our results suggested that MRI systems with a higher magnetic flux density might not cause cell proliferative or functional damages on insulin-secreting cells, and that SMF with a high magnetic field gradient might be used clinically after thorough in vivo investigations are conducted.     

Ferritin conjugates as specific magnetic labels. Implications for cell separation

Concanavalin A coupled to the naturally occurring iron storage protein ferritin is used to label rat erythrocytes and increase the cells' magnetic susceptibility. Labeled cells are introduced into a chamber containing spherical iron particles and the chamber is placed in a uniform 5.2 kG (gauss) magnetic field. The trajectory of cells in the inhomogeneous magnetic field around the iron particles and the polar distributions of cells bound to the iron particles compare well with the theoretical predictions for high gradient magnetic systems. On the basis of these findings we suggest that ferritin conjugated ligands can be used for selective magnetic separation of labeled cells.     

Devices for gradient static magnetic field exposure

We describe devices designed for magnetic field exposures in which field amplitude and gradients are controlled simultaneously. Dosimetry based on field continuation of high resolution magnetic field scans and numerical models is compared with validation measurements. The dosimetry variables we consider are based on the assumption that the biological or chemical system under study has field transducers that are spatially isotropic, so that absolute field amplitude and two gradient components fully describe local exposure.     

Analysis of the distribution of flowing erythrocytes in a model vessel under an inhomogeneous magnetic field

Changes in the distribution of flowing erythrocytes in a straight cylinder were studied under an inhomogeneous magnetic field. The magnetic field was applied perpendicular to a cylinder, which had a 90° side vessel at the end (oriented towards the magnetic field) to detect changes in the erythrocyte distribution within the cylinder. (1) The attraction of paramagnetic erythrocytes by the magnetic field was demonstrated by an increase in the concentration (or number) of erythrocytes drawn into the side vessel. The flow of diamagnetic, oxygenated erythrocytes was unaffected. (2) The degree of attraction of the paramagnetic erythrocytes was proportional to ``(magnetic susceptibility)' and to ``(magnetic flux density) × (magnetic field gradient)' up to 10 T²/m, but it saturated at high magnetic field. The onset of the saturation depended on the magnetic susceptibility of the erythrocytes. (3) The degree of attraction depended on the hematocrit of the flowing erythrocyte suspension, with a maximum value at a low hematocrit. These phenomena are explained on the basis of the balance between the paramagnetic attractive force of the magnetic field and the collision rate between erythrocytes. Received: 2 May 1996 / Accepted: 1 July 1996     

A Two-Dimensional Simulation Model of the Bicoid Gradient in Drosophila

Background

Bicoid (Bcd) is a Drosophila morphogenetic protein responsible for patterning the anterior structures in embryos. Recent experimental studies have revealed important insights into the behavior of this morphogen gradient, making it necessary to develop a model that can recapitulate the biological features of the system, including its dynamic and scaling properties.

Methodology/Principal Findings

We present a biologically realistic 2-D model of the dynamics of the Bcd gradient in Drosophila embryos. This model is based on equilibrium binding of Bcd molecules to non-specific, low affinity DNA sites throughout the Drosophila genome. It considers both the diffusion media within which the Bcd gradient is formed and the dynamic and other relevant properties of bcd mRNA from which Bcd protein is produced. Our model recapitulates key features of the Bcd protein gradient observed experimentally, including its scaling properties and the stability of its nuclear concentrations during development. Our simulation model also allows us to evaluate the effects of other biological activities on Bcd gradient formation, including the dynamic redistribution of bcd mRNA in early embryos. Our simulation results suggest that, in our model, Bcd protein diffusion is important for the formation of an exponential gradient in embryos.

Conclusions/Significance

The 2-D model described in this report is a simple and versatile simulation procedure, providing a quantitative evaluation of the Bcd gradient system. Our results suggest an important role of Bcd binding to non-specific, low-affinity DNA sites in proper formation of the Bcd gradient in our model. They demonstrate that highly complex biological systems can be effectively modeled with relatively few parameters.     

Anomalous diffusion of water in biological tissues.

This article deals with the characterization of biological tissues and their pathological alterations. For this purpose, diffusion is measured by NMR in the fringe field of a large superconductor with a field gradient of 50 T/m, which is rather homogenous and stable. It is due to the unprecedented properties of the gradient that we are able not only to determine the usual diffusion coefficient, but also to observe the pronounced Non-Debye feature of the relaxation function due to cellular structure. The dynamics of the probability density follow a stretched exponential or Kohlrausch-Williams-Watts function. In the long time limit the Fourier transform of the probability density follows a long-tail Lévy function, whose asymptotic is related to the fractal dimension of the underlying cellular structure. Some of the properties of Lévy walk statistics are discussed and its potential importance in understanding certain biophysical phenomena like diffusion processes in biological tissues are pointed out. We present and discuss for the first time NMR data giving evidence for Lévy processes that capture the essential features of the observed power law (scaling) dynamics of water diffusion in fresh tissue specimens: carcinomas, fibrous mastopathies, adipose and liver tissues.     

Magnetophoresis and ferromagnetic resonance of magnetically labeled cells

We develop in this paper two methods, based on different physical concepts, to quantify the uptake of magnetic nanoparticles in biological cells. The first one, magnetophoresis, is based on the measurement of the velocity of magnetically labeled cells submitted to a magnetic field gradient. The second one quantitates the particles' electronic spin using an electron paramagnetic resonance experiment. We show a quantitative agreement between both methods for macrophagic cells. The uptake kinetics and uptake capacity are discussed for macrophagic cells and other cell lines.     

Lack of chick embryotoxicity after 20 kHz, 1.1 mT magnetic field exposure

This investigation was undertaken because biological studies to evaluate the effects of intermediate frequency magnetic fields are insufficient. White Leghorn fertile eggs (60/group) were either exposed to a 20 kHz, 1.1 mT(rms) sinusoidal magnetic field or sham‐exposed during the first 2, 7, or 11 days of embryogenesis. Lower dose exposures at 0.011 and 0.11 mT(rms) for 2 days were also conducted to elucidate possible dose–response relationships. Additional eggs given all‐trans‐retinoic acid, a teratogen, were exposed to the 1.1 mT(rms) magnetic field for the same periods to investigate the modification of embryotoxicity. After exposure, embryos were examined for mortality and developmental abnormalities. Developmental stage, number of somite pairs, and other developmental endpoints were also evaluated. Experiments were triplicated and conducted in a blind fashion. No exposure‐related changes were found in any of the endpoints in intact embryos exposed to1.1 mT(rms) or to the lower doses of 0.11 and 0.011 mT(rms) magnetic fields. Retinoic acid administration produced embryotoxic responses, which were embryonic death and developmental abnormalities, in 40–60% of embryos in the sham‐exposed groups. The magnitude of these responses was not changed significantly by the magnetic field exposures. Under the present experimental conditions, exposure to 20 kHz magnetic field up to 1.1 mT(rms) was not embryotoxic in the chick and did not potentiate the embryotoxic action of retinoic acid. Bioelectromagnetics 30:573–582, 2009. © 2009 Wiley‐Liss, Inc.     

Effects of an inhomogeneous magnetic field on flowing erythrocytes

Effects of an inhomogeneous magnetic field on narrow erythrocyte streams in a wide and transparent laminar buffer flow were studied. The stream line of erythrocytes containing paramagnetic hemoglobin showed distinct displacement toward the stronger magnetic field. The displacement increased in the order, oxygenated erythrocytes (no displacement), erythrocytes containing cyanomethemoglobin, deoxygenated erythrocytes, erythrocytes containing methemoglobin in the high spin state; more precisely the displacement was proportional to the square of the paramagnetic moment of hemoglobin contained in the erythrocytes. In addition, the displacement was proportional to the product of the magnetic flux density and its gradient, and approximately proportional to the hematocrit of the flowing-erythrocyte suspension, and was much larger than that calculated for a single erythrocyte. These phenomena could be successfully interpreted by the interaction of paramagnetic erythrocytes with the inhomogeneous magnetic field, the resistance force (Stokes Law) from the bulk water, and the hydrodynamic interaction between erythrocytes.     

Myotube orientation using strong static magnetic fields

In this experiment, we evaluated the effects of strong static magnetic fields (SMF) on the orientation of myotubes formed from a mouse-derived myoblast cell line, C2C12. Myogenic differentiation of C2C12 cells was conducted under exposure to SMF at a magnetic flux density of 0-10 T and a magnetic gradient of 0-41.7 T/m. Exposure to SMF at 10 T led to significant formation of oriented myotubes. Under the high magnetic field gradient and a high value of the product of the magnetic flux density and magnetic field gradient, myotube orientation increased as the myogenic differentiation period increased. At the 3 T exposure position, where there was a moderate magnetic flux density and moderate magnetic field gradient, myotube orientation was not observed. We demonstrated that SMF induced the formation of oriented myotubes depending on the magnetic flux density, and that a high magnetic field gradient and a high value of the product of the magnetic flux density and magnetic field gradient induced the formation of oriented myotubes 6 days after myogenic differentiation. We did not detect any effect of the static magnetic fields on myogenic differentiation or cell number. To the best of our knowledge, this is the first report to demonstrate that myotubes orient to each other under a SMF without affecting the cell number and myogenic differentiation.     

Life on Magnets: Stem Cell Networking on Micro-Magnet Arrays

Interactions between a micro-magnet array and living cells may guide the establishment of cell networks due to the cellular response to a magnetic field. To manipulate mesenchymal stem cells free of magnetic nanoparticles by a high magnetic field gradient, we used high quality micro-patterned NdFeB films around which the stray field’s value and direction drastically change across the cell body. Such micro-magnet arrays coated with parylene produce high magnetic field gradients that affect the cells in two main ways: i) causing cell migration and adherence to a covered magnetic surface and ii) elongating the cells in the directions parallel to the edges of the micro-magnet. To explain these effects, three putative mechanisms that incorporate both physical and biological factors influencing the cells are suggested. It is shown that the static high magnetic field gradient generated by the micro-magnet arrays are capable of assisting cell migration to those areas with the strongest magnetic field gradient, thereby allowing the build up of tunable interconnected stem cell networks, which is an elegant route for tissue engineering and regenerative medicine.     

Design of a magnetic field generator for experiments on magnetic effects in cell cultures

A magnetic field generator constructed of rare earth-cobalt magnets is proposed for examining the biological effects of static magnetic fields (less than 1 T) on tissue cultures. Important quantities of a magnetic field from a biological-effects viewpoint, ie, its strength and the product of strength and gradient, are analysed. A practical procedure for designing the generator with optimum parameters is given. Also, parameters are determined which will yield a sinusoidal spatial field distribution.     

Measurement and analysis of static magnetic fields that block action potentials in cultured neurons

To characterize the properties of static magnetic fields on firing of action potentials (AP) by sensory neurons in cell culture, we developed a mathematical formalism based on the expression for the magnetic field of a single circular current loop. The calculated fields fit closely the field measurements taken with a Hall effect gaussmeter. The biological effect induced by different arrays of permanent magnets depended principally on the spatial variation of the fields, quantified by the value of the gradient of the field magnitude. Magnetic arrays of different sizes (macroarray: four center-charged neodymium magnets of ?14 mm diameter; microarray: four micromagnets of the same material but of ?0.4 mm diameter) allowed comparison of fields with similar gradients but different intensities at the cell position. These two arrays had a common gradient value of ?1 mT/mm and blocked >70% of AP. Alternatively, cells placed in a field strength of ?0.2 mT and a gradient of ?0.02 mT/mm produced by the macroarray resulted in no significant reduction of firing; a microarray field of the same strength but with a higher gradient of ?1.5 mT/mm caused ?80% AP blockade. The experimental threshold gradient and the calculated threshold field intensity for blockade of action potentials by these arrays were estimated to be ?0.02 mT/mm and ?0.02 mT, respectively. In conclusion, these findings suggest that spatial variation of the magnetic field is the principal cause of AP blockade in dorsal root ganglia in vitro. © 1995 Wiley-Liss, Inc.