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PubMed2005

Magnetic nanostructures as amplifiers of transverse fields in magnetic resonance.

We introduce the concept of amplifying the transverse magnetic fields produced and/or detected with inductive coils in magnetic resonance settings by using the reversible transverse susceptibility properties of magnetic nanostructures. First, we describe the theoretical formalism of magnetic flux amplification through the coil in the presence of a large perpendicular DC magnetic field (typical of magnetic resonance systems) achieved through the singularity in the reversible transverse susceptibility in anisotropic single domain magnetic nanoparticles. We experimentally demonstrate the concept of transverse magnetic flux amplification in an inductive coil system using oriented nanoparticles with uni-axial magnetic anisotropy. We also propose a composite ferromagnetic/anti-ferromagnetic core/shell nanostructure system with uni-directional magnetic anisotropy that, in principle, provides maximal transverse magnetic flux amplification.

Journal Article↗

PubMed2002

Magnetic fluctuations with a zero mean field in a random fluid flow with a finite correlation time and a small magnetic diffusion.

Magnetic fluctuations with a zero mean field in a random flow with a finite correlation time and a small yet finite magnetic diffusion are studied. Equation for the second-order correlation function of a magnetic field is derived. This equation comprises spatial derivatives of high orders due to a nonlocal nature of magnetic field transport in a random velocity field with a finite correlation time. For a random Gaussian velocity field with a small correlation time the equation for the second-order correlation function of the magnetic field is a third-order partial differential equation. For this velocity field and a small magnetic diffusion with large magnetic Prandtl numbers the growth rate of the second moment of magnetic field is estimated. The finite correlation time of a turbulent velocity field causes an increase of the growth rate of magnetic fluctuations. It is demonstrated that the results obtained for the cases of a small yet finite magnetic diffusion and a zero magnetic diffusion are different.

Journal Article↗

PubMed1999

High-resolution magnetic relaxation dispersion measurements of solute spin probes using a dual-magnet system.

The magnetic field dependence of the nuclear spin-lattice relaxation rate provides a detailed report of the spectral density functions that characterize the intra- and intermolecular fluctuations that drive magnetic relaxation. We have addressed the difficult sensitivity and resolution problems associated with low magnetic field strengths by using two magnets in close proximity and shielded from each other. The sample is stored in the high magnetic field, pneumatically driven to the variable satellite field, then returned to the high field for detection at high resolution. A magnetic shield effectively decouples the two magnets so that varying the satellite field strength has minimal effect on the field strength and shim of the high field magnet. The disadvantage of the sample-shuttle magnet-pair system is the restriction imposed on the relaxation times by the finite shuttle times. Experiments not described here have shown this rate maximum to be about 20 s(-1) for most practical solutions. However, we demonstrate here that the sensitivity gains over switched-current magnet systems permit characterization of solute inter- and intramolecular dynamics over the time scale range from tens of microseconds to less than a picosecond. This range permits investigation of a number of crucial chemical dynamics questions, while high sensitivity permits examination of a variety of solute spins. Representative data are presented for (1)H, (111)Cd, and (7)Li.

Cadmium↗

PubMed1995

[A functional orthodontic magnetic appliance (FOMA) after Vardimon. 1. A three-dimensional analysis of the force system of the attractive magnets].

The functional magnetic system (FMS) is a removable functional appliance which induces mandibular advance by means of mandibular and maxillary magnets in an attracting configuration. The maxillary and mandibular plates are each equipped with 2 cylindrically shaped cobalt-samarium magnets, 4 mm in diameter and 3 mm in height, which are welded into stainless steel housings. The force system of this magnetic configuration was analyzed using the orthodontic measurement and simulation system (OMSS). OMSS simulated the mandibular jaw movements by separating the installed magnets vertically, corresponding to a mouth opening of X = -10 mm, transversally (right excursion, +/left excursion, -) at Y = +/- 10 mm and sagittally (anterior displacement, +/posterior displacement, -) at Z = +/- 10 mm. The resulting 2D and 3D force/displacement diagrams elucidate the outstanding centripetal-spatial orientation characteristics of the functional magnetic appliance in reference to the full overlap brought about by the attraction of the mandibular magnet by the maxillary magnet. The maximum centripetal forces reached a value of approximately FY, max = 0.65 N for the vertical attracting force at full overlap of the mandibular and maxillary magnets (X = 0.55 mm, Y = Z = 0 mm), a value of FY, max = 0.65 N for the medial shearing force at a partial transversal overlap Z = 0, Y = +/- 2 mm and Y = +/- 6 mm), and for the sagittal shearing force a value of FZ, max = 1.2 N at a partial sagittal overlap of the magnets (Y = 0 mm, Z = +/- 2 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

Cobalt↗

PubMed2003

Magnetic drug targeting--biodistribution of the magnetic carrier and the chemotherapeutic agent mitoxantrone after locoregional cancer treatment.

Magnetic Drug Targeting means the specific delivery of chemotherapeutic agents to their desired targets, e.g. tumors, by using magnetic nanoparticles (ferrofluids) bound to these agents and an external magnetic field which is focused on the tumor. This type of target directed drug injection attempts to concentrate a pharmacologic agent by enhancing its efficacy while simultaneously minimizing deleterious side effects. In previous studies, we have been able to demonstrate the efficacy of this type of localized intraarterial chemotherapy in VX2 squamous cell carcinoma among rabbits [Alexiou, C., Arnold, W., Klein, R.J., Parak, F.G., Hulin, P., Bergemann, C., Erhardt, W., Wagenpfeil, S. and Lübbe, A.S. "Locoregional cancer treatment with Magnetic Drug Targeting", Cancer Res. 60 (2000) 6641-6648]. In the present investigation, we have studied the biodistribution of ferrofluids and chemotherapeutic agent by measuring the amount in the tumor, peritumoral area, various organs and body fluids (e.g. blood and urine), with and without Magnetic Drug Targeting. We compared results to that of administering a chemotherapeutic agent soley. An external magnetic field was directed toward the tumor for 60 min. Biodistribution of ferrofluids in the tumor was investigated using histological cross sections and measured semi-quantitatively using 123I-labeled nanoparticles and quantitatively by the use of radioactive 59Fe-ferrofluids. Mitoxantrone was quantitatively measured using HPLC-analysis. The strength of the external magnetic field was 0.6 Tesla (permanent magnet) in the 123iodine study and 1.7 Tesla (electromagnet) in the 59Fe-study and HPLC-analysis. The concentration of the ferrofluids (FFs) in the tumor region i.e. the tumor tissue and the surrounding area, which was under the influence of an external magnetic field, was found to be much higher than in the absence of one. In contrast to systemic chemotherapy, a much higher concentration of mitoxantrone in the tumor and the peritumoral area (region surrounding the tumor < or = 1 cm), by using only 50% and 20% of the normal dose was seen. Thus, the higher concentration of mitoxantrone could explain the therapeutic efficacy of Magnetic Drug Targeting in treatment of VX2 squamous cell carcinoma in rabbits in our previous studies with the advantage of no adverse clinical side effects.

Animals↗

PubMed2002

[Establishment of two-dimensional magnetic field finite element analysis model of cup-yoke-type magnetic attachment].

OBJECTIVE: The purpose of this study was to establish two-dimensional magnetic field finite element analysis model of cup-yoke-type magnetic attachment for optmizing the design of magnetic attachments. METHODS: Because the magnetic field of cup-yoke-type magnetic attachment is stable axial-symmetrical, the authors only analyzed two-dimensional magnetic field of 1/2 section. The Maxwell stress between magnet and keeper was integral analyzed using the finite element method, and the attractive force between magnetic attachments was obtained. RESULTS: Compared the value of calculated attractive force with that of examined, the authors found that the procedure veritably reflected influencing trend of variable factors on attractive force, and the value of former one was 10% less than the later one. CONCLUSION: This procedure can be used in magnetic field calculation of cup-yoke-type magnetic attachments.

Computer Simulation↗

PubMed2005

[MnIII2 (5-Rsaltmen)2NiII(pao)2(L)]2+: an S(T)=3 building block for a single-chain magnet that behaves as a single-molecule magnet.

Mn(III)-Ni(II)-Mn(III) linear-type trinuclear complexes bridged by oximate groups were selectively synthesized by the assembly reaction of [Mn2(5-Rsaltmen)2(H2O)2](ClO4)2 (5-Rsaltmen2-=N,N'-(1,1,2,2-tetramethylethylene) bis(5-R-salicylideneiminate); R=Cl, Br) with [Ni(pao)2(phen)] (pao-=pyridine-2-aldoximate; phen=1,10-phenanthroline) in methanol/water: [Mn2(5-Rsaltmen)2Ni(pao)2(phen)](ClO4)2 (R=Cl, 1; R=Br, 2). Structural analysis revealed that the [Mn(III)-ON-Ni(II)-NO-Mn(III)] skeleton of these trimers is in every respect similar to the repeating unit found in the previously reported series of 1D materials [Mn2(saltmen)2Ni(pao)2(L1)2](A)(2) (L(1)=pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole; A=ClO4-, BF4-, PF6-, ReO4-). Recently, these 1D compounds have attracted a great deal of attention for their magnetic properties, since they exhibit slow relaxation of the magnetization (also called single-chain magnet (SCM) behavior). This unique magnetic behavior was explained in the framework of Glauber's theory, generalized for chains of ferromagnetically coupled anisotropic spins. Thus, in these 1D compounds, the [Mn(III)-ON-Ni(II)-NO-Mn(III)] unit was considered as an S(T)=3 anisotropic spin. Direct-current magnetic measurements on 1 and 2 confirm their S(T)=3 ground state and strong uniaxial anisotropy (D/k(B) approximately -2.4 K), in excellent agreement with the magnetic characteristic deduced in the study on the SCM series. The ac magnetic susceptibility of these trimers is strongly frequency-dependent and characteristic of single-molecule magnet (SMM) behavior. The relaxation time tau shows a thermally activated (Arrhenius) behavior with tau0 approximately 1x10(-7) s and Delta(eff)/k(B) approximately 18 K. The effective energy barrier for reversal of the magnetization Delta(eff) is consistent with the theoretical value (21 K) estimated from |D| S2T. The present results reinforce consistently the interpretation of the SCM behavior observed in the [Mn2(saltmen)2Ni(pao)2(L1)2](A)2 series and opens new perspectives to design single-chain magnets.

Journal Article↗

PubMed2005

The internal magnetic field distribution, and single exponential magnetic resonance free induction decay, in rocks.

When fluid saturated porous media are subjected to an applied uniform magnetic field, an internal magnetic field, inside the pore space, is induced due to magnetic susceptibility differences between the pore-filling fluid and the solid matrix. The microscopic distribution of the internal magnetic field, and its gradients, was simulated based on the thin-section pore structure of a sedimentary rock. The simulation results were verified experimentally. We show that the 'decay due to diffusion in internal field' magnetic resonance technique may be applied to measure the pore size distribution in partially saturated porous media. For the first time, we have observed that the internal magnetic field and its gradients in porous rocks have a Lorentzian distribution, with an average gradient value of zero. The Lorentzian distribution of internal magnetic field arises from the large susceptibility contrast and an intrinsic disordered pore structure in these porous media. We confirm that the single exponential magnetic resonance free induction decay commonly observed in fluid saturated porous media arises from a Lorentzian internal field distribution. A linear relationship between the magnetic resonance linewidth, and the product of the susceptibility difference in the porous media and the applied magnetic field, is observed through simulation and experiment.

Journal Article↗

PubMed2004

Mixed-valence MnIIIMnIV clusters [Mn7O8(O2SePh)8(O2CMe)(H2O)] and [Mn7O8(O2SePh)9(H2O)]: single-chain magnets exhibiting quantum tunneling of magnetization.

The syntheses, structures, and magnetic properties of two new Mn7 complexes containing phenylseleninate ligands are reported. [Mn7O8(O2SePh)8(O2CMe)(H2O)] (1) and [Mn7O8(O2SePh)9(H2O)] (2) were both prepared by the reaction of 18 equiv of benzeneseleninic acid (PhSeO2H) with [Mn12O12(O2CMe)16(H2O)4] in MeCN. Complex 1 x 6MeCN crystallizes in the triclinic space group P, and complex 2 x 2CH2Cl2 crystallizes in the monoclinic space group P2(1)/m. Both compounds possess an unprecedented [Mn7O8]9+ core comprising a central [MnIII3(micro3-O)4]+ unit attached to [MnIV2(micro-O)2]4+ and [MnIV2(micro-O)(micro3-O)]4+ units on either side. In each cluster, the PhSeO2- groups function as bridging ligands between adjacent Mn centers. The structure reveals strong Se.O intermolecular contacts between Mn7 units to give a one-dimensional chain structure, with weak interchain interactions. Solid-state DC magnetic susceptibility measurements of complexes 1 and 2 reveal that they have very similar properties, and detailed studies on 1 by AC susceptibility measurements confirm an S = 2 ground-state spin value. In addition, out-of-phase AC signals are observed, suggesting slow magnetization relaxation. Magnetization versus DC field sweeps down to 0.04 K reveals hysteresis loops, but the temperature dependence of the coercivity is not what is expected of a single-molecule magnet. Instead, the behavior is due to single-chain magnetism, albeit with weak antiferromagnetic interactions between the chains, with the barrier to relaxation arising from a combination of molecular anisotropy and ferromagnetic intermolecular exchange interactions mediated by the Se...O contacts. An Arrhenius plot was constructed from the magnetization versus time decay data. The thermally activated region at > 0.5 K gave an effective relaxation barrier (Ueff) of 14.2 K. Below approximately 0.1 K, the relaxation is independent of temperature, which is characteristic of magnetization quantum tunneling through the anisotropy barrier. These Mn7 compounds are thus the first single-chain magnets to comprise polynuclear metal clusters and also the first for which the temperature-independent relaxation characteristic of tunneling has been identified. The work also emphasizes that out-of-phase AC signals for ostensibly molecular compounds are not sufficient proof by themselves of a single-molecule magnet.

Journal Article↗

PubMed2002

Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping.

Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire memory cell is desired, because reversal by domain-wall motion is much too slow. In principle, the fundamental limit of the switching speed via precession is given by half of the precession period. However, under-critically damped systems exhibit severe ringing and simulations show that, as a consequence, undesired back-switching of magnetic elements of an MRAM can easily be initiated by subsequent write pulses, threatening data integrity. We present a method to reverse the magnetization in under-critically damped systems by coherent rotation of the magnetization while avoiding any ringing. This is achieved by applying specifically shaped magnetic field pulses that match the intrinsic properties of the magnetic elements. We demonstrate, by probing all three magnetization components, that reliable precessional reversal in lithographically structured micrometre-sized elliptical permalloy elements is possible at switching times of about 200 ps, which is ten times faster than the natural damping time constant.

Journal Article↗

PubMed2005

Single-molecule magnets: structural characterization, magnetic properties, and (19)F NMR spectroscopy of a Mn(12) family spanning three oxidation levels.

The syntheses, crystal structures, and magnetic properties of [Mn(12)O(12)(O(2)CC(6)F(5))(16)(H(2)O)(4)] (2), (NMe(4))[Mn(12)O(12)(O(2)CC(6)F(5))(16)(H(2)O)(4)] (3), and (NMe(4))(2)[Mn(12)O(12)(O(2)CC(6)F(5))(16)(H(2)O)(4)] (4) are reported. Complex 2 displays quasi-reversible redox couples when examined by cyclic voltammetry in CH(2)Cl(2): one-electron reductions are observed at 0.64 and 0.30 V vs ferrocene. The reaction of complex 2 with 1 and 2 equiv of NMe(4)I yields the one- and two-electron reduced analogues, 3 and 4, respectively. Complexes 2.3CH(2)Cl(2), 3.4.5CH(2)Cl(2).(1)/(2)H(2)O, and 4.6C(7)H(8) crystallize in the triclinic P, monoclinic P2/c, and monoclinic C2/c space groups, respectively. The molecular structures are all very similar, consisting of a central [Mn(IV)O(4)] cubane surrounded by a nonplanar alternating ring of eight Mn and eight mu(3)-O(2)(-) ions. Peripheral ligation is provided by 16 bridging C(6)F(5)CO(2)(-) and 4 H(2)O ligands. Bond valence sum calculations establish that the added electrons in 3 and 4 are localized on former Mn(III) ions giving trapped-valence Mn(IV)(4)Mn(III)(7)Mn(II) and Mn(IV)(4)Mn(III)(6)Mn(II)(2) anions, respectively. (19)F NMR spectroscopy in CD(2)Cl(2) shows retention of the solid-state structure upon dissolution and detrapping of the added electrons in 3 and 4 among the outer ring of Mn ions on the (19)F NMR time scale. DC studies on dried microcrystalline samples of 2, 3, and 4.2.5C(7)H(8) restrained in eicosane in the 1.80-10.0 K and 1-70 kG ranges were fit to give S = 10, D = -0.40 cm(-)(1), g = 1.87, D/g = 0.21 cm(-)(1) for 2, S = 19/2, D = -0.34 cm(-)(1), g = 2.04, D/g = 0.17 cm(-)(1) for 3, and S = 10, D = -0.29 cm(-)(1), g = 2.05, D/g = 0.14 cm(-)(1) for 4, where D is the axial zero-field splitting parameter. The clusters exhibit out-of-phase AC susceptibility signals (chi(M)' ') indicative of slow magnetization relaxation in the 6-8 K range for 2, 4-6 K range for 3, and 2-4 K range for 4; the shift to lower temperatures reflects the decreasing magnetic anisotropy upon successive reduction and, hence, the decreasing energy barrier to magnetization relaxation. Relaxation rate vs T data obtained from chi(M)' ' vs AC oscillation frequency studies down to 1.8 K were combined with rate vs T data from DC magnetization decay vs time measurements at lower temperatures to generate an Arrhenius plot from which the effective barrier (U(eff)) to magnetization reversal was obtained; the U(eff) values are 59 K for 2, 49 and 21 K for the slower- and faster-relaxing species of 3, respectively, and 25 K for 4. Hysteresis loops obtained from single-crystal magnetization vs DC field scans are typical of single-molecule magnets with the coercivities increasing with decreasing T and increasing field sweep rate and containing steps caused by the quantum tunneling of magnetization (QTM). The step separations gave D/g values of 0.22 cm(-)(1) for 2, 0.15 and 0.042 cm(-)(1) for the slower- and faster-relaxing species of 3, and 0.15 cm(-)(1) for 4.

Crystallography, X-Ray↗

PubMed2004

Effect of magnetic resonance imaging on internal magnet strength in Med-El Combi 40+ cochlear implants.

OBJECTIVE: Magnetic resonance imaging (MRI) has been contraindicated when cochlear implants containing an internal magnet are in place because of concerns regarding torque, force, demagnetization, artifacts, induced voltages, and heating. The objective was to determine the magnetic field strength of Med-El Combi 40+ cochlear implant internal magnets after MRI studies. STUDY DESIGN/METHODS: Two fresh cadavers were used to study demagnetization using a repeated measures design and a magnetometer. Pre- and postMRI measurement of magnetic field strength was completed. Five sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 0.2 Tesla in the device-up and device-down positions. In the other cadaver, 15 sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 1.5 Tesla were conducted, 5 each with the head oriented at 80, 90, and 100 degrees rotated around the yaw plane (rotated around the z-axis). Subsequently, three cochlear implant patients completed 0.2 Tesla MRIs. For these patients, subjective and objective assessment of cochlear implant performance was performed. SETTING: Academic medical center. RESULTS: In the cadaver studies, analysis of variance showed no significant difference in the magnetic field strength after the 0.2 or 1.5 Tesla scans. There was no significant difference in the magnetic field strength for the three patients undergoing 0.2 Tesla MRIs and no adverse consequences, including no changes in telemetry, auditory sensations, nonauditory sensations, and sound quality. CONCLUSIONS: No significant demagnetization of the internal magnet occurred during repeated 1.5 Tesla MRI scans with the head orientations used in this study. In the cochlear implant patients, no significant demagnetization of the internal magnet occurred after a 0.2 Tesla MRI.

Artifacts↗

PubMed2003

Composition and element solubility of magnetic and non-magnetic fly ash fractions.

Magnetic and non-magnetic fractions of coal fly ashes from SE US electric power plants were characterized with special emphasis on the potential environmental consequences of their terrestrial disposal. Quartz and mullite were the crystalline minerals dominating the non-magnetic fractions. Magnetic fractions contained magnetite, hematite, and, to a lesser extent, quartz and mullite. Chemical analyses revealed that magnetic fractions had about 10 times higher concentrations of Fe, and 2-4 times higher concentrations of Co, Ni, and Mn. Non-magnetic fractions were enriched in K, Al and Ca. Iron content within fly ash particles was negatively correlated with elements associated with aluminosilicate matrix (Si, Al, K, Na). Solubility of most elements was higher in the non-magnetic than in the magnetic fractions of alkaline fly ashes at comparable pH. Calcium was associated with the non-magnetic fraction of the alkaline fly ashes which resulted in a higher pH buffering capacity of this fraction.

Calcium↗

PubMed2005

On-chip magnetic bead microarray using hydrodynamic focusing in a passive magnetic separator.

Implementing DNA and protein microarrays into lab-on-a-chip systems can be problematic since these are sensitive to heat and strong chemicals. Here, we describe the functionalization of a microchannel with two types of magnetic beads using hydrodynamic focusing combined with a passive magnetic separator with arrays of soft magnetic elements. The soft magnetic elements placed on both sides of the channel are magnetized by a relatively weak applied external magnetic field (21 mT) and provide magnetic field gradients attracting magnetic beads. Flows with two differently functionalized magnetic beads and a separating barrier flow are introduced simultaneously at the two channel sides and the centre of the microfluidic channel, respectively. On-chip experiments with fluorescence labeled beads demonstrate that the two types of beads are captured at each of the channel sidewalls. On-chip hybridization experiments show that the microfluidic systems can be functionalized with two sets of beads carrying different probes that selectively recognize a single base pair mismatch in target DNA. By switching the places of the two types of beads it is shown that the microsystem can be cleaned and functionalized repeatedly with different beads with no cross-talk between experiments.

Magnetics↗

PubMed2002

Pacemaker reed switch behavior in 0.5, 1.5, and 3.0 Tesla magnetic resonance imaging units: are reed switches always closed in strong magnetic fields?

MRI is established as an important diagnostic tool in medicine. However, the presence of a cardiac pacemaker is usually regarded as a contraindication for MRI due to safety reasons. The aim of this study was to investigate the state of a pacemaker reed switch in different orientations and positions in the main magnetic field of 0.5-, 1.5-, and 3.0-T MRI scanners. Reed switches used in current pacemakers and ICDs were tested in 0.5-, 1.5-, and 3.0-T MRI scanners. The closure of isolated reed switches was evaluated for different orientations and positions relative to the main magnetic field. The field strengths to close and open the reed switch and the orientation dependency of the closed state inside the main magnetic field were investigated. The measurements were repeated using two intact pacemakers to evaluate the potential influence of the other magnetic components, like the battery. If the reed switches were oriented parallel to the magnetic fields, they closed at 1.0 +/- 0.2 mT and opened at 0.7 +/- 0.2 mT. Two different reed switch behaviors were observed at different magnetic field strengths. In low magnetic fields (< 50 mT), the reed switches were closed. However, in high magnetic fields (> 200 mT), the reed switches opened in 50% of all tested orientations. No difference between the three scanners could be demonstrated. The reed switches showed the same behavior whether they were isolated or an integral part of the pacemakers. The reed switch in a pacemaker or an ICD does not necessarily remain closed in strong magnetic fields at 0.5, 1.5, or 3.0 T and the state of the reed switch may not be predictable with certainty in clinical situations.

Defibrillators, Implantable↗

PubMedDate not supplied

Magnetically suspended centrifugal blood pump with a radial magnetic driver.

A new magnetic bearing has been designed to achieve a low electronic power requirement and high stiffness. The magnetic bearing consists of 1) radial passive forces between the permanent magnet ring mounted inside the impeller rotor and the electromagnet core materials in the pump casing and 2) radial active forces generated by the electromagnets using the two gap sensor signals. The magnetic bearing was assembled into a centrifugal rotary blood pump (CRBP) driven with a radial, magnetic coupled driver. The impeller vane shape was designed based upon the computational fluid dynamic simulation. The diameter and height of the CRBP were 75 mm and 50 mm, respectively. The magnetic bearing system required the power of 1.0-1.4 W. The radial impeller movement was controlled to within +/- 10 microm. High stiffness in the noncontrolled axes, Z, phi, and theta, was obtained by the passive magnetic forces. The pump flow of 5 L/min against 100 mm Hg head pressure was obtained at 1,800 rpm with the electrical to hydraulic efficiency being greater than 15%. The Normalized Index of Hemolysis (NIH) of the magnetic bearing CRBP was one fifth of the BioPump BP-80 and one half of the NIKKISO HPM-15 after 4 hours. The newly designed magnetic bearing with two degrees of freedom control in combination with optimized impeller vane was successful in achieving an excellent hemolytic performance in comparison with the clinical centrifugal blood pumps.

Biomedical Engineering↗

PubMedDate not supplied

Cellular uptake of magnetic fluid particles and their effects on human adenocarcinoma cells exposed to AC magnetic fields in vitro.

Suspensions of coated superparamagnetic particles (magnetic fluids, MF) in AC magnetic fields have a pronounced specific absorption rate (SAR) per mass compared to multidomain particles. The aim of the present study was to investigate cellular uptake and the biological effects of AC magnetic field excited bio-compatible magnetic fluids on human carcinoma cells in vitro. One of the fluids tested was a dextran magnetite, which has a very low cyto-toxicity with survival fractions (SF) between 0.8 and 0.9 at concentrations of up to 5 mg ferrite per ml. Human carcinoma cells intracellularly accumulate up to 1 pg ferrite/cell which has been demonstrated by electron microscopy (TEM), X-ray spectroscopy and measurements of intracellular iron. It has been shown that the ferrite core is not altered intracellularly, but many of the dextran shells are degraded which yields particle chains and other aggregates observed in TEM. Semi-solid pellets of the tumour cells were treated with AC magnetic fields (520 kHz, 4-12.5 kA/m) or waterbath hyperthermia at 43 and 45 degrees C, in presence of extracellular and/or intracellular magnetic fluid particles. Although MF heating is produced from individual particles, the survival fractions of MF heated and water bath heated cells are equal. In fact, the extracellular MF particle distribution is homogeneous enough to obtain similar inactivation. In contrast to earlier reports intracellular dextran magnetite particles in AC magnetic fields did not induce cell inactivation. Since the amount of intracellular ferrite should be indeed large enough for cell inactivation, the loss of dextran shells is most probably the main cause of limited effectiveness of the intracellular magnetite particles. The present work has demonstrated that: (1) MFH is able to inactivate tumour cells in vitro to at least the same extent as water bath hyperthermia; and (2) that there is a sensitizer effect of ferrofluids at 43 degrees C probably caused by free ferric ions which induce oxidative stress; and (3) that there is no cytotoxic effect of intracellular dextran magnetite particles 30-180 min excited with AC magnetic fields used in this study. For the new method the term 'magnetic fluid hyperthermia (MFH)' is proposed.

Adenocarcinoma↗

PubMed1985

[Use of permanent magnets and magnetic fluids in experimental oncology].

The use of permanent magnets and magnetic fields (magnetic fluids and magnetic suspensions) alone or in complex with the antitumour compounds for the treatment of malignancies of various localizations is considered. Methods and forms of the use of permanent magnets are discussed. It is concluded that permanent magnets (as magnetic suspensions and magnetic fluids) used alone, in complex with chemical substances or in combination with other affecting factors (the temperature rise) induce a considerable regression of the tumour. Besides, permanent magnets may promote an increase of the antitumour drug concentration in the tissue of the diseased organ.

Albumins↗