Ferromagnetic Microspheres Research Articles

Optimisation of the Flame Spheroidisation Process for the Rapid Manufacture of Fe3O4-Based Porous and Dense Microspheres

The rapid, single-stage, flame-spheroidisation process, as applied to varying Fe3O4:CaCO3 powder combinations, provides for the rapid production of a mixture of dense and porous ferromagnetic microspheres with homogeneous composition, high levels of interconnected porosity and microsphere size control. This study describes the production of dense (35-80 µm) and highly porous (125-180 µm) Ca2Fe2O5 ferromagnetic microspheres. Correlated backscattered electron imaging and mineral liberation analysis investigations provide insight into the microsphere formation mechanisms, as a function of Fe3O4/porogen mass ratios and gas flow settings. Optimised conditions for the processing of highly homogeneous Ca2Fe2O5 porous and dense microspheres are identified. Induction heating studies of the materials produced delivered a controlled temperature increase to 43.7 °C, indicating that these flame-spheroidised Ca2Fe2O5 ferromagnetic microspheres could be highly promising candidates for magnetic induced hyperthermia and other biomedical applications.

Non‐Reciprocity in High‐Q Ferromagnetic Microspheres via Photonic Spin–Orbit Coupling

AbstractNon‐reciprocal devices serving as fundamental elements in photonic and microwave circuits have attracted great attention for its applications in both classical and quantum information processing. The spin–orbit coupling (SOC) of light in microstructures shows that the polarization affects and controls the spatial degrees of freedom of light, which could been exploited to break the reciprocity of light transmission. Here, non‐reciprocal light transmission is demonstrated experimentally in high‐quality factor yttrium iron garnet microspheres via photonic SOC and Faraday effect. By applying an magnetic field in the vertical direction of resonator equator, the degeneracy of the clockwise and counter‐clockwise whispering gallery modes are lifted. The non‐reciprocal effect is shown for both polarizations and promises applications including non‐reciprocal photonic devices, magneto‐optic modulators, and magnetometers.

Reorientation Response of Magnetic Microspheres Attached to Gold Electrodes Under an Applied Magnetic Field

In this work, we report the mechanical reorientation of thiolated ferromagnetic microspheres bridging a pair of gold electrodes under an external magnetic field. When an external magnetic field (7 kG) is applied during the measurement of the current–voltage characteristics of a carboxyl ferromagnetic microsphere (4 μm diameter) attached to two gold electrodes by self-assembled monolayers (SAMs) of octane dithiol (C8H18S2), the current signal is distorted. Rather than due to magnetoresistance, this effect is caused by a mechanical reorientation of the ferromagnetic sphere, which alters the number of SAMs between the sphere and the electrodes and therefore affects conduction. To study the physical reorientation of the ferromagnetic particles, we measure their hysteresis loops while suspended in a liquid solution.

Arterial Embolization Hyperthermia in Porcine Renal Tissue

Background. Arterial embolization hyperthermia (AEH) consists of arterially embolizing tumors with ferromagnetic particles that generate hysteretic heating on exposure to an alternating magnetic field. It was the objective of this study to evaluate AEH using the kidney of a large animal as a tumor model.Methods. Between 50 and 400 mg of ferromagnetic microspheres (32 μm in diameter) was arterially infused into the kidneys of three pigs. Temperature probes were inserted into renal tissue, skin, and subcutaneous fat. Each subject was then exposed to an alternating magnetic field for 5 min, while under a general anesthetic. A femoral artery catheter was used to monitor the cardiac pulse. Three days after treatment the renal tissue was chemically analyzed for iron content, which was then correlated with tissue heating rates.Results. There was a linear relationship between heating rate and iron concentration (N = 18, correlation = 0.72, P < 0.001) that suggested tissue iron concentrations in the range of 1.55 to 4.05 mg/g would yield tissue heating rates of 0.5 to 1.0°C/min. No temperature increases were detected in control renal tissue (N = 6). The median increase in skin temperature after 5 min of heating was 0.8°C (N = 6, min = 0.7°C, max = 1.3°C), and that in subcutaneous fat was 1.1°C (N = 6, min = 0.8°C, max = 1.2°C). There was no detectable stimulation of cardiac or skeletal muscle or peripheral nerves during treatment. All subjects had uneventful 3-day posttreatment survivals.Conclusion. This study has shown that AEH can target deep-seated, vascularized tissue in a large animal with therapeutic temperatures (> 42°C), and that the treatment is safe and well tolerated. Further assessment of treatment schedules should allow for a human trial in the near future.

Treatment of experimental rabbit liver tumours by selectively targeted hyperthermia

Experimental rabbit liver tumours were preferentially heated to therapeutic temperatures without compromising the surrounding normal hepatic parenchyma. This was achieved by the use of hepatic arterially infused ferromagnetic microspheres that heat as a result of magnetic hysteresis loss when exposed to an alternating magnetic field. Treatment sessions involving a single 20-min exposure to the alternating field resulted in total suppression of tumour growth at 14 days compared to controls, in which tumour sizes increased dramatically over the same period. Histopathological examination of treated tumour sections showed total tumour destruction in some cases. Separate animal groups used to control for the effects of the embolized microspheres alone and for the effect of the applied magnetic field yielded similar tumour growth responses to a control group with no intervention whatsoever. The achievement of positive temperature differentials between tumour and normal liver and the consequent therapeutic responses encourages further development of this technology for the treatment of liver cancer in humans.

Experimental examination of a targeted hyperthermia system usinginductively heated ferromagnetic microspheres in rabbit kidney

It is known that significant heating can be generated by magnetic hysteresiseffects in small ferromagnetic particles exposed to a rapidly alternatingmagnetic field. If such particles can be made to infiltrate the vascular bedsurrounding a tumour by intravascular infusion then it may be possible togenerate sufficient heating to destroy the tumour by hyperthermia. One of theconstraints on such a technique is the limited amount of magnetic materialthat can be delivered to a tumour via the intravascular route and theconsequent heating that can be induced by this material. Here, we report on aseries of experiments in which doses of microspheres containing differentamounts of ferromagnetic material were infused into rabbit kidneys via therenal artery with the aim of testing whether adequate tissue heating could beachieved using realistic concentrations of the embolised material. Heatingrates were measured for each infused quantity under similar conditions withthe animal alive and dead to examine the role of blood flow in the heatingprocess. The results show that tissue temperatures above the therapeuticthreshold of 42 °C can be readily achieved using this method withclinically relevant concentrations of microspheres in living tissue.