Magnetic nanoparticles are attracting attention not only for their applications in recording materials and electronic devices, but also in the medical field. "Theranostics" is a coined term denoting the simultaneous performance of therapy and diagnostics. The authors have developed various magnetic nanoparticles using their original reparation methods and have challenged themselves to apply them for biomedical purposes. This report introduces the gnetic relaxation phenomenon characteristic of the nanoscopic system of magnetic nanoparticles, and the potential for hyperthermia treatment and contrast imaging functions that leverage this characteristic.

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Magnetic Particle Imaging (MPI) is a novel imaging technique that visualizes the spatial distribution of magnetic nanoparticles by detecting their nonlinear magnetization responses under an oscillating magnetic field. Since its principle was first proposed by Gleich and Weizenecker in 2005, MPI has attracted increasing attention, particularly for biomedical applications such as vascular imaging and brain perfusion monitoring. This article provides an overview of MPI principles, system configurations, and recent technological developments. I introduce the generation and detection of MPI signals based on field-free regions (FFP/FFL), describe representative instrument designs ranging from small preclinical setups to emerging human-scale systems, and highlight the role of superparamagnetic iron oxide nanoparticles (SPIONs) as biocompatible tracers. Advances in nanoparticle surface engineering and signal processing methods have improved spatial resolution, multi-tracer imaging, and functional applications such as temperature mapping. Compared to existing modalities, MPI offers radiation-free, high-sensitivity imaging similar to PET, with potential for complementary clinical use in environments lacking nuclear medicine facilities. Nevertheless, significant challenges remain, including device scalability, power requirements for human-scale systems, and integration with anatomical imaging techniques such as CT or MRI. Continued research on instrumentation, tracer development, and hybrid imaging approaches will be essential to realize the clinical potential of MPI.

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Cancer theranostics using magnetic nanoparticles such as the hyperthermia treatment and magnetic particle imaging have been developed. Magnetic relaxation was the important mechanism determining magnetization dynamics of magnetic nanoparticles. In this study, to observe the tumor microenvironment with magnetic particle imaging, the magnetic relaxation property of magnetic nanoparticles injected into tumor implanted on a mouse body was investigated. The magnetic relaxation time spectrum as the magnetization distribution was analyzed from the magnetic relaxation process by the time-domain measurement, which affected by the properties of surroundings of magnetic nanoparticles particularly because of Brownian relaxation. Magnetic nanoparticles dispersed in the viscous medium and solidified with an epoxy resin were also prepared as the non-biological samples. By comparing the magnetic relaxation time spectrum in the tumor with that in non-biological samples, the properties of the tumor microenvironment were evaluated, which is applicable to the low-invasive approach for analyzing a tumor tissue without dissection.

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We aim to apply protein sensors to rapid intraoperative diagnosis of lymph node metastasis. In the present study, cytokeratin, which is a biomarker of lymph node metastasis, was bound to protein G-coated magnetic nanoparticles (FG beads, 180 nmφ) via primary antibody (Anti-Cytokeratin AE1/AE3 Antibody (Monoclonal Mouse IgG1)). The increase of the protein aggregated the magnetic nanoparticles and enhanced the magnetic signal. We have observed magnetic nanoparticles and protein aggregates by cryo-electron microscopy to obtain evidence for this hypothesis. By adding gold nanoparticles to the antibody, we observed the cross-bridging of magnetic nanoparticles via the antigen. Lymph nodes were obtained from two esophageal cancer patients and one non-cancer patient (corrosive esophagitis). Lymph nodes from cancer patients contain cytokeratin, which promotes the aggregation of magnetic nanoparticles and increases the magnetic signal. Statistically significant differences could be assessed between two cancer and non-cancer patients, suggesting the potential of intraoperative rapid diagnosis.

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Magnetite (Fe3O4) nanoparticles have been clinically used as MRI contrast agents and are known as highly biocompatible magnetic nanoparticles. The magnetic nanoparticles have been applied to medical fields since they are attracted to magnetic fields and also generate heat in an alternating magnetic field. In this review, we introduce our research on “magnetic pattering of cells”, “skeletal muscle tissue engineering using magnetic force”, and “nanowarming” as a technology for thawing frozen cells using magnetic particles.

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Lure fishing and fly-fishing have been positioned as sports deliberately different from the traditional Japanese fishing-style. In the case of fly-fishing, casting is the element which anglers must master to cast a fly, done so by using the weight of a line. This study uses experimental and computational analysis to investigate the dynamic behavior of a fly line. Fly-fishing is constituted by various elements, but the importance that casting holds is extremely large. Flying speed, the casting process, and the loop shape of the line while in flight are important for the proper presentation of flies. In the previous research, experiments and simulations were conducted to validate the adequacy of analytical modeling. However, there has been no application to casting devices for positioning lightweight fly. In this study, a fly-casting device that imitates a human arm is constructed using stepping motors. The device is verified whether fly casting is possible.

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Conventional mechanical gears are widely used in industries but face issues such as precision control, noise, and wear. Flux-modulated magnetic gears, which offer non-contact operation, low noise, and maintenance-free performance, have the potential to overcome these issues. However, they suffer from leakage flux and inefficient torque transmission. This study develops a flux-modulated magnetic gear model and analyzes its magnetic characteristics using the finite element method (FEM). Special focus is given to understanding starting operational characteristics through time-step simulations. A prototype model was fabricated for comparison, and measurements under various conditions were conducted to clarify the starting behavior and validate the analyzed results.

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