<p style="text-align: justify">A magnetic particle suspension is a hopeful functional fluid in a variety of application fields and the medical engineering is a typical application field of magnetic particle suspensions. Representative applications in this field are magnetic hyperthermia and magnetic drug delivery system. The magnetic hyperthermia treatment is a medical therapy for killing tumor or cancer cells by means of a heating effect, and has been attracting attention as a new cancer treatment. Conventional studies on the magnetic hyperthermia are mainly based on magnetic spherical particles. In a previous study, we considered such a magnetic particle suspension in order to elucidate the relationship between the heating effect and the aggregate structures by means of Brownian dynamics simulations. From this study, it is clarified that chain-like clusters effectively function to give rise to a more significant heat generation effect under certain conditions. In recently days, the synthesis technology of magnetic particles has been significantly improved and therefore it is possible to synthesize magnetic particles with more complex geometrical shapes, such as rod-like, disk-like and cube-like. It may be expected that magnetic rod-like particles are able to yield a more significant heating performance than spherical particles since they exhibits a larger resistance in a flow field. However, there are no studies that elucidate the relationship between the aggregate structures of rod-like particles and the heating effect in the situation of a time-changing applied magnetic field. From this background, in the present study, we elucidate the behavior of the magnetic rod-like particles, which have a magnetic moment along the major axis direction, in an alternating magnetic field by means of Brownian dynamics simulations. Moreover, we attempt to clarify the influence of the aggregate structures on the heat generation performance. Several main results obtained from the present simulations are summarized in the following. If an applied magnetic field is strong and the magnetic particle-particle interaction strength is weak, the rod-like particles do not aggregate to form significantly stable clusters. This implies that the rod-like particles solely move and respond to the time-dependent magnetic field. In this situation, the rod-like particles rotate to follow the change in the direction of the alternating with a large delay, which gives rise to a significant heating effect. In the situation where the magnetic particle-particle and particle-field interactions are of the same order and sufficiently strong in comparison with thermal energy, the particles tend to aggregate to form long chain-like and raft-like clusters. Different from the case of a spherical particle suspension, the aggregate structures do not effectively function in exhibiting a more significant heat generation, but to the contrary, the heat generation performance rather diminishes. In the case of the magnetic particle-particle interaction strength being dominant, raft-like clusters are largely formed in the system. These clusters are significantly stable to the change in the time-dependent magnetic field, and therefore the rod-like particles constituting these raft -like clusters do not sufficiently rotate to follow the alternating magnetic field. As a result, a large heating effect is not able to be obtained in this situation.</p>

The Behavior of the Magnetic Rod-Like Particles in an Alternating Magnetic Field (Brownian Dynamics Simulations)

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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