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Magnetic nanoparticles are used in a wide range of medical applications. However, the accurate steering of the particles through the vascular system is still an open research question. Thus, this paper introduces a novel hybrid magnetic array for steering magnetic nanoparticles through a bifurcation. The array consists of permanent plus electromagnets and is based on a Halbach structure. It combines the advantages of the strong magnetic field of low-cost permanent magnets with the adjustability of electromagnets. The array is investigated numerically in a 3D model using COMSOL Multiphysics. In the simulations, the propagation of the particles in a symmetrical bifurcation is analyzed for discrete coil currents in the range of −10A to 10 A. The results reveal that for low negative currents of −1A to −0.5 A, the influence of the magnetic field of the permanent magnets can be almost completely eliminated, and only 0.5% and 0.9 %, respectively, of the particles were trapped by the magnets. Thus, the hybrid array outperforms the reference of a Halbach array fully built of permanent magnets. Overall, the proposed hybrid array is much more flexible, and the magnetic force can be adjusted more precisely compared to an array of permanent magnets.

Magnetic Drug Targeting is a new approach in cancer therapy, where magnetic nanoparticles are used as carriers for cancer drugs. Commonly, external magnets are employed for steering the particles inside the blood vessels towards a desired direction. However, an unwanted side effect of the steering is the accumulation of the particles underneath the steering magnet. Many researchers address the number of accumulated particles, but, to the best of the authors’ knowledge, the retroaction of the accumulation profile on the generated magnetic field and, therefore, on the magnetic steering force, has not been investigated so far. Thus, in the proposed study, the influence of the accumulation profile on the magnetic force was numerically investigated. Therefore, a 2D model of a blood vessel with particles assumed as an accumulation profile and a nearby magnet was examined. Moreover, the length, thickness, and effective susceptibility of the approximated accumulation profile and the magnet size were varied. The results reveal that the field distribution is significantly affected, especially for high effective susceptibilities. The initially applied profile amplified the magnetic force; however, when the profile accumulated, it reduced the force up to 50 %. Overall, the results reveal that the retroaction of the particle distribution on the magnetic field must be considered in a simulation model.

The main challenge in magnetic drug targeting lies in steering the magnetic particles, especially in deeper body layers. For this purpose, linear Halbach arrays are currently in focus. However, to the best of the authors' knowledge, the impact of the magnetization angle between two neighboring magnets in Halbach arrays has not been investigated for particle steering so far. Therefore, in this paper, a systematic numerical parameter study of varying the magnetization angle of linear Halbach arrays is conducted. This is completed by undertaking a typical magnetic drug targeting scenario, where magnetic particles have to be steered in an optimized manner. This includes the calculation of the magnetic flux density, its gradient, the total magnetic energy, and the resulting magnetic force based on a fitting function for the different Halbach constellations in the context of examining their potential for predicting the particle distribution. In general, increased magnetization angles result in an increased effective range of the magnetic force. However, as there is a trade-off between a weak force on the weak side of the array and a simple manufacturing process, a magnetization angle of 90 ∘ is recommended. For evaluating the steering performance, a numerical or experimental evaluation of the particle distribution is mandatory. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles offer numerous promising biomedical applications, e.g. magnetic drug targeting. Here, magnetic drug carriers inside the human body are directed towards tumorous tissue by an external magnetic field. However, the success of the treatment strongly depends on the amount of drug carriers, reaching the desired tumor region. This steering process is still an open research topic. In this paper, the previous study of a linear Halbach array is extended by an additional Halbach array with different magnetization angles between two adjacent magnets and investigated numerically using COMSOL Multiphysics. The Halbach arrays are arranged with permanent magnets and generate a relatively large region of a moderately homogeneous, high magnetic field while having a strong gradient. This results in a strong magnetic force, trapping many particles at the magnets. Afterwards, to avoid particle agglomeration, the Halbach array is flipped to its weak side. Therefore, the magnetic flux density, its gradient and the resulting magnetic force are computed for the different Halbach arrays with different constellations of magnetization directions. Since the calculation of the gradient can lead to high errors due to the used mesh in Comsol, the gradient was derived analytically by investigating two different fitting functions. Overall, the array with a 90 ∘ shifted magnetization performs best, changing the magnetic sides of the array easily and deflecting more particles. Besides, the results revealed that the magnetic force dominates directly underneath the magnets compared to the other existing forces on the SPIONS. Summarized, the results depict that the magnetic force and, thus, the region where the particles are able to get washed out, can be adjusted using low-cost permanent magnets. [ABSTRACT FROM AUTHOR]