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. 2020 Nov 21;11(11):1020.
doi: 10.3390/mi11111020.

Localization and Actuation for MNPs Based on Magnetic Field-Free Point: Feasibility of Movable Electromagnetic Actuations

Chan Kim  1 , Jayoung Kim  2 , Jong-Oh Park  1   2 , Eunpyo Choi  1   2 , Chang-Sei Kim  1   2
Affiliations

Localization and Actuation for MNPs Based on Magnetic Field-Free Point: Feasibility of Movable Electromagnetic Actuations

Chan Kim et al. Micromachines (Basel). .

Abstract

Targeted drug delivery (TDD) based on magnetic nanoparticles (MNPs) and external magnetic actuation is a promising drug delivery technology compared to conventional treatments usually utilized in cancer therapy. However, the implementation of a TDD system at a clinical site based on considerations for the actual size of the human body requires a simplified structure capable of both external actuation and localization. To address these requirements, we propose a novel approach to localize drug carriers containing MNPs by manipulating the field-free point (FFP) mechanism in the principal magnetic field. To this end, we devise a versatile electromagnetic actuation (EMA) system for FFP generation based on four coils affixed to a movable frame. By the Biot-Savart law, the FFP can be manipulated by appropriately controlling the gradient field strength at the target area using the EMA system. Further, weighted-norm solutions are utilized to correct the positions of FFP to improve the accuracy of FFP displacement in the region of interest (ROI). As MNPs, ferrofluid is used to experiment with 2D and 3D localizations in a blocked phantom placed in the designed ROI. The resultant root mean square error of the localizations is observed to be approximately 1.4 mm in the 2D case and 1.6 mm in the 3D case. Further, the proposed movable EMA is verified to be capable of simultaneously scanning multiple points as well as the actuation and imaging of MNPs. Based on the success of the experiments in this study, further research is intended to be conducted in scale-up system development to design precise TDD systems at clinical sites.

Keywords: 3D localization; field-free point; movable electromagnetic actuation system.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The configuration of the proposed movable system for magnetic particle imaging (MPI) based on four coils. The mainframe of the system can be moved one-dimensionally by the actuation motor to scan the Z-axis. (a) To receive the signals reflected by the particles, a combined coil comprising a transmitting coil and a receiver coil was installed at the center of the region of interest (ROI).
Figure 2
Figure 2
The simulated field-free point (FFP) obtained from COMSOL on the XY-plane. (a) A simulation model of the proposed system. (b–e) The flexible mobility of the proposed FFP actuation structure in the system. The FFP is located at (−5,5) in (b), (5,5) in (c), (−5,−5) in (d), and (5,−5) in (e).
Figure 3
Figure 3
The desired FFP location is assumed to be (8,0). (a) The FFP field mapping corresponding to a weight of 30. (b) The FFP field mapping corresponding to a weight 50. (c) The FFP field mapping corresponding to a weight of 90. (d) The FFP field mapping corresponding to a weight of 141. The position corresponding to the minimum value (red mark in each field map) is at (8,7) in (a), (8,4) in (b), (8,2) in (c), and (8,0) in (d).
Figure 4
Figure 4
The four-coil scanning system.
Figure 5
Figure 5
Flow chart depicting the sequence of operations in the proposed system. The signal graph on the right side shows the comparison of signal noise, depending on the filtering system in the Labview system. The peak to peak value of amplitude is 0.2 mV for the filtered case, 0.6 mV for the original case.
Figure 6
Figure 6
(a) The magnetic nanoparticle (MNP) material property (ferrofluid, EMG 707) used for scanning experiments. (b) The nonlinear response of magnetization of EMG 707.
Figure 7
Figure 7
Comparison of locations of the highest intensity points of the particles and area. (a) The sequence of 2D scanning. (b) The reconstructed image based on the reflected signals.
Figure 8
Figure 8
Experimentally obtained 3D localization; (a) phantom model, (b) 2D imaging on XY-plane, and (c) a side view of 3D imaging.
Figure 9
Figure 9
Phantom corresponding to multiple positions. The red and blue points in (b) and (d) indicate the geometric center point and the measured points of the MNP group through a 3D scan, respectively; (a) frontal view of the phantom, (b) frontal view of the 3D imaging result, (c) sidelong view of the phantom, and (d) sidelong view of the 3D imaging result.
Figure 10
Figure 10
Nanoparticle manipulation to drive them to the targeted point: (a) schematic of steering the particles and (b) experimental results.
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