In TDDS, it is critical to focus MNPs deep into the body. The proposed concept was optimized within the constraints of the available resources by employing an optimum approach and commercially accessible software. The proposed design’s theory, modeling descriptions, and simulation results were provided. The findings show that the suggested EMA system is capable of steering MNPs. Because of the basic coil construction and simple guidance system, this technique has a high practical application. This chapter investigates the design of an electromagnetic system to steer the magnetic nanoparticles in the desired direction for targeted drug delivery. We have also optimized the coil parameters. The system comprises of four coils, where all the four coils are operated simultaneously to produce a sufficient magnetophoretic force, which steers the MNPs. In conclusion, we propose a new design of an electromagnetic actuator for navigating the MNPs in a targeted drug delivery system with enhanced accuracy of steering the drug to the desired location.
Chapter 4
Stiction Mitigation and Disaggregation of Magnetic Particles in TDDS
Contents
4.1 Introduction . . . 52 4.2 System Model . . . 54 4.3 Simulation Framework . . . 58 4.4 Results and Discussions . . . 58 4.5 Chapter Summary . . . 63
4.1 Introduction
Targeted Drug Delivery is a technique whereby drug loaded MNPs in the microflu- idic channel are navigated to the target location under the influence of an external magnetic field [90,100]. More precisely, the MNPs are injected into the inlet of a Y-shaped bifurcating microfluidic channel. From the injection point, the MNPs are propelled by the fluidic force, resulting from the laminar flow of fluid in the microchannel. To steer the MNPs to the target outlet, an external magnetic field is applied, which produces a magnetic force orthogonal to the direction of the fluidic force. The parabolic profile of fluid flow velocity results in the dominance of magnetic force over fluidic force at side-walls of the channel. This results in aggregation and stiction of MNPs to the inner walls of the channel.
Several actuation methodologies are proposed in the open literature to miti- gate the stiction and aggregation problem of MNPs [87,89,109]. The concept of a functionalized magnetic field is proposed in [87,109], whereby a time-varying multiplier function reverses the direction of magnetic force in alternate time slots for steering and detaching the MNPs, respectively. In these works, it is observed that the magnitude of the force exerted for steering the MNPs is the same as that during pull back operation of the stuck MNPs. However, pulling back the MNPs with such high force may cause some MNPs to cross over to the wrong direction, thus leading to a reduction of navigation efficiency. To address this issue, a dis- continuous asymmetrical field function is applied in [89], whereby the stuck MNPs are detached with a much lower magnetic force, as compared to that for steering.
Specifically, the scheme uses three different time slots, the first two being used for steering and stiction removal, while the third time slot comprises of a null mag- netic field intended for disaggregation of the MNPs. However, it may be noted that during the null slot, there will be no control of the actuation system over the MNPs. This may lead to the random propulsion of MNPs to the undesired outlet along with the fluid flow.
Motivated by the above works, we present a time-varying magnetic field (TVMF) for effective steering of MNPs to the correct outlet of the bifurcated channel, while taking into account the stiction and aggregation of MNPs during navigation oper- ation. Specifically, we emphasize on the fact that, in contrast to [89], the stiction removal and disaggregation of MNPs can be achieved in a single time slot by ad- justing both the magnetic force as well as the slot duration. The TVMF operates by switching between two modes of operation viz, (i) Mode 1 and (ii) Mode 2. In Mode 1, the TVMF is applied for a certain duration so as to facilitate steering of the MNPs towards the target outlet. During this process, some MNPs which
4.1 Introduction 53
Figure 4.1: 3D view of the electromagnetic actuation system and Y-shaped fluidic channel.
aggregate and get stuck to the side-walls are released by applying the TVMF in the reverse direction to that in Mode 1. The magnetic force resulting from the TVMF in Mode 2 has a small magnitude, which can release the stuck MNPs at side-walls but cannot steer them into the incorrect outlet. Furthermore, the fluidic force dominates over this small magnetic force as the MNPs are pulled back from the side walls (due to the former’s parabolic nature), thereby minimizing the ag- gregation of MNPs. However, the influence of fluid force could result in a random flow of MNPs in the channel. Hence, the duration for applying TVMF in Mode 2 has to be adjusted in such a way that the MNPs are confined within the desired region of interest. This work aims to analyze the coupling of applied magnetic field and switching time for effective navigation of MNPs in the channel. Simulation results are presented to highlight the optimal switching time with respect to the applied magnetic field, which is required to obtain the desired particle trajectory.
Table 4.1: Coil parameters of the proposed EMA system wi hi wo ho IoL IiL IiR IoR
(mm) (mm) (mm) (mm) (A) (A) (A) (A)
84.54 68.64 59.7 30.1 13.88 0.523 14.38 3.7
Figure 4.2: XY cross-sectional view of proposed EMA system and Y-shaped chan- nel.