2.1. Paradigm
The internal thoracic artery (ITA) with an external permanent magnet was represented using a two-dimensional model. Figure 1a shows the ITA and its branches in the human body. The schematic depiction for the MDT model is illustrated in Fig. 1b, an external permanent magnet is implanted at the target drug release site, which generates a magnetic field that attracts the MNP. The ITA as a blood vessel, is an artery that supplies the anterior chest wall and the breasts. The left internal thoracic artery (LITA) and right internal thoracic artery (RITA) originated directly from the subclavian artery. The length of LITA is different from 159 to 220 mm, with a mean of 182.60 mm from the origin to the end point, and a diameter of 2.31 ± 0.70 mm. The RITA varied from 150 to 231 mm, with a mean length of 185 mm and a diameter1.98 ± 0.04 mm [23].
Dasatinib (DAS) was selected as a breast anticancer drug encapsulated in nano magnetic self-assembled micelles as reported in our previously reported work [24]; [25]. Briefly, the magnetite nanomicelles (MNMs) were prepared using the co-precipitation technique. The magnetite nanoparticle was prepared by dissolved 2.2 g of FeCl2.4H2O and 5.8 g of FeCl3.6H2O in 200 mL of distilled water at room temperature. Then, the solution was heated to 70 oC and 10 mL of NH₄OH (30%) was added rapidly under higher stirring to produce a black precipitate. After that, 5 mL of hexane was added to 20 mg of magnetite nanoparticles, the magnetite solution was added dropwise to 50 mL of distilled water containing 100 mg of zein-lactoferrin micelles. The MNM was formed by sonication the mixture for 30 min at 50 oC under nitrogen flow. DAS is a highly hydrophobic anti-cancer drug, the solvent evaporation method was used to encapsulate DAS into the inner MNM core. The DAS was dissolved in ethanol (1 mg/mL) and added slowly to 50 mL of MNM solution (2 mg/mL), Afterward, it was stirred at a moderate magnetic field overnight to let the ethanol evaporate and encapsulate the DAS into the inner hydrophobic core of the zein-lactoferrin micelles [24]. A model has been developed to simulate DAS-MNM released into the ITA blood vessels and trajectory to specific targets by an external magnetic field.
2.2. Governing Equations
To simulate DAS-MNM delivery at the target sites, the blood flow, magnetic static field, and particle tracking domains were used in this model. The laminar blood flow and far from the heart are considered. Navier–Stokes continuity and momentum equations (Equations (1) and (2)) are used to derive the blood velocity and pressure profiles into ITA [8].
$$\rho \nabla .\left(\overrightarrow{u}\right)=0 \left(1\right)$$
$$\rho \left(\overrightarrow{u}.\nabla \right)\overrightarrow{u}=-\overrightarrow{\nabla }P+\mu {\nabla }^{2}\overrightarrow{u}+\overrightarrow{F} \left(2\right)$$
where \(\overrightarrow{u}\) (m/s) refers to the velocity vector; ρ (kg/m3) is the blood density; µ (Pa∙s) is blood dynamic viscosity; P (Pa) is the pressure; and \(\overrightarrow{F}\) (N/m3) is the external forces. Since the model deals with a low Reynolds number blood flow, the inertial term can be ignored in Eq. (2).
The rheology of blood flow can be explained by several models. Johnson and colleagues investigated one Newtonian blood flow model and five non-Newtonian blood viscosity models simulation [27], It was established that the power-law model is satisfactory for fitting the experimental results over strain rates range (γ ̇), 0.1 < γ ̇ < 1000 s−1. Additionally, many other blood models behaviors summarizes the power-law behavior at low strain rates and Newtonian behavior at high strain rates [27]. Thus, the power-law model was used to define the rheology of blood in our model [28].
$$\eta =\lambda \left(\dot{\gamma }\right){\left|\dot{\gamma }\right|}^{n\left(\dot{\gamma }\right)-1} \left(3\right)$$
$$\lambda \left(\dot{\gamma }\right)={\eta }_{\infty }+\varDelta \eta exp\left[-\left(1+\frac{\left|\dot{\gamma }\right|}{a}\right)exp\left(\frac{-b}{\left|\dot{\gamma }\right|}\right)\right] \left(4\right)$$
$$n\left(\dot{\gamma }\right)={n}_{\infty }+\varDelta n exp\left[-\left(1+\frac{\left|\dot{\gamma }\right|}{c}\right)exp\left(\frac{-d}{\left|\dot{\gamma }\right|}\right)\right] \left(5\right)$$
where | \(\dot{\gamma }\) | is the strain rate magnitude. The parameters values used in our model were quoted from the work of Ballyk and co-workers [28]: η∞ = 0.0035 kg/(m.s), \({\Delta }\eta\) = 0.025 kg/(m.s), \(a\)= 50 s−1, b = 3 s− 1, n∞ = 1, \({\Delta }n\) = 0.45, c = 50 s−1, and d = 4 s− 1.
The magnetic field surrounding a permanent magnet is defined by the following Equations [29].
Ampere-Maxwell equation for static magnetic field:
$$\nabla \times H=J, \left(6\right)$$
Gauss’s law for the magnetic flux density:
$$\nabla .B=0 \left(7\right)$$
The magnetic flux density in different domains can be described by the relation between H and B.
$$\nabla .\left({\mu }_{o}{\mu }_{r}\left(H+B\right)\right)=0 \left(8\right)$$
where H (A/m) is magnetic field strength; and B (A/m) is the magnetization of the magnet. µo and µr are the relative magnetic permeability of free space and fluid respectively.
In the particles tracing domain, there are a number of factors that have an impact on the DAS-MNM motion including magnetophoretic force, viscous force, inertial force, gravitational force, Brownian motion, and interparticle interaction. It might be possible to synthesize the particles in a way to prevent interparticle interactions that would lead to agglomeration [30]. Since the particle diameters are greater than 50 (nm), Brownian motion is neglected [8]. Furlani and Ng [31] observed that magnetization and viscous forces are the dominant forces in diluted particle suspensions. Newton’s second law is considered for the particle tracing domain as shown by Eq. (9) [29].
$$\frac{d\left({m}_{p}\overrightarrow{V}\right)}{dt}=\sum \overrightarrow{F } \left(9\right)$$
where \({m}_{p}\) is the mass of particles and \(\overrightarrow{V}\) is particle velocity. F is the sum of magnetophoretic and viscous forces acting on the particles.
In presence of an external magnetic field, Ferro particles are magnetized and steered towards a magnet. From Eq. (10) can determine the resultant magnetophoretic force [32].
$$\overrightarrow{{F}_{MP}}=\frac{\pi }{4}{d}_{p}^{3}{\mu }_{o}{\mu }_{r}K\overrightarrow{\nabla }{H}^{2} \left(10\right)$$
$$K=\frac{{\mu }_{p}-{\mu }_{r}}{{\mu }_{p}+2{\mu }_{r}} \left(11\right)$$
Where dP is particle diameter; µP is particles permeability.
Stokes drag model is utilized to estimate the drag force acting on particles. [33].
$${Re}_{r}=\frac{\rho \left|\overrightarrow{u}-\overrightarrow{V}\right|{d}_{p}}{\mu } \left(12\right)$$
$$\overrightarrow{{F}_{D}}=\frac{{\rho }_{p}{d}_{p}^{2}}{18\mu }{m}_{p}\left(\overrightarrow{u}-\overrightarrow{V}\right) \left(13\right)$$
where ρ (kg/m3) is the density of blood; µ (Pa∙s) is blood viscosity; \({d}_{p}\) (m), \({\rho }_{p}\) (kg/m3), \({m}_{p}\)(kg), indicate particles diameter, density, and mass respectively; \(\overrightarrow{u}\) (m/s) is blood velocity, and \(\overrightarrow{V}\) (m/s) is particles velocity.
According to Calandrini et al., capture efficiency is assessed using Eq. (14), [34].
$${\eta }_{C}=\frac{{N}_{in}-{N}_{out}}{{N}_{in}} \left(14\right)$$
where \({\eta }_{C}\)is the capture efficiency; Nin is the total number of DAS-MNM injected; and Nout is the total number of MNMs swept away.
The numerator in Eq. (14) is a good indicator of the MDT's ability in delivering DAS-MNM, which equates to the number of DAS-MNM delivered to the target zone.
2.3. Geometry Meshing and Numerical Procedures
To mimic the truthful flow conditions of ITAs, a well-defined geometry and a fairly simple approach were utilized. Figure 2 illustrates three different domains were generated with various numerical grids. The maximum element size for numerical free triangular mesh in magnetic field domain (1), external magnet domain (2), and blood vessel domain (3) were 0.25, 0.08, and 0.04 mm, respectively. The geometry included only one main inlet (Dinlet ≈ 3 mm) and eight outlets (Doutlet ≈ 2–1.5 mm). The magnetic field and a velocity profile in the artery are the two characteristics of the model that describe blood flow during magnetic drug targeting.
In this model, all calculations were implemented by commercial software COMSOL Multiphysics® 6.0. Initially, the model required several interfaces physics to be applied:
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CFD module involving sophisticated blood flow models.
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AC/DC module for generating magnetic fields.
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Particle trajectories module
Through the COMSOL Multiphysics, it is possible to create a 2D geometry of the artery and an external magnet implanted as shown in Fig. 2. Equations (1–14) were used to simulate non-Newtonian blood flow, magnetic fields, and particle trajectories. In this study, 5000 particles of DAS-M&M are released and their retention with the magnetic field is studied. Simulators have been applied to the magnetization domains using the stationary solver, and the derived values have been used as well-known values in the time-dependent simulation. Table 1 shows a detailed of the material properties used in the simulation.
Table 1
Physical properties of blood and DAS-MNM
Property | Blood | DAS-MNM |
Density (kg/m3) | 1060 | 5230 |
Viscosity (Pa.s) | 0.0035 | ---- |
DAS-MNM particle size (nm) | ---- | 100–500 |
Relative magnetic permeability (A/m) | 1.0 | 3.0–15.0 |
Magnetic field strength (T) | ---- | 0.5–2.0 |
Temperature (K) | 293.15 | ---- |