Article
Magnetic Control of Fe3O4 Nanomaterial for Fat Ablation in Microchannel Ming Chang 1,2, *, Ming-Yi Chang 2 , Wei-Siou Lin 2 and Jacque Lynn Gabayno 3 Received: 14 October 2015 ; Accepted: 13 November 2015 ; Published: 19 November 2015 Academic Editor: Wen-Hsiang Hsieh 1 2 3
*
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, Fujian, China Department of Mechanical Engineering, Chung Yuan Christian University, Chungli, Taoyuan 32023, Taiwan;
[email protected] (M.-Y.C.);
[email protected] (W.-S.L.) Mapua Institute of Technology, Intramuros, Manila 1002, Philippines;
[email protected] Correspondence:
[email protected]; Tel.: +886-3265-4303
Abstract: In this study, surface modification of iron (II, III) oxide Fe3 O4 nanoparticles by oleic acid (OA) coating is investigated for the microablation of fat in a microchannel. The nanoparticles are synthesized by the co-precipitation method and then dispersed in organic solvent prior to mixing with the OA. The magnetization, agglomeration, and particle size distribution properties of the OA-coated Fe3 O4 nanoparticles are characterized. The surface modification of the Fe3 O4 nanoparticles reveals that upon injection into a microchannel, the lipophilicity of the OA coating influences the movement of the nanoparticles across an oil-phase barrier. The motion of the nanoparticles is controlled using an AC magnetic field to induce magnetic torque and a static gradient field to control linear translation. The fat microablation process in a microchannel is demonstrated using an oscillating driving field of less than 1200 Am´1 . Keywords: Fe3 O4 nanoparticles; magnetic control; oleic-acid; fat ablation
1. Introduction The use of magnetic nanoparticles (NPs) for biomedical applications such as microsurgery and drug delivery is a topic that draws significant interest [1,2]. One of the challenges to magnetically controlled NPs includes finding a biocompatible material that has a large magnetic moment so it can react to an external magnetic field source. Iron oxides (IO) are one of such materials which exhibit stable magnetic properties and favorable biocompatibility. Although many practical applications of IOs can be limited by their weak surface functionality, recent investigations sought methods that can improve their surface properties for optimized movement in aqueous environments [3]. The development of surface coating to improve functionality and magnetic stability is emphasized. Surface coating IO-NPs with organic molecules or surfactants, biomolecules, and polymers or grafting with inorganic layers such as silica, metal oxide, etc. [4–6], is actively investigated. Surfactants are shown as important stabilizing agents for controlling particle size and agglomeration of NPs in a suspension. Bare magnetic Fe3 O4 NPs in suspension can be controlled to move in a low gradient and oscillating magnetic fields [7]. A velocity field created by the movement of the NPs was necessary to facilitate the microablation of a thrombus in a microchannel. Due to the oleophobic property of IO materials, the use of a similar magnetic control system to steer NPs through a fat occlusion can be difficult without surface modification. In this study, oil-soluble oleic acid (OA) is used as a coating for the Fe3 O4 NPs in order to decrease their agglomeration as well as enhance lipophilicity and magnetic stability. The NPs are dispersed in long-chain OA that acts as a dense protective layer around the NPs, thereby providing a monodispersed and highly uniform particle distribution. The size distribution Materials 2015, 8, 7813–7820; doi:10.3390/ma8115429
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of surface-coated NPs was compared to bare (or uncoated) NPs using scanning electron microscope The size distribution of surface‐coated NPs was compared to bare (or uncoated) NPs using scanning (SEM) and transmission electron microscopy (TEM) measurements. The saturation magnetization electron microscope (SEM) and transmission electron microscopy (TEM) measurements. The saturation was evaluated by superconducting quantum interference device (SQUID) magnetometer and the oleic magnetization was evaluated by superconducting quantum interference device (SQUID) magnetometer acid coating was confirmed by Fourier transform infrared (FTIR) spectroscopy. and the oleic acid coating was confirmed by Fourier transform infrared (FTIR) spectroscopy. By injecting the OA-coated Fe3 O4 NPs in a microchannel, experimental investigations were By injecting the OA‐coated Fe3O4 NPs in a microchannel, experimental investigations were carried out to demonstrate a feasible application of the surface-modified NPs. The movement of carried out to demonstrate a feasible application of the surface‐modified NPs. The movement of the the NPs was controlled using an external oscillating magnetic field to remove a fat occlusion in the NPs was controlled using an external oscillating magnetic field to remove a fat occlusion in the microchannel. By demonstrating that the NPs can be transported across the immiscible barrier of the microchannel. By demonstrating that the NPs can be transported across the immiscible barrier of the suspension medium and fat layer, the system can be utilized for targeted delivery of NPs between the suspension medium and fat layer, the system can be utilized for targeted delivery of NPs between bloodstream and fatty tissue membranes. the bloodstream and fatty tissue membranes. 2. Synthesis of Surface-Coated Nanomaterials 2. Synthesis of Surface‐Coated Nanomaterials 2.1. Preparation of OA-Coated Fe3 O4 NPs 2.1. Preparation of OA‐Coated Fe3O4 NPs Bare Fe3 O4 NPs were first prepared at room temperature via the co-precipitation reaction Bare Fe3chloride O4 NPs were first prepared at room via the co‐precipitation of of iron (II) tetrahydrate and iron (III) temperature chloride hexahydrate with sodium reaction hydroxide. iron (II) chloride tetrahydrate and iron (III) chloride hexahydrate with sodium hydroxide. The reaction is shown below: The reaction is shown below: FeCl2 ` 2 FeCl3 ` 8 NaOH “ Fe3 O4 ` 8 NaCl ` 4 H2 O (1) (1) FeCl2 + 2 FeCl3 + 8 NaOH = Fe3O4 + 8 NaCl + 4 H2O Afterwards, two grams of the bare 3Fe O4 nanopowders were mixed with 50 mL HCl at a O43 nanopowders were mixed with 50 mL HCl at a pH = 5 Afterwards, two grams of the bare Fe pH = 5 to make a solution as illustrated in Figure 1. The solution was ultrasonicated for about to make a solution as illustrated in Figure 1. The solution was ultrasonicated for about 5 min before 5adding min before adding ethanol mL) OA then (5 g) re‐sonicated and then re-sonicated for 30 another 30 min. The ethanol (20 mL) and (20 OA (5 and g) and for another min. The mixture mixture was centrifuged min at 6000 oven-dried beforegrinding grindingto to produce produce was centrifuged for 30 for min 30at 6000 rpm rpm and and oven‐dried for for 24 24 h hbefore Fe3O O44‐OA nanopowder. -OA nanopowder.
Figure 1. 1. (a) of Fe Fe33O Bare Fe Fe33O Figure (a) Preparation Preparation of O44 coated coated with with oleic oleic acid; acid; (b) (b) Bare O44 nanopowder nanopowder prepared prepared by by co‐precipitation method. co-precipitation method.
2.2. Characterization of OA‐Coated Fe 2.2. Characterization of OA-Coated Fe33O O44 NPs NPs Figure 22 shows shows the the particle particle distribution distribution of of bare bare Fe Fe3O O4 NPs and OA‐coated NPs. Due to their Figure 3 4 NPs and OA-coated NPs. Due to their smaller particle size and larger surface energy, agglomeration in bare bare NPs NPs isis more more evident. evident. The smaller particle size and larger surface energy, agglomeration in The surface‐coated Fe 3O4 NPs are observed to be monodispersed. The size distribution after coating is surface-coated Fe3 O4 NPs are observed to be monodispersed. The size distribution after coating also more uniform, which can be attributed to the adsorption of the carboxyl OA on the hydroxyl is also more uniform, which can be attributed to the adsorption of the carboxyl OA on the hydroxyl Fe3O 4 surface to lessen the formation of aggregates among the NPs. Fe 3 O4 surface to lessen the formation of aggregates among the NPs. Figure 3 compares the size distribution of the NPs based on TEM images. The bare Fe O4 NPs Figure 3 compares the size distribution of the NPs based on TEM images. The bare Fe3 O4 3NPs are are smaller in size, averaging from 10 to 15 nm, and form clusters as shown in Figure 3a. The smaller in size, averaging from 10 to 15 nm, and form clusters as shown in Figure 3a. The Fe3 O4 -OA Fe3Oare 4‐OA NPs are dispersed and have an average diameter of 100–150 nm as shown in Figure 3b,c. NPs dispersed and have an average diameter of 100–150 nm as shown in Figure 3b,c. To observe the response of the NPs to a static magnetic field, bare and surface‐coated NPs in To observe the response of the NPs to a static magnetic field, bare and surface-coated NPs suspension were initially exposed to a magnetic field for about 30 s and then oven‐dried. The baking in suspension were initially exposed to a magnetic field for about 30 s and then oven-dried. The temperature was set to 80 °C for 10 min. Figure 4 shows the SEM images of the bare and OA‐coated baking temperature was set to 80 ˝ C for 10 min. Figure 4 shows the SEM images of the bare and Fe3O4 NPs magnetized at ~250 A∙m−1. The bare NPs form rod‐like structures 20 to 25 μm in length while Fe3O4‐OA NPs form chains with an average length of 30 μm. The chain‐like structures in 7814 magnetized NPs can be attributed to their magnetorheological properties, owing to the induced 2
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OA-coated Fe3 O4 NPs magnetized at ~250 A¨ m´1 . The bare NPs form rod-like structures 20 to 25 µm in length while Fe3 O4 -OA NPs form chains with an average length of 30 µm. The chain-like Materials 2015, 8, page–page structures in magnetized NPs can be attributed to their magnetorheological properties, owing to the induced magnetic interactions among dispersed nanoparticles during magnetization [8,9]. magnetic dipole dipole interactions among the the dispersed nanoparticles during magnetization [8,9]. AsAs shown in Figure 2, magnetic NPs become randomly dispersed in the absence of the magnetic field. shown in Figure 2, magnetic NPs become randomly dispersed in the absence of the magnetic field. Materials 2015, 8, page–page Figure 5 5 shows NPs measured measured using using SQUID. SQUID.The Thesaturation saturation Figure shows the the magnetization magnetization of of the the NPs magnetization of Fe O -OA is constant at 70 emu/g while the coercivity in both bare and coated magnetization of Fe O at 70 emu/g while the coercivity both bare and coated 3 3interactions 4 4‐OA is constant Materials 2015, 8, page–page magnetic dipole among the dispersed nanoparticles during in magnetization [8,9]. samples is negligible, which reveals that the magnetic property of the Fe33OO4 NPs was not altered by samples is negligible, which reveals that the magnetic property of the Fe 4 NPs was not altered by As shown in Figure 2, magnetic NPs become randomly dispersed in the absence of the magnetic field. magnetic dipole interactions among the during magnetization [8,9]. thethe surface coating. surface coating. Figure 5 shows the magnetization of dispersed the NPs nanoparticles measured using SQUID. The saturation As shown in Figure 2, magnetic NPs become randomly dispersed in the absence of the magnetic field. ´−1 1 the ´, both 1 ,there −1 magnetization of Fe O 4‐OA is 6 constant at 70 while coercivity bare coated The FTIR results Figure 6 show that at 2925 cm and and 2853 cmin is isand –CH 2 and –CH 3 3 The FTIR results in3in Figure show that atemu/g 2925 cm 2853 there –CH –CH 2 and Figure 5 shows the magnetization of the NPs measured using SQUID. The saturation samples is negligible, which reveals that the magnetic property of the Fe 3O4 NPs was not altered by absorption, respectively, from the OA molecule. The OA double‐bond and –COO absorption are also absorption, respectively, from the OA molecule. The OA double-bond and –COO absorption are also magnetization of Fe3O4‐OA −1 is constant at 70 emu/g while the coercivity in both bare and coated the surface coating. confirmed at 1623 and 1408 cm confirmed at 1623 and 1408 cm´1 .. samples is negligible, which reveals that the magnetic property of the Fe 4 NPs was not altered by The FTIR results in Figure 6 show that at 2925 cm−1 and 2853 cm−13, Othere is –CH2 and –CH3 the surface coating. absorption, respectively, from the OA molecule. The OA double‐bond and –COO absorption are also The FTIR results in Figure −1. 6 show that at 2925 cm−1 and 2853 cm−1, there is –CH2 and –CH3 confirmed at 1623 and 1408 cm absorption, respectively, from the OA molecule. The OA double‐bond and –COO absorption are also confirmed at 1623 and 1408 cm−1.
Figure 2. Size distribution of (a), (b) bare Fe O4 NPs and (c), (d) Fe 3O4‐OA NPs investigated under Figure 2. Size distribution of (a), (b) bare Fe33O 4 NPs and (c), (d) Fe3 O4 -OA NPs investigated under Figure 2. Size distribution of (a), (b) bare Fe 3O4 NPs and (c), (d) Fe3O4‐OA NPs investigated under scanning electron microscope (SEM). scanning electron microscope (SEM). scanning electron microscope (SEM). Figure 2. Size distribution of (a), (b) bare Fe3O4 NPs and (c), (d) Fe3O4‐OA NPs investigated under scanning electron microscope (SEM).
Figure 3. Transmission electron microscopy (TEM) images of (a) bare Fe3O4 NPs and (b), (c) Fe3O4‐OA NPs.
Figure 3. Transmission electron microscopy (TEM) images of3O(a) bare Fe3 O4 NPs and (b), Figure 3. Transmission electron microscopy (TEM) images of (a) bare Fe 4 NPs and (b), (c) Fe 3O4‐OA NPs. (c) Fe3 O -OA NPs. 4 Figure 3. Transmission electron microscopy (TEM) images of (a) bare Fe 3O4 NPs and (b), (c) Fe3O4‐OA NPs.
Figure 4. SEM images of magnetized (a) bare Fe3O4 and (b) Fe3O4‐OA NPs.
Figure 4. SEM images of magnetized (a) bare Fe3O 4 and (b) Fe3O4‐OA NPs. Figure 4. SEM images of magnetized (a) bare Fe 3O4 and (b) Fe3O4‐OA NPs.
Figure 4. SEM images of magnetized (a) bare Fe3 O4 and (b) Fe3 O4 -OA NPs. 3
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Figure 5. Magnetic saturation of (a) bare Fe3O4 and (b) Fe3O4‐OA NPs. Figure 5. Magnetic saturation of (a) bare Fe3 O and (b) Fe O 4‐OA NPs. -OA NPs. Figure 5. Magnetic saturation of (a) bare Fe 3O44 and (b) Fe33O4
Figure 6. FTIR images of (a) bare Fe3O4 and (b) Fe3O4‐OA NPs. Figure 6. FTIR images of (a) bare Fe3O4 and (b) Fe3O4‐OA NPs. Figure 6. FTIR images of (a) bare Fe3 O4 and (b) Fe3 O4 -OA NPs.
3. Magnetically Controlled Motion of Nanoparticles 3. Magnetically Controlled Motion of Nanoparticles 3. Magnetically Controlled Motion of and Nanoparticles Assuming that the electrostatic van der Waals forces are negligible, a generalized Assuming that the electrostatic and van der Waals forces are negligible, a generalized formulation based on the magnetic field gradient can be used to describe the movement of the NPs Assuming that the electrostatic and van der Waals forces are negligible, a generalized formulation based on the magnetic field gradient can be used to describe the movement of the NPs in a viscous fluid. The linear translation of the NPs along the microchannel responds to a magnetic formulation based on the magnetic field gradient can be used to describe the movement of the NPs in a viscous fluid. The linear translation of the NPs along the microchannel responds to a magnetic force (F x) given by [7]: in a viscous fluid. The linear translation of the NPs along the microchannel responds to a magnetic force (Fx) given by [7]: force (Fx ) given by [7]: Ñ H y (2) Ñ μ χ Hyy BH (2) Fx “ μµ0χχHy V¨ x (2) Bx x where µ μ00 is permeability, χ χ is is the the material material susceptibility, susceptibility, V V is is the the volume volume of of the the where is the the vacuum vacuum permeability, where μ0 is the vacuum permeability, χ is the material Ñsusceptibility, V is the volume of the B HH y y the gradient field. surface-coated NPs, Hy is the magnetic field strength, and x is is the gradient field. surface‐coated NPs, Hy is the magnetic field strength, and BH y surface‐coated NPs, Hy is the magnetic field strength, and x is the gradient field. x Therefore, the linear velocity of spherical NPs along the direction of the gradient subjected to a Therefore, the linear velocity of spherical NPs along the direction of the gradient subjected to a hydrodynamic Stokes’ drag force, Fd 3d v , can be expressed as: hydrodynamic Stokes’ drag force, Fd 3d v , can be expressed as: 7816 4 4
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Therefore, the linear velocity of spherical NPs along the direction of the gradient subjected to a Ñ
hydrodynamic Stokes’ drag force, F d “ ´3πdη v , can be expressed as: Ñ
μ χ η 3π µ0 χV
H y
(3) Ñ BH xy v “ Hy ¨ (3) 3πdη Bx where d is the equivalent diameter of a sphere with the same volume as the NPs and η is the liquid viscosity. where d is the equivalent diameter of a sphere with the same volume as the NPs and η is the liquidThe expression shows that the terminal velocity of the NPs changes linearly with the quantity viscosity. Ñ
H The shows that the terminal velocity of the NPs changes linearly with the quantity ¯ expression ´ H H B H , which , which is a coupled effect of the driving magnetic field and the gradient field. is a coupled effect of the driving magnetic field and the gradient field. B xx The rotation The rotation of of the the NPs NPs is is dependent dependent on on the the interaction interaction of of the the induced induced magnetization magnetization to to the the oscillating magnetic field. The magnetic torque can be expressed as [7]: oscillating magnetic field. The magnetic torque can be expressed as [7]: χ2 µ00H H22 sin sin p2θq 2 2 p2 ` χq 2 2 2
τmm “ VV
(4) (4)
where angle between thethe magnetic dipole moment of the andm H.and TheH. expression shows where θθ isis the the angle between magnetic dipole moment of NPs the m NPs The expression that the magnetic torque quadratically changes with H. For a NP of radius r, the rotation is subjected shows that the magnetic torque quadratically changes with H. For a NP of radius r, the rotation is Ñ Ñ to a viscous drag force, τ D “ 3π2 ηr4ω, which the magnetic torque. Therefore, the 2 counterbalances 4 subjected to a viscous drag force, D 3 r , which counterbalances the magnetic torque. rotation speed of the NPs can be expressed as: Therefore, the rotation speed of the NPs can be expressed as: ωω“
Vx2 µμ0 H 2 sin sin p2θq 2θ 2 ηr4 3π 3π η
(5) (5)
Equation controllable fashion Equation (5) (5) implies implies that that the the NPs NPs can can be be rotated rotated in in aa controllable fashion by by modulating modulating the the time-dependent magnetic field source. Thus, the movement of the NPs can be stopped or resumed time‐dependent magnetic field source. Thus, the movement of the NPs can be stopped or resumed at at will simplyswitching switchingthe thealternating alternatingcurrent current source. source. A Acommon common optical optical inspection inspection camera will by by simply camera (X-Stream XS-3, Intergrated Design Tools, Tallahassee, FL, USA) attached to an optical microscope (X‐Stream XS‐3, Intergrated Design Tools, Tallahassee, FL, USA) attached to an optical microscope was used to track the movement of the surface-coated NPs under the action of a specific magnetic was used to track the movement of the surface‐coated NPs under the action of a specific magnetic field. Video recordings recordings of of the the moving moving nanostructures nanostructures were magnification and field. Video were captured captured at at 100ˆ 100× magnification and subsequently Figure 7 7 shows shows the the nonlinear nonlinear dependence dependence of subsequently loaded loaded onto onto aa central central computer. computer. Figure of the the rotation speed to H, which was also verified experimentally on Fe33O4‐OA NPs. -OA NPs. rotation speed to H, which was also verified experimentally on Fe
Figure 7. Rotation speed of the Fe Figure 7. Rotation speed of the Fe33O O44‐OA as a function of the oscillating magnetic field. -OA as a function of the oscillating magnetic field.
4. Application of Fe3O4‐OA for Fat Microablation 4. Application of Fe3 O4 -OA for Fat Microablation The application of the OA‐coated NPs is investigated for fat removal. The Fe3O4‐OA suspension The application of the OA-coated NPs is investigated for fat removal. The Fe3 O4 -OA suspension (0.03 wt %) was injected into a microchannel (width = 0.8 mm, length = 25 mm) as shown in Figure 7. (0.03 wt %) was injected into a microchannel (width = 0.8 mm, length = 25 mm) as shown in Figure 7. Because of the gradient field, the magnetic NPs are steered towards the target consisting of a fat occlusion on the left‐hand side of the microchannel, as shown in Figure 7a. Without a lipophilic 7817 surface activator such as the oleic acid to which the NPs are attached, magnetic guidance of the NPs 5
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Because of the gradient field, the magnetic NPs are steered towards the target consisting of a fat occlusion on the left-hand side of the microchannel, as shown in Figure 7a. Without a lipophilic Materials 2015, 8, page–page surface activator such as the oleic acid to which the NPs are attached, magnetic guidance of the NPs through the immiscible boundary of the suspension and fat occlusion is expectedly difficult. Surface through the immiscible boundary of the suspension and fat occlusion is expectedly difficult. Surface modification of the the Fe33O44 NPs modification of NPs by by their their attachment attachment to to the the OA OA chains chains weakens weakens the the surface surface tension tension along the boundary, thereby allowing the transport of NPs across the microchannel. along the boundary, thereby allowing the transport of NPs across the microchannel. A magnetic control control system system consisting consisting of of an an oscillating oscillating field field source source (~1200 (~1200 A¨ A∙m A magnetic m´−11) ) and and a a static static ´ 1 −1 magnetic field (80 A∙m ) was used in the investigation. A magnetic coil connected to an AC source magnetic field (80 A¨ m ) was used in the investigation. A magnetic coil connected to an AC source was used to generate the oscillating field. The coil was positioned under the microchannel stage. The was used to generate the oscillating field. The coil was positioned under the microchannel stage. static magnetic field field was was produced by two NdFeB permanent magnets that that were positioned as The static magnetic produced by two NdFeB permanent magnets were positioned shown in Figure 8a, and were separated by a distance of 6 cm. Using this configuration, the velocity as shown in Figure 8a, and were separated by a distance of 6 cm. Using this configuration, the distribution of the NPs is shown in Figure 8b, revealing a maximum speed in the central vicinity of velocity distribution of the NPs is shown in Figure 8b, revealing a maximum speed in the central the microchannel, which then tapers off, almost approaching the zero value near the location of the vicinity of the microchannel, which then tapers off, almost approaching the zero value near the two magnets. Because the microchannel width is narrower compared to the gap that separates the location of the two magnets. Because the microchannel width is narrower compared to the gap that two magnets, the NPs can then be assumed to have uniform velocity as they move in the magnetic separates the two magnets, the NPs can then be assumed to have uniform velocity as they move in the field region. The optical inspection images in Figure 8c reveal the formation of a parabolic velocity magnetic field region. The optical inspection images in Figure 8c reveal the formation of a parabolic streamline as the NPs along the the microchannel. The streamline velocity streamline as themove NPs move along microchannel. The streamlinedelineates delineatesthe the boundary boundary separating the dense fat layer on the left‐hand side of the microchannel and the suspension carrying separating the dense fat layer on the left-hand side of the microchannel and the suspension carrying the OA‐coated NPs NPs injected right‐hand of microchannel. the microchannel. Such streamlines were the OA-coated injected onon thethe right-hand sideside of the Such streamlines were absent absent upon injection of bare NPs, indicating immobility and transport difficulty of the NPs through upon injection of bare NPs, indicating immobility and transport difficulty of the NPs through the fat the fat layer in the absence of the OA coating. layer in the absence of the OA coating.
Figure 8. (a) from two two permanent permanent magnets. magnets. The Figure 8. (a) External External magnetic magnetic field field source source from The oscillating oscillating field field source is not shown; (b) Calculated velocity distribution of magnetic Fe source is not shown; (b) Calculated velocity distribution of magnetic Fe33O44‐OA NPs due to the static -OA NPs due to the static magnetic field; (c) Velocity streamlines between the suspension and fat layer along the microchannel. magnetic field; (c) Velocity streamlines between the suspension and fat layer along the microchannel.
Because the size of the surface‐coated Fe3O4 particles is very small, roughly at 100–150 nm, the bolus caused by the ablation process in Figure 8c is expected to be in the same range of several 7818 hundred nanometers and is, therefore, difficult to observe directly. In comparison, the diameter of human capillaries is roughly several (six or seven) micrometers; thus, the bolus released into the bloodstream by this process can pose very minimal risk for a heart attack or an induced stroke.
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Because the size of the surface-coated Fe3 O4 particles is very small, roughly at 100–150 nm, the bolus caused by the ablation process in Figure 8c is expected to be in the same range of several hundred nanometers and is, therefore, difficult to observe directly. In comparison, the diameter of human capillaries is roughly several (six or seven) micrometers; thus, the bolus released into the bloodstream by this process can pose very minimal risk for a heart attack or an induced stroke. Moreover, the flow behavior of the magnetic field-driven Fe3 O4 -NPs along the fat layer was observed to be laminar. Between the time that the NPs were injected until t = 4 s, the viscosity effect from the wall boundaries was negligible as revealed by the small radius of the meniscus layer separating the suspension and the fat target. As the NPs move towards the target from t = 16 s to t = 40 s, shear stresses from the microchannel walls become significant, hence the evident parabolic streamline between the two layers. Such a streamline would suggest that there is a dense concentration of the OA-coated NPs where the velocity is a maximum, which is near the center of the microchannel. Thus, the increased density and speed of the coated NPs can enhance surface interaction as they rotate to remove the fat target. The calculated flow rate speed in the middle is nearly constant at vx « 3 µm¨ s´1 . This is equivalent to a Reynolds number of less than 0.001, suggesting a laminar flow. 5. Conclusions Oleic acid-coated Fe3 O4 NPs were prepared in suspension to surface-functionalize the NPs. The magnetic properties of OA-coated Fe3 O4 nanoparticles were characterized, revealing that their saturation magnetization was preserved and the particle aggregation was minimized because of the OA coating. Surface-modified Fe3 O4 NPs that were injected in an occluded microchannel were able to demonstrate controlled targeting through a fat layer. The removal of fat occlusion using an oscillating magnetic field to control the NPs was demonstrated. This work can be used as a model system for targeted delivery of drug-loaded magnetic NPs from the bloodstream to fatty tissue membranes. Acknowledgments: This research is financially supported by the Ministry of Science and Technology of Taiwan under grant No. MOST 103-2218-E-033-038-MY3. Author Contributions: Ming Chang conceived and designed the study; Ming-Yi Chang and Wei-Siou Lin performed the experiments; Jacque Lynn Gabayno wrote the original version of the manuscript. All authors were involved in the discussion of the experimental results and commented the manuscript. Conflicts of Interest: The authors declare no conflict of interest.
References 1.
2.
3.
4.
5. 6.
Yeap, S.W.; Toh, P.Y.; Ahmad, A.L.; Low, S.C.; Majetich, A.; Lim, J.K. Colloidal stability and magnetophoresis of gold-coated iron oxide nanorods in biological media. J. Phys. Chem. C 2012, 116, 22561–22569. [CrossRef] Chao, X.; Zhang, Z.; Guo, L.; Zhu, J.; Peng, M.; Vermoken, A.; van de Ven, W.; Chen, C.; Cui, Y. A novel magnetic nanoparticle drug carrier for enhanced cancer chemotherapy. PLoS ONE 2012, 7, e40388. [CrossRef] [PubMed] Bloemen, M.; Brullot, W.; Luong, T.T.; Geukens, N.; Gils, A.; Verbiest, T. Improved functionalization of oleic acid-coated iron oxide nanoparticles for biomedical applications. J. Nanopart. Res. 2012, 14, 1100. [CrossRef] [PubMed] Patil, R.M.; Shete, P.B.; Thorat, N.D.; Otari, S.V.; Barick, K.C.; Prasad, A.; Ningthoujam, R.S.; Tiwale, B.M.; Pawar, S.H. Non-aqueous to aqueous phase transfer of oleic acid coated iron oxide nanoparticles for hyperthermia application. RSC Adv. 2014, 4, 4515–4522. [CrossRef] Wu, W.; He, Q.; Jiang, C. Magnetic iron oxide nanoparticles: Synthesis and surface functionalization strategies. Nanoscale Res. Lett. 2008, 3, 397–415. [CrossRef] [PubMed] Morales, M.A.; Jain, T.K.; Labhasetwar, V.; Leslie-Pelecky, D.L. Magnetic studies of iron oxide nanoparticles coated with oleic acid and Pluronicr block copolymer. J. Appl. Phys. 2005, 97. [CrossRef]
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7.
8. 9.
Gabayno, J.L.; Liu, D.-W.; Chang, M.; Lin, Y.-H. Controlled manipulation of Fe3 O4 nanoparticles in an oscillating magnetic field for fast ablation of microchannel occlusion. Nanoscale 2015, 7, 3947–3953. [CrossRef] [PubMed] Park, B.J.; Fang, F.F.; Choi, H.J. Magnetorheology: Materials and application. Soft Matter 2010, 6, 5246–5253. [CrossRef] Jung, H.S.; Choi, H.J. Hydrothermal fabrication of octahedral-shaped Fe3 O4 nanoparticles and their magnetorheological response. J. Appl. Phys. 2015, 117, 17E708. [CrossRef] © 2015 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
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