Letter Cite This: Nano Lett. 2018, 18, 838−845
pubs.acs.org/NanoLett
Design of Magnetically Labeled Cells (Mag-Cells) for in Vivo Control of Stem Cell Migration and Differentiation Seokhwan Yun,† Tae-Hyun Shin,‡,§,∥ Jae-Hyun Lee,‡,§,∥ Mi Hyeon Cho,‡,§,∥ Il-Sun Kim,⊥ Ji-wook Kim,‡,§,∥ Kwangsoo Jung,⊥ Il-Shin Lee,⊥ Jinwoo Cheon,*,‡,§,∥ and Kook In Park*,†,⊥ †
Brain Korea 21 Plus Project for Medical Science, Yonsei University College of Medicine, Seoul 03722, Korea Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, Korea § Yonsei-IBS Institute, Yonsei University, Seoul 03722, Korea ∥ Department of Chemistry, Yonsei University, Seoul 03722, Korea ⊥ Department of Pediatrics, Severance Children’s Hospital, Yonsei University College of Medicine, Seoul 03722, Korea ‡
S Supporting Information *
ABSTRACT: Cell-based therapies are attractive for treating various degenerative disorders and cancer but delivering functional cells to the region of interest in vivo remains difficult. The problem is exacerbated in dense biological matrices such as solid tissues because these environments impose significant steric hindrances for cell movement. Here, we show that neural stem cells transfected with zinc-doped ferrite magnetic nanoparticles (ZnMNPs) can be pulled by an external magnet to migrate to the desired location in the brain. These magnetically labeled cells (Mag-Cells) can migrate because ZnMNPs generate sufficiently strong mechanical forces to overcome steric hindrances in the brain tissues. Once at the site of lesion, Mag-Cells show enhanced neuronal differentiation and greater secretion of neurotrophic factors than unlabeled control stem cells. Our study shows that ZnMNPs activate zinc-mediated Wnt signaling to facilitate neuronal differentiation. When implemented in a rodent brain stroke model, Mag-Cells led to significant recovery of locomotor performance in the impaired limbs of the animals. Our findings provide a simple magnetic method for controlling migration of stem cells with high therapeutic functions, offering a valuable tool for other cell-based therapies. KEYWORDS: Magnetic nanoparticles, magnetic targeting, stem cell delivery, stem cell differentiation, cell therapy
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(for example, frictional forces imposed by the three-dimensional (3D) meshwork of cells and extracellular matrix in tissues) that prevent cell movement.20 The forces required for propelling some types of cells in a 3D tissue environment are known to be a few piconewton (pN).21 However, achieving such an amount of force with typical ferrite MNPs is challenging. In particular, because magnetic field gradient decreases with distance from the external magnet, cells that are deep within the body would experience a low magnetic force. Indeed, most studies reported so far demonstrate magnetic targeting under liquid biological environments such as blood,9−11 cerebrospinal fluid in spinal cord,12−15 vitreous gel in eye,16,17 and synovial fluid in cartilage18,19 but not in tissues. For magnetic targeting to work effectively in tissues, it is important to use MNPs that can generate a strong mechanical force. In this study, we introduce Mag-Cells that can be magnetically targeted in tissues, offering a noninvasive way to control
he efficacy of cell-based therapies depends on the number of functional cells that are delivered to the target lesions.1,2 Many attempts have been made to enhance the migration and maintain the function of these cells at target sites. For example, genetic modifications3 and preconditioning of stem cells in conditions resembling their physiological niches4 have been used to overexpress receptors that recognize chemoattractants and promote cell migration. Nonetheless, the migration efficiency of stem cells in vivo is unsatisfactory; for example, a few percent of injected stem cells are delivered to targets.5 Local injection of chemoattractants has also been used to attract stem cells to the injury site.6 Because chemoattractants are endogenous molecules that exist both at the injection site and throughout the body, this method is prone to off-target migration.7 Magnetic targeting of cells can potentially evade some of the challenges. Because magnetic field is bioorthogonal, it can be used to control cell migration without interferences with native biochemical processes.8 Cells labeled with MNPs can be mechanically pulled toward the high magnetic field gradient.9−19 For migration in tissues, the MNPs in cells should exert sufficient mechanical force to overcome the steric barriers © 2018 American Chemical Society
Received: September 22, 2017 Revised: December 22, 2017 Published: February 2, 2018 838
DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
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Figure 1. Mag-Cells and their magnetically targeted migration capabilities. (a) Schematic showing the forces that a Mag-Cell needs to overcome when migrating through the tissues. Left: zinc-doped ferrite magnetic nanoparticles (ZnMNPs) in a Mag-Cell provide the mechanical force required for a cell to overcome movement-resisting steric hindrances such as friction and/or viscous drag in extracellular matrix (ECM). Right: The Mag-Cells can be pulled to the magnet and can travel a few tens of millimeter distance in tissue environments. (b−f) Magnetic gradient force and velocity of Mag-Cells. (b) Calculated plots showing the magnetic gradient force per cell of Mag-Cell-1 (neural stem cell (NSC) with 15 nm ZnMNPs), MagCell-2 (NSC with 15 nm Fe3O4 MNPs), and Mag-Cell-3 (NSC with Feridex) at varying distances from a 1 Tesla NdFeB magnet. Mag-Cell-1 has the largest force among all tested Mag-Cells. (c) Schematic showing the experimental setup for measuring the migration velocity of Mag-Cell at varying distances from the magnet. The position of the magnet is controlled by a micromanipulator and the migration of Mag-Cell-1 is tracked using an optical microscope. (d) Optical microscope images with time interval of 5 s showing migration of a single Mag-Cell-1 in phosphate buffered saline (PBS) that is 15 mm away from the magnet. (e) Plot showing measured velocity of Mag-Cell-1 in PBS versus distance from the magnet. (f) Schematic illustration of a phantom consisting of a PBS- and agarose-filled capillary tube. The Mag-Cells are loaded at one end of the phantom. Distance-dependent magnetic field strength of 1 T NdFeB magnet is calculated and visualized using color gradients. (g) Bioluminescence images of cell migration in the capillary tubes and (h) graphs of cell number versus cell migration of Mag-Cells-1 and Mag-Cells-2. At 24 h of magnetic field exposure, only Mag-Cells-1 reach the other end of the capillary tube. (i) Velocity of Mag-Cells-1 at varying distance from the magnet, in agarose gel.
cell migration remotely using an external magnetic field (Figure 1a). To ensure the Mag-Cells have sufficient mechanical force to migrate through tissues, we used 15 nm ZnMNPs (Zn0.4Fe2.6O4) with a saturation magnetization of 161 emu/ g (metal). Because these nanoparticles are about 2.5 times stronger than the typical ferrite MNPs (for example, Feridex, commercial ferrite MNPs, Figure S1), they will provide a stronger mechanical force to pull cells in tissues. Furthermore,
we found that the ZnMNPs activate Wnt signaling cascades and affect neuronal differentiation and the secretion of neurotrophic factors in neural stem cells (NSCs), ensuring that the ZnMNPs serve dual functions of stem cell migration and differentiation. To construct the Mag-Cells (Figure S2), we modified the ZnMNPs with a transfection agent, poly-L-lysine, before transfecting them into NSCs known to promote the replacement of damaged neural tissue and support neuro839
DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
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Figure 2. Magnetically targeted migration of Mag-Cells-1 in in vivo rat brain. (a) Schematic illustrations showing the characteristic migratory pathways of NSCs. Upon injection into the ventricle (V, purple) and subventricular zone (SVZ, orange) of intact rat brain, NSCs are known to migrate toward the olfactory bulb (OB) through the rostral migratory stream (RMS) (sagittal view) or toward the corpus callosum (CC) and white matter (WM) (coronal view). (b) Fluorescent images of brain tissues showing the migration of injected Mag-Cells-1 in the rat brain (n = 7). (i) Sagittal view of the brain tissue at day 5 postinjection show that Mag-Cells-1 traveled to the OB. (ii) Coronal view of the brain tissue at day 0 and day 5 postinjection show that injected Mag-Cells-1 were initially located at V and SVZ but traveled to the CC and WM after 5 days. Green and white dotted lines indicate border of brain and V, respectively. (c) Magnetic control of Mag-Cells-1’s migration pathway (n = 7). (i) Illustration and photograph showing a 1 T NdFeB magnet attached to the rat head as a magnetic guide. (ii) In magnetic targeted cases, no Mag-Cells-1 were observed in the OB at day 5 postinjection. (iii) Mag-Cells-1 initially injected at V and SVZ (day 0) migrated toward the magnet via subcortex (subCx, day 3 and 5), and cortex (Cx, day 7).
protection.22,23 The zinc and iron metal contents in a single Mag-Cell were measured to be about 4.6 picogram, which corresponds to approximately 6.9 × 105 ZnMNPs. From the size, magnetization, and number of internalized MNPs that we measured, we calculated the magnetic gradient force (Fm) exerted by a single Mag-Cell which is plotted at varying distances from a 1 Tesla NdFeB magnet (Figure 1b). Compared to other control Mag-Cells with different MNPs (Mag-Cell-2 with 15 nm Fe3O4 MNPs and Mag-Cell-3 with Feridex), the Mag-Cell with ZnMNPs (Mag-Cell-1) exhibits the largest Fm owing to the highest magnetization of ZnMNPs (Figure S1 and Table S1). As Mag-Cell-1 moves closer to the magnet, Fm increases gradually from about 1.6 to 61 pN. MagCell-2 shows about 25−30% lower Fm and Mag-Cell-3 shows about an order of magnitude lower Fm (about 0.15−8.0 pN) than Mag-Cell-1. In liquid environments such as phosphate buffered saline (PBS), Mag-Cells-1 migrated toward the magnet at velocities of about 2.1, 2.6, 3.3, 5.7, 8.8, and 20 μm/s when the magnet is at a distance of 30, 25, 20, 15, 10, and 5 mm, respectively (Figure 1c−e). Considering forces of a few pN is required to pull cells in a 3D tissue environment,21 the migration of Mag-Cells-1 can be remotely controlled even when they are located at a few centimeters deep inside the body. Magnetic targeting of Mag-Cells was then examined in agarose gel, which is widely utilized for mimicking brain tissue.24 A 30 mm long capillary tube is loaded with PBS (forming a 20 mm long region) and agarose gel (a 10 mm long region). Mag-Cells labeled with luciferase were loaded to the
PBS end (Figure 1f) and their migration was tracked with bioluminescence imaging (BLI) (Figure 1g,h). Mag-Cells-1 passed through both regions and reached the other end of the capillary tube within 24 h. Migration velocity in agarose varies from about 5.5, 17, to 34 μm/min when the distance from magnet changes from 20, 10, to 5 mm, respectively (Figure 1i). In contrast, Mag-Cells-2 showed slower migration and did not reach the other end of the capillary. In the case of unlabeled control NSCs, they were diffused in the PBS region without showing any meaningful migration. These results demonstrate that MNPs with high magnetic moment is critical for endowing NSCs with magnetic targeting capability and for controlling cell migration in tissue environments. We further tested the magnetic targeting of Mag-Cells-1 in in vivo rat brain. Mag-Cells-1 were labeled with a green fluorescent protein and transplanted into the lateral ventricle (V) using stereotaxic microinjection (Figure 2a). We first assessed whether Mag-Cells-1 possess NSCs’ innate in vivo migration capability. It is known that NSCs injected in the V or subventricular zone (SVZ) will migrate either along the rostral migratory stream (RMS) toward the olfactory bulb (OB) or along the corpus callosum (CC) and white matter (WM) (Figure 2a).25 In fluorescence histology images obtained at 5 days postinjection without magnetic guidance (Figure 2b), the injected Mag-Cells-1 were found in the OB, CC, and WM indicating that Mag-Cells-1 retained NSCs’ innate migration capability.25 In contrast, when magnetic field is introduced by attaching a magnet on the rat’s head, the migration of MagCells-1 was redirected toward the magnet. They migrated from 840
DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
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Figure 3. Enhanced migration and neuronal differentiation of Mag-Cells-1 in in vivo stroke-induced brain. (a) Schematic illustrations of middle cerebral artery occlusion (MCAO) brain infarction model and magnetic targeting of Mag-Cells-1 injected via internal carotid artery (ICA). Red dashed arrows indicate possible migration routes of magnetically targeted Mag-Cells-1. (b,c) Serial T2 MRI brain images obtained at preinjection, 1 day, and 3 weeks postinjection. In the magnetically targeted group (b), Mag-Cells-1 (blue dotted line) were seen migrating from the ventral area toward the magnet at day 1, and at 3 weeks postinjection they were seen in the striatum (ST), external capsule (EC), and Cx. In the nonmagnetically targeted group (c), most of the Mag-Cells-1 (red dotted line) remained in the ventral area even after 3 weeks postinjection. (d) Immunohistochemistry images of (i) magnetically targeted and (ii) nonmagnetically targeted groups obtained at 3 weeks postinjection. ZnMNPs and NSCs are stained with Prussian blue and STEM121 antibody (brown), respectively. The location of Mag-Cells-1 (blue and red dotted lines) matched the MRI images. (e) Quantitative BLI analyses show that about 60-fold more live Mag-Cells-1 were delivered when they were magnetically targeted than when untargeted (n = 4, respectively). (f) Differentiation patterns of the Mag-Cells-1 in rat brain. (i) Z-stack confocal images are obtained from the EC region in the brain and stained with TuJ1, Nestin, and glial fibrillary acidic protein (GFAP). (ii) Graph shows percentages of TuJ1-, Nestin-, and GFAP-positive cells per total number of NSCs. The number of TuJ1-positive cells for Mag-Cells-1 increased more than 4-fold compared to unlabeled control NSCs (n = 3, respectively). *p < 0.05 compared to unlabeled control NSCs.
brain stroke, the blood-brain barrier (BBB) is known to be disrupted and its permeability increases.26 The damaged BBB in our brain stroke model acts as an access point for Mag-Cells-1 injected into blood vessel (Figure S4). Mag-Cells-1 were injected via the right internal carotid artery (ICA) and the magnet was mounted on the rat’s head (Figure 3a). Mag-Cells1 were expected to first enter the ventral area of the brain through the compromised BBB before moving toward the magnet through the WM (white) or striatum (ST, green) (Figure 3a).
the injection site (V and SVZ) to the basal region of the skull via the subcortex (sub-Cx) and cortex (Cx) (Figure 2c). No Mag-Cells-1 were observed in the OB. When tested for MagCells-2, some cells were found at the upper region of SVZ but the others still remained at their injection site (Figure S3). These results showed that magnetic targeting of Mag-Cells-1 can be used to deliver cells to a user-defined location in tissues such as a rodent’s brain. Next, we applied the Mag-Cells-1 in a neurodegenerative brain injury model, where brain stroke was induced using the middle cerebral artery occlusion (MCAO) method. In a typical 841
DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
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Figure 4. Facilitated neuronal differentiation of Mag-Cells-1 by ZnMNPs. (a) Schematic of Mag-Cells-1 displaying enhanced neuronal differentiation (thicker arrows). (b) In vitro immunocytochemistry images showing differentiation patterns of Mag-Cells-1, unlabeled control NSCs, Mag-Cells-2, and Mag-Cells-1-DKK1. All images are obtained at 1 week post-transfection of MNPs. Green fluorescence represents TuJ1 (neuronal marker), Nestin (stem cell marker), and GFAP (astrocyte marker) in each column. Blue fluorescence (4′,6-diamidino-2-phenylindole, DAPI) shows nucleus of cells. TuJ1 intensity is the highest for Mag-Cells-1. (c) Quantitative data showing the percentages of TuJ1-, Nestin-, and GFAP-positive cells per total number of cells. Mag-Cells-1 show significantly higher neuronal differentiation (TuJ1-positive) compared to unlabeled control NSCs, MagCells-2, and Mag-Cells-1-DKK1 (n = 5, respectively). *p < 0.05 compared to unlabeled control NSCs, †p < 0.05 compared to Mag-Cells-2, §p < 0.05 compared to Mag-Cells-1-DKK1. 842
DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
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Figure 5. Functional recovery of impaired forelimb of Mag-Cells-1-treated MCAO rats. (a) Schematic illustrations of the asymmetric cylinder test used to evaluate locomotor performance of MCAO rats injected with magnetically targeted Mag-Cells-1. The number of forelimb wall contacts are counted. (b) Plots of the impairment score versus time. At 3 weeks following cell injection, locomotor performance of Mag-Cells-1-treated group is significantly improved compared to control groups (n = 8, respectively). (c) A z-stack 3D confocal image obtained from rat brain infarction. Nuclei, cytosol of Mag-Cells-1 (guest cells), and synaptic vesicles are stained with DAPI (blue), STEM121 (green), and synapsin-1 (red), respectively. White arrows indicate the colocalization of the cytosol of Mag-Cells-1 and synaptic vesicles. (d) MAP2 (mature neuron marker, white) costained image of panel (c) and its schematic presentation. The presence of synaptic vesicles (red dots) in Mag-Cells-1 shows synaptic connection with host rat neurons. *p < 0.05 compared to unlabeled control NSCs-treated group and †p < 0.05 compared to nontreated group.
entiation. In vivo immunohistochemistry data (Figure 3f), showed that for rat brain injected with Mag-Cells-1, the TuJ1 (neuronal marker) signal intensity was about 4-fold higher than the control group injected with unlabeled control NSCs. No differences in signal intensities for Nestin (stem cell marker) and GFAP (astrocyte marker) were seen for both groups. The increased neuronal differentiation of in vivo injected Mag-Cells1 was also confirmed for intact rat brain (Figures S6 and S7). In the case of Mag-Cells-2, there was no changes in the differentiation in comparison to unlabeled control NSCs (Figures S6 and S7). Through in vitro studies, we found that the ZnMNPs facilitate neuronal differentiation of NSCs (Figure 4a). Immunocytochemistry data (Figure 4b,c) showed that the number of TuJ1-positive cells in Mag-Cells-1 group is about 150% higher than that of control groups (Mag-Cells-2 and unlabeled control NSCs). For Mag-Cells-1, neuronal differentiation transcription factors such as NEUROG2 and, neuronal differentiation markers such as TuJ1 and microtubuleassociated protein 2 (MAP2) A/B increased about 5.0-, 1.6-, and 2.8-fold, respectively, compared to control groups (Figure S8).28,29 Additionally, Mag-Cells-1 exhibited about 2.5- and 2.2fold increased secretion of nerve growth factor (NGF) and
The migration of Mag-Cells-1 was tracked via magnetic resonance imaging (MRI) for 3 weeks postinjection (Figure 3b,c) and confirmed by histological analyses (Figure 3d). In the magnetically targeted group (Figure 3b), Mag-Cells-1 (dark spots in MRI images, indicated with blue dotted lines) were detected near the ventral area at day 1. They moved toward the magnet and were observed in both the ischemic core and the peri-infarct region including the Cx, ST, and EC at 3 weeks postinjection (Figure 3b,d). In the control group where the same number of Mag-Cells-1 were injected but not guided by a magnet, Mag-Cells-1 (indicated with red dotted lines) showed no migration for 3 weeks of postinjection period (Figure 3c,d). Using BLI, we determined that the number of viable cells delivered to the brain in the magnetically targeted group was about 60-fold larger than the nonmagnetically targeted group (that is, around 13.1% of injected cells were delivered, Figure 3e and Figure S5). These results are noteworthy because such engraftment efficiency is comparable to that of direct intracerebral transplantation, which is effective but requires invasive brain surgery.27 Besides the significant enhancement in migration and delivery, Mag-Cells-1 also showed increased neuronal differ843
DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
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cerebral cortex and some regions of white matter which are brain parts easily damaged by external physical force and stroke (c.f., average thicknesses of skull, about 0.63 cm; cerebral cortex, about 0.25 cm).33,34 Since the ZnMNPs labeled Mag-Cells can be noninvasively delivered at specific sites of interest in tissue and have enhanced therapeutic effects, they can serve as a useful platform for cell-based therapies, especially for treating neurodegenerative diseases.
neurotrophin 3 (NTF3), respectively, compared to control groups (Figure S8). In short, the ZnMNPs promoted both neuronal differentiation and neurotrophic factor secretion of NSCs. To understand the underlying mechanisms of these phenomena, we performed control experiments by treating Mag-Cells-1 with a Wnt signal blocker, Dikkopf1 (DKK1). DKK1-treated Mag-Cells-1 (Mag-Cells-1-DKK1) showed significantly lower neuronal differentiation and neurotrophic factor secretion (Figure 4b,c and Figure S8). Western blot and quantitative polymerase chain reaction analyses (Figure S8) showed that both Mag-Cells-1 and Mag-Cells-1-DKK1 increased zinc finger transcription factors ZIC1 and ZIC2, which are upstream of the Wnt signaling pathway. The expression of Wnt signaling ligands such as WNT1 and WNT3a also increased for both groups. However, only MagCells-1 showed increased expression of β-catenin and axis inhibition protein 2 (AXIN2), which are downstream molecules of the Wnt signaling pathway. For Mag-Cells-1-DKK1, neither β-catenin nor AXIN2 expressions were increased. These results suggest that ZnMNPs facilitate neuronal differentiation and secretion of neurotrophic factors by activating zinc-mediated Wnt signaling pathways.30,31 Finally, the therapeutic effects of Mag-Cells-1 in an MCAO rat brain stroke model having impaired forelimb functions were assessed using the asymmetric cylinder test,32 which is a wellknown method to evaluate locomotor performance of rodent models with neurological disorders (Figure 5a). Mag-Cells-1 were injected in the MCAO rats (n = 8) via ICA and guided with a magnet mounted on the rat’s head. At 3 weeks postinjection, the Mag-Cells-1-treated group showed recovery of locomotor function in the impaired forelimb (Figure 5b); their impairment score decreased about 16% and 20% when compared to magnetically targeted saline- and unlabeled NSCstreated control groups, respectively. Immunohistochemistry studies at 21 days postinjection (Figure 5c,d) showed that MagCells-1 differentiated into neurons and connected with host rat neurons. Cell nuclei, host rat neuronal cells, Mag-Cells-1derived guest cells, and synaptic vesicles were fluorescently stained with 4′,6-diamidino-2-phenylindole (DAPI, blue), MAP2 (white), STEM121 (green), and synapsin-1 (red), respectively. A STEM121 positive guest cell was seen to make close contact with MAP2-labeled host neurons, and both expressed abundant synapsin-1 (synaptic vesicles), displaying the existence of synaptic connectivity in the injured brain (Figure 5c,d). These results indicate that Mag-Cells-1 treatments significantly aided locomotor function recovery of impaired forelimb and such therapeutic effects are reasonably well associated with augmented synaptic integration and subsequent restoration of neural connectivity. In this study, we demonstrate that the use of ZnMNPs with strong magnetic moment allows noninvasive magnetically targeted cell migration in solid tissue environments. Additionally, the ZnMNPs can enhance the therapeutic functions of NSCs, by increasing neuronal differentiability and neurotrophic factor secretion. This dual-function of migration and differentiation control is hardly achievable with typical ferrite nanoparticles or other magnetic nanoparticles. For stem cell delivery, the ZnMNPs can provide a working distance of up to a few centimeters which can cover most of the region of the rodents’ brains (Figure 1f−i). With such working distance, magnetically targeted delivery of stem cell can be in principle operative for surface regions of the human brain, for example,
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.7b04089. Detailed methods and supplementary figures and table: syntheses and characterization of MNPs, preparation of Mag-Cells, transmission electron microscope and optical microscope images of Mag-Cells-1, in vivo migration of Mag-Cells-2, BBB disruption test of MCAO model, BLI imaging, in vivo differentiation patterns of Mag-Cells, Western blot and quantitative polymerase chain reaction analyses of Mag-Cells, and summary of magnetic properties of typical ferrite MNPs (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. Phone: (+82) 2-2123-5631. *E-mail:
[email protected]. Phone: (+82) 2-2228-2059. ORCID
Jae-Hyun Lee: 0000-0002-9236-157X Mi Hyeon Cho: 0000-0001-9429-4692 Jinwoo Cheon: 0000-0001-8948-5929 Author Contributions
S.Y., T.-H.S. and J.-H.L. contributed equally to this work. J.C. and K.I.P. conceived and designed the experiments. S.Y., I.-S.K., K.J., and I.-S.L. performed cell and animal experiments. T.-H.S., J.-H.L., M.H.C., and J.-w.K. performed syntheses, characterization, and magnetic gradient force calculation of magnetic nanoparticles. T.-H.S., J.-H.L., J.C., and K.I.P. wrote the manuscript. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by grants from National Research Foundation (NRF; 2013M3A9B4076545 to K.I.P.), Korea Healthcare Technology R&D Project, Ministry for Health & Welfare Affairs (HI14C1564 and HI16C1089 to K.I.P., HI08C2149 to J.C.), and Institute for Basic Science (IBSR026-D1 to J.C.). The authors thank Dr. Minsuk Kwak for helpful comments and discussions.
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REFERENCES
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DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
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DOI: 10.1021/acs.nanolett.7b04089 Nano Lett. 2018, 18, 838−845
