Self-assembled superparamagnetic nanoparticles as MRI contrast agents — A review

Recent progress of the preparation and applications of superparamagnetic iron oxide（SPIO） clusters as magnetic resonance imaging（MRI） probes is reviewed with regard to their applications in labeling and tracking cells in vivo, in diagnosis of cardiovascular diseases and tumors, and in drug delivery systems. Magnetic nanoparticles（NPs）, especially SPIO nanoparticles, have long been used as MRI contrast agents and as an advantageous nanoplatform for drug delivery,taking advantage of their unique magnetic properties and ability to function at the molecular and cellular levels. Due to advances in nanotechnology, various means to control SPIO NPs＇ size, composition, magnetization and relaxivity have been developed, as well as ways to usefully modify their surface. Recently, self-assembly of SPIO NP clusters in particulate carriers — such as polymeric micelles, vesicles, liposomes, and layer-by-layer（Lb L） capsules — have been widely studied for application as ultrasensitive MRI probes, owing to their remarkably high spin–spin（T2） relaxivity and convenience for further functionalization.

Recent Progress in Superparamagnetic Iron Oxide Nanoparticles

Superparamagnetic iron oxide nanoparticles(SPIONs)have immeasurable potentials in many fields such as nanobiotechnology and biomedical engineering because of their superparamagnetic properties and small particle size.This review introduces the methods for SPIONs synthesis,including co-precipitation,thermal decomposition,microemulsion and hydrothermal reaction,and surface modification of SPIONs with organometallic and inorganic metals,surface modification for targeted drug delivery,and the use of SPIONs as a contrast agent.In addition,this article also provides an overview of recent progress in SPIONs for the treatment of glioma,lung cancer and breast cancer.

Toxicity of superparamagnetic iron oxide nanoparticles: Research strategies and implications for nanomedicine

Superparamagnetic iron oxide nanoparticles （SPIONs） are one of the most versatile and safe nanoparticles in a wide variety of biomedical applications. In the past decades, considerable efforts have been made to investigate the potential adverse biological effects and safety issues associated with SPIONs, which is essential for the development of next-generation SPIONs and for continued progress in translational research. In this mini review, we summarize recent developments in toxicity studies on SPIONs, focusing on the relationship between the physicochemical properties of SPIONs and their induced toxic biological responses for a better toxicological understanding of SPIONs.

Magnetic labeling of primary murine monocytes using very small superparamagnetic iron oxide nanoparticles

Due to their very small size,nanoparticles can interact with all cells in the central nervous system.One of the most promising nanoparticle subgroups are very small superparamagnetic iron oxide nanoparticles(VSOP)that are citrate coated for electrostatic stabilization.To determine their influence on murine blood-derived monocytes,which easily enter the injured central nervous system,we applied VSOP and carboxydextran-coated superparamagnetic iron oxide nanoparticles(Resovist).We assessed their impact on the viability,cytokine,and chemokine secretion,as well as iron uptake of murine blood-derived monocytes.We found that(1)the monocytes accumulated VSOP and Resovist,(2)this uptake seemed to be nanoparticle-and time-dependent,(3)the decrease of monocytes viability was treatment-related,(4)VSOP and Resovist incubation did not alter cytokine homeostasis,and(5)overall a 6-hour treatment with 0.75 mM VSOP-R1 was probably sufficient to effectively label monocytes for future experiments.Since homeostasis is not altered,it is safe to label blood-derived monocles with VSOP.VSOP labeled monocytes can be used to study injured central nervous system sites further,for example with drug-carrying VSOP.

Superparamagnetic iron oxide nanoparticles: promote neuronal regenerative capacity?

Currently,we know that neuronal outgrowth during development and regeneration requires a complex interaction of intra-and extracellular molecules such as growth factors,neurotransmitters and extracellular matrix proteins（O’Donnell et al.,2009）.Furthermore,the discovery of a broad spectrum of growth-promoting cues has led to novel concepts for thera-peutic strategies.

Fluorescence detection of Europiumdoped very small superparamagnetic iron oxide nanoparticles in murine hippocampal slice cultures

In the late 1980s,superparamagnetic iron oxide nanoparticles（SPIO）moved into focus as contrast agents in magnetic resonance imaging（MRI）,due to their strong relaxivity and resulting higher resolution of images.At the time,no one anticipated their high potential in basic research or for medical diagnostic andtreatment. Since then, SPIO have been evaluated notonly as spe- cific markers for MRI, but also for cell labeling and tracking （Li et al., 2013）.

Magnetic Behaviour and Heating Effect of Fe3O4 Ferrofluids Composed of Monodisperse Nanoparticles

Fe3O4 ferrofluids containing monodisperse Fe3O4 nanoparticles with different diameters of 8, 12, 16 and 18nm are prepared by using high-temperature solution phase reaction. The particles have single crystal structures with narrow size distributions. At room temperature, the 8-nm ferrofluid shows superparamagnetic behaviour, whereas the others display hysteresis properties and the coercivity increases with the increasing particle size. The spin glass-like behaviour and cusps near 190K are observed on all ferrofluids according to the temperature variation of field-cooled （FC） and zero-field-cooled （ZFC） magnetization measurements. The cusps are found to be associated with the freezing point of the solvent. As a comparison, the ferrofluids are dried and the FC and ZFC magnetization curves of powdery samples are also investigated. It is found that the blocking temperatures for the powdery samples are higher than those for their corresponding ferrofluids. Moreover, the size dependent heating effect of the ferrofluids is also investigated in ac magnetic field with a frequency of 55 kHz and amplitude of 200 Oe.

Suzuki Reaction of Aryl Bromides Using a Phosphine-Free Magnetic Nanoparticle-Supported Palladium Catalyst

A palladium catalyst immobilized on superparaganetic nanoparticles was prepared with a palladium loading of 0.30 mmol/g. The catalyst was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, thermogravimetric analysis, Fourier transform infrared, atomic absorption spectrophotometry, and nitrogen adsorption. The immobilized palladium catalyst was an efficient catalyst without added phosphine ligands for the Suzuki cross-coupling reaction of several aryl bromides with phenylboronic acid. The recovery of catalyst was simply by magnetic decantation in the presence of a magnet. The immobilized palladium catalyst can be reused many times without significant degradation in catalytic activity. No leaching of active palladium species into the reaction solution was detected.

Magnetic nanoparticles conjugated with “RPE cell-MCP-1 antibody-VEGF antibody” compounds for the targeted therapy of age-related macular degeneration: a hypothesis

Age-related macular degeneration（AMD） is the leading cause of vision loss in the elderly throughout the world. Treatment of AMD utilizing retinal pigment epithelium（RPE） transplantation represents a promising therapy. However, simplex RPE transplantation can only replace the diseased RPE cells, but has no abilities to stop the development of AMD. It has been indicated that oxidization triggers the development of AMD by inducing the dysfunction and degeneration of RPE cells, which results in the upregulation of local monocyte chemotactic protein-1（MCP-1） expression. MCP-1 induces macrophage recruiment which triggers local inflammation. As a result, the expression of vascular endothelial growth factor（VEGF） is upregulated by MCP-1mediated inflammation and results in the formation of choroidal neovascularization（CNV）. We accordingly propose a targeted therapy of AMD by subretinal transplanting the compound of RPE cell, MCP-1 antibody, and VEGF antibody and using a magnetic system to guide RPE cell compounds conjugated with superparamagnetic iron oxide nanoparticles（SPIONs）. Furthermore, SPION-labelled RPE cells can be tracked and detected in vivo by non-invasive magnetic resonance imaging（MRI）. This novel RPE cell transplantation methodology seems very promising to provide a new therapeutic approach for the treatment of AMD.

Magnet-targeted delivery of bone marrow-derived mesenchymal stem cells improves therapeutic efficacy following hypoxic-ischemic brain injury

hypoxicischemic brain injury;however,the therapeutic efficacy of bone marrow-derived mesenchymal stem cells largely depends on the number of cells that are successfully transferred to the target.Magnet-targeted drug delivery systems can use a specific magnetic field to attract the drug to the target site,increasing the drug concentration.In this study,we found that the double-labeling using superparamagnetic iron oxide nanoparticle and poly-L-lysine(SPIO-PLL)of bone marrow-derived mesenchymal stem cells had no effect on cell survival but decreased cell proliferation 48 hours after labeling.Rat models of hypoxic-ischemic brain injury were established by ligating the left common carotid artery.One day after modeling,intraventricular and caudal vein injections of 1×105 SPIO-PLL-labeled bone marrow-derived mesenchymal stem cells were performed.Twenty-four hours after the intraventricular injection,magnets were fixed to the left side of the rats’heads for 2 hours.Intravoxel incoherent motion magnetic resonance imaging revealed that the perfusion fraction and the diffusion coefficient of rat brain tissue were significantly increased in rats treated with SPIO-PLL-labeled cells through intraventricular injection combined with magnetic guidance,compared with those treated with SPIO-PLL-labeled cells through intraventricular or tail vein injections without magnetic guidance.Hematoxylin-eosin and terminal deoxynucleotidyl transferase dUTP nick-end labeling(TUNEL)staining revealed that in rats treated with SPIO-PLL-labeled cells through intraventricular injection under magnetic guidance,cerebral edema was alleviated,and apoptosis was decreased.These findings suggest that targeted magnetic guidance can be used to improve the therapeutic efficacy of bone marrow-derived mesenchymal stem cell transplantation for hypoxic-ischemic brain injury.This study was approved by the Animal Care and Use Committee of The Second Hospital of Dalian Medical University,China(approval No.2016-060)on March 2,2016.

Encapsulation of superparamagnetic Fe_3O_4@SiO_2 core/shell nanoparticles in MnO_2 microflowers with high surface areas

Microflowers made of interconnected MnO2 nanosheets have been successfully synthesized in a microwave reactor through a hydrothermal reduction of KMnO4 with aqueous HCI at elevated temperatures in the presence of superparamagnetic Fe3O4SiO2 core-shell nanoparticles.Due to the chemical compatibility between SiO2 and MnO2,the heterogeneous reaction leads to the spontaneous encapsulation of the Fe3O4@SiO2 core-shell nanoparticles in the MnO2 microflowers.The resulting hybrid particles exhibit multiple properties including high surface area associated with the MnO2nanosheets and superparamagnetism originated from the Fe3O4@SiO2 core-shell nanoparticles.which are beneficial for applications requiring both high surface area and magnetic separation.

Synthesis and characteristics of multifunctional Fe_3O_4-SiO_2-CdS magnetic-fluorescent nanocomposites

A luminescent superparamagnetic nanocomposite with an Fe3O4 SiO2-CdS structure is synthesised. Coated with a silica shell, Fe3O4 nanoparticles and CdS quantum dots （QDs） are successfully assembled together. Analysed from the test results of X-ray diffraction （XRD）, transmission electron microscopy （TEM）, high resolution transimission electron microscopy （HRTEM）, hysteresis loop, and photoluminescence （PL） spectrum, these nanocomposites exhibit superparamagnetic and photoluminescent properties.

Superparamagnetic iron oxide nanoparticle targeting of adipose tissue-derived stem cells in diabetes-associated erectile dysfunction

Erectile dysfunction （ED） is a major complication of diabetes, and many diabetic men with ED are refractory to common ED therapies. Adipose tissue-derived stem cells （ADSCs） have been shown to improve erectile function in diabetic animal models. However, inadequate cell homing to damaged sites has limited their efficacy. Therefore, we explored the effect of ADSCs labeled with superparamagnetic iron oxide nanoparticles （SPIONs） on improving the erectile function of streptozotocin-induced diabetic rats with an external magnetic field. We found that SPIONs effectively incorporated into ADSCs and did not exert any negative effects on stem cell properties. Magnetic targeting of ADSCs contributed to long-term cell retention in the corpus cavernosum and improved the erectile function of diabetic rats compared with ADSC injection alone. In addition, the paracrine effect of ADSCs appeared to play the major role in functional and structural recovery. Accordingly, magnetic field-guided ADSC therapy is an effective approach for diabetes-associated ED therapy.

MRI tracking of human Wharton’s jelly stem cells seeded onto acellular dermal matrix labeled with superparamagnetic iron oxide nanoparticles in burn wounds

Background:In vivo cell tracking after transplantation in regenerative medicine remains an unmet challenge and limits current understanding of the wound healing mechanism through cell-based therapies.This study investigated tracking of human Wharton’s jelly stem cells(hWJSCs)seeded onto an acellular dermal matrix(ADM)and labeled with superparamagnetic iron oxide nanoparti-cles(SPIONs)by magnetic resonance imaging(MRI)in burn injury.Method:The hWJSCs were characterized and assessed for growth kinetics.A total of 30 rats were enrolled in three equal groups.Group 1 underwent scald burn injury left without treatment,the group 2 was treated by an ADM that was prepared from cosmetic surgery skin samples and the group 3 received hWJSCs labeled with SPIONs seeded onto an ADM.Tensile strength was evaluated before and after interventions,real time PCR assessed apoptosis,and Prussian blue staining,scanning electron microscopy(SEM)and MRI were used for the tracking of labeled cells.Results:The hWJSCs exhibited mesenchymal stem cell properties.Population doubling time was 40.1 hours.SPIONs did not show any toxic effect.The hWJSCs seeded onto an ADM decreased Bax and increased Bcl-2 gene expression.Internalization of SPIONs within hWJSCs was confirmed by Prussian blue staining,SEM and MRI until day 21.There was a significant difference between the Young’s moduli of normal skin and the group receiving hWJSCs seeded onto an ADM.Histological observations and SEM imaging confirmed that MRI is an accurate method to track SPION-labeled hWJSCs in vivo.Conclusions:This study showed that SPION labeling coupled with MRI can be used to further understand the fate of stem cells after transplantation in a burn model.

Fe_(3)O_(4)@Angelica sinensis polysaccharide nanoparticles as an ultralow-toxicity contrast agent for magnetic resonance imaging

Although iron oxide(Fe_(3)O_(4)) nanoparticles have broad application prospects as magnetic resonance imaging(MRI) contrast agent, their biocompatibility and biotoxicity still need to be improved. In this study, we prepared Fe_(3)O_(4)@Angelica sinensis polysaccharide nanoparticles(Fe_(3)O_(4)@ASP NPs) with a 9 nm Fe_(3)O_(4) core and ASP as the coating material. The Fe_(3)O_(4)@ASP NPs are superparamagnetic, can be taken up by liver and spleen macrophages in the circulatory system in vivo, and are a good-biocompatibility and low-toxicity transverse relaxation time(T_(2)) and T_(2)-star(T_(2)^(*)) magnetic resonance imaging(MRI) contrast agent for the liver. The cytotoxicity assessment using HeLa cells and the pathological tests in mice validate that Fe_(3)O_(4)@ASP NPs have low toxicity and good biocompatibility in vivo, which can be attributed to the ASP as a natural polysaccharide with good biocompatibility and its function of protecting the liver. Fe_(3)O_(4)@ASP NPs are a potential new MRI contrast agent with high signal intensity in vivo.

(Super)paramagnetic nanoparticles as platform materials for environmental applications: From synthesis to demonstration

Over the past few decades,engineered,(super)paramagnetic nanoparticles have drawn extensive research attention for a broad range of applications based on their tunable size and shape,surface chemistries,and magnetic properties.This review summaries our recent work on the synthesis,surface modification,and environmental application of(super)paramagnetic nanoparticles.By utilizing high-temperature thermo-decomposition methods,first,we have broadly demonstrated the synthesis of highly monodispersed,(super)paramagnetic nanoparticles,via the pyrolysis of metal carboxylate salts in an organic phase.Highly uniform magnetic nanoparticles with various size,composition,and shape can be precisely tuned by controlled reaction parameters,such as the initial precursors,heating rate,final reaction temperature,reaction time,and the additives.These materials can be further rendered water stable via functionalization with surface mono/bi-layer coating structure using a series of tunable ionic/non-ionic surfactants.Finally,we have demonstrated platform potential of these materials for heavy metal ions sensing,sorption,and separation from the aqueous phase.

Sorafenib delivery nanoplatform based on superpara- magnetic iron oxide nanoparticles magnetically targets hepatocellular carcinoma

Currently, sorafenib is the only systemic therapy capable of increasing overall survival of hepatocellular carcinoma patients. Unfortunately, its side effects, particularly its overall toxicity, limit the therapeutic response that can be achieved. Superparamagnetic iron oxide nanoparticles （SPIONs） are very attractive for drug delivery because they can be targeted to specific sites in the body through application of a magnetic field, thus improving intratumoral accumulation and reducing adverse effects. Here, nanoformulations based on polyethylene glycol modified phospholipid micelles, loaded with both SPIONs and sorafenib, were successfully prepared and thoroughly investigated by complementary techniques. This nanovector system provided effective drug delivery, had an average hydrodynamic diameter of about 125 nm, had good stability in aqueous medium, and allowed controlled drug loading. Magnetic analysis allowed accurate determination of the amount of SPIONs embedded in each micelle. An in vitro system was designed to test whether the SPION micelles can be efficiently held using a magnetic field under typical flow conditions found in the human liver. Human hepatocellular carcinoma （HepG2） cells were selected as an in vitro system to evaluate tumor cell targeting efficacy of the superparamagnetic micelles loaded with sorafenib. These experiments demonstrated that this delivery platform is able to enhance sorafenib＇s antitumor effectiveness by magnetic targeting. The magnetic nanovectors described here represent promising candidates for targeting specific hepatic tumor sites, where selective release of sorafenib can improve its efficacy and safety profile.

Uptake of citrate-coated iron oxide nanoparticles into atherosclerotic lesions in mice occurs via accelerated transcytosis through plaque endothelial cells

Very small superparamagnetic iron oxide nanoparticles （VSOPs） rapidly accumulate in atherosclerotic lesions, thereby enabling plaque visualization by magnetic resonance imaging （MRI）. This study was performed to identify the uptake mechanisms of VSOPs into atherosclerotic plaques. Low-density lipoprotein receptor-deficient （LDLR^-/-） mice with advanced atherosclerosis were analyzed using MRI and transmission electron microscopy （TEM） at various time points after intravenous administration of VSOPs. Post-mortem MRI detected VSOP labeling of atherosclerotic plaques 10 min after injection, and the signal increased over the first 3 h. TEM revealed that the intensive plaque labeling was mediated by accelerated transcytosis of VSOPs through endothelial cells overlaying atherosclerotic lesions. Experiments with endocytosis inhibitors and small interfering RNA （siRNA） revealed a dynamin-dependent mechanism involving both clathrin- and caveolin-mediated processes. In cell culture experiments, endothelial VSOP uptake was enhanced under proatherogenic flow and TNFα stimulation, conditions that are both present in plaque areas. Our study demonstrates that VSOPs enable non-invasive MRI assessment of accelerated endothelial transcytosis, an important pathomechanism in atherosclerotic plaque formation.

Extracellular magnetic labeling of biomimetic hydrogel-induced human mesenchymal stem cell spheroids with ferumoxytol for MRI tracking

Labeling of mesenchymal stem cells(MSCs)with superparamagnetic iron oxide nanoparticles(SPIONs)has emerged as a potential method for magnetic resonance imaging(MRI)tracking of transplanted cells in tissue repair studies and clinical trials.Labeling of MSCs using clinically approved SPIONs(ferumoxytol)requires the use of transfection reagents or magnetic field,which largely limits their clinical application.To overcome this obstacle,we established a novel and highly effective method for magnetic labeling of MSC spheroids using ferumoxytol.Unlike conventional methods,ferumoxytol labeling was done in the formation of a mechanically tunable biomimetic hydrogel-induced MSC spheroids.Moreover,the labeled MSC spheroids exhibited strong MRI T2 signals and good biosafety.Strikingly,the encapsulated ferumoxytol was localized in the extracellular matrix(ECM)of the spheroids instead of the cytoplasm,minimizing the cytotoxicity of ferumoxytol and maintaining the viability and stemness properties of biomimetic hydrogel-induced MSC spheroids.This demonstrates the potential of this method for post-transplantation MRI tracking in the clinic.

Magneto-mechanical effect of magnetic microhydrogel for improvement of magnetic neuro-stimulation

Superparamagnetic iron oxide(SPIO)nanoparticles play an important role in mediating precise and effective magnetic neurostimulation and can help overcome limitations related to penetration depth and spatial resolution.However,nanoparticles readily diffuse in vivo,decreasing the spatial resolution and activation efficiency.In this study,we employed a microfluidic means to fabricate injectable microhydrogels encapsulated with SPIO nanoparticles,which significantly improved the stability of nanoparticles,increased the magnetic properties,reinforced the stimulation effectivity.The fabricated magnetic microhydrogels were highly uniform in size and sphericity,enabling minimally invasive injection into brain tissue.The long-term residency in the cortex up to 22 weeks and the safety of brain tissue were shown using a mouse model.In addition,we quantitatively determined the magneto-mechanical force yielded by only one magnetic microhydrogel using a video-based method.The force was found to be within 7–8 pN under 10 Hz magnetic stimulation by both theoretical simulation and experimental measurement.Lastly,electrophysiological measurement of brain slices showed that the magnetic microhydrogels offer significant advantages in terms of neural activation relative to dissociative SPIO nanoparticles.A universal strategy is thus offered for performing magnetic neuro-stimulation with an improved prospect for biomedical translation.