Biomedical applications of maghemite ferrofluid

Cell-Penetrating Peptidic GRP78 Ligand-Conjugated Iron Oxide Magnetic Nanoparticles for Tumor-Targeted Doxorubicin Delivery and Imaging

Although chemotherapy is regarded as an essential option in cancer treatment, it is still far from being perfect. Inadequate tumor drug concentration and systemic toxicity along with broad biodistribution have diminished the utility of chemotherapy. Tumor-targeting peptide-conjugated multifunctional nanoplatforms have emerged as an effective strategy for site-directed tumor tissues in cancer treatment and imaging. Herein, Pep42-targeted iron oxide magnetic nanoparticles (IONPs) functionalized with β-cyclodextrin (ßCD) containing doxorubicin (DOX) (Fe₃O₄-ßCD-Pep42-DOX) were successfully developed. The physical effects of the prepared NPs were characterized by employing various techniques. Transmission electron microscopy (TEM) images disclosed that the developed Fe₃O₄-ßCD-Pep42-DOX nanoplatforms had a spherical morphology and a core-shell structure with a size of nearly 17 nm. Fourier transform infrared (FT-IR) spectroscopy showed that β-cyclodextrin, DOX, and Pep42 molecules were successfully loaded on the IONPs. In vitro cytotoxicity analysis revealed that the fabricated multifunctional Fe₃O₄-ßCD-Pep42 nanoplatforms possessed excellent biosafety toward BT-474, MDA-MB468 (cancerous cells), and MCF10A normal cells, while Fe₃O₄-ßCD-Pep42-DOX exhibited great cancer cell killing ability. The high cellular uptake along with intracellular trafficking of Fe₃O₄-ßCD-Pep42-DOX highlights the usefulness of the Pep42-targeting peptide. In vivo results strongly supported the in vitro results, i.e., significant tumor size reduction was observed by single-dose injection of Fe₃O₄-ßCD-Pep42-DOX into tumor-bearing mice. Interestingly, in vivo MR imaging (MRI) of Fe₃O₄-ßCD-Pep42-DOX revealed T₂ contrast improvement in the tumor cells and therapeutic ability in cancer theranostics. Taken together, these findings provided strong evidence for the potential capability of Fe₃O₄-ßCD-Pep42-DOX as a multifunctional nanoplatform in cancer therapy and imaging and opens up a new avenue of research in this area.

Tuning of Magnetic Hyperthermia Response in the Systems Containing Magnetosomes

A number of materials are studied in the field of magnetic hyperthermia. In general, the most promising ones appear to be iron oxide particle nanosystems. This is also indicated in some clinical trial studies where iron-based oxides were used. On the other hand, the type of material itself provides a number of variations on how to tune hyperthermia indicators. In this paper, magnetite nanoparticles in various forms were analyzed. The nanoparticles differed in the core size as well as in the form of their arrangement. The arrangement was determined by the nature of the surfactant. The individual particles were covered chemically by dextran; in the case of chain-like particles, they were encapsulated naturally in a lipid bilayer. It was shown that in the case of chain-like nanoparticles, except for relaxation, a contribution from magnetic hysteresis to the heating process also appears. The influence of the chosen methodology of magnetic field generation was also analyzed. In addition, the influence of the chosen methodology of magnetic field generation was analyzed. The application of a rotating magnetic field was shown to be more efficient in generating heat than the application of an alternating magnetic field. However, the degree of efficiency depended on the arrangement of the magnetite nanoparticles. The difference in the efficiency of the rotating magnetic field versus the alternating magnetic field was much more pronounced for individual nanoparticles (in the form of a magnetic fluid) than for systems containing chain nanoparticles (magnetosomes and a mix of magnetic fluid with magnetosomes in a ratio 1:1).

Synthesis of magnetic Fe3O4 micro/nanospheres in organic solvent

INTRODUCTION

Micro/nanostructured materials have attracted a great deal of attention, and many strategies have been developed to fabricate micro/nanostructured materials.

METHODS

Amine-functionalized micro/nanostructured Fe₃O₄ with different sizes was synthesized conveniently in organic media. The chemical structures of as-synthesized products were characterized by FTIR, TEM, SEM, and XRD.

RESULTS

The ligand binds to the Fe₃O₄ core by hydrogen bond between the oxygen atom on the surface of Fe₃O₄ and the hydrogen atom in molecular ethylenediamine. Their magnetic properties were also investigated.

CONCLUSIONS

First, there is no need to control the reaction under a nitrogen atmosphere, and just one salt is used as an iron source. The growth and the surface modification of Fe₃O₄ crystalline nucleation happen at the same time. Second, monodispersed Fe₃O₄ micro/nanospheres were prepared without additional surfactant or external magnetic fields. Third, this method is preferred compared with the conventional organic phase method, as the reaction condition is milder and less pollutant will be produced.

Effective in-field thermal conductivity of ferrofluids

A structural model to predict in-field thermal conductivity of ferrofluids is proposed in this study and is validated by the experimental data from the literature. The model is able to capture the aggregation development of the magnetic particles with increasing magnetic field strength. Introducing a compression function that can be found empirically, the model can accurately predict the thermal conductivity, especially the plateauing at low and high magnetic fields.

Synthesis of highly stable γ-Fe2O3 ferrofluid dispersed in liquid paraffin, motor oil and sunflower oil for heat transfer applications

This article aims at the synthesis of highly stable γ-Fe₂O₃ magnetic nanoparticles and their ferrofluids using different base liquids such as liquid paraffin, motor oil and sunflower oil for heat transfer applications. Phase and morphology of the synthesized nanoparticles were probed using XRD, SEM and FTIR spectroscopy. The average nanoparticle size of γ-Fe₂O₃ magnetic nanoparticles was found to be 13 nm. Stability of the ferrofluids was monitored by visually observing the aggregation nature of the nanoparticles for 180 days. The ferrofluid prepared using motor oil as a base fluid exhibited high stability (for more than 1 year) and a mean enhancement of 77% in thermal conductivity at 1.5 vol% nanoparticles was observed as compared to base fluid. The viscosity of the ferrofluids was also measured and found to be 18, 38 and 8 cP at 27 °C for the liquid paraffin based, motor oil based and sunflower oil based ferrofluid, respectively.

Highly stable ferrofluid for greater enhancement of thermal conductivity.

Detailed toxicity evaluation of β-cyclodextrin coated iron oxide nanoparticles for biomedical applications

The application of iron oxide nanoparticles [IONPs] in biomedical research is progressively increasing, leading to the rapid development of biocompatible and surface modified IONPs. However, there is still a need of information pertaining to its cellular and acute toxicity profile. This work reports the synthesis of β-cyclodextrin coated iron oxide nanoparticles (βCD-IONPs) and their characterization using spectroscopic (FT-IR), thermal (TGA) and surface analysis (TEM, SEM, BET and Zeta potential). All the characterization techniques displayed the synthesis of well dispersed, rod shaped βCD-IONPs of 45nm. Time dependent cellular uptake of these nanoparticles was also evaluated using Prussian blue staining. Further, cytocompatibility analysis was executed in mouse fibroblast cell line (NIH 3T3) using MTT and LDH assays, respectively which did not show any cytotoxic indications of βCD-IONPs. Finally, acute toxicity analysis was carried out in female Wistar rats according to OECD guidelines 420. Rats were exposed to the highest dose (2000mg/kg) of βCD-IONPs along with control and observed for 14days. After two weeks of administration, tissues and blood were collected and subjected to histopathological and biochemical analysis (SGOT, SGPT and ALP). Animals were sacrificed and gross necropsy was carried out. It has been shown that βCD-IONPs does not have any significant toxic effect at the cellular level. Thus, this study provides new perspectives for future biomedical applications.

Gold nanorod@iron oxide core-shell heterostructures: synthesis, characterization, and photocatalytic performance

Iron oxides are directly coated on the surface of cetyl-trimethylammonium bromide (CTAB)-capped gold nanorods (AuNRs) in aqueous solutions at room temperature, which results in AuNR@Fe₂O₃, AuNR@Fe₃O₄, and AuNR@Fe₂O₃@Fe₃O₄ core-shell heterostructures. The iron oxide shells are uniform, smooth, with characteristic porous structure, and their thickness can be readily tuned. The shell formation is highly dependent on the reaction parameters including pH and CTAB concentration. The Fe₂O₃ shell is amorphous and exhibits nearly zero remanence and coercivity, while the Fe₃O₄ shell is ferromagnetic with a low saturation magnetization of about 0.5 emu g^-1 due to its low crystallinity and the porous structure. At elevated temperatures achieved by plasmonic heating of the Au core, the Fe₂O₃ shell transforms from amorphous to γ-Fe₂O₃ and α-Fe₂O₃ phases, while the Fe₃O₄ phase disappears because of the oxidation of Fe²⁺. A 1.4-fold increase of photocatalytic performance is observed due to the plasmonic resonance provided by the Au core. The photocatalytic efficiency of Fe₃O₄ is about 1.7-fold higher than Fe₂O₃ as more surface defects are present on the Fe₃O₄ shell, promoting the adsorption and activation of reagents on the surface during the catalytic reactions. This approach can be readily extended to other nanostructures including Au spherical nanoparticles and nanostars. These highly uniform and multifunctional core-shell heterostructures can be of great potential in a variety of energy, magnetic, and environment applications.

Evaluation of High-Yield Purification Methods on Monodisperse PEG-Grafted Iron Oxide Nanoparticles

Fundamental research on nanoparticle (NP) interactions and development of next-generation biomedical NP applications relies on synthesis of monodisperse, functional, core-shell nanoparticles free of residual dispersants with truly homogeneous and controlled physical properties. Still, synthesis and purification of e.g. such superparamagnetic iron oxide NPs remain a challenge. Comparing the success of different methods is marred by the sensitivity of analysis methods to the purity of the product. We synthesize monodisperse, oleic acid (OA)-capped, Fe3O4 NPs in the superparamagnetic size range (3-10 nm). Ligand exchange of OA for poly(ethylene glycol) (PEG) was performed with the PEG irreversibly grafted to the NP surface by a nitrodopamine (NDA) anchor. Four different methods were investigated to remove excess ligands and residual OA: membrane centrifugation, dialysis, size exclusion chromatography, and precipitation combined with magnetic decantation. Infrared spectroscopy and thermogravimetric analysis were used to determine the purity of samples after each purification step. Importantly, only magnetic decantation yielded pure NPs at high yields with sufficient grafting density for biomedical applications (∼1 NDA-PEG(5 kDa)/nm(2), irrespective of size). The purified NPs withstand challenging tests such as temperature cycling in serum and long-term storage in biological buffers. Dynamic light scattering, transmission electron microscopy, and small-angle X-ray scattering show stability over at least 4 months also in serum. The successful synthesis and purification route is compatible with any conceivable functionalization for biomedical or biomaterial applications of PEGylated Fe3O4 NPs.

Core-Shell Structure of Monodisperse Poly(ethylene glycol)-Grafted Iron Oxide Nanoparticles Studied by Small-Angle X-ray Scattering

The promising applications of core-shell nanoparticles in the biological and medical field have been well investigated in recent years. One remaining challenge is the characterization of the structure of the hydrated polymer shell. Here we use small-angle X-ray scattering (SAXS) to investigate iron oxide core-poly(ethylene glycol) brush shell nanoparticles with extremely high polymer grafting density. It is shown that the shell density profile can be described by a scaling model that takes into account the locally very high grafting density near the core. A good fit to a constant density region followed by a star-polymer-like, monotonously decaying density profile is shown, which could help explain the unique colloidal properties of such densely grafted core-shell nanoparticles. SAXS experiments probing the thermally induced dehydration of the shell and the response to dilution confirmed that the observed features are associated with the brush and not attributed to structure factors from particle aggregates. We thereby demonstrate that the structure of monodisperse core-shell nanoparticles with dense solvated shells can be well studied with SAXS and that different density models can be distinguished from each other.

Melt-grafting for the synthesis of core-shell nanoparticles with ultra-high dispersant density

Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of applications in e.g. the biomedical field, for which brushes of biocompatible polymers such as poly(ethylene glycol) (PEG) have to be densely grafted to the core. Grafting of such shells to monodisperse iron oxide NPs has remained a challenge mainly due to the conflicting requirements to replace the ligand shell of as-synthesized NPs with irreversibly bound PEG dispersants. We introduce a general two-step method to graft PEG dispersants from a melt to iron oxide NPs first functionalized with nitrodopamine (NDA). This method yields uniquely dense spherical PEG-brushes (∼3 chains per nm(2) of PEG(5 kDa)) compared to existing methods, and remarkably colloidally stable NPs also under challenging conditions.

Superparamagnetic iron oxide nanoparticles for in vivo molecular and cellular imaging

In the last decade, the biomedical applications of nanoparticles (NPs) (e.g. cell tracking, biosensing, magnetic resonance imaging (MRI), targeted drug delivery, and tissue engineering) have been increasingly developed. Among the various NP types, superparamagnetic iron oxide NPs (SPIONs) have attracted considerable attention for early detection of diseases due to their specific physicochemical properties and their molecular imaging capabilities. A comprehensive review is presented on the recent advances in the development of in vitro and in vivo SPION applications for molecular imaging, along with opportunities and challenges.

Curcumin and 5-fluorouracil-loaded, folate- and transferrin-decorated polymeric magnetic nanoformulation: a synergistic cancer therapeutic approach, accelerated by magnetic hyperthermia

The efficient targeting and therapeutic efficacy of a combination of drugs (curcumin and 5-Fluorouracil [5FU]) and magnetic nanoparticles encapsulated poly(D,L-lactic-co-glycolic acid) nanoparticles, functionalized with two cancer-specific ligands are discussed in our work. This multifunctional, highly specific nanoconjugate resulted in the superior uptake of nanoparticles by cancer cells. Upon magnetic hyperthermia, we could harness the advantages of incorporating magnetic nanoparticles that synergistically acted with the drugs to destroy cancer cells within a very short period of time. The remarkable multimodal efficacy attained by this therapeutic nanoformulation offers the potential for targeting, imaging, and treatment of cancer within a short period of time (120 minutes) by initiating early and late apoptosis.

Thermal potentiation of chemotherapy by magnetic nanoparticles

Clinical studies have demonstrated the effectiveness of hyperthermia as an adjuvant for chemotherapy and radiotherapy. However, significant clinical challenges have been encountered, such as a broader spectrum of toxicity, lack of patient tolerance, temperature control and significant invasiveness. Hyperthermia induced by magnetic nanoparticles in high-frequency oscillating magnetic fields, commonly termed magnetic fluid hyperthermia, is a promising form of heat delivery in which thermal energy is supplied at the nanoscale to the tumor. This review discusses the mechanisms of heat dissipation of iron oxide-based magnetic nanoparticles, current methods and challenges to deliver heat in the clinic, and the current work related to the use of magnetic nanoparticles for the thermal-chemopotentiation of therapeutic drugs.

The cytotoxicity evaluation of magnetic iron oxide nanoparticles on human aortic endothelial cells

One major obstacle for successful application of nanoparticles in medicine is its potential nanotoxicity on the environment and human health. In this study, we evaluated the cytotoxicity effect of dimercaptosuccinic acid-coated iron oxide (DMSA-Fe2O3) using cultured human aortic endothelial cells (HAECs). Our results showed that DMSA-Fe2O3 in the culture medium could be absorbed into HAECs, and dispersed in the cytoplasm. The cytotoxicity effect of DMSA-Fe2O3 on HAECs was dose-dependent, and the concentrations no more than 0.02 mg/ml had little toxic effect which were revealed by tetrazolium dye assay. Meanwhile, the cell injury biomarker, lactate dehydrogenase, was not significantly higher than that from control cells (without DMSA-Fe2O3). However, the endocrine function for endothelin-1 and prostacyclin I-2, as well as the urea transporter function, was altered even without obvious evidence of cell injury in this context. We also showed by real-time PCR analysis that DMSA-Fe2O3 exposure resulted in differential effects on the expressions of pro- and anti-apoptosis genes of HAECs. Meanwhile, it was noted that DMSA-Fe2O3 exposure could activate the expression of genes related to oxidative stress and adhesion molecules, which suggested that inflammatory response might be evoked. Moreover, we demonstrated by in vitro endothelial tube formation that even a small amount of DMSA-Fe2O3 (0.01 and 0.02 mg/ml) could inhibit angiogenesis by the HAECs. Altogether, these results indicate that DMSA-Fe2O3 have some cytotoxicity that may cause side effects on normal endothelial cells.

Synthesis of novel CoCx@C nanoparticles

CoC(x) nanoparticles encapsulated in carbon shells were synthesized using a pulsed plasma in liquid ethanol. This is the first time that monolithic cubic phase cobalt carbide nanoparticles have been obtained. X-ray diffraction refinement of the nanoparticles showed that the lattice parameter of prepared cubic phase cobalt carbide is larger than that of CoC(x) (44-0962) and cubic phase Co (15-0806 and 01-1259). The x-ray absorption fine structure spectra near the Co K-edge of the synthesized sample indicated differences from commercial metallic cobalt and cobalt oxide samples. High resolution transmission electron microscopy revealed that a thin carbon coating covered the surface of the nanoparticles. These carbon layers might isolate core CoC(x) material from the outside environment, and allow functionalization by carboxyl groups for the further purpose of targeted drug delivery. The obtained CoC(x)@C particles, with a crystallite size of about 10 nm confirmed by the electron microscope, aggregate into 20-40 nm secondary particles in distilled water as shown by dynamic light scattering, and possess high saturation magnetization of about 120 emu g(-1). The sodium 3'-[1-(phenylaminocarbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid hydrate assay and defragmentation of deoxyribonucleic acid on MCF-7 cells after incubation with particles indicate relatively low cytotoxicity of CoC(x)@C nanoparticles, compared with micro-sized and nano-sized metallic cobalt particles and commonly used iron oxides. For the small sized CoC(x)@C particles, the release of cobalt ions was checked by a chelation method with ethylenediaminetetraacetic acid solution to be at a very low level compared with other reference materials.

Photoacoustic investigation of maghemite-based nanocomposite

Photoacoustic spectroscopy was used to investigate magnetic nanocomposites incorporating nanosized maghemite particles into styrene-divinylbenzene copolymer template. Typical photoacoustic features were observed in bands C, S and L in the wavelength region of 300-1000 nm. The relative intensity of band-C scaled with the nominal concentration of nanosized maghemite incorporated into the polymeric template whereas the lowest relative intensity of band-S was found in the sample in which the template polymerization took place in the presence of the highest polar-like reaction medium. X-ray diffraction and transmission electron microscopy were used to characterize the magnetic nanosized phase as maghemite, with average particle diameter of 6.9 nm (sample Est34), 7.0 nm (sample H30), and 7.9 nm (sample Em15).

Stabilization and functionalization of iron oxide nanoparticles for biomedical applications

Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface presentation of functionalities. This review is focused on different aspects of the stability of superparamagnetic iron oxide NPs, from its practical definition to its implementation by molecular design of the dispersant shell around the iron oxide core and further on to its influence on the magnetic properties of the superparamagnetic iron oxide NPs. Special attention is given to the selection of molecular anchors for the dispersant shell, because of their importance to ensure colloidal and functional stability of sterically stabilized superparamagnetic iron oxide NPs. We further detail how dispersants have been optimized to gain close control over iron oxide NP stability, size and functionalities by independently considering the influences of anchors and the attached sterically repulsive polymer brushes. A critical evaluation of different strategies to stabilize and functionalize core-shell superparamagnetic iron oxide NPs as well as a brief introduction to characterization methods to compare those strategies is given.

Annexin A5-functionalized bimodal nanoparticles for MRI and fluorescence imaging of atherosclerotic plaques

Apoptosis and macrophage burden are believed to correlate with atherosclerotic plaque vulnerability and are therefore considered important diagnostic and therapeutic targets for atherosclerosis. These cell types are characterized by the exposure of phosphatidylserine (PS) at their surface. In the present study, we developed and applied a small micellar fluorescent annexin A5-functionalized nanoparticle for noninvasive magnetic resonance imaging (MRI) of PS exposing cells in atherosclerotic lesions. Annexin A5-mediated target-specificity was confirmed with ellipsometry and in vitro binding to apoptotic Jurkat cells. In vivo T(1)-weighted MRI of the abdominal aorta in atherosclerotic ApoE(-/-) mice revealed enhanced uptake of the annexin A5-micelles as compared to control-micelles, which was corroborated with ex vivo near-infrared fluorescence images of excised whole aortas. Confocal laser scanning microscopy (CLSM) demonstrated that the targeted agent was associated with macrophages and apoptotic cells, whereas the nonspecific control agent showed no clear uptake by such cells. In conclusion, the annexin A5-conjugated bimodal micelles displayed potential for noninvasive assessment of cell types that are considered to significantly contribute to plaque instability and therefore may be of great value in the assessment of atherosclerotic lesion phenotype.

Challenges in the development of magnetic particles for therapeutic applications

Certain iron-based particle formulations have useful magnetic properties that, when combined with low toxicity and desirable pharmacokinetics, encourage their development for therapeutic applications. This mini-review begins with background information on magnetic particle use as MRI contrast agents and the influence of material size on pharmacokinetics and tissue penetration. Therapeutic investigations, including (1) the loading of bioactive materials, (2) the use of stationary, high-gradient (HG) magnetic fields to concentrate magnetic particles in tissues or to separate material bound to the particles from the body, and (3) the application of high power alternating magnetic fields (AMF) to generate heat in magnetic particles for hyperthermic therapeutic applications are then surveyed. Attention is directed mainly to cancer treatment, as selective distribution to tumors is well-suited to particulate approaches and has been a focus of most development efforts. While magnetic particles have been explored for several decades, their use in therapeutic products remains minimal; a discussion of future directions and potential ways to better leverage magnetic properties and to integrate their use into therapeutic regimens is discussed.

The Effect of Iron Oxide Magnetic Nanoparticles on Smooth Muscle Cells

Recently, magnetic nanoparticles of iron oxide (Fe₃O₄, γ-Fe₂O₃) have shown an increasing number of applications in the field of biomedicine, but some questions have been raised about the potential impact of these nanoparticles on the environment and human health. In this work, the three types of magnetic nanoparticles (DMSA-Fe₂O₃, APTS-Fe₂O₃, and GLU-Fe₂O₃) with the same crystal structure, magnetic properties, and size distribution was designed, prepared, and characterized by transmission electronic microscopy, powder X-ray diffraction, zeta potential analyzer, vibrating sample magnetometer, and Fourier transform Infrared spectroscopy. Then, we have investigated the effect of the three types of magnetic nanoparticles (DMSA-Fe₂O₃, APTS-Fe₂O₃, and GLU-Fe₂O₃) on smooth muscle cells (SMCs). Cellular uptake of nanoparticles by SMC displays the dose, the incubation time and surface property dependent patterns. Through the thin section TEM images, we observe that DMSA-Fe₂O₃is incorporated into the lysosome of SMCs. The magnetic nanoparticles have no inflammation impact, but decrease the viability of SMCs. The other questions about metabolism and other impacts will be the next subject of further studies.

Multifunctional magnetic nanoparticles for targeted imaging and therapy

Magnetic nanoparticles have become important tools for the imaging of prevalent diseases, such as cancer, atherosclerosis, diabetes, and others. While first generation nanoparticles were fairly nonspecific, newer generations have been targeted to specific cell types and molecular targets via affinity ligands. Commonly, these ligands emerge from phage or small molecule screens, or are based on antibodies or aptamers. Secondary reporters and combined therapeutic molecules have further opened potential clinical applications of these materials. This review summarizes some of the recent biomedical applications of these newer magnetic nanomaterials.

Gold-magnetite nanocomposite materials formed via sonochemical methods

Treatment of preformed magnetite nanoparticles with ultrasound in aqueous media with dissolved tetrachloroauric acid resulted in the formation of gold-magnetite nanocomposite materials. These materials maintained the morphology of the original magnetite particles. The loading of gold particles could be controlled by adjusting experimental parameters, including the addition of small amounts of solvent modifiers such as methanol, diethylene glycol, and oleic acid. The nanocomposite materials were magnetic and exhibited optical properties similar to pure gold nanoparticles.

Targeted delivery of multifunctional magnetic nanoparticles

Magnetic nanoparticles and their magnetofluorescent analogues have become important tools for in vivo imaging using magnetic resonance imaging and fluorescent optical methods. A number of monodisperse magnetic nanoparticle preparations have been developed over the last decade for angiogenesis imaging, cancer staging, tracking of immune cells (monocyte/macrophage, T cells) and for molecular and cellular targeting. Phage display and data mining have enabled the procurement of novel tissue- or receptor-specific peptides, while high-throughput screening of diversity-oriented synthesis libraries has identified small molecules that permit or prevent uptake by specific cell types. Next-generation magnetic nanoparticles are expected to be truly multifunctional, incorporating therapeutic functionalities and further enhancing an already diverse repertoire of capabilities.

In vitro interactions between DMSA-coated maghemite nanoparticles and human fibroblasts: A physicochemical and cyto-genotoxical study

Although the current production of oxide nanoparticles may be modest, the wide range of proposed applications and forecasted growth in production has raised questions about the potential impact of these nanoparticles on the environment and human health. Iron oxide nanoparticles have been proposed for an increasing number of biomedical applications although in vitro toxicity depending on the particles coating has been evidenced. The aim of this study was to examine the potential in vitro cyto- and genotoxicity on human dermal fibroblasts of DMSA-coated maghemite nanoparticles (NmDMSA) as a function of well-defined physicochemical states. Well-stabilized NmDMSA produced weak cytotoxic and no genotoxic effects. This is attributed in part to the DMSA coating, which serves as a barrier for a direct contact between nano-oxide and fibroblasts, inhibiting a potential toxic effect.

Nanotechnology: intelligent design to treat complex disease

The purpose of this expert review is to discuss the impact of nanotechnology in the treatment of the major health threats including cancer, infections, metabolic diseases, autoimmune diseases, and inflammations. Indeed, during the past 30 years, the explosive growth of nanotechnology has burst into challenging innovations in pharmacology, the main input being the ability to perform temporal and spatial site-specific delivery. This has led to some marketed compounds through the last decade. Although the introduction of nanotechnology obviously permitted to step over numerous milestones toward the development of the "magic bullet" proposed a century ago by the immunologist Paul Ehrlich, there are, however, unresolved delivery problems to be still addressed. These scientific and technological locks are discussed along this review together with an analysis of the current situation concerning the industrial development.

Fluorescence-modified superparamagnetic nanoparticles: intracellular uptake and use in cellular imaging

This report describes the preparation and characterization of new magnetic fluorescent nanoparticles and our success in using them to label living cells. The bifunctional nanoparticles possess a magnetic oxide core composed of a dimercaptosuccinic acid (DMSA) ligand at the surface and a covalently attached fluorescent dye. The nanoparticles exhibited a high affinity for cells, which was demonstrated by fluorescence microscopy and magnetophoresis. Fluorescence microscopy was used to monitor the localization patterns of magnetic nanoparticles associated with cells. We observed two types of magnetic labeling: adsorption of the nanoparticles on the cell membrane (membranous fluorescence) and internalization of the nanoparticles inside the cell (intracellular vesicular fluorescence). After internalization, nanoparticles were confined inside endosomes, which are submicrometric vesicles of the endocytotic pathway. We demonstrated that endosome movement could be piloted inside the cell by external magnetic fields such that small fluorescent chains of magnetic endosomes were formed in the cell cytoplasm in the direction of the applied magnetic field. Finally, by measuring the critical cellular magnetic load (quantitated by magnetophoresis), we have demonstrated the potential of this new magneto-fluorescent nanoagent for medical use.

Magnetic Targeting of Magnetoliposomes to Solid Tumors with MR Imaging Monitoring in Mice: Feasibility

PURPOSE

To establish the feasibility of magnetoliposome tumor targeting with an extracorporeal magnet.

MATERIALS AND METHODS

Animal experiments were performed in compliance with Institut National de la Santé Et de la Recherche Médicale animal protection guidelines and were approved by local government authorities. Magnetophoresis was used to measure the velocity of magnetoliposomes constituted of polyethylene glycol-lipids and anionic maghemite nanocrystals in a calibrated magnetic field in vitro. For in vivo studies, 38 male Swiss nude mice bearing a PC3 human prostate carcinoma tumor in each flank received an intravenous injection of magnetoliposomes (n = 27), saline (n = 9), or nonencapsulated superparamagnetic particles (n = 2) after a small magnet with a magnetic field of 0.3 T and a field gradient of 11 T/m was fixed to the skin above one tumor. The animals were examined at magnetic resonance (MR) imaging with eight different sequences, iron doses (13 mice), and magnet-application durations (12 mice). Their excised tumors were then stained with Perls Prussian blue and hematoxylin-eosin and were examined histologically. With use of the paired Student t test, signal intensity, tumor surface enhancement, and number of stained cells were compared between the control and magnet-exposed tumors to determine significant differences (P </= .01).

RESULTS

The mean magnetoliposome velocity ranged from 10 to 40 mum/sec when the magnetic field equaled 0.13 T and the field gradient equaled 25 T/m. At T1-weighted three-dimensional spoiled gradient-echo MR imaging in vivo, the tumor exposed to the magnet showed strong negative enhancement, -52%, compared with the -7% enhancement of the other tumor. Maximal enhancement occurred after 3 hours of magnet application. After 24 hours of magnet application, intracapillary iron particle accumulation was observed in the targeted tumors only.

CONCLUSION

Magnetic targeting of sterically stabilized magnetoliposomes after they are intravenously injected is feasible in vivo.

Ferrite-enhanced MRI monitoring in hyperthermia

In an MRI hyperthermia hybrid system, T1 changes are investigated for monitoring thermal therapy at 0.2 T. The water bolus, which is needed for power transmission and cooling of the skin, limits MR image quality by signal compression and artifacts. Superparamagnetic ferrofluid in different concentration was investigated with MR relaxometry and MRI methods. We found that using ferrofluid in a low concentration of 70-90 ppm magnetite the water signal can be suppressed without susceptibility artifacts. With our method of signal suppression, a significant improvement of spatial and temporal resolution is possible. The ferrofluid is stable and allows RF heating at 100 MHz. This method of signal extinction may also be useful for other experimental setups where suppression of water is necessary.

Generation of superparamagnetic liposomes revealed as highly efficient MRI contrast agents for in vivo imaging

Maghemite (gamma-Fe2O3) nanocrystals stable at neutral pH and in isotonic aqueous media were synthesized and encapsulated within large unilamellar vesicles of egg phosphatidylcholine (EPC) and distearoyl-SN-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG(2000), 5 mol %), formed by film hydration coupled with sequential extrusion. The nonentrapped particles were removed by flash gel exclusion chromatography. The magnetic-fluid-loaded liposomes (MFLs) were homogeneous in size (195 +/- 33 hydrodynamic diameters from quasi-elastic light scattering). Iron loading was varied from 35 up to 167 Fe(III)/lipid mol %. Physical and superparamagnetic characteristics of the iron oxide particles were preserved after liposome encapsulation as shown by cryogenic transmission electron microscopy and magnetization curve recording. In biological media, MFLs were highly stable and avoided ferrofluid flocculation while being nontoxic toward the J774 macrophage cell line. Moreover, steric stabilization ensured by PEG-surface-grafting significantly reduced liposome association with the macrophages. The ratios of the transversal (r2) and longitudinal (r1) magnetic resonance (MR) relaxivities of water protons in MFL dispersions (6 < r2/r1 < 18) ranked them among the best T2 contrast agents, the higher iron loading the better the T2 contrast enhancement. Magnetophoresis demonstrated the possible guidance of MFLs by applying a magnetic field gradient. Mouse MR imaging assessed MFLs efficiency as contrast agents in vivo: MR angiography performed 24 h after intravenous injection of the contrast agent provided the first direct evidence of the stealthiness of PEG-ylated magnetic-fluid-loaded liposomes.

In vivo cellular imaging of magnetically labeled hybridomas in the spleen with a 1.5-T clinical MRI system

The feasibility of in vivo cellular imaging using a 1.5 T clinical magnet was studied in the mouse. Hybridoma cells were labeled with anionic gamma-Fe2O3 superparamagnetic iron oxide nanoparticles. These were internalized by the endocytose pathway. Both electron spin resonance and magnetophoresis as a measure of the labeled cells migration velocity under a magnetic field were used to quantify particle uptake. A fast (< 2 hr) and substantial (up to 5 pg of iron per cell) internalization of nanoparticles by hybridomas was found, with good agreement between the two methods used. Hybridomas labeled with 2.5 pg iron per cell were injected intraperitoneally to male Swiss nude mice. A decrease in the spleen signal, suggesting a "homing" of labeled hybridomas to this organ, was found 24 hr later by MRI performed at 1.5 T. Furthermore, in labeled cells recovered from the spleen by ex vivo magnetic sorting, a mean of 0.5 pg iron per cell was found, i.e., a value five times lower than that of the injected hybridomas. This finding is consistent with in vivo proliferation of these cells. In addition, the amount of labeled hybridomas present in the spleen was found to correlate with MRI signal intensity.

Effect of the concentration of magnetic grains on the linear-optical-absorption coefficient of ferrofluid-doped lyotropic mesophases: deviation from the Beer-Lambert law

In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.

Evidence of surfactant-induced formation of transient pores in lipid bilayers by using magnetic-fluid-loaded liposomes

It is often assumed that surfactant-induced permeability of lipid membranes obeys a pore-formation mechanism, but, to date, this has not been totally proven. A novel approach is developed using a magnetic fluid composed of calibrated nanocrystals of maghemite (gamma-Fe2O3) as a permeability marker. It is shown that low amounts of surfactant molecules catalyze the transient opening of unilamellar phospholipid vesicles which permit the passage of 8 nm maghemite nanospheres before closing up.