Synthesis of Iron Oxide Nanoparticles Used as MRI Contrast Agents: A Parametric Study

Colloidal iron oxides play an important role as magnetic resonance imaging (MRI) contrast agents. The superparamagnetic particles actually used are constituted by solid cores (diameter of 5-15 nm), generally coated by a thick polysaccharidic layer (hydrodynamic radii of 30-100 nm), and formulated by direct coprecipitation of iron salts in the presence of polymeric material. To better control the synthesis, we attempted to formulate new stable uncoated superparamagnetic nanoparticles. Colloids were generated by coprecipitation of an aqueous solution of iron salts and tetramethylammonium hydroxide (TMAOH) solution. The influence of parameters such as media composition, iron media, injection fluxes, Fe and TMAOH concentrations, temperature, and oxygen on size, magnetic and magnetic resonance relaxometric properties, and colloidal stability of particles were evaluated. We have determined the relative importance of these parameters as well as the optimal conditions for obtaining uncoated stable particles with an average size of 5 nm and interesting relaxivities. The interpretation of the observed limits takes into account diffusibilities of reactants and product, feeding rates of reactants, and surface properties of nanoparticles. A model of synthesis, related to spontaneous emulsification of suspensions, is proposed. Copyright 1999 Academic Press.     

Long-circulating gadolinium-loaded liposomes: potential use for magnetic resonance imaging of the blood pool

In our previous paper, we reported a method of liposome loading with Gadolinium (Gd) via so called polychelating amphiphilic polymer (PAP). A novel Gd-containing polymeric probe, suitable for the incorporation into the liposomal membrane, was prepared from a low-molecular-weight DTPA-polylysine by linking its N-terminus to a lipid anchor, NGPE-PE. When compared with known membranotropic MR probes, such as Gd-DTPA-SA and Gd-DTPA-PE, liposomes containing new membrane-bound polychelator possess enhanced relaxivity for water protons resulting in an increase of tissue signal intensity on MR images. In this study, we developed the optimized protocol to prepare a liposomal MR contrast agent with high relaxivity and narrow size distribution. Gd-containing liposomes were additionally modified with PEG to provide longevity in vivo. We also demonstrated that upon intravenous administration in rabbit and dog, the new preparation causes a prolonged decrease in the blood T₁ value (reflecting the proton relaxation rate in the blood) and may be considered as a potential contrast agent for MRI of the blood pool.     

Antibiofouling polymer-coated superparamagnetic iron oxide nanoparticles as potential magnetic resonance contrast agents for in vivo cancer imaging

We report the fabrication and characterization of antifouling polymer-coated magnetic nanoparticles as nanoprobes for magnetic resonance (MR) contrast agents. Magnetite superparamagnetic iron oxide nanoparticles (SPION) were coated with the protein- or cell-resistant polymer, poly(TMSMA-r-PEGMA), to generate stable, protein-resistant MR probes. Coated magnetic nanoparticles synthesized using two different preparation methods (in situ and stepwise, respectively) were both well dispersed in PBS buffer at a variety of pH conditions (pH 1-10). In addition, dynamic light scattering data revealed that their sizes were not altered even after 24 h of incubation in 10% serum containing cell culture medium, indicative of a lack of protein adsorption on their surfaces. When the antibiofouling polymer-coated SPION were incubated with macrophage cells, uptake was significantly lower in comparison to that of the popular contrast agent, Feridex I.V., suggesting that the polymer-coated SPION can be long-circulated in plasma by escaping from uptake by the reticular endothelial system (RES) such as macrophages. Indeed, when the coated SPION were administered to tumor xenograft mice by intravenous injection, the tumor could be detected in T2-weighted MR images within 1 h as a result of the accumulation of the nanomagnets within the tumor site. Although the poly(TMSMA-r-PEGMA)-coated SPION do not have any targeting ligands on their surface, they are potentially useful for cancer diagnosis in vivo.     

Gadolinium-based cancer therapeutic liposomes for chemotherapeutics and diagnostics

Gadolinium (Gd)-based cancer therapeutic liposomes can be used for chemotherapeutics and diagnostics. In this study, dual functional liposomes co-encapsulating doxorubicin (Dox) and Gd were prepared by Dox-transition metal complexation. Preparation conditions were optimized to obtain liposomes containing high concentrations of Dox and Gd. The optimized liposomes Gd250 co-encapsulated 3.6 mM of Dox and 1.9 mM of Gd. The magnetic resonance (MR) properties of Gd250 liposomes were determined using a 4.7 T MR system. Cellular uptake of Dox was determined using a flow cytometer and a confocal microscopy and that of Gd was measured using an inductively coupled plasma-atomic emission spectrometer. Although encapsulated Gd exhibited lower relaxivity than MRbester?, which is widely used for clinical diagnosis, because of limited diffusion across the liposome membrane, Gd250 liposomes showed much higher cellular uptake than that of MRbester?. In Gd250 liposomes, Gd was highly accumulated in B16F10 cells, which could provide improved contrast sensitivity for molecular imaging. Additionally, in Gd250 liposomes, Dox was highly internalized, which could enhance its cancer therapeutic effects. Consequently, we suggest that dual functional liposomes can be used as therapeutic and diagnostic carriers.     

Preparation of sulfur‐quinone polyurethanes and their use to inhibit the corrosion of iron particles

A sulfur‐quinone diol monomer, 2,5‐bis‐(2‐hydroxyethylthio)‐1,4‐benzoquinone (SQM‐2), was prepared by the reaction of 2‐mercaptoethanol with benzoquinone. SQM‐2 and polycaprolactone diol (number‐average molecular weight = 1250) were condensed with toluene diisocyanate to give sulfur‐quinone polyurethanes. Two compositions were prepared, SQPU‐1 containing 7 mol % SQM‐2 and SQPU‐2 containing 35 mol % SQM‐2. These thermoplastic polyurethanes were soluble in solvents used in magnetic tape coating processes. The polymers were used to prepare magnetic coatings containing state‐of‐the‐art commercial iron particles. The sulfur‐quinone polyurethanes protected the iron particles against corrosion from a pH 2.0 aqueous buffer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3278–3283, 2000     

Physico-chemical properties and cytotoxicity assessment of PEG-modified liposomes containing human hemoglobin

PEGylated liposomes encapsulating human hemoglobin as oxygen carriers were prepared from purified carbonylhemoglobin (HbCO) solution and a lipid mixture composed of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), cholesterol, 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-[poly(ethylene glycol) 2000] (DMPE-PEG(2000)) and palmitic acid. Hemoglobin was extracted and purified from human blood samples. SDS-PAGE was used to assess its purity. Diameter of liposomes containing hemoglobin was controlled to approximately 200 nm using extrusion as measured by dynamic light scattering and transmission electron microscopy. Liposome size distributions were shown to remain unimodal over 14 days, even at different storage temperatures. Zeta potential measurements revealed that liposome containing hemoglobin have a net surface charge of -7.16+/-0.33 mV. Also, hemoglobin encapsulated in liposomes was able to perform several cycles of oxygen loading and unloading using oxygen (O(2)) and carbon monoxide (CO). The hemoglobin vesicle dispersion showed some toxicity as revealed by three in vitro assays in which endothelial cell (HUVECs) monolayers were exposed to these dispersions. Cytotoxicity was function of the liposome concentration in the culture medium.     

Influence of iron content on thermal stability of magnetic polyurethane foams

Magnetorheological (MR) materials are a group of smart materials which have the controllable magnetic properties with an external magnetic field. Magnetic foams, a specific type of MR solids, were synthesized from flexible polyurethane (PU) foams and carbonyl iron particles. Effects of the carbonyl iron particles on the thermal stability of the magnetic foams have been studied. Thermogravimetric analysis (TGA) was applied to characterize the thermal degradation process of the magnetic foams and then the apparent activation energy of degradation was calculated by using Ozawa's method [Ozawa T. A new method of analyzing thermogravimetric data. Bulletin of the Chemical Society of Japan 1965; 38: 1881-1886.]. The carbonyl iron particles were found to improve the thermal stability of magnetic foams in nitrogen by showing higher 10 wt% loss temperature, slower weight loss rate and higher apparent activation energy than pure PU foams. But the magnetic foams were observed to have slightly worse thermal stability in air than pure PU foams at the earlier degradation stage. At the later degradation stage, the magnetic foams exhibited the higher activation energy than pure PU foams in air.     

Cationic gel-phase liposomes with "decorated" anionic SPIO nanoparticles: morphology, colloidal, and bilayer properties

The assembly and complexation of oppositely charged colloids are important phenomena in many natural and synthetic processes. Liposome-nanoparticle assemblies (LNAs) represent an interesting hybrid system that combines "soft" and "hard" colloidal materials. This work describes the formation and characterization of gel-phase LNAs formed by the binding of anionic superparamagnetic iron oxide (SPIO) nanoparticles to cationic dipalmitoylphosphatidylcholine (DPPC)/dipalmitoyltrimethylammonium propane (DPTAP) liposomes. Particles were examined with hydrodynamic diameters below (16 nm) and above (30 nm) the cutoff reported for supported lipid bilayer formation. LNA formation with 16 nm particles was entropically driven and particles bound individually to yield "decorated" structures. In this case, increasing nanoparticle concentration yielded colloidal LNA aggregates and eventual charge inversion. In contrast, LNA formation with 30 nm particles was enthalpically driven, and the nanoparticles aggregated at the bilayer interface. These aggregates led to significant LNA aggregation and large bilayer sheets due to liposome rupture despite minimal charge screening of the liposome surface. In this case SLBs were present, but these structures were not dominant. Differences in LNA structure were also revealed through the lipid phase transition behavior. This work infers size-dependent nanoparticle binding and LNA formation mechanisms that can be used to tailor colloidal and bilayer properties. Analogies are made to polyelectrolyte patch charge heterogeneities and DNA complexation with cationic liposomes.     

Lipid bilayer elasticity measurements in giant liposomes in contact with a solubilizing surfactant

A new method to probe the modification of the elasticity of phospholipid bilayers is presented. The purpose here concerns the action of a solubilizing surfactant on a vesicle bilayer. This method is based on the measure of the under-field elongation of giant magnetic-fluid-loaded liposomes. The addition of the nonionic surfactant octyl-beta-d-glucopyranoside (OG) to vesicles at sublytic levels increases the elasticity of the membrane, as shown by the value of the bending modulus K(b), which decreases. K(b) measured around 20 kT for a pure 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayer indeed reaches a few kT in the case of the mixed OG-DOPC bilayer. The purpose and interest of this study are to allow the determination of the membrane bending modulus before and after the addition of OG on the same magnetic liposome. Moreover, the experimental conditions used in this work allow the control of lipid and surfactant molar fractions in the mixed aggregates. Then, optical microscopy observation can be performed on samples in well-defined regions of the OG-phospholipid state diagram.     

有机分子修饰铁粒子表面改善水基磁流变液的抗氧化性和稳定性

采用有机分子N-葡萄糖基乙二胺三乙酸(GED3A)修饰羰基铁(CI)粒子表面的方法, 制备了复合磁性粒子(CMPs)和水基磁流变(MR)液; 用扫描电镜(SEM)、振动样品磁强计(VSM)和带磁场供应和控制器的流变仪表征了CMPs及水基MR液的性能; 同时, 通过稳定性试验、空气氧化试验、酸腐蚀试验分别分析了水基MR液的分散稳定性和抗氧化性. 结果表明, 用此方法制备的CMPs具有良好的软磁性能, 饱和磁化强度(Ms)为182.2 emu·g-1, 矫顽力(Hc)为4.17 Oe, 剩磁(Mr)为0.1944 emu·g-1. 与原CI粒子水基MR液比较, 制备的水基MR液的沉降率下降了约24.4%; 在酸的浓度为0.02-0.10 mol·L-1范围内, 抗HCl氧化的能力提高了92.6%-95.7%, 抗HNO3氧化的能力提高了86.1%-93.8%.     

DYE-SENSITIZED DESTABILIZATION OF LIPOSOMES BEARING PHOTOOXIDIZABLE LIPID HEAD GROUPS

Abstract— Liposomes were prepared from mixtures of dipalmitoyl-i.-α-phosphatidylcholine and up to 40% mol:mol of N-stearoyl-L-histidine (NSH) in the presencc or the hydrophobic sensitizer DHE. In the dark such liposomes are stable and retain entrapped salts. On photolysis with visible light, liposomes leak trapped ions at NSH concentrations greater than 10% mol:mol. Up to 15% mol:mol NSH concentration leakage is seen only during the illumination period, whereas at higher concentration the liposomes continue to leak contents after illumination and fuse to form larger structures. Photolysis of the liposomes is accompanied by oxygen uptake in proportion to the NSH concentration within the bilayer. Photocontrol of liposome permeability through oxidation of membrane additives such as NSH offers a potential means for controlled drug delivery and might he useful as an adjunct to photodynamic therapy.     

Enumeration of Liposomes by Multinuclear NMR and Photon Correlation Spectroscopy

Diamagnetic dipalmitoylphosphatidylcholine (DPPC) liposomes dispersed in glucose solution as well as their paramagnetic analogs encapsulating a paramagnetic contrast agent used in magnetic resonance imaging (Gd-HPDO3A, ProHance ® ) were prepared and characterized. The vesicle diameter was assessed by photon correlation spectroscopy (PCS). 31 P NMR spectroscopy was used to measure the phospholipid content and to confirm the highly unilamellar character of the liposome membrane. For both types of liposome preparation, the internal water volume was evaluated below the phase transition temperature ( T m ) by natural abundance 17 O NMR spectroscopy in the presence of a shift reagent confined to the external compartment. For the paramagnetic vesicles, the internal water content was independently assessed by analysis of the biexponential decay of the proton transverse magnetization below T m . Knowing the unilamellarity of the vesicles ( 31 P NMR measurements), the number concentration of liposomes was assessed from the liposomal internal volume calculated from PCS data and the total internal water content obtained by 17 O NMR spectroscopy or 1 H relaxometry. The results obtained are in good agreement and validate these techniques as non invasive methods for the assessment of the number concentration of liposome in suspension.     

Magnetite nanocrystal clusters with ultra-high sensitivity in magnetic resonance imaging

Magnetic iron oxide particles are widely used as contrast agents to improve the sensitivity of magnetic resonance imaging (MRI). Their efficiency in MRI is usually quantified by transverse relaxivity (r(2)) in solution. Herein, we synthesized a series of magnetite nanocrystal clusters (MNCs) with ultra-high transverse relaxivity by a polyol process and studied the relationship between r(2) and size of the MNCs. The sizes of MNCs can be tuned over a wide range from 13 to 179 nm. The r(2) of MNC suspensions as a function of the size of the cluster was analyzed and compared with a theoretical model. We found that MNCs of 64 nm had an r(2) value of 650 mM(-1) s(-1), which was more than three times that of the commercial contrast agent and was among the highest reported for iron oxide materials. Compared with the theoretical model, the r(2) value of the MNC suspension is approximately 0.93 of the theoretical prediction. Imaging of the MNC suspensions was performed in a clinical 1.5 T MRI instrument and a comparison was made between MNCs and commercial contrast agents. MRI indicated that the decrease of signal intensity induced by MNCs was in proportion to the r(2) value, which was in accordance with theoretical predictions. These results demonstrate that MNCs with ultra-high transverse relaxivity and tunable size are promising candidates for molecular imaging and clinical diagnosis in MRI.     

Synthesis and characterization of monodisperse magnetic composite particles for magnetorheological fluid materials

Monodisperse magnetic composite particles (MCP) were prepared and characterized for a study of magnetic field-responsive fluids. Magnetic composite particles used are iron oxide-coated polymer composite particles, which were synthesized through in situ coating of iron oxide onto pre-existing polymer particles by the reduction of ferrous fluids. For a uniform and bulk coating of iron oxide, the porous structure was introduced into the substrate polymer particles through a two-step seeded polymerization method. Moreover, surface cyano-functionality was born from acrylonitrile unit of substrate polymer and it played an important role in obtaining successful uniform coating. The structure of the composite particle was analyzed by using a thermo gravimetric analysis (TGA) and a X-ray diffraction (XRD) analysis. The magnetization property of the particle was also observed. Then, the rheological properties of monodisperse magnetorheological (MR) suspensions of magnetic composite particles were examined under a magnetic field using a parallel-plate type commercial rheometer. From the rheological measurements, it was found that MR properties of the magnetic composite suspensions are dependent on the iron oxide content and the fluid composition.     

Synthesis, characterization and examination of Gd[DO3A-hexylamine]-functionalized silica nanoparticles as contrast agent for MRI-applications

Spherical, nonporous and monodisperse silica nanoparticles (NPs) with a diameter of about 100 nm were synthesized and covalently functionalized with lanthanoid(III) (Ln=Gd or Y) chelate complexes, which serve as contrast agents (CAs) for magnetic resonance imaging (MRI). The materials were fully characterized after each synthetic step by different analytical methods, such as dynamic light scattering, scanning electron microscopy, DRIFT and NMR spectroscopy, thermogravimetry and elemental analysis, as well as zetapotential measurements. High surface concentrations of Gd(III) complexes (up to 50 μmol g(-1)) were determined by ICP-AES and T(1)-measurements, respectively. MRI experiments show the typical concentration-dependent increase of the longitudinal relaxation rate. T(1)-weighted images of samples with more than 25 μg NPs per 100 μL agar display a clear contrast enhancement in the agar layer. The transverse relaxivities r(2) of the materials are significantly higher than r(2) of the corresponding free Gd(III) complexes in water and medium, whereas the longitudinal relaxivities r(1) are slightly increased. Due to the high loading of Gd(III) complexes, the relaxivities per particle are remarkably high (up to 2.78×10(5) mM(-1) s(-1) for r(1)). Thus, new hybrid materials, based on nonporous silica NPs with high local relaxivity values were synthesized, which can serve as very effective CAs for MRI.     

Facile preparation of zwitterion-stabilized superparamagnetic iron oxide nanoparticles (ZSPIONs) as an MR contrast agent for in vivo applications

We describe a simple method for synthesizing superparamagnetic nanoparticles (SPIONs) as small, stable contrast agents for magnetic resonance imaging (MRI) based on sulfobetaine zwitterionic ligands. SPIONs synthesized by thermal decomposition were coated with zwitterions to impart water dispersibility and high in vivo stability through the nanoemulsion method. Zwitterion surfactant coating layers are formed easily on oleic acid-stabilized SPIONs via hydrophobic and van der Waals interactions. Our zwitterion-coated SPIONs (ZSPIONs) had ultrathin (～5 nm) coating layers with mean sizes of 12.0 ± 2.5 nm, as measured by dynamic light scattering (DLS). Upon incubation in 1 M NaCl and 10% FBS, the ZSPIONs showed high colloidal stabilities without precipitating, as monitored by DLS. The T2 relaxivity coefficient of the ZSPIONs, obtained by measuring the relaxation rate on the basis of the iron concentration, was 261 mM(-1) s(-1). This value was much higher than that of the commercial T2 contrast agent because of the ultrathin coating layer. Furthermore, we confirmed that ZSPIONs can be used as MR contrast agents for in vivo applications such as tumor imaging and lymph node mapping.     

Innovative synthesis of citrate-coated superparamagnetic Fe3O4 nanoparticles and its preliminary applications

In this study, we describe the development of a facile and effective route for the synthesis of Fe(3)O(4)-based T(1) contrast agent, which can be useful for in vivo magnetic resonance (MR) imaging. Citrate-coated Fe(3)O(4) nanoparticles (6 nm) with a narrow size distribution were synthesized by "one-pot green chemistry route" in diethylene glycol (DEG) solvent. The synthesized nanoparticles were characterized by different analytical techniques including XRD, TEM, HRTEM, and FTIR. At room temperature, nanoparticles exhibited superparamagnetic nature with high saturation magnetization. The longitudinal (r(1)) and transverse (r(2)) relaxivities were found to be 35.45 and 51.81 mM(-1)s(-1), respectively. Contrast agent developed by this method showed a relatively higher longitudinal relaxivity (r(1)) and the lowest relaxivity ratio (r(2)/r(1)=1.46) at 3T MR field. The anionic nature of citric acid facilitated non-specific internalization without impairment of cell viability and functionality. The in vitro studies showed both phagocitic and non-phagocytic uptake of these NPs. In vivo MR imaging of swine showed both T(1) and T(2) contrast effect.     

LIPID-ASSOCIATED METHYLPHEOPHORBIDE-A (HEXYL-ETHER) AS A PHOTODYNAMIC AGENT IN TUMOR-BEARING MICE

Abstract Liposomes are a potential system for more selective delivery of photosensitizers (PS) to tumors. Pheo-phorbides are one series of new PS under investigation for use in photodynamic therapy. The pharmacokinetics, anti-tumor response and normal tissue effects of methylpheophorbide- a -(hexyl-ether) (MPH) associated with negatively charged phospholipid vesicles composed of high and low transition temperature lipids were determined in mice. In some preparations monosialoganglioside, which is known to impart long circulation time to liposomes was also included. Normally water-insoluble MPH could be quantitatively incorporated in multilamellar liposomes up to at least 20 mol MPH/mol lipid% for most liposome compositions and sonicated to form clear suspensions. Evidence from electron microscopy and entrapment of aqueous space markers indicated that the particles formed by sonication were not standard liposomes. Anti-tumor responses to light treatment (135 J/cm², 665 nm argon-dye laser) 24 h after MPH (0.4 μmol/kg) administration were slightly but significantly greater ( P < 0.05) for lipid associated MPH compared to MPH solubilized in Tween 80. There were no major differences in tumor uptake and tumor cell photosensitization between lipid or Tween 80 formulations of MPH, whereas, dependent on lipid composition and time after MPH administration, the doses of light required to cause occlusive vascular damage were increased for the lipid formulations. Pharmacokinetic studies showed rapid dissociation between lipids and MPH in vivo . Lipid formulations are useful for solubilizing MPH and may improve the therapeutic effects of this PS.     

Large-scale synthesis of uniform and extremely small-sized iron oxide nanoparticles for high-resolution T1 magnetic resonance imaging contrast agents

Uniform and extremely small-sized iron oxide nanoparticles (ESIONs) of < 4 nm were synthesized via the thermal decomposition of iron-oleate complex in the presence of oleyl alcohol. Oleyl alcohol lowered the reaction temperature by reducing iron-oleate complex, resulting in the production of small-sized nanoparticles. XRD pattern of 3 nm-sized nanoparticles revealed maghemite crystal structure. These nanoparticles exhibited very low magnetization derived from the spin-canting effect. The hydrophobic nanoparticles can be easily transformed to water-dispersible and biocompatible nanoparticles by capping with the poly(ethylene glycol)-derivatized phosphine oxide (PO-PEG) ligands. Toxic response was not observed with Fe concentration up to 100 μg/mL in MTT cell proliferation assay of POPEG-capped 3 nm-sized iron oxide nanoparticles. The 3 nm-sized nanoparticles exhibited a high r(1) relaxivity of 4.78 mM(-1) s(-1) and low r(2)/r(1) ratio of 6.12, demonstrating that ESIONs can be efficient T(1) contrast agents. The high r(1) relaxivities of ESIONs can be attributed to the large number of surface Fe(3+) ions with 5 unpaired valence electrons. In the in vivo T(1)-weighted magnetic resonance imaging (MRI), ESIONs showed longer circulation time than the clinically used gadolinium complex-based contrast agent, enabling high-resolution imaging. High-resolution blood pool MR imaging using ESIONs enabled clear observation of various blood vessels with sizes down to 0.2 mm. These results demonstrate the potential of ESIONs as T(1) MRI contrast agents in clinical settings.     

聚乙二醇包裹羰基铁核壳粒子的制备及水基磁流变液的性能

以羰基铁粉(CI)为原料用共溶胶-凝胶反应制备CI/聚乙二醇核壳复合粒子，并将其与水组成了磁流变液. 用SEM、TEM、FT-IR和VSM表征了核壳复合粒子的微观结构和静磁特性，并测试了水基磁流变液的性能. 结果表明，核壳复合粒子表面有SiO_x和聚乙二醇的包覆层，它有较好的亲水性和优良的软磁特性，用它组成的水基磁流变液具有抗沉降性优良、零场粘度低、磁流变效应显著等特点.