Dispersion Of Magnetic Nanoparticles Research Articles

Simulation of Magnetophoretic Separation Processes in Dispersions of Superparamagnetic Nanoparticles in the Noncooperative Regime

Magnetic separation has gained much attention due to its implications in different fields, becoming feasible as an alternative to existent technologies at the industrial and lab scale. Substantial efforts are focused to improve the magnetic particles used in these applications. Here we show how a relatively simple and low‐cost simulation strategy (tracer simulations) can be employed to predict the effect of various key factors in magnetic separation processes, namely, particle properties and magnetic separator designs. For concreteness, we consider here specific problems in magnetic separation. The first one is the effect of different profiles of the magnetic field in the separation of magnetic nanoparticles, and the second one is the magnetophoresis of colloidal particles in a dispersion of magnetic nanoparticles.

THE BIDISPERSED MODEL SYSTEM AND BINARY SYSTEM FOR FERROFLUIDS

Ferrofluids, dispersions of magnetic nanoparticles, are typical dipolar fluids whose behaviors can be modified using an external magnetic field. Such magnetically controlled effects result from interactions between the magnetic particles, which are enhanced by an applied magnetic field. Since the system of particles always possesses a size distribution, real ferrofluids represent a polydispersed system. A theoretical model of a bidispersed system, which contains only particles of two sizes, large and small, is presented. Experimentally, some binary ferrofluids based on two types of nanoparticles, with different magnetization or containing a mixture of micron-sized particles doped in ferrofluids are investigated. These magnetic colloidal systems have two dispersion phases in which at least one is magnetic nanoparticles and can exhibit novel behavior. This may result in novel physical properties and new potential applications. A model of a bidispersed system based on aggregated and non-aggregated particles, in which some non-aggregated particles could transform into aggregated particles with increasing magnetic field while total particles’ number is constant, may help to advance general theories of ferrofluids.

Stable dispersions of ferromagnetic carbon-coated metal nanoparticles: preparation via surface initiated atom transfer radical polymerization

Magnetic nanoparticle dispersions are traditionally made from superparamagnetic materials since the absence of magnetic particle–particle attraction under normal conditions (no external field) easily allows preparation of stable dispersions. For inductive heating in medicinal chemistry or material science, however, the much higher magnetization of ferromagnetic metals over the currently used oxides is attractive. Traditional attempts to prepare stable dispersions of ferromagnetic particles, however, failed since the strong magnetic particle–particle attraction usually overcomes repulsive effects from surfactants or steric stabilizers (typically polymers). In the present work, we demonstrate how the direct, covalent attachment of highly charged polymers can circumvent stabilizer detachment and loss, and permits preparation of stable dispersions of ferromagnetic particles. More specifically, carbon-coated metal nanoparticles were covalently functionalized with positively charged polymer brushes via surface initiated atom transfer radical polymerization (SI-ATRP). Particle size distributions with an average diameter of 24 nm provided a ferromagnetic liquid with unprecedented stability in water over several months. The stability was discussed by comparison of the potentials of non-functionalized and modified nanomagnets within a modified Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Measurements for inductive heating at different frequencies and various field strengths showed an average specific absorption rate of 360 W g−1. Altogether, this suggests that efficiently stabilized dispersions of ferromagnetic nanoparticles could be an alternative to superparamagnetic iron oxide particles in a number of applications.

Manipulation of magnetic nanoparticle retention and hemodynamic consequences in microcirculation: assessment by laser speckle imaging

Magnetic nanoparticles (MNPs) have been proposed for targeted or embolization therapeutics. How MNP retention occurs in circulation may critically determine local hemodynamics, tissue distribution of MNPs, and the therapeutic effects. We attempted to establish a microcirculation model to study the magnetic capture of MNPs in small vessels and to determine the factors affecting MNP retention. Two-dimensional hemodynamic changes in response to magnet-induced MNP retention in the microvessels of the cremaster muscle in vivo were observed in a real-time manner using a laser speckle imaging technique. Changes in tissue perfusion of the cremaster muscle appeared to be closely correlated with the location of the magnet placement underneath the muscle in response to intra-arterial administration of dextran-coated MNPs. Magnet-related retention was observed along the edge of the magnet, as corroborated by the results of histology analysis and microcomputed tomography. In these preparations, tissue iron content almost doubled, as revealed by inductively coupled plasma optical emission spectroscopy. In addition, MNP retention was associated with reduced downstream flow in a dose-dependent manner. Dissipation of MNPs (5 mg/kg) occurred shortly after removal of the magnet, which was associated with significant recovery of tissue flow. However, MNP dissipation did not easily occur after administration of a higher MNP dose (10 mg/kg) or prolonged exposure to the magnetic field. An ultrasound after removal of the magnet may induce the partial dispersion of MNPs and thus partially improve hemodynamics. In conclusion, our results revealed the important correlation of local MNP retention and hemodynamic changes in microcirculation, which can be crucial in the application of MNPs for effective targeted therapeutics.

Numerical Study of Temperature Distribution in a Spherical Tissue in Magnetic Fluid Hyperthermia Using Lattice Boltzmann Method

This work applies a three-dimensional lattice Boltzmann method (LBM), to solve the Pennes bio-heat equation (BHE), in order to predict the temperature distribution in a spherical tissue, with blood perfusion, metabolism and magnetic nanoparticles (MNPs) heat sources, during magnetic fluid hyperthermia (MFH). So, heat dissipation of MNPs under an alternating magnetic field has been studied and effect of different factors such as induction and frequency of magnetic field and volume fraction of MNPs has been investigated. Then, effect of MNPs dispersion on temperature distribution inside tumor and its surrounding healthy tissue has been shown. Also, effect of blood perfusion, thermal conductivity of tumor, frequency and amplitude of magnetic field on temperature distribution has been explained. Results show that the LBM has a good accuracy to solve the bio-heat transfer problems.

Isolation and manipulation of living adherent cells by micromolded magnetic rafts

A new strategy for magnetically manipulating and isolating adherent cells with extremely high post-collection purity and viability is reported. Micromolded magnetic elements (termed microrafts) were fabricated in an array format and used as culture surfaces and carriers for living, adherent cells. A poly(styrene-co-acrylic acid) polymer containing well dispersed magnetic nanoparticles was developed for creating the microstructures by molding. Nanoparticles of γFe(2)O(3) at concentrations up to 1% wt.∕wt. could be used to fabricate microrafts that were optically transparent, highly magnetic, biocompatible, and minimally fluorescent. To prevent cellular uptake of nanoparticles from the magnetic polymer, a poly(styrene-co-acrylic acid) layer lacking γFe(2)O(3) nanoparticles was placed over the initial magnetic microraft layer to prevent cellular uptake of the γFe(2)O(3) during culture. The microraft surface geometry and physical properties were altered by varying the polymer concentration or layering different polymers during fabrication. Cells plated on the magnetic microrafts were visualized using standard imaging techniques including brightfield, epifluorescence, and confocal microscopy. Magnetic microrafts possessing cells of interest were dislodged from the array and efficiently collected with an external magnet. To demonstrate the feasibility of cell isolation using the magnetic microrafts, a mixed population of wild-type cells and cells stably transfected with a fluorescent protein was plated onto an array. Microrafts possessing single, fluorescent cells were released from the array and magnetically collected. A post-sorting single-cell cloning rate of 92% and a purity of 100% were attained.

Fabrication, characterization, and measurement of viscosity of α-Fe 2O 3-glycerol nanofluids

Magnetic nanofluids, ferrofluids, are a special category of smart nanomaterials, consisting of stable dispersion of magnetic nanoparticles in different fluids. In this study, magnetic nanoparticles of hematite, α-Fe 2O 3, were prepared by solvothermal method using Fe(NO 3) 3 as a starting material. The nanoparticles were characterized by X-ray diffraction (XRD) and transmission electronic microscope (TEM). To the best of our knowledge, this is the first research on the rheological properties of nanofluids of α-Fe 2O 3 nanoparticles and glycerol. The experimental results showed that the viscosity of α-Fe 2O 3-glycerol nanofluids increases with increasing the particle volume fraction and decreases with increasing temperature. Our results clearly showed that the α-Fe 2O 3-glycerol nanofluids are non-Newtonian shear-thinning and their shear viscosity depends strongly on temperature. The experimental data were compared with some theoretical models. The measured values of the effective viscosity of nanofluids are underestimated by the theoretical models.

Synthesis of magnetic nanoparticle into bacterial cellulose matrix by ammonia gas-enhancing in situ co-precipitation method

In this study, magnetically responsive bacterial cellulose sheets were prepared by using an ammonia gas-enhancing in situ co-precipitation method operated in a closed system without oxygen. Instead of using the traditional concentrated liquid basic solutions, ammonia gas was used in the closed system to achieve the homogeneous dispersion of magnetic nanoparticles as evidence by the uniform black color of magnetic nanoparticles across the cross-sectional area of bacterial cellulose sheets. In addition, under the condition without oxygen, the synthesized magnetic would be in the form of magnetite (Fe3O4). The formation of magnetic nanoparticles inside bacterial cellulose sheets was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX). The average particle size of the magnetic nanoparticles was determined by using transmission electron microscopy (TEM) and was found to be in the range of 19.6–38.9nm. The homogeneous dispersion of magnetic nanoparticles across the cross-sectional area of the bacterial cellulose samples was also evidenced by SEM and TEM images. Moreover, the magnetic field responsive behavior of the magnetic nanoparticle-incorporated bacterial cellulose sheets was investigated by vibrating sample magnetometry (VSM). The saturation magnetization of the magnetic nanoparticle-incorporated bacterial cellulose sheets ranged from 1.92 to 26.20emu/g at 300K and ranged from 2.96 to 28.10emu/g at 100K.

The effect of magnetic nanoparticle dispersion on temperature distribution in a spherical tissue in magnetic fluid hyperthermia using the lattice Boltzmann method

In clinical applications of magnetic fluid hyperthermia (MFH) for cancer treatment it is very important to ensure maximum damage to the tumour while protecting the normal tissue. The resultant heating pattern by magnetic nanoparticles (MNPs) in the tumour is closely related to the dispersion of MNPs. In this study the effect of MNPs dispersion on temperature distribution in a tumour and surrounding healthy tissue, during MFH, has been investigated. Accordingly, the Pennes bio-heat equation (BHE) in a spherical tissue with Neumann curved boundary condition has been resolved. The effects of blood perfusion, metabolism heat generation as well as MNPs heat dissipation in an alternating magnetic field as source term, have been considered. To solve the Pennes BHE, the three dimensional lattice Boltzmann method (LBM) has been used. To show the accuracy of the model, simulations have been compared with analytical, experimental and numerical results, reported in the literature. Then, temperature distribution within tissue has been investigated in two cases, homogeneous distribution and Gaussian distribution of specific absorption rate (SAR). Results showed that for the studied cases, unlike homogeneous distribution, Gaussian distribution of SAR is able to raise the temperature of tumour cells above the treatment temperature.

Controlled Magnetic Propulsion of Floating Polymeric Two-Dimensional Nano-Objects

Soft-bodied magnetically actuated microrobots could be developed by including controlled dispersions of magnetic nanoparticles into polymeric micro-fabricated structures. The characterization and actuation of magnetically active soft-bodied microrobots by tailored magnetic fields is, thus, a key issue for the design, full control and further development of these mobile micro-systems. In this work, the authors demonstrate the predictable and controllable transportation of polymeric flexible nanofilms embedding super-paramagnetic nanoparticles, by developing and quantitatively validating a model of the magnetic force acting on such structures, thus paving the way towards the wireless magnetic actuation of soft-bodied microrobots. The magnetic forces generated in our experimental conditions range from about 10 –9 to 10–6 N, with typical velocities for the nanofilms ranging between about 0.1 and 2.3 mm/s. For the entire range, a good agreement between theoretical model predictions and measured data is obtained (average normalized error δ =3. 65%). The proposed approach for microrobotic development targets challenging environments, where keywords are liquid or wet micro-structured environments, like in biomedical applications.

State of Dispersion of Magnetic Nanoparticles in an Aqueous Medium: Experiments and Monte Carlo Simulation

Monte Carlo simulation results predicting the state of dispersion (single, dimer, trimer, and so on) of coated superparamagnetic iron oxide (Fe(3)O(4)) nanoparticles in an aqueous medium are compared with our experimental data for the same. Measured values of the volume percentage of particles in the dispersion, core particle diameter, coating-shell thickness, grafting density of the coating agent, saturation magnetization, and zeta potential for the citric acid-coated and poly(acrylic acid) [PAA]-coated particles have been used in our simulation. The simulation was performed by calculating the total interaction potential between two nanoparticles as a function of their interparticle distance and applying a criterion for the two particles to aggregate, with the criterion being that the minimum depth of the secondary minima in the total interaction potential must be at least equal to k(B)T. Simulation results successfully predicted both experimental trends-aggregates for citric acid-coated particles and an individual isolated state for PAA-coated particles. We have also investigated how this state changes for both kind of coating agents by varying the particle volume percentage from 0.01 to 25%, the particle diameter from 2 to 19 nm, the shell thickness from 1 to 14 nm, and grafting density from 10(15) to 10(22) molecules/m(2). We find that the use of a lower shell thickness and a higher particle volume percentage leads to the formation of larger aggregates. The possible range of values of these four variables, which can be used experimentally to prepare a stable aqueous dispersion of isolated particles, is recommended on the basis of predictions from our simulation.

Parametric investigation of heating due to magnetic fluid hyperthermia in a tumor with blood perfusion

Magnetic fluid hyperthermia (MFH) is a cancer treatment that can selectively elevate the tumor temperature without significantly damaging the surrounding healthy tissue. Optimal MFH design requires a fundamental parametric investigation of the heating of soft materials by magnetic fluids. We model the problem of a spherical tumor and its surrounding healthy tissue that are heated by exciting a homogeneous dispersion of magnetic nanoparticles infused only into the tumor with an external AC magnetic field. The key dimensionless parameters influencing thermotherapy are the Péclet, Fourier, and Joule numbers. Analytical solutions for transient and steady hyperthermia provide correlations between these parameters and the portions of tumor and healthy tissue that are subjected to a threshold temperature beyond which they are damaged. Increasing the ratio of the Fourier and Joule numbers also increases the tumor temperature, but doing so can damage the healthy tissue. Higher magnetic heating is required for larger Péclet numbers due to the larger convection heat loss that occurs through blood perfusion. A comparison of the model predictions with previous experimental data for MFH applied to rabbit tumors shows good agreement. The optimal MFH conditions are identified based on two indices, the fraction IT of the tumor volume in which the local temperature is above a threshold temperature and the ratio IN of the damaged normal tissue volume to the tumor tissue volume that also lies above it. The spatial variation in the nanoparticle concentration is also considered. A Gaussian distribution provides efficacy while minimizing the possibility of generating a tumor hot spot. Varying the thermal properties of tumor and normal tissue alters ITand IN but the nature of the temperature distribution remains unchanged.

Magneto-Optical Characterization of Colloidal Dispersions. Application to Nickel Nanoparticles

We report here on a fast magneto-optical characterization method for colloidal liquid dispersions of magnetic nanoparticles. We have applied our methodology to Ni nanoparticles with size equal or below 15 nm synthesized by a ligand stabilized solution-phase synthesis. We have measured the magnetic circular dichroism (MCD) of colloidal dispersions and found that we can probe the intrinsic magnetic properties within a wide concentration range, from 10(-5) up to 10(-2) M, with sensitivity to concentrations below 1 microg/mL of magnetic Ni particles. We found that the measured MCD signal scales up with the concentration thus providing a means of determining the concentration values of highly diluted dispersions. The methodology presented here exhibits large flexibility and versatility and might be suitable to study either fundamental problems related to properties of nanosize particles including surface related effects which are highly relevant for magnetic colloids in biomedical applications or to be applied to in situ testing and integration in production lines.

Silica coated magnetic nanoparticles for separation of nuclear acidic waste

Fe 2 O 3 magnetic nanoparticles (MNPs) have been coated with silica, followed by covalent attachment of the actinide specific chelators to separate nuclear waste in acidic conditions. A general model is developed to relate the surface coating to the particle’s magnetization change, providing an alternative way to characterize the size-distribution/aggregation of MNPs. The optimized silica coating protects the Fe2O3 MNPs from iron leaching under highly acidic conditions, facilitates the dispersion of MNPs, and dramatically increases the loading capacity of chelator onto the MNPs. Compared with the uncoated counterparts, the silica coated MNPs show enhanced actinide separation efficiency.

Strontium hexaferrite nanomagnets suspended in a cosmetic preparation: a convenient tool to evaluate the biological effects of surface magnetism on human skin

Magnetic therapy has been popular for ages, but its therapeutic abilities remain to be demonstrated. We aimed to develop a homogeneous, stable dispersion of magnetic nanoparticles in a skin-care preparation, as a tool to analyze the biological and physiological effects of superficial magnetism in skin. SrFe(12)O(19) nanoparticles were generated by ultrasound, dispersed in glycerol, stabilized in Dermud cream and permanently magnetized. The magnetic cream was applied on the epidermis of human skin organ cultures. The effects on UV-induced cell toxicity, apoptosis and inflammatory cytokine expression were analyzed. A clinical test was performed to check skin moisturization. Nanomagnets were found to be homogenously and stably dispersed. After magnetization, the preparation generated a magnetic field of 1-2 G. Upon cream application, no cytotoxicity and no impairment of cellular vitality were found after 24 and 48 h, respectively. The anti-apoptotic and anti-inflammatory properties of Dermud were not modified, but its long-term effect on moisturization in vivo was slightly increased. Nanomagnetic Dermud cream can be used as a tool to analyze the biological effects of nanomagnets dispersed on the skin surface at the cellular and molecular levels, thus allowing to explore the possible therapeutic uses of superficial magnetism for skin care.

Immobilization of cholesterol oxidase to finely dispersed silica-coated maghemite nanoparticles based magnetic fluid

In the recent years, the potential applicability of magnetic nanoparticles (MNPs) has witnessed a significant increase in interest towards the medical field, in particular, towards the usage of novel nanoparticles in diagnostics and disease treatment, respectively. In a present study, cholesterol oxidase (ChOx) was covalently immobilized to magnetic nanoparticles of maghemite (γ-Fe 2O 3) and further functionalized by silica (SiO 2) and amino-silane molecules. The activity of the bound enzyme was retained up to 60%, respectively. The binding of cholesterol oxidase was confirmed using FT-IR spectrophotometer. SEM analysis showed uniformly dispersed functional magnetic nanoparticles, which ranged in size from 22.5 to 50.8 nm, surrounded by amorphous silica. In this paper, the potential applications of chemically modified magnetic nanoparticles as carriers for cholesterol oxidase and other enzymes are discussed.

Fabrication of novel hierarchically ordered porous magnetic nanocomposites for bio-catalysis

Novel hierarchically ordered porous magnetic nanocomposites with interconnecting macroporous windows and meso-microporous walls containing well dispersed magnetic nanoparticles have been fabricated and used as a support to immobilise lipase for the efficient hydrolysis of ester.

ESR line shape of paramagnetic particles in a magnetic liquid. Theory and experiment

A basic model has been proposed to describe the resonance spectra of the paramagnetic sensor particles in dispersions of magnetic nanoparticles aggregated in chains. A theory of the line shape of low-mobility sensors has been developed in the case of chains of a sufficiently homogeneous length. A specific line shift has been shown to appear in such systems and the spectrum may be asymmetric. The ESR spectra of a magnetite-based magnetic liquid have been measured and the main parameters of the chains have been determined.

Cobalt iron-oxide nanoparticle modified poly(methyl methacrylate) nanodielectrics

In this paper, we report the dielectric properties of composite systems (nanodielectrics) made of small amounts of mono dispersed magnetic nanoparticles embedded in a polymer matrix. It is observed from the transmission electron microscope images that the matrix polymeric material is confined in approximately 100 nm size cages between particle clusters. The particle clusters are composed of separated spherical particles which comprise unconnected networks in the matrix. The dielectric relaxation and breakdown characteristics of the matrix polymeric material are altered with the addition of nanometer size cobalt iron-oxide particles. The dielectric breakdown measurements performed at 77 K showed that these nanodielectrics are potentially useful as an electrical insulation material for cryogenic high voltage applications. Finally, structural and dielectric properties of nanocomposite dielectrics are discussed to present plausible reasons for the observed low effective dielectric permittivity values in the present and similar nanodielectric systems. It is concluded that polymeric nanoparticle composites would have low dielectric permittivity regardless of the permittivity of nanoparticles are when the particles are coordinated with a low dielectric permittivity surfactant.

Synthesis, characterization and MRI application of dextran-coated Fe3O4 magnetic nanoparticles

Biocompatible ferrofluid based on dextran-coated Fe3O4 magnetic nanoparticles (MNPs) was prepared through a one-step method. In contrast to the conventional co-precipitation method, hydrazine hydrate was added as reducing agent and precipitator in the present investigation. The effects of hydrazine hydrate, the weight ratio of dextran to MNPs and the molecular weight of dextran on the dispersibility of MNPs in water were investigated. Also, the particles size of modified MNP and coating efficiency of dextran on MNPs were measured. In addition, biocompatible ferrofluid was intravenously injected into rabbits, the iron content in blood and organs at different times were measured by atomic absorption spectrometer, and the bio-distribution and the bio-transportation of ferrofluid in organs was examined. Then, the magnetic resonance (MR) images of liver, marrow and lymph were acquired by MRI experiments before and after intravenous injection of ferrofluid. Image analysis revealed that the MR signal intensity of these organs notably decreased after intensified by ferrofluid. However, when there existed tumors in organs, the signal intensity of tumor did not change after injection. From that the tumor can easily be identified, which indicated a potential application of the as-prepared MNP in functional molecular imaging for biomedical research and clinical diagnosis.