Aggregation Of Magnetic Particles Research Articles

Magnetic Hercules Swarm for Precise and Effective Deep Biofilm Eradication

AbstractOver the past decade, significant advancements in micro‐nano robots have enabled non‐invasive operations in hazardous, confined environments, particularly targeting persistent bacterial biofilms in hard‐to‐reach areas. However, many of these robots are limited by poor magnetic properties, hindering their effectiveness against biofilms. This study proposes a novel strategy using a swarm with strong magnetic effects (Hercules swarm) combined with near‐infrared (NIR) light for effective biofilm eradication. Carbonyl iron particles coated with polydopamine (CI@PDA), averaging ≈3 µm in diameter, demonstrate clustering and significant magneto‐force under a rotating magnetic field due to their large magnetic saturation. This enables the Hercules swarm to achieve rapid delivery (100 mm s−1), efficient cargo transport (carrying twice its own weight), and effective catheter clearance (1 mm min−1). The controllable motion and high photothermal activity enable precise biofilm eradication without toxic agents. The aggregation of magnetic particles into chains and their rotation are explored by improved particle dynamic model. Simulations also reveal enhanced fluid convection and mechanical pressure around the particle chain. Due to its easy operation, straightforward controllability, and environmental compatibility, the magnetic Hercules swarm emerges as a promising treatment modality for eliminating biofilms entrenched within intricate, narrow, and convoluted medical implants or industrial conduits.

Magnetic solid-phase extraction-based surface-enhanced Raman spectroscopy for label-free therapeutic drug monitoring of carbamazepine and clozapine in human serum

Determination of antiepileptic drugs and antipsychotics in human serum is significant in individualized drug administration and therapeutic drug monitoring (TDM). In this study, we developed a rapid label-free TDM method for the antiepileptic drug carbamazepine (CBZ) and the antipsychotic clozapine (CLO) in human serum. This detection strategy is based on the combination of surface-enhanced Raman scattering (SERS) and magnetic solid-phase extraction (MSPE). Initially, Fe3O4@SiO2@MIL-101(Fe) nanocomposites were synthesized by the layer-by-layer self-assembly method and characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, ultraviolet–visible, and Fourier transform infrared analyses. Subsequently, CBZ and CLO were detected in human serum using Fe3O4@SiO2@MIL-101(Fe) as the solid-phase extraction adsorbent and Ag nanoparticles as SERS substrates. The potential of the MSPE–SERS method for the label-free TDM of CBZ and CLO was then investigated. Fe3O4@SiO2@MIL-101(Fe) prevents magnetic particle aggregation and demonstrates rapid magnetic separation capability that simplifies the pretreatment process and reduces interference from complex matrices. Its large surface area can effectively enrich targets in complex matrices, thereby improving the SERS detection sensitivity. The linearity between CBZ and CLO was excellent over the concentration range of 0.1–100 µg/mL (calculated as the intensity of the SERS characteristic peaks of CBZ and CLO at 728 cm and 1054 cm−1, respectively), with correlation coefficients (R2) of 0.9987 and 0.9957, and detection limits of 0.072 and 0.12 µg/mL, respectively. The recoveries of CBZ with CLO ranged from 94.0 % to 105.0 %, and their relative standard deviations were <6.8 %. Compared to other assays, the developed MSPE–SERS method has the advantages of simple sample pretreatment, rapid detection, and good reproducibility, which provides a novel approach for the TDM of other drugs.

Exploiting mechanochemical activation and molten-salt-assisted reduction-diffusion approach in bottom-up synthesis of Sm2Fe17N3

Sm2Fe17N3 powders were prepared by a novel molten-salt mechanochemically assisted reduction-diffusion (RD) approach. CaCl2, plays a critical role during mechanochemical processing as a dispersant, facilitating the RD process by dissolving the precursors in a molten flux and further assisting during the washing step by efficient removal of by-products thus minimizing the surface oxidation of Sm2Fe17N3 powder particles. Various milling times and RD temperatures were examined, and synthesis conditions were optimized to achieve pure-phase Sm2Fe17N3 powders with low aggregation of magnetic particles. Powders synthesized at 950 °C RD exhibited the highest hard-magnetic properties: coercivity Hc of 13.5 kOe, and maximum energy product (BH)max of 19.4 MGOe. This was attributed to the formation of fine single-phase Sm2Fe17N3 particles as well as minimal oxidation of particle surface. Furthermore, by densifying the Sm2Fe17N3 powders with high-pressure spark plasma sintering, a bulk magnet with (BH)max of 16.5 MGOe and a relative density of 86 % was produced indicating that the obtained Sm2Fe17N3 powders had low oxygen content.

Extremely Long Chains of Magnetic Particles via Large Plastic Beads Observed in Bimodal Magnetic Elastomers

The relationship between the magnetorheology of bimodal magnetic elastomers with high concentrations (60 vol %) of plastic beads with diameters of 8 or 200 μm and the meso-structure of the particles was investigated. Dynamic viscoelasticity measurements revealed that the change in storage modulus of the bimodal elastomer with 200 μm beads was 2.8 × 105 Pa at a magnetic field of 370 mT. The change in the storage modulus for monomodal elastomer without beads was 4.9 × 104 Pa. The bimodal elastomer with 8 μm beads hardly responded to the magnetic field. In-situ observation for the particle morphology was performed using synchrotron X-ray CT. For the bimodal elastomer with 200 μm beads, a highly aligned structure of magnetic particles was observed in the gaps between the beads when the magnetic field was applied. On the other hand, for the bimodal elastomer with 8 μm beads, no chain structure of magnetic particles was observed. The orientation angle between the long axis of the aggregation of magnetic particles and the magnetic field direction was determined by an image analysis in three dimensions. The orientation angle varied from 56° to 11° for the bimodal elastomer with 200 μm beads and from 64° to 49° for that with 8 μm beads by applying the magnetic field. The orientation angle of the monomodal elastomer without beads changed from 63° to 21°. It was found that the addition of beads with a diameter of 200 μm linked the chains of magnetic particles, while beads with a diameter of 8 μm prevented the chain formation of the magnetic particles.

Facile green synthesis of core–shell magnetic MOF composites (Fe3O4@SiO2@HKUST-1) for enhanced adsorption capacity of methylene blue

In general, the synthesis of magnetic composites by in-situ, ex-situ, layer-by-layer and self-template methods provide desired properties, such as magnetic properties. However, syntheses using these methods still have the difficulty of controlling and avoiding aggregation of magnetic particles in the matrix. In this research, the magnetic MOF composite Fe3O4@SiO2@HKUST-1 with a core–shell form has been successfully synthesized through a facile green route using a pre-grinding method and less solvent. The morphology and structure of the core–shell, as confirmed by TEM and SEM, showed that the magnetic composite was spherical and not agglomerated. The incorporation of Fe3O4@SiO2 magnetic particles with mass variations of 50 and 100% to HKUST-1 was able to increase the pore size and resulted in the formation of mesopores. The composite when used as an adsorbent for synthetic dyes showed an adsorption capacity of 2.3 times higher (434.78 mg/g) than pure HKUST-1 (188.7 mg/g). The kinetic and isotherm study of the adsorption process followed a pseudo-second-order model and the Langmuir isotherm model. In addition, the feature of Fe3O4@SiO2 magnetic on the composite gave a stability enhancement of the adsorbent when used in aqueous media, being evidenced by the high adsorption capacity of the composite (71.95%) after being recycled five times.

Controlled intracellular aggregation of magnetic particles improves permeation and retention for magnetic hyperthermia promotion and immune activation.

Rationale: Magnetic nanoparticles (MNPs) are the most used inorganic nanoparticles in clinics with therapeutic and imaging functions, but the inefficient magneto-thermal conversion efficiency, fast leakage, and uneven distribution impair their imaging sensitivity and therapeutic efficacy in tumors. Methods: Herein, we rationally designed a system containing pH-controllable charge-reversible MNPs (M20@DPA/HA) and negatively charged MMPs with different sizes (M5 and M20), which could induce intracellular aggregation. The dynamic hydrazone bonds with pH controllability were formed by the surface hydrazides on MNPs and aldehydes of hyaluronic acid (HA). Under the acidic pH, intracellular aggregation of the complex composed by M20@DPA/HA and M5 (M5&20), or M20@DPA/HA and M20 (M20&20) were investigated. In addition, the magnetic hyperthermia therapy (MHT) efficiency of tumor cells, tumor-associated macrophages polarization, giant cells formation and immune activation of tumor microenvironment were explored via a series of cell and animal model experiments. Results: Through physical and chemical characterization, the aggregation system (M20&20) exhibited a remarkable 20-fold increase in magnetothermal conversion efficiency compared to individual MNPs, together with enhanced penetration and retention inside the tumor tissues. In addition, it could promote immune activation, including repolarization of tumor-associated macrophages, as well as the formation of giant cells for T cell recruitment. As a result, the M20&20 aggregation system achieved a high degree of inhibition in 4T1 mouse mammary tumor model, with little tumor growth and metastasis after magnetic hyperthermia therapy. Conclusions: A controlled intracellular aggregation system was herein developed, which displayed an aggregation behavior under the acidic tumor microenvironment. The system significantly enhanced MHT effect on tumor cells as well as induced M1 polarization and multinucleated giant cells (MGC) formation of TAM for immune activation. This controlled aggregation system achieved barely tumor growth and metastasis, showing a promising strategy to improve MNPs based MHT on deteriorate cancers.

Study of lateral assembly of magnetic particles in magnetorheological fluids under magnetic fields

This study uses a numerical simulation method to investigate the lateral assembly mechanism exhibited by equal-radius circular magnetic particles in magnetorheological fluids (MRFs). We used a direct numerical simulation method based on the finite element and arbitrary Lagrangian–Eulerian methods to establish a two-dimensional numerical model on particle–particle, particle–magnetic field, and particle–flow field interactions. The critical lines of gravitational and repulsive forces between magnetic particles and magnetic particle chains in a uniform magnetic field were investigated. The lateral assembly areas were found through these critical lines. Experiments confirmed that the sizes of the lateral assembly areas of the magnetic particle chains positively correlated with the lengths of the magnetic particle chains. In addition, the coarsening mechanism of magnetic particle chains was investigated by lateral assembly areas. Hence, this work offers insights toward understanding the mechanisms of microstructure formation in MRFs under magnetic fields.

Magnetic Particle Reinforced Elastomer Composites for Additive Manufacturing

Development of magnetorheological elastomer (MRE) materials suitable for fused filament fabrication (FFF)-type additive manufacturing processes is performed. Filament materials are thermoplastic polyurethane (TPU) pellets and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> magnetic particles. A trickling method is employed to introduce the materials into the filament extruder at a constant rate, after which they are mixed in a hopper and extruded at 160 °C. The trickling rate of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> was controlled to produce different volume concentrations [0%–13% (v/v)]. Micrograph analysis on the cross section of the filaments indicates that magnetic particles are uniformly dispersed in the TPU matrix. As the volume concentration of particles in the matrix is increased over 10% (v/v), the size distribution of magnetic particles is slightly increased, indicating formation of aggregation of magnetic particles. Micropores are observed in the filaments, and the number of pores seem to increase with increasing volume concentration of magnetic particles. A commercial off the shelf (COTS) FFF 3-D printer is successfully used to produce cylindrical MRE samples with different magnetic particle volume concentrations. Magnetorheological (MR) properties of the printed MRE samples are characterized by uniaxial compression testing under different applied magnetic field. Material elastic modulus was found to increase with the intensity of magnetic field for a given magnetic particle volume concentration. The relative MR effect varies from −1.3% to 60% within the studied volume concentrations and applied fields. The samples with 5% (v/v) show the highest MR effect when compared with samples with higher magnetic particle volume concentrations. The results of these experiments confirm that the equivalent energy dissipation of the material rises with the increase in the Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> concentration of MRE.

Reusable surface plasmon resonance biosensor chip for the detection of H1N1 influenza virus

We developed a reusable magnetic surface plasmon resonance (SPR) sensor chip for detecting various target molecules repeatedly in a conventional SPR system. Here, ferromagnetic patterns on a SPR sensor chip were utilized to trap a layer of magnetic particles, and they were utilized as a solid substrate for SPR sensing in a conventional SPR system. After a sensing experiment, the used magnetic particles were removed by external magnetic fields, and a new layer of magnetic particles was immobilized to the SPR sensor chip for additional sensing measurements. Since magnetic particles were trapped on the ferromagnetic patterns, we could use our reusable SPR chip for SPR sensing measurements in a traditional SPR system without any applied magnetic fields. Significantly, ferromagnetic patterns on the sensor chip surface deflected the strong external fields, so that the large aggregation of magnetic particles on the sensor surface was reduced. We demonstrated using a single reusable SPR sensor chip to measure the nucleoprotein (NP) of H1N1 influenza virus solution ranging repeatedly for more than 7 times without significant signal degradation. Also, different target molecules could be repeatedly measured in a single SPR chip. Since our reusable SPR sensor chip can be repeatedly used in a conventional SPR system without any chemical processes for refreshment, the cost for SPR sensing should be significantly reduced. In this case, our reusable SPR sensor chip can be a major breakthrough and can be used for versatile practical applications of SPR sensors.

Controlled Movement of Complex Double Emulsions via Interfacially Confined Magnetic Nanoparticles.

Controlled, dynamic movement of materials through noncontacting forces provides interesting opportunities in systems design. Confinement of magnetic nanoparticles to the interfaces of double emulsions introduces exceptional control of double emulsion movement. We report the selective magnetic functionalization of emulsions by the in situ selective reactions of amine-functionalized magnetic nanoparticles and oil-soluble aldehydes at only one of the double emulsion’s interfaces. We demonstrate morphology-dependent macroscopic ferromagnetic behavior of emulsions induced by the interfacial confinement of the magnetic nanoparticles. The attraction and repulsion of the emulsions to applied magnetic fields results in controlled orientation changes and rotational movement. Furthermore, incorporation of liquid crystals into the double emulsions adds additional templating capabilities for precision assembly of magnetic nanoparticles, both along the interface and at point defects. Applying a magnetic field to liquid crystal complex emulsions can produce movement as well as reorganization of the director field in the droplets. The combination of interfacial chemistry and precise assembly of magnetic particles creates new systems with potentially useful field-responsive properties.

Magnetic structure factor of correlated moments in small-angle neutron scattering

The interplay between structural and magnetic properties of nanostructured magnetic materials allows to realize unconventional magnetic effects, which results in a demand for experimental techniques to determine the magnetization profile with nanoscale resolution. Magnetic small-angle neutron scattering (SANS) probes both the chemical and magnetic nanostructure and is thus a powerful technique e.g. for the characterization of magnetic nanoparticles. Here, we show that the conventionally used particle-matrix approach to describe SANS of magnetic particle assemblies, however, leads to a flawed interpretation. As remedy, we provide general expressions for the field-dependent 2D magnetic SANS cross-section of correlated moments. It is shown that for structurally disordered ensembles the magnetic structure factor is in general, and contrary to common assumptions, (i) anisotropic also in zero field, and (ii) that even in saturation the magnetic structure factor deviates from the nuclear one. These theoretical predictions explain qualitatively the intriguing experimental, polarized SANS data of an ensemble of dipolar-coupled iron oxide nanoparticles.

On the Role of Size Differences in Synchronized Motion of Magnetic Particles in Fluid: A Study on Trimers

Synchronized motion and pattern formation of magnetic particle aggregates in variable magnetic field is of growing interest from the point of view of both fundamental science and its applications. In this article, the role of size differences in synchronized motion of magnetic particles under external rotating magnetic field at low Reynolds number flow regimes is considered. Several different motion regimes are observed in simulations as a function of particle size differences and field rotation rate. Simulation indicates phase-like transitions between different motion regimes when particle size differences become significant. It is also shown that particle size differences permit the possibility of locomotion for particle aggregates which cannot be observed for uniform particle sizes.

Effect of Magnetic Field and Aggregation on Electrical Characteristics of Magnetically Responsive Suspensions for Novel Hybrid Liquid Capacitor

Magnetically responsive fluid based on polymers of natural rubber (NR-latex) involves a magnetic compound fluid (MCF) rubber liquid. For a wide range of engineering applications of suspensions or liquids with particles, their electrical characteristics of fluidic suspensions are investigated to obtain useful results that might be important in the study of devices, such as fluidic sensors and capacitors. The author of the present paper proposes that MCF rubber liquid can be produced by combining MCF and rubber latex. The influence of the aggregation of magnetic particles and rubber molecules on electrical characteristics under a magnetic field was investigated by measuring electrical properties under an applied voltage. The electrical characteristics change with a linear or a nonlinear response, based on conditions of particle aggregation. The capacity of the electric charge also changes with the conditions of particle aggregation. These results show that MCF rubber liquid is a novel hybrid capacitor.

Three-dimensional simulation study on the aggregation behavior and shear properties of magnetorheological fluid

Abstract In this article, the aggregation behavior and shear properties of magnetorheological fluid (MRF) under different magnetic field strengths, volume fraction of magnetic particles (MPs) and shear rates were investigated by coarse-grained molecular dynamics simulations. With the formation of a wall-like structure, the shear stress (τ) of the MRF increased linearly in the shear strains region 0 0.58), the stress began to decrease and finally tended to be stable. The relationship between the aggregation of MPs and shear stress under a magnetic field-shear field was determined at the microscopic level.

Superparamagnetic Relaxation in Interacting Magnetic Particle Assemblies

Magnetic dipolar interaction between nanoparticles affects the relaxation time and consequently the superparamagnetic behavior of the assembly. Understanding how the relaxation mechanisms depend on the interaction is important due to the wide use of these materials in the different fields of nanotechnology. In this work we have investigated the effect of dipolar interaction on superparamagnetic behavior of magnetic particle assemblies. The interaction was considered through an interaction magnetic field and was calculated using the mean field model. The relaxation time of an interacting system can be written in two equivalent ways, the first as a perturbation in the energy barrier of the isolated particle and the second as a perturbation in the thermal energy. With this equivalence, it was possible to determine that the shift in the blocking temperature is associated with the type of interaction that predominates in the assembly. Blocking temperature increases (decreases) if ferromagnetic (antiferromagnetic) interaction is the dominant interaction.

Fragmentation of magnetic particle aggregates in turbulence

Particle aggregation is an ubiquitous phenomenon encountered in many natural and industrial environments. We describe here the equilibrium state of the ag-gregation/fragmentation process of inertial scale particles clustering in turbulence i.e. when the particles and the aggregates are larger than the Kolmogorov dissipa-tive scale η. For this purpose, we seeded a high Reynolds number turbulent von Karman flow with millimetric nearly neutrally buoyant magnetic particles. Each magnetic dipole imposes a torque and a force on the other magnets at the origin of the cohesion of the aggregates. On the contrary, turbulent fluctuations impose external stresses which tend to fragment the aggregates. Using video image analyses , we have performed the three-dimensional reconstruction of the aggregates and measured their characteristic sizes. The average number of particles inside each aggregate as a function of the intensity of turbulence can then be deduced. Assuming a Kolmogorov inertial scaling law for the turbulent velocity increments, we predict theoretically the aggregate mean size which is in agreement with our experimental results. 2 LED camera 1 camera 2 FIG. 1. Sketch of the turbulent von Karman flow setup.

Particle Dispersibility and sound propagation of ultrasounds for magnetic soft composites

We measured the sound velocity for magnetic soft composites consisting of a polymeric matrix of polyurethane and a magnetic particle of carbonyl iron or barium ferrite, and investigated the effect of the particle dispersibility on the sound velocity at 10 MHz for the composites. Morphological observations and dynamic viscoelastic measurements at 1 Hz were also carried out, and the results revealed that the carbonyl iron was dispersive particle and the barium ferrite was aggregative particle in the polyurethane matrix. The sound velocity for polyurethane elastomer without magnetic particles was 1444 ± 12 m/s and it decreased with the volume fraction of magnetic particles. The sound velocity of magnetic composites with barium ferrite obeyed the Reuss model at whole volume fractions, however, magnetic composites with carbonyl iron exhibited an under deviation from the Reuss model at volume fractions above ~0.053. It was also found that the longitudinal modulus was insensitive to the creation of the particle network and sensitive to the aggregation of magnetic particles. The threshold seen in the longitudinal modulus was different from that in the nonlinear parameter of viscoelasticity, indicating that the ultrasound of 10 MHz detects microscopic heterogeneity of particle dispersion.

Fractional rheological models of dynamic mechanical behavior of magnetoactive elastomers in magnetic fields

Several fractional rheological models containing one or two fractional elements in addition to the classical springs and dashpots have been proposed to describe the dynamic behavior of magnetoactive elastomers (MAEs) in magnetic fields. To test the models, MAEs containing 70, 75 and 80 wt% of carbonyl iron particles with the diameter of 3–5 μm have been synthesized. Theoretical model parameters have been obtained via fitting experimental frequency dependences of MAE's dynamic modulus measured under dynamic torsion oscillations in linear viscoelastic regime. It has been shown that the simplest rheological models with one fractional element can adequately describe MAEs behavior at low and for some cases high magnetic fields where the main contribution to the MAEs elasticity arises either from polymer network or magnetic particle aggregates, respectively. However, these models fail in describing MAE's dynamics in intermediate magnetic fields where the major restructuring of the magnetic filler particles is expected. The best fitting is realized with two-fractional-element models for a wide range of magnetic fields. The role of two fractional elements in generalized Maxwell model has been interpreted in terms of two main MAE components (namely, polymer network and magnetic particles) whose contributions to material elasticity and viscosity depend considerably on the material composition and magnetic field strength.

Influence of behaviors of magnetic particles in ferrofluids under alternating magnetic fields on harmonic responses

We describe the relationship between the excitation frequency dependence of harmonic signal intensity under alternating magnetic fields and the hydrodynamic size of magnetic particles in ferrofluids. The hydrodynamic size estimated from magnetic susceptibility increases with the increase in ion and particle concentrations in the ferrofluids. The excitation frequency dependence of the fifth-harmonic signal intensity exhibits a minimum point at a certain frequency. The frequency of the minimum point shifts to the lower-frequency range, and after reaching the minimum, it increases with the increase in ion and particle concentrations, reflecting the increase in hydrodynamic size owing to the aggregation of magnetic particles. These behaviors may be useful for applications in ion sensing by a magnetic technique.

Thermal activation in statistical clusters of magnetic nanoparticles

This article presents a kinetic Monte-Carlo study of thermally activated magnetisation dynamics in clusters of statistically distributed magnetic nanoparticles. The structure of clusters is assumed to be of fractal nature, consistently with recent observations of magnetic particle aggregation in cellular environments. The computed magnetisation relaxation decay and frequency-dependent hysteresis loops are seen to significantly depend on the fractal dimension of aggregates, leading to accelerated magnetisation relaxation and reduction in the size of hysteresis loops as the fractal dimension increases from one-dimensional-like to three-dimensional-like clusters. Discussed are implications for applications in nanomedicine, such as magnetic hyperthermia or magnetic particle imaging.