Magnetic Particles Research Articles

Umbrella-rib-like multi-section three-jawed soft gripper by hybrid pneumatic and magnetic

Abstract Multi-stimuli-responsive can respond to multiple stimuli and overcome the limitations of a single stimulus, especially in biomimetic applications where large deformations and high stiffness are in high demand. This soft gripper fabricated with a new multi-section design and is a novel multi-stimulus-responsive soft actuator that combines silicone and magnetic NdFeB particles, highlighting the advantages of a hybrid pneumatic and magnetic drive to achieve bending behavior with high efficient and high stiffness at low pressure. The position of the bending center of the soft section is changed by adjusting the internal pressure. Here, an umbrella-rib-like soft actuator is proposed, inspired by the process of umbrella using deployable and foldable mechanisms, an efficient joint is designed for the soft actuator to act like umbrella ribs such that the joint bend-folding location does not change much on the robot for different internal pressures. The design and preparation of this multi-section soft actuator for grippers provides proficiency and wide application in medical, industry and so on.

Development and Application of a Fully Automated Chemiluminescence Enzyme Immunoassay for the Detection of Antibodies Against Porcine Circovirus 3 Cap

Porcine circovirus 3 (PCV3) is a small non-enveloped circovirus associated with porcine dermatitis and nephropathy syndrome (PDNS). It has occurred worldwide and poses a serious threat to the pig industry. However, there is no commercially available vaccine. PCV3 capsid protein (Cap) is an ideal antigen candidate for serodiagnosis. Here, a novel fully automated chemiluminescence enzyme immunoassay (CLEIA) was developed to detect antibodies (Abs) to Cap in porcine serum. Recombinant PCV3 Cap, self-assembled into virus-like particles (VLPs), was produced using baculovirus and coupled to magnetic particles (Cap-MPs) as carriers. Combined with an alkaline phosphatase (AP)–adamantane (AMPPD) system, Cap-Abs can be rapidly measured on a fully automated chemiluminescence analyzer. Under optimal conditions, a cut-off value of 31,508 was determined, with a diagnostic sensitivity of 96.8% and specificity of 97.3%. No cross-reactivity was observed with PCV1 and PCV2 and other common porcine pathogens, and both intra-assay and inter-assay coefficients were less than 5% and 10%, respectively. Prepared Cap-MPs can be stored at 4 °C for more than 6 months. Importantly, this CLEIA had a good agreement of 95.19% with the commercially available kit, demonstrating excellent analytical sensitivity and significantly reduced operating time and labor. A serological survey was then conducted, and showed that PCV3 continues to spread widely in South China. In conclusion, our CLEIA provides time and labor-saving, and a reliable tool for PCV3 epidemiological surveillance.

Preclinical and Clinical-Scale Magnetic Particle Imaging of Natural Killer Cells: in vitro and ex vivo Demonstration of Cellular Sensitivity, Resolution, and Quantification.

Clinical adoption of NK cell immunotherapy is underway for medulloblastoma and osteosarcoma, however there is currently little feedback on cell fate after administration. We propose magnetic particle imaging (MPI) may have applications for the quantitative detection of NK cells. Human-derived NK-92 cells were labeled by co-incubation with iron oxide nanoparticles (VivoTrax™) for 24h then excess nanoparticles were washed with centrifugation. Cytolytic activity of labeled versus unlabeled NK-92 cells was assessed after 4h of co-incubation with medulloblastoma cells (DAOY) or osteosarcoma cells (LM7 or OS17). Labeled NK-92 cells at two different doses (0.5 or 1 × 106) were administered to excised mouse brains (cerebellum), fibulas, and lungs then imaged by 3D preclinical MPI (MOMENTUM™) for detection relative to fiducial markers. NK-92 cells were also imaged by clinical-scale MPI under development at Magnetic Insight Inc. NK-92 cells were labeled with an average of 3.17 pg Fe/cell with no measurable effects on cell viability or cytolytic activity against 3 tumor cell lines. MPI signal was directly quantitative with the number of labeled NK-92 cells, with preclinical limit of detection of 3.1 × 104 cells on MOMENTUM imager. Labeled NK-92 cells could be accurately localized in mouse brains, fibulas, and lungs within < 1mm of stereotactic injection coordinates with preclinical scanner. Feasibility for detection on a clinical-scale MPI scanner was demonstrated using 4 × 107 labeled NK-92 cells, which is in the range of NK cell doses administered in our previous clinical trial. MPI can provide sensitive, quantitative, and accurate spatial information on NK cells soon after delivery, showing initial promise to address a significant unmet clinical need to track NK cell fate in patients.

Construction of novel magnetic systems for cancer immunotherapy via cancer-immunity cycle circuits.

The tumor microenvironment (TME) is enriched with immunosuppressive factors that inhibit the recruitment and activation of dendritic cells (DCs), thereby reducing the efficacy of tumor immunotherapy. To address this challenge, we propose an innovative strategy involving the sequential administration of MCM magnetic nanoparticles carrying PROTAC drugs (MCM/ARV) and M-BMDCs in the TEM. This approach not only replenishes DCs in the TEM, but also increases antigen uptake through the attraction between the magnetic particles and promotes DC activation and antigen presentation, thus continuously enhancing the tumor immune cycle. MCM nanoparticles (magnetic nanoclusters coated with calcium-doped manganese carbonate) efficiently load the tumor-targeting drug PROTAC (ARV-825), enhancing its bioavailability, leading to specific degradation of BRD4 in tumor cells, and releasing a large number of tumor-associated antigens. These antigens were captured by MCM nanoparticles to construct magnetized tumor vaccines. Magnetic M-BMDCs introduced at the tumor site are attracted to these magnetized vaccines, resulting in a significant increase in antigen uptake and activation of DCs, significantly enhancing the tumor immune cycle. This co-administration strategy of magnetized vaccines and magnetized BMDCs provides a unique combination therapy for reversing immunosuppressive TEM and enhancing the efficacy of tumor immunotherapy.

Engineering Zn/Fe Mixed Metal Oxides with Tunable Structural and Magnetic Properties for Magnetic Particle Imaging.

Engineering magnetic nanoparticles with tunable structural properties and magnetism is critical to develop desirable magnetic particle imaging (MPI) tracers for biomedical applications. Here we present a new superparamagnetic metal oxide nanoparticle with a controllable chemical composition and magnetism for imaging tumor xenografts in living mice. Superparamagnetic Zn/Fe mixed metal oxide (ZnFe-MMO) nanoparticles are fabricated via a facile one-pot co-precipitation method in water followed by thermal decomposition with tunable Zn/Fe ratios and at various calcination temperatures. This work, for the first time, presented LDH-derived metal oxides for an MPI application. The metal composition is tunable to present an optimized MPI performance. The analytical results demonstrate that ZnFe-MMO nanoparticles at the designed molar ratio of Zn/Fe = 2:1 after 650 °C calcination demonstrate a higher saturation magnetization (MS) value and optimal MPI signal than the samples presented with other conditions. The excellent biocompatibility of ZnFe-MMO is demonstrated in both breast cancer cells and fibroblast cell cultures. In vivo imaging of 4T1 tumor xenografts in mice using ZnFe-MMO as a tracer showed that the mean signal intensity is 1.27-fold higher than the commercial tracer VivoTrax at 72 h post-injection, indicating ZnFe-MMO's promise for prolonged MPI imaging applications.

Assessing Particulate Matter Deposition and Resuspension by Living Wall Systems in a Wind Tunnel Setup

This study examines the particulate matter (PM) capture capacity of living wall systems (LWSs), focusing on leaf traits that facilitate PM deposition. Six LWS designs, differing in structure and substrate, were tested under constant airflow conditions with and without additional PM. Results showed that planter-based LWSs reduced PM0.1 by 2% and PM2.5 by 4%, while a textile LWS reduced PM0.1 by 23% and PM2.5 by 5%, though geotextile textile increased PM by 11% for both fractions. A moss substrate LWS worsened air quality, raising PM0.1 by 2% and PM2.5 by 5%. Magnetic analysis of leaf-deposited PM (SIRM) revealed species-specific differences (p &lt; 0.001), with SIRM values ranging from 5 ± 1 µA to 260 ± 1 µA and higher PM accumulation in plants with lower specific leaf areas. No differences were observed in SIRM between deposition and resuspension phases, indicating the PM source lacked sufficient magnetisable particles. The findings highlight the potential of LWSs in urban environments for air quality improvement but underscore the importance of selecting suitable LWS structures and plant species.

Spatial magnetic force and magnetic energy density analysis of microsphere medium in high gradient magnetic fields: a 3D simulation

Abstract High gradient magnetic separation technology is the key technology for green and efficient separation and purification of mineral resources. Existing studies are vague about the division of the attraction and repulsion zones of the medium, and there are fewer explorations of the effect of various conditions on the attraction zones. In this work, a novel method for calculating the magnetic force is derived, which provides an accurate calculation of the 3D magnetic force. The attraction and repulsion zones are divided clearly by analyzing the relationship between the spatial angle of the spherical medium and the magnetic force density per unit volume, with the magnetic force density per unit volume tangent to the spherical surface as the dividing line. The attraction and repulsion zones are divided by β = 30°~35°, and the attraction region accounts for 45%~50% of the total space volume. Furthermore, the influence of different conditions on the attraction zone is studied. It was found that the zone of attraction decreases as one moves away from the spherical medium, which results in an ellipsoid with the effective zone of attraction of the spherical medium having the magnetic field direction as its long axis. The attraction region increases from 45.49% to 49.87% of the space occupied with increasing the relative permeability of the spherical medium. It does not affect the proportion of the attraction zone in space by changing the background magnetic field and the size of the spherical medium, but it will change the depth of the magnetic force. It provides a theoretical basis for the design of high-efficiency magnetic media, and gives a reference for further improving the selection effect of high gradient magnetic separation technology on fine and weak magnetic particles.

Detection of TNF-α using the established ab-MPs-CLIA

Tumor necrosis factor alpha (TNF-α) is a key cytokine in inflammation and immune responses, making its rapid and accurate detection essential for disease diagnosis and management. In this study, we developed a highly sensitive chemiluminescence immunoassay (CLIA) using antibody-coated magnetic particles (Ab-MPs-CLIA) for TNF-α detection. From nine candidate antibodies, we identified an optimal pair through epitope competition and affinity assessments, significantly improving assay performance. The Ab-MPs-CLIA achieved a detection limit of 0.25 pg/mL, 6.8 times more sensitive than Siemens commercial kits, with a broad linear range of 9.2–1077 pg/mL. The method demonstrated excellent stability, both under accelerated conditions at 37 °C for 7 days and long-term storage at 4 °C for 12 months. It showed no cross-reactivity with common interfering substances in human serum, ensuring high specificity. Notably, the entire process, from sample preparation to result, takes just 25 min, compared to 3–4 h for both ELISA and RIA, and CLIA typically offers 10–100 times higher sensitivity than these methods. These advantages make the Ab-MPs-CLIA an ideal option for clinical laboratories, providing superior sensitivity, specificity, broader dynamic range, and greater operational efficiency than existing TNF-α detection technologies.

Study on the stability and magnetically induced demulsification performance of Pickering emulsions based on arginine-modified lignin/Fe3O4 nanoparticles

In this study, four different arginine-modified lignin composites (Lig-Arg-x) were synthesized via the Mannich reaction, followed by the preparation of Lig-Arg-x/Fe3O4 magnetic nanoparticles (NPs) using hydrothermal reduction. The magnetic particles were characterized, and their emulsification properties were investigated. The highest grafting degree was achieved at a 1:1 M ratio of arginine to lignin. Pickering emulsions were formulated and Lig-Arg-x/Fe3O4 NPs as the emulsifier. The study examined the impact of arginine grafting degree, oil-to-water volume ratio, and nanoparticle concentration on emulsion stability and demulsification performance. Optimal emulsion stability, characterized by the smallest droplet size of 20.57 μm, was achieved with a 1:1 M ratio of lignin to arginine, a 7:3 oil-to-water volume ratio, and a nanoparticle concentration of 1.0 w/v%. Magnetic induction experiments demonstrated significant phase separation in the stable emulsion under a magnetic field, confirming the magnetic-induced demulsification capability of the composite particles. Oil displacement experiments demonstrated that Lig-Arg-x/Fe3O4 NPs modulate oil droplet diffusion via the Marangoni effect, indicating their potential for oil recovery applications. After three cycles, Lig-Arg-1/Fe3O4 NPs retained 80 % of their saturation magnetization, demonstrating strong reusability. This study showcases lignin-magnetite nanocomposites' versatility in stabilizing emulsions and exhibiting magnetic responsiveness, advancing demulsification and oil spill recovery technologies.

Hierarchical Polyimide Nonwoven Fabric with Ultralow-Reflectivity Electromagnetic Interference Shielding and High-Temperature Resistant Infrared Stealth Performance

Designing and fabricating a compatible low-reflectivity electromagnetic interference (EMI) shielding/high-temperature resistant infrared stealth material possesses a critical significance in the field of military. Hence, a hierarchical polyimide (PI) nonwoven fabric is fabricated by alkali treatment, in-situ growth of magnetic particles and "self-activated" electroless Ag plating process. Especially, the hierarchical impedance matching can be constructed by systematically assembling Fe3O4/Ag-loaded PI nonwoven fabric (PFA) and pure Ag-coated PI nonwoven fabric (PA), endowing it with an ultralow-reflectivity EMI shielding performance. In addition, thermal insulation of fluffy three-dimensional (3D) space structure in PFA and low infrared emissivity of PA originated from Ag plating bring an excellent infrared stealth performance. More importantly, the strong bonding interaction between Fe3O4, Ag, and PI fiber improves thermal stability in EMI shielding and high-temperature resistant infrared stealth performance. Such excellent comprehensive performance makes it promising for military tents to protect internal equipment from electromagnetic interference stemmed from adjacent equipment and/or enemy, and inhibit external infrared detection.

Global Identification of Anti-Melanoma Cellular Targets by Photochemically Induced Coupling of L-Shikonin Reactions on the Surface of Magnetic Particles

Background: L-Shikonin, an active component of Arnebia euchroma (Royle) Johnst., has remarkable pharmacological effects, particularly in its anti-tumour activity. Nonetheless, the specific targets and mechanisms of action remain to be further explored. Methods: A novel Fe3O4@L-Shikonin was designed and synthesized in this study by linking Fe3O4 and L-Shikonin through benzophenone. Fe3O4@L-Shikonin was characterized using several techniques, including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and drug removal methods, to determine the content of L-Shikonin on the surface of the magnetic particles. Target hooking technology was utilized to identify the target proteins of the compound in melanoma. The synthesized Fe3O4@L-Shikonin was co-incubated with A375 cell lysate, followed by the target proteins, which were purified by magnetic enrichment using magnetic microspheres and identified by high-resolution mass spectrometry. Results: AutoDock Vina software was employed for molecular docking analysis, where it was found that L-Shikonin targets RPN1, CPEB4, and HNRNPUL1 proteins. Subsequently, A375 cells were treated with L-Shikonin at different concentrations (2.5, 5.0, 10.0 μM) for 48 h, and the expressions of the three proteins were observed. The results showed a significant reduction in the relative expression of CPEB4 in the high-dose group compared to the control group (p &lt; 0.01). Moreover, the relative expression of HNRNPUL1 was decreased in the medium- and high-dose groups (p &lt; 0.05). Conclusions: This study initially revealed from the source that L-Shikonin may regulate melanoma-specific markers, melanosomes, tyrosine kinases related to abnormal tyrosine metabolism, and melanoma through multiple targets such as CPEB4 and HNRNPUL1. Proliferation and metastasis work together to exert an anti-melanoma mechanism, which provides a new idea for the follow-up study of the molecular pharmacological mechanism of the complex system of total naphthoquinones in Arnebia euchroma (Royle) Johns.

The Role of Glycocalyx Diversity and Thickness for Nanoparticle Internalization in M1-/M2-like Macrophages.

Very small superparamagnetic iron oxide nanoparticles (VSOPs) show diagnostic value in multiple diseases as a promising MRI contrast agent. Macrophages predominantly ingest VSOPs, but the mechanism remains unclear. This study identifies differences in VSOP uptake between pro-inflammatory M1 and anti-inflammatory M2 macrophages and explores the role of the pericellular glycocalyx. Glycosaminoglycans (GAG) synthesis activities and the pericellular glycocalyx for M1/M2-like macrophages were assessed by RT-qPCR, Click-iT reaction, and WGA-FITC staining. The uptake of europium-VSOP and Synomag by the two subtypes was measured using Prussian blue staining, fluorescent microscopy, and magnetic particle spectroscopy. The findings revealed that M2-like macrophages had higher GAG synthesis activity, a thicker glycocalyx, and increased nanoparticle uptake compared to M1-like macrophages. Enzymatic glycocalyx degradation significantly decreased nanoparticle uptake. This study demonstrates a positive correlation between glycocalyx and nanoparticle uptake that could be exploited for imaging and targeted therapy, particularly in cancer, where macrophage subtypes play distinct roles.

Experimental and Simulative Analysis of Magnetic Nanoparticle Accumulation Using Various Halbach Arrays

Abstract One of the major challenges in using magnetic nanoparticles in biomedical applications is still the accurate steering and trapping of these particles at a desired location, like at a tumor. Halbach arrays are well-established here as they generate the strongest magnetic force. However, these arrays are mechanically unstable, and thus, their potential to attract magnetic particles is often investigated fully numerically. Hence, this paper provides instructions on how to easily produce Halbach arrays using permanent magnets and metal glue. In total, three Halbach arrays of five, seven, and nine magnets were produced and analyzed regarding their potential for capturing magnetic particles in a background flow, numerically using COMSOL Multiphysics and in measurements. Furthermore, the Halbach arrays are compared with two other array configurations with all magnetizations in the same directions and alternating once. Overall, the simulation results were in good agreement with the measurement results. The amount of captured particles was significantly higher in measurements for the Halbach arrays with 8.2 %, compared to the array with alternating magnetization direction with 6.6% captured particles. Therefore, using Halbach arrays to capture or steer magnetic nanoparticles in a background flow is strongly recommended.

Biodiesel production from the transesterification of waste cooking oil via CaO/HAP/MnFe@K magnetic nanocatalyst derived from eggshells and chicken bones: Diesel engine and kinetic studies

This study focuses on the biodiesel generation from waste cooking oil (WCO) utilizing eggshells/chicken bones-derived magnetic nanocatalyst (CaO/HAp/MnFe@K). Various assessments were applied to demonstrate the CaO/HAp/MnFe@K nanocatalyst surface. These assessments showed that CaO/HAp/MnFe@K nanocatalyst has considerable catalytic attributes (e.g., highly crystalline, suitable surface area, and favorable porosity). The highest biodiesel efficiency employing CaO/HAp/MnFe@K magnetic nanocatalysts was 99.10%, which was obtained at a molar proportion of 15.24:1, catalyst content of 2.97 wt.%, reaction time of 175.72 min, and temperature of 67.72 °C (optimal conditions). Further, the reaction kinetics demonstrated that the transesterification of WCO in the attendance of CaO/HAp/MnFe@K nanocatalyst follows the pseudo-first-order model. Besides, the activation energy and exponential factor reflection reveal that the conversion of WCO to biodiesel is 41.51 kJ/mol and 1.66×105 min-1, respectively. By adding WCO-derived biodiesel to diesel, the release of carbon dioxide (CO2) and nitrogen oxides (NOx) increases while the carbon monoxide (CO) and unburned hydrocarbon (UHC) amounts diminish. By boosting biodiesel in the fuel combination, the quantities of brake specific fuel consumption (BSFC) and exhaust gas temperature (EGT) increased while the Brake Thermal Efficiency (BTE) amount decreased. Moreover, reusability of the CaO/HAp/MnFe@K nanocatalyst revealed that the magnetic particles were considerably stability.

Development of an automatic tubular chemiluminescence immunoassay using magnetic particles for the detection of antibodies against foot-and-mouth disease virus serotype A.

Foot-and-mouth disease virus (FMDV) causes significant financial losses in animal farms worldwide. Specific antibody monitoring of FMDV post-vaccination is important for evaluating vaccine efficacy, as well as the prevention and control of foot-and-mouth disease (FMD). In this study, we developed a fully automatic tubular chemiluminescence immunoassay method based on magnetic particles (A-MPCLIA) to specifically detect antibodies against FMDV serotype A. The diagnostic sensitivity (Dsn) and diagnostic specificity (Dsp) of A-MPCLIA were determined to be 96.05% and 99%, respectively, with a cut-off value of 30 activity units (U) by detecting the known background swine, cattle, and sheep serum. The developed method presented good Dsn, Dsp, and repeatability (CV < 10%). The activity units of A-MPCLIA, determined using 23 animals vaccinated with FMDV serotypes O, A, and Asia 1 univalent inactivated vaccine and nine serum samples from naïve animals, were significantly positively correlated with the titers of liquid-phase-blocking enzyme-linked immunosorbent assay (R2 = 0.992) and the titer of the virus neutralization test (R2 = 0.9577). In addition, A-MPCLIA requires less than 20 min, and it is fully automatic in detection. These results showed that A-MPCLIA is a suitable method for the detection of antibodies against FMDV serotype A in the future.

Electrochemical magneto-immunoassay based on Mycobacterium leprae mimotope for serological diagnosis of leprosy

Leprosy is an infectious disease classified as Neglected Tropical Disease (NTD) by the World Health Organization (WHO). Its diagnosis is challenging, relying on clinical symptoms and invasive procedures. Delays can cause severe physical disability, including hand, foot, and eye impairments. Herein, we describe the development of a magneto-immunoassay based on an electrochemical disposable microfluidic device for the serological diagnosis of leprosy. The assay makes use of magnetic particles (MPs) modified with Mycobacterium leprae mimotope as a probe to capture and separate target-specific antibodies from serum samples. The antibody anti-M. leprae was detected using the anti-human antibody IgG conjugated with horseradish peroxidase enzyme as an electrochemical maker. The magneto-immunoassay was applied in serum samples from healthy subjects and patients diagnosed with leprosy classified as paucibacillary (PB) and multibacillary (MB). The results showed that the method could differentiate between negative and positive patients (AUC = 0.990) with high clinical sensitivity (91.2%) and specificity (100.0%). In addition, the assay showed the capability to differentiate between paucibacillary and multibacillary with sensitivities of 88.9% and 93.7%, respectively, indicating that the device can be used to guide the treatment of positive cases. Thus, magneto-immunoassay based on the use of a disposable microfluidic device demonstrated to be a valuable tool for the early diagnosis of leprosy which can help the public health system to reduce disability cases and even control and eliminate the disease by interrupting the chain of transmission.

Research on propagation characteristics of an electromagnetic wave in magnetized fully ionized dusty plasma

When some spacecraft fly at high speed in near-earth space, the dusty plasma is attached to the surface of the spacecraft due to the intense friction between the spacecraft and the space. The dusty plasma attached to the aircraft hinders the propagation of electromagnetic (EM) waves and affects the flight safety of the pilot. In this paper, we replace the collision term of the general Boltzmann equation with the Fokker-Planck-Landau collision term and obtain the general correlation expression of the electron distribution function in the fully ionized dusty plasma. The dielectric relation of EM waves in magnetized fully ionized dusty plasma is calculated considering the impact effect and charging effect of dust particles in the case of an external magnetic field. The reflection coefficient (R) and transmission coefficient (T) of the EM wave in magnetized fully ionized dusty plasma are calculated by a scattering matrix method. The effects of applied magnetic field intensity and dust particle parameters on the propagation characteristics of EM waves in magnetized fully ionized dusty plasma are discussed by simulation. In addition, the propagation characteristics of EM waves in ordinary plasma and magnetized fully ionized dusty plasma are compared. The results show that with the increase in the additional magnetic field, the reflection of the EM wave in the fully ionized dusty plasma decreases and the transmission increases. In the 0–100 GHz band, dust particles block EM waves from penetrating fully ionized dusty plasma. Other dusty plasma parameters also affect the propagation characteristics of EM waves to varying degrees. These results provide a theoretical reference for solving the communication related problems of high-speed aircraft.

Drop-on-Demand 3D Printing of Programable Magnetic Composites for Soft Robotics

Soft robotics have become increasingly popular as a versatile alternative to traditional robotics. Magnetic composite materials, which respond to external magnetic fields, have attracted significant interest in this field due to their programmable two-way actuation and shape-morphing capabilities. Additive manufacturing (AM), also known as 3D printing, allows for the incorporation of different functional composite materials to create active components for soft robotic systems. However, current AM methods have limitations, especially when it comes to printing smart composite materials with high functional material content. This is a key requirement for enhancing responsiveness to external stimuli. Commonly used AM methods for smart magnetic composites, such as direct ink writing (DIW), confront challenges in achieving discontinuous printing, and enabling multi-material control at the voxel level, while some AM techniques are not suitable for producing composite materials. To address these limitations, we employed high-viscosity drop-on-demand (DoD) jetting and developed versatile programmable magnetic composites filled with micron-sized hard magnetic particles. This method bridges the gap between conventional ink-jetting and DIW, which require inks with viscosities at opposite ends of the spectrum. This high-viscosity DoD jetting enables continuous, discontinuous, and non-contact printing, making it a versatile and effective method for printing functional magnetic composites even with micron-sized fillers. Furthermore, we demonstrated stable magnetic domain programming and two-way shape-morphing actuations of printed structures for soft robotics. In summary, our work highlights high-viscosity DoD jetting as a promising method for printing functional magnetic composites and other similar materials for a wide range of applications.

Axial Field of View Expansion by Switchable Halbach Dipole Rings: A Simulation Study

Abstract In Magnetic particle imaging (MPI), the spatial encoding of the particle response is achieved by a magnetic gradient field called selection field. In this work a selection field generator based on two pairs of nested and freely rotatable Halbach cylinders in dipole configuration generating a gradient field in form of a linear field free region (FFR) is proposed. Through adequate rotation of the Halbach dipoles the FFR can be moved continuously along the cylinder axis. To understand and evaluate the movement of the FFR for different sequences of dipole rotations a simulation study is conducted. The simulation is based on the approximation of a permanent magnet’s field as a magnetic dipole field, so that the Halbach cylinder field results from the superposition of circularly arranged magnetic dipole moments. By the summation of four Halbach dipole fields the selection field can be calculated. It has turned out that the opposite rotation and the matching field strengths of the dipoles of a pair are prerequisites for the movement of the FFR. With regard to the gradient field strengths and the movement speed of the FFR within a potential imaging area, a phase-shifted rotation of two pairs seems promising for the use in MPI.

Using NMR linewidth broadening for magnetic characterization of micrometer-size particles in silicone matrix

Standard magnetization measurements on samples of small magnetic particles may generate conflicting results. We compare the mass magnetization of MgZn ferrite particles in a compressed bulk material and in dry powder and find that at low fields the values can differ by as much as 50%. We show here that embedding the particles in a silicone matrix and measuring the NMR linewidth in combination with simulations establishes a new method to evaluate the magnetization of the particles at different fields and temperatures. The NMR results agree with the direct magnetization measurements of the powder samples and the magnetization measurements of the particles embedded in silicone. This work is motivated, in part, by studies on using small magnetic particles as MRI temperature indicators, and we compare the effectiveness of these particles for low-field and high-field MRI thermometry.