Alternating Magnetic Field Research Articles

Regulation of Bacterial Behavior by Light and Magnetism Mediated by Mesoporous Silica-Coated MnFe2O4@CoFe2O4 Nanoparticles

Unicellular bacterial cells exhibit diverse population behaviors (i.e., aggregation, dispersion, directed assembly, biofilm formation, etc.) to facilitate communication and cooperation. Suitable bacterial behaviors are required for efficient nutrient uptake, cell recycling, and stress response for environmental and industrial application of bacterial populations. However, it remains a great challenge to artificially control bacterial behaviors because of complicated genetic and biochemical mechanisms. In this study, we designed facile mesoporous silica nanoparticle (MSN)-based assemblies to intelligently regulate bacterial behaviors with the help of light and magnetic field. This system was composed of magnetic MSNs, i.e., MnFe2O4@CoFe2O4@MSN modified by photoactive spiropyran (SP), and the chitosan-based polymers ChiPSP, i.e., chitosan grafted by triphenylphosphine and SP. The assembly strongly bound bacterial cells, inducing reversible bacterial aggregation by visible-light irradiation and dark. Moreover, the formed bacterial aggregates could be further governed by a directed magnetic field (DMF) to form microfibers and by an alternating magnetic field (AMF) to form biofilms. This study realized stimulus-triggered regulation of bacterial behaviors by MSNs and implied the great power of chemical strategies in intelligent control of diverse biological processes for environmental and industrial applications.

Atomic Magnetic Heating Effect Enhanced Hydrogen Evolution Reaction of Gd@MoS2 Single-Atom Catalysts.

Atomic heating on single atoms (SAs) to maximize the catalytic efficiency of each active site would be a fascinating solution to break the bottleneck for the performance improvement of single-atom catalysts (SACs) but highly challenging task. Here, based on the Gd@MoS2 SACs synthesized by a facile laser molecular beam epitaxy method, high-frequency alternating magnetic field (AMF) technology is employed to induce atomic magnetic heating on Gd SAs that is meanwhile demonstrated to be the catalytic active center. Significant improvement in catalytic kinetics under AMF excitation (3.9 mT) is achieved, yielding a remarkable enhancement of hydrogen evolution reaction magnetothermal-current by ≈924%. Through theoretical calculations and spin-related electrochemical experiments, such promotion in catalyst activity can be attributed to spin flip (or canting) in Gd SAs leading to the atomic magnetic heating effect on catalytic active center. Together with the embodied high stability, the implement of AMF to the SAs field is demonstrated in this work, and the precisely atomic magnetic heating on specific SAs offers unprecedented thinking for further improvement of SACs performance in the future.

Hyperthermia of Magnetically Soft-Soft Core-Shell Ferrite Nanoparticles

Magnetically soft-soft MnFe2O4-Fe3O4 core-shell nanoparticles were synthesized through a seed-mediated method using the organometallic decomposition of metal acetyl acetonates. Two sets of core-shell nanoparticles (S1 and S2) of similar core sizes of 5.0 nm and different shell thicknesses (4.1 nm for S1 and 5.7 nm for S2) were obtained by changing the number of nucleating sites. Magnetic measurements were conducted on the nanoparticles at low and room temperatures to study the shell thickness and temperature dependence of the magnetic properties. Interestingly, both core-shell nanoparticles showed similar saturation magnetization, revealing the ineffective role of the shell thickness. In addition, the coercivity in both samples displayed similar temperature dependencies and magnitudes. Signatures of spin glass (SG) like behavior were observed from the field-cooled temperature-dependent magnetization measurements. It was suggested to be due to interface spin freezing. We observed a slight and non-monotonic temperature-dependent exchange bias in both samples with slightly higher values for S2. The effective magnetic anisotropy constant was calculated to be slightly larger in S2 than that in S1. The magnetothermal efficiency of the chitosan-coated nanoparticles was determined by measuring the specific absorption rate (SAR) under an alternating magnetic field (AMF) at 200-350 G field strengths and frequencies (495.25-167.30 kHz). The S2 nanoparticles displayed larger SAR values than the S1 nanoparticles at all field parameters. A maximum SAR value of 356.5 W/g was obtained for S2 at 495.25 kHz and 350 G for the 1 mg/mL nanoparticle concentration of ferrogel. We attributed this behavior to the larger interface SG regions in S2, which mediated the interaction between the core and shell and thus provided indirect exchange coupling between the core and shell phases. The SAR values of the core-shell nanoparticles roughly agreed with the predictions of the linear response theory. The concentration of the nanoparticles was found to affect heat conversion to a great extent. The in vitro treatment of the MDA-MB-231 human breast cancer cell line and HT-29 human colorectal cancer cell was conducted at selected frequencies and field strengths to evaluate the efficiency of the nanoparticles in killing cancer cells. The cellular cytotoxicity was estimated using flow cytometry and an MTT assay at 0 and 24 h after treatment with the AMF. The cells subjected to a 45 min treatment of the AMF (384.50 kHz and 350 G) showed a remarkable decrease in cell viability. The enhanced SAR values of the core-shell nanoparticles compared to the seeds with the most enhancement in S2 is an indication of the potential for tailoring nanoparticle structures and hence their magnetic properties for effective heat generation.

Alternating Magnetic Field Induced Magnetic Heating in Ferromagnetic Cobalt Single-Atom Catalysts for Efficient Oxygen Evolution Reaction.

Alternating magnetic field (AMF) is a promising methodology for further improving magnetic single-atom catalyst (SAC) activity toward oxygen evolution reaction (OER). Herein, the anchoring of Co single atoms on MoS2 support (Co@MoS2), leading to the appearance of in-plane room-temperature ferromagnetic properties, is favorable for the parallel spin arrangement of oxygen atoms when a magnetic field is applied. Moreover, field-assisted electrocatalytic experiments confirmed that the spin direction of Co@MoS2 is changing with the applied magnetic field. On this basis, under AMF, the active sites in ferromagnetic Co@MoS2 were heated by exploiting the magnetic heating generated from spin polarization flip of these SACs to further expedite OER efficiency, with overpotential at 10 mA cm-2 reduced from 317 mV to 250 mV. This work introduces a feasible and efficient approach to enhance the OER performance of Co@MoS2 by AMF, shedding some light on the further development of magnetic SACs for energy conversion.

Enhancing hydrogen evolution reaction of confined monodispersed NiSe2−X nanoparticles by high-frequency alternating magnetic fields

Introduction of alternating magnetic field (AMF) to electrocatalytic process has been proved an effective strategy for significantly enhancing catalytic performance of magnetic nanoparticles (NPs) electrocatalysts. Coupling AMF with currently highly promising monodispersed NPs electrocatalysts could be an interesting tactics. However, magnetic heating effect under AMF may cause agglomeration and even falloff of NPs, and how to efficiently and stably utilize AMF in monodispersed NPs electrocatalysts to enhance the catalytic performance is an urgent issue. In this work, room-temperature ferromagnetism is introduced into NiSe2−X nanoparticle by vacancy engineering, and proposes a feasible design to confine monodispersed ultra-small NiSe2−X NPs in an amorphous carbon matrix. Under AMF, the spin flips of the magnetic domains in confined NiSe2−X NPs generate magnetic heating related to Néel relaxation, which achieve rapid local heating of NiSe2−X NPs electrocatalyst and greatly improves hydrogen evolution reaction performance (a significantly increase of current density by ∼400 %). This work provides new ideas for the preparation of ultra-small monodispersed NPs electrocatalysts that can utilize AMF to enhance catalytic performance, and has an important significance in accelerating clean energy production.

Design and construction of a lab-made calorimetric system for specific loss power (SLP) measurements in suspensions of magnetic nanoparticles

The specific loss power (SLP) is a figure of merit in nanomagnetism, which allows to classify systems of magnetic nanoparticles (MNPs) according to their capability to dissipate heating power in response to the energy absorbed from an alternating magnetic field (AMF) at radiofrequencies. SLP magnitude is relevant in biological applications of MNPs, such as nanomedicine, where the thermal energy released by these nanostructures can be used to produce apoptosis in cancer cells, becoming a promising alternative for the treatment of malignant tumors. In this work we present details of the design and construction of a lab-made electromagnetic system to perform SLP measurements in systems of MNPs. The system is composed by an actuation stage, which generates the AMF to excite the sample, a thermal insulation stage between the sample and its surroundings, and two sensing stages: the first one for measuring the magnetic field applied to the sample and the second one for measuring the changes of temperature of the sample. The system developed allows to reach AMFs around 7.7 kA m−1 in the center of the actuation coil, operating at 260 kHz and with a power consumption less than 150 W. The architecture of the system allows the automatization and control of SLP measurements from remote places through the IEEE 488 bus available in the power source and a graphic interface developed in LabVIEW software, which allows to visualize temperature versus time measurements, control the magnetic field amplitude and store the data in a public folder available in the cloud. Some results are presented, where the system is employed to measure the SLP of a colloidal suspension of MNPs of maghemite (γ-Fe2O3) stabilized with sodium polyacrylate. The results obtained show a satisfactory performance of the device to measure the SLP of samples of MNPs for different purposes.

Magnetically Induced Brownian Motion of Iron Oxide Nanocages in Alternating Magnetic Fields and Their Application for Efficient siRNA Delivery.

Hyperthermia of superparamagnetic nanoparticles driven by Néel relaxation in an alternating magnetic field (AMF) has been studied in biomedical areas; however, Brownian motion, induced by another magnetic relaxation mechanism, has not been explored extensively despite its potential in intracellular mechanoresponsive applications. We investigated whether superparamagnetic cage-shaped iron oxide nanoparticles (IO-nanocages), previously demonstrated to carry payloads inside their cavities for drug delivery, can generate Brownian motion by tuning the nanoparticle size at 335 kHz AMF frequency. The motivation of this work is to examine the magnetically driven Brownian motion for the delivery of nanoparticles allowing escape from endosomes before digestion in lysosomes and efficient delivery of siRNA cargoes to the cytoplasm. Superconducting quantum interference device (SQUID) measurements reveal the nanocage size dependence of Brownian relaxation, and a magnetic Brownian motion of 20 nm IO-nanocages improved the efficiency of siRNA delivery while endosomal membranes were observed to be compromised to release IO-nanocages in AMFs during the delivery process.

Self-healable printed magnetic field sensors using alternating magnetic fields

We employ alternating magnetic fields (AMF) to drive magnetic fillers actively and guide the formation and self-healing of percolation networks. Relying on AMF, we fabricate printable magnetoresistive sensors revealing an enhancement in sensitivity and figure of merit of more than one and two orders of magnitude relative to previous reports. These sensors display low noise, high resolution, and are readily processable using various printing techniques that can be applied to different substrates. The AMF-mediated self-healing has six characteristics: 100% performance recovery; repeatable healing over multiple cycles; room-temperature operation; healing in seconds; no need for manual reassembly; humidity insensitivity. It is found that the above advantages arise from the AMF-induced attraction of magnetic microparticles and the determinative oscillation that work synergistically to improve the quantity and quality of filler contacts. By virtue of these advantages, the AMF-mediated sensors are used in safety application, medical therapy, and human-machine interfaces for augmented reality.

An injectable hyperthermic nanofiber mesh with switchable drug release to stimulate chemotherapy potency.

We developed a smart nanofiber mesh (SNM) with anticancer abilities as well as injectability and fast recovery from irregular to non-compressible shapes. The mesh can be injected at the tumor site to modulate and control anticancer effects by loading the chemotherapeutic drug, paclitaxel (PTX), as well as magnetic nanoparticles (MNPs). The storage modulus of the mesh decreases when applied with a certain shear strain, and the mesh can pass through a 14-gauge needle. Moreover, the fibrous morphology is maintained even after injection. In heat-generation measurements, the mesh achieved an effective temperature of mild hyperthermia (41-43°C) within 5min of exposure to alternating magnetic field (AMF) irradiation. An electrospinning method was employed to fabricate the mesh using a copolymer of N-isopropylacrylamide (NIPAAm) and N-hydroxyethyl acrylamide (HMAAm), whose phase transition temperature was adjusted to a mildly hyperthermic temperature range. Pplyvinyl alcohol (PVA) was also incorporated to add shear-thinning property to the interactions between polymer chains derived from hydrogen bonding, The "on-off" switchable release of PTX from the mesh was detected by the drug release test. Approximately 73% of loaded PTX was released from the mesh after eight cycles, whereas only a tiny amount of PTX was released during the cooling phase. Furthermore, hyperthermia combined with chemotherapy after exposure to an AMF showed significantly reduced cancer cell survival compared to the control group. Subsequent investigations have proven that a new injectable local hyperthermia chemotherapy platform could be developed for cancer treatment using this SNM.

Wireless neuromodulation in vitro and in vivo by intrinsic TRPC-mediated magnetomechanical stimulation

Various magnetic deep brain stimulation (DBS) methods have been developing rapidly in the last decade for minimizing the invasiveness of DBS. However, current magnetic DBS methods, such as magnetothermal and magnetomechanical stimulation, require overexpressing exogeneous ion channels in the central nervous system (CNS). It is unclear whether magnetomechanical stimulation can modulate non-transgenic CNS neurons or not. Here, we reveal that the torque of magnetic nanodiscs with weak and slow alternative magnetic field (50 mT at 10 Hz) could activate neurons through the intrinsic transient receptor potential canonical channels (TRPC), which are mechanosensitive ion channels widely expressed in the brain. The immunostaining with c-fos shows the increasement of neuronal activity by wireless DBS with magnetomechanical approach in vivo. Overall, this research demonstrates a magnetic nanodiscs-based magnetomechanical approach that can be used for wireless neuronal stimulation in vitro and untethered DBS in vivo without implants or genetic manipulation.

Study on the droplet transfer behavior and microstructure of wire arc additive manufactured Inconel 718 alloy assisted by an alternating magnetic field

• The alternating magnetic field changes arc morphology and reduces droplet size. • Appropriate excitation current effectively reduces surface roughness. • The alternating magnetic field can effectively refine the grains and deflect the grains growth direction. In this paper, the bead geometric characteristics, droplet transfer behavior and microstructure of wire arc additive manufactured Inconel 718 alloy using cold metal transfer process assisted by an alternating magnetic field (AMF) are investigated by varying the excitation current. The results show that the AMF reduces the droplet size from 1.7 mm to 1.4 mm, and changes the arc shape from bell shape to “broom shape”. With increasing excitation current, the surface roughness first drops from 0.14 at 0 A to 0.08 at 20 A and then rises to 0.25 at 40 A, finally reaching a maximum value of 0.39 at 60 A. The grain growth direction is deflected along the build direction by the AMF, and the average grain size decreases to 69.5 μm.

An Advanced Thermal Decomposition Method to Produce Magnetic Nanoparticles with Ultrahigh Heating Efficiency for Systemic Magnetic Hyperthermia.

Due to the limited heating efficiency of available magnetic nanoparticles, it is difficult to achieve therapeutic temperatures above 44°C in relatively inaccessible tumors during magnetic hyperthermia following systemic administration of nanoparticles at clinical dosage (≤10mg kg-1 ). To address this, a method for the preparation of magnetic nanoparticles with ultrahigh heating capacity in the presence of an alternating magnetic field (AMF) is presented. The low nitrogen flow rate of 10mL min-1 during the thermal decomposition reaction results in cobalt-doped nanoparticles with a magnetite (Fe3 O4 ) core and a maghemite (γ-Fe2 O3 ) shell that exhibit the highest intrinsic loss power reported to date of 47.5 nH m2 kg-1 . The heating efficiency of these nanoparticles correlates positively with increasing shell thickness, which can be controlled by the flow rate of nitrogen. Intravenous injection of nanoparticles at a low dose of 4mg kg-1 elevates intratumoral temperatures to 50°C in mice-bearing subcutaneous and metastatic cancer grafts during exposure to AMF. This approach can also be applied to the synthesis of other metal-doped nanoparticles with core-shell structures. Consequently, this method can potentially be used for the development of novel nanoparticles with high heating performance, further advancing systemic magnetic hyperthermia for cancer treatment.

Enhanced Inactivation of Pseudoparticles Containing SARS-CoV-2 S Protein Using Magnetic Nanoparticles and an Alternating Magnetic Field.

Severe acute respiratory syndrome coronavirus 2's (SARS-CoV-2) rapid global spread has posed a significant threat to human health, and similar outbreaks could occur in the future. Developing effective virus inactivation technologies is critical to preventing and overcoming pandemics. The infection of SARS-CoV-2 depends on the binding of the spike glycoprotein (S) receptor binding domain (RBD) to the host cellular surface receptor angiotensin-converting enzyme 2 (ACE2). If this interaction is disrupted, SARS-CoV-2 infection could be inhibited. Magnetic nanoparticle (MNP) dispersions exposed to an alternating magnetic field (AMF) possess the unique ability for magnetically mediated energy delivery (MagMED); this localized energy delivery and associated mechanical, chemical, and thermal effects are a possible technique for inactivating viruses. This study investigates the MNPs' effect on vesicular stomatitis virus pseudoparticles containing the SARS-CoV-2 S protein when exposed to AMF or a water bath (WB) with varying target steady-state temperatures (45, 50, and 55 °C) for different exposure times (5, 15, and 30 min). In comparison to WB exposures at the same temperatures, AMF exposures resulted in significantly greater inactivation in multiple cases. This is likely due to AMF-induced localized heating and rotation of MNPs. In brief, our findings demonstrate a potential strategy for combating the SARS-CoV-2 pandemic or future ones.

Dual-responsive targeted atherosclerosis therapy through a multi-effective nanoplatform with anti-inflammatory, lipid-regulating and autophagy

The traditional treatment of atherosclerosis (AS) is mainly focused on lipid-lowering therapy, through oral statins to reduce blood lipid levels and control the progress of AS. However, current oral drug therapy has suffered from poor targeting and single efficacy. Here, a pH-responsive magnetic nanoplatforms (MMNS@AT-CS-DS) was developed. The dextran sulfate (DS) was encapsulated on MMNS@AT-CS to endow the nanoplatforms with the property of targeting atherosclerotic plaques. In vitro and in vivo results showed that MMNS@AT-CS-DS could target lesion areas and release statins to slow the progression of AS due to the magnetocaloric effect under alternating magnetic field (AMF) and dissolution of chitosan (CS) in the AS induced low pH environment. More importantly, its magneto-thermal responsiveness could induce protective autophagy to treat AS synergistically. In addition, the magnetic nanoplatforms could perform magnetic resonance (MR) imaging of atherosclerotic plaques, which shed new light on the integration of diagnosis and treatment of AS.

An integrated lab-on-a-chip platform for pre-concentration and detection of colorectal cancer exosomes using anti-CD63 aptamer as a recognition element

Colorectal cancer (CC) is one of the common causes of cancer-related deaths around the globe. Identification of a novel biomarker for CC is of paramount importance for early diagnostics and reducing its mortality. Among the most promising biomarker candidates, exosomes hold great potential for cancer diagnosis, management, and treatment. Exosomes are extracellular vesicles secreted from cells and they contribute to the intercellular communication, immune response and the pathogenesis of many diseases including cardiovascular diseases, neurodegenerative diseases, and cancer. Several methods have been developed/utilized for exosome isolation and purification. However, these methods are time-consuming and have low purification efficiency. In this work, we developed the “apta-magnetic biosensor” platform for isolation, purification and detection of exosomes from cell culture. Anti-CD63 aptamer, which is conjugated to the surface of magnetic nanobeads, was used as a recognition element. A dynamic separation system was used which employs a transverse magnetic field along a microfluidic channel. The channel was exposed to an alternate magnetic field which imposes alternate magnetic force onto the magnetic bead-exosome complex. The combination of the fluid flow and magnetic force generates several “alternate trapping and releasing” events under continuous-flow conditions with each event representing a washing cycle. The graphene coated onto the surface of the magnetic nanobeads was used as a quencher for the fluorescently labeled aptamer (OFF state) in the absence of the target. Upon the addition of CD63 target protein, the aptamer dissociates from the graphene and binds to the target hence increasing the fluorescence intensity (ON state). A calibration plot of variable concentrations of exosomes vs fluorescence intensity was obtained and the detection limit was calculated as 1457 particles/mL. The specificity of the sensor was tested using closely associated proteins. The results showed that the aptamagnetic isolation, pre-concentration of exosomes and quantification demonstrate great potential for various clinical applications.

Multifunctional Magnetic Nanoclusters Can Induce Immunogenic Cell Death and Suppress Tumor Recurrence and Metastasis.

Metastasis is the predominant cause of cancer deaths due to solid organ malignancies; however, anticancer drugs are not effective in treating metastatic cancer. Here we report a nanotherapeutic approach that combines magnetic nanocluster-based hyperthermia and free radical generation with an immune checkpoint blockade (ICB) for effective suppression of both primary and secondary tumors. We attached 2,2'-azobis(2-midinopropane) dihydrochloride (AAPH) molecules to magnetic iron oxide nanoclusters (IONCs) to form an IONC-AAPH nanoplatform. The IONC can generate a high level of localized heat under an alternating magnetic field (AMF), which decomposes the AAPH on the cluster surface and produces a large number of carbon-centered free radicals. A combination of localized heating and free radicals can effectively kill tumor cells under both normoxic and hypoxic conditions. The tumor cell death caused by the combination of magnetic heating and free radicals led to the release or exposure of various damage-associated molecule patterns, which promoted the maturation of dendritic cells. Treating the tumor-bearing mice with IONC-AAPH under AMF not only eradicated the tumors but also generated systemic antitumor immune responses. The combination of IONC-AAPH under AMF with anti-PD-1 ICB dramatically suppressed the growth of untreated distant tumors and induced long-term immune memory. This IONC-AAPH based magneto-immunotherapy has the potential to effectively combat metastasis and control cancer recurrence.

Magnetic chitosan-silk fibroin hydrogel/graphene oxide nanobiocomposite for biological and hyperthermia applications

This work represents a biocompatible magnetic nanobiocomposite prepared by the composition of chitosan (CS) hydrogel, silk fibroin (SF), graphene oxide (GO), and Fe3O4 NPs. Terephthaloyl thiourea was applied as a cross-linking agent to cross-link the CS strings. The CS hydrogel/SF/GO/Fe3O4 nanobiocomposite with many characteristics, such as high structural uniformity, thermal stability, biocompatibility, and stability in an aqueous solution. Various characteristics of this novel magnetic nanobiocomposite were distinguished by FT-IR, EDX, FE-SEM, XRD, TGA, and VSM analysis. The FE-SEM images were taken to evaluate the size distribution of the magnetic nanoparticles (MNPs) between 39.9 and 73.3 nm as well. The performance of the prepared nanobiocomposite was assessed by the magnetic fluid hyperthermia process. Under the alternating magnetic field (AMF), the mean value of the specific absorption rate (SAR) was determined at 43.15 w/g.

Clickable Polymer Ligand-Functionalized Iron Oxide Nanocubes: A Promising Nanoplatform for 'Local Hot Spots' Magnetically Triggered Drug Release.

Exploiting the local heat on the surface of magnetic nanoparticles (MNPs) upon exposure to an alternating magnetic field (AMF) to cleave thermal labile bonds represents an interesting approach in the context of remotely triggered drug delivery. Here, taking advantages of a simple and scalable two-step ligand exchange reaction, we have prepared iron oxide nanocubes (IONCs) functionalized with a novel multifunctional polymer ligand having multiple catechol moieties, furfuryl pendants, and polyethylene glycol (PEG) side chains. Catechol groups ensure a strong binding of the polymer ligands to the IONCs surface, while the PEG chains provide good colloidal stability to the polymer-coated IONCs. More importantly, furfuryl pendants on the polymer enable to click the molecules of interest (either maleimide-fluorescein or maleimide-doxorubicin) via a thermal labile Diels-Alder adduct. The resulting IONCs functionalized with a fluorescein/doxorubicin-conjugated polymer ligand exhibit good colloidal stability in buffer saline and serum solution along with outstanding heating performance in aqueous solution or even in viscous media (81% glycerol/water) when exposed to the AMF of clinical use. The release of conjugated bioactive molecules such as fluorescein and doxorubicin could be boosted by applying AMF conditions of clinical use (16 kAm-1 and 110 kHz). It is remarkable that the magnetic hyperthermia-mediated release of the dye/drug falls in the concentration range 1.0-5.0 μM at an IONCs dose as low as 0.5 gFe/L and at no macroscopical temperature change. This local release effect makes this magnetic nanoplatform a potential tool for drug delivery with remote magnetic hyperthermia actuation and with a dose-independent action of MNPs.

Enhanced Magnetic Hyperthermia Performance of Zinc Ferrite Nanoparticles under a Parallel and a Transverse Bias DC Magnetic Field.

The collective organization of magnetic nanoparticles (MNPs) influences significantly their hyperthermic properties, relevant for their in vitro and in vivo applications. We report a systematic investigation of the effects of the concentration and the static bias direct current (DC) magnetic field superposed over the alternating magnetic field (AMF), both in a parallel and perpendicular configuration, on the specific absorption rate (SAR) by using zinc ferrite MNPs. The nonmonotonic dependence of the SAR on the concentration, with a maximum at very small concentrations (c ≤ 0.1 mgFe/mL), followed by a minimum at 0.25 mgFe/mL, and the second maximum of 3.3 kW/gFe at around 1 mgFe/mL, was explained by the passage of the MNPs from a single particle behavior to a collective one and the role of the dipolar interactions. By superposing a static 10 kA/m bias DC field on the AMF we obtained an increase in the SAR for both parallel and perpendicular orientations, up to 4285 W/gFe and 4070 W/gFe, respectively. To the best of our knowledge, this is the first experimental proof of a significant enhancement of the SAR produced by a perpendicular DC field. The effect of the DC field to increase the SAR is accompanied by an increase in the hyperthermia coercive field (HcHyp) for both configurations. No enhancement of the DC fields was noticed for the MNPs immobilized in a solid matrix but the DC field increases the HcHyp only in the parallel configuration. This translates into a higher SAR value for the perpendicular configuration as compared to the parallel configuration. These results have practical applications for magnetic hyperthermia.

Interfacial engineered iron oxide nanoring for T2-weighted magnetic resonance imaging-guided magnetothermal-chemotherapy.

Due to no penetration depth limitation, low cost, and easy control, magnetic nanoparticles mediated magnetic hyperthermia therapy (MHT) has shown great potential in experimental and clinal treatments of various diseases. However, the low heating conversion efficiencies and short circulation times are major drawback for most existing magnetic-thermal materials. Additionally, single MHT treatment always leads to resistance and recurrence. Herein, a highly efficient magnetic-thermal conversion, ferrimagnetic vortex nanoring Fe3O4 coated with hyaluronic acid (HA) nanoparticles (Fe3O4@HA, FVNH NPs) was firstly constructed. Additionally, the doxorubicin (DOX) was successfully enclosed inside the FVNH and released remotely for synergetic magnetic–thermal/chemo cancer therapy. Due to the ferrimagnetic vortex-domain state, the ring shape Fe3O4 displays a high specific absorption rate (SAR) under an external alternating magnetic field (AMF). Additionally, antitumor drug (DOX) can be encapsulated inside the single large hole of FVNH by the hyaluronic acid (HA) shell and quickly released in response the tumor acidic microenvironments and AMF. What’s more, the non-loaded FVNH NPs show good biocompatibility but high cytotoxicity after loading DOX under AMF. Furthermore, the synthesized FVNH can efficiently reduce the transverse relaxation time and enhance negative magnetic resonance imaging (MRI). The impressive in vivo systemic therapeutic efficacy of FVNH was also proved in this work. Taken together, the results of this study demonstrate that the synthesized FVNH NPs offer the promise of serving as multifunctional theranostic nanoplatforms for medical imaging-guided tumor therapies.