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Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices. [ABSTRACT FROM AUTHOR]

We report on the structure of cobalt cluster films obtained by aggregation of metal atoms sputter-deposited on amorphous alumina. The cluster layers were encapsulated with a second amorphous alumina layer, also made by sputtering in the same chamber. Electron energy loss spectroscopy (EELS) indicates that encapsulation with sputtered alumina keeps the clusters free from cobalt oxide. Transmission electron microscopy (TEM) exhibits relatively narrow distributions of the cluster sizes and of the inter-cluster distances, which results in a noticeable local order. Size distributions appear quasi-Gaussian, but TEM misses an important number of small particles. Extended X-ray absorption fine structure (EXAFS) data shows that the actual average sizes are smaller, and Monte Carlo simulations suggest that the actual distributions could be bimodal, with a secondary peak in the small-size range. [ABSTRACT FROM AUTHOR]

The article mentions that all online versions of the article "Simple models for dynamic hysteresis loop calculations of magnetic single-domain nanoparticles: Application to magnetic hyperthermia optimization," which was published online on April 21, 2011 were corrected on April 26, 2011.

Background: There are limited evidence-based guidelines to predict which osteochondritis dissecans (OCD) lesions will heal with nonoperative treatment., Purpose: To train a set of classification algorithms to predict nonoperative OCD healing while identifying new clinically meaningful predictors., Study Design: Case-control study; Level of evidence, 3., Methods: Patients with OCD of the knee with open physes undergoing nonoperative management were prospectively queried from the Research on OCD of the Knee (ROCK) cohort (https://kneeocd.org) in April 2022. Patients were included if they met the study criteria for nonoperative treatment success or failure. Nonoperative treatment success was defined as complete healing on magnetic resonance imaging (MRI) and total return to sports participation. Failure was defined as the crossover from nonoperative management to surgery at any point at or beyond the 3-month follow-up. If a patient did not meet one of these criteria, they were not included. Normalized lesion size, lesion location, patient characteristics, and symptoms were used as clinically relevant predictors., Results: A total of 64 patients were included, of whom 24 (37.5%) patients successfully healed with nonoperative management. Multivariate logistic regression revealed that a 1% increase in normalized lesion width was associated with an increase in the likelihood of nonoperative failure (odds ratio [OR], 1.41 [95% CI, 1.17-1.81]; P < .01). By contrast, lesions in the posterior sagittal zone (OR, 0.08 [95% CI, 0.009-0.43]; P < .01) or the medial-most coronal zone (for lesions of the medial femoral) and lateral-most coronal zone (for lesions of the lateral femoral condyle) on MRI (OR, 0.05 [95% CI, 0.004-0.44]; P < .01) were associated with a decrease in the likelihood of nonoperative treatment failure. Support vector machines had a cross-validated area under the receiver operating characteristic curve of 0.89 and a classification accuracy of 83.3%., Conclusion: Lesion location in the posterior aspect of the condyle on sagittal MRI and lesion location in the medial-most or lateral-most locations on coronal MRI were identified as statistically significant predictors of increased nonoperative treatment success on multivariate analysis. Machine learning models can predict which OCD lesions will heal with nonoperative management with superior accuracy compared with previously published models., Competing Interests: One or more of the authors has declared the following potential conflict of interest or source of funding: M.T. has received hospitality payments from Aesculap Biologics. M.D.M. has received education payments from Kairos Surgical. K.G.S. has received education payments from Evolution Surgical and hospitality payments from Arthrex. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto., (© The Author(s) 2024.)

Core-shell nanocomposites made of iron oxide core (IO NPs) coated with mesoporous silica (MS) shells are promising theranostic agents. While the core is being used as an efficient heating nanoagent under alternating magnetic field (AMF) and near infra-red (NIR) light and as a suitable contrast agent for magnetic resonance imaging (MRI), the MS shell is particularly relevant to ensure colloidal stability in a biological buffer and to transport a variety of therapeutics. However, a major challenge with such inorganic nanostructures is the design of adjustable silica structures, especially with tunable large pores which would be useful, for instance, for the delivery of large therapeutic biomolecule loading and further sustained release. Furthermore, the effect of tailoring a porous silica structure on the magneto- or photothermal dissipation still remains poorly investigated. In this work, we undertake an in-depth investigation of the growth of stellate mesoporous silica (STMS) shells around IO NPs cores and of their micro/mesoporous features respectively through time-lapse and in situ liquid phase transmission electron microscopy (LPTEM) and detailed nitrogen isotherm adsorption studies. We found here that the STMS shell features (thickness, pore size, surface area) can be finely tuned by simply controlling the sol-gel reaction time, affording a novel range of IO@STMS core@shell NPs. Finally, regarding the responses under alternating magnetic fields and NIR light which are evaluated as a function of the silica structure, IO@STMS NPs having a tunable silica shell structure are shown to be efficient as T 2 -weighted MRI agents and as heating agents for magneto- and photoinduced hyperthermia. Furthermore, such IO@STMS are found to display anti-cancer effects in pancreatic cancer cells under magnetic fields (both alternating and rotating).

The origin of cell death in the magnetomechanical actuation of cells induced by magnetic nanoparticle motion under low-frequency magnetic fields is still elusive. Here, a miniaturized electromagnet fitted under a confocal microscope is used to observe in real time cells specifically targeted by superparamagnetic nanoparticles and exposed to a low-frequency rotating magnetic field. Our analysis reveals that the lysosome membrane is permeabilized in only a few minutes after the start of magnetic field application, concomitant with lysosome movements toward the nucleus. Those events are associated with disorganization of the tubulin microtubule network and a change in cell morphology. This miniaturized electromagnet will allow a deeper insight into the physical, molecular, and biological process occurring during the magnetomechanical actuation of magnetic nanoparticles.

The destruction of cells using the mechanical activation of magnetic nanoparticles with low-frequency magnetic fields constitutes a recent and interesting approach in cancer therapy. Here, we showed that superparamagnetic iron oxide nanoparticles as small as 6 nm were able to induce the death of pancreatic cancer-associated fibroblasts, chosen as a model. An exhaustive screening of the amplitude, frequency, and type (alternating vs. rotating) of magnetic field demonstrated that the best efficacy was obtained for a rotating low-amplitude low-frequency magnetic field (1 Hz and 40 mT), reaching a 34% ratio in cell death induction; interestingly, the cell death was not maximized for the largest amplitudes of the magnetic field. State-of-the-art kinetic Monte-Carlo simulations able to calculate the torque undergone by assemblies of magnetic nanoparticles explained these features and were in agreement with cell death experiments. Simulations showed that the force generated by the nanoparticles once internalized inside the lysosome was around 3 pN, which is in principle not large enough to induce direct membrane disruption. Other biological mechanisms were explored to explain cell death: the mechanical activation of magnetic nanoparticles induced lysosome membrane permeabilization and the release of the lysosome content and cell death was mediated through a lysosomal pathway depending on cathepsin-B activity. Finally, we showed that repeated rotating magnetic field exposure halted drastically the cell proliferation. This study established a proof-of-concept that ultra-small nanoparticles can disrupt the tumor microenvironment through mechanical forces generated by mechanical activation of magnetic nanoparticles upon low-frequency rotating magnetic field exposure, opening new opportunities for cancer therapy., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Magnetite nanoparticles (MNPs) with 12, 34 and 53 nm sizes have been measured by AC-magnetometry at 50 kHz and 57 mT maximum applied field. The MNPs form chains under the AC-field, and the dynamics of the formation can be studied by measuring hysteresis cycles at different times. The measurement time has been varied from 5 ms to 10 s and for different initial temperatures of 5, 25 and 50 °C. The chain formation, identified by the increase of susceptibility and remanence with the measurement time, appears only for 34 nm particles. It has been observed that saturation, remanence and susceptibility at low (high) fields increase (decrease) with time. For the other two samples, these magnitudes are independent of time. At low fields, the heating efficiency is higher at 5 °C than at 50 °C, whereas it shows an opposite behaviour at higher fields; the origin of this behaviour is discussed in the article. Additionally, the relaxation times, τ N and τ B , have been calculated by considering the influence of the applied field. Chain formation requires translation and rotation of MNPs; therefore, the Brownian mechanism plays a fundamental role. It is found that magnetic reversal for 12 nm MNPs is mainly due to Néel relaxation. However, in the case of 34 nm MNPs, both mechanisms, Néel and Brownian relaxation, can be present depending on the amplitude of the field; for μ 0 H < 22 mT, the physical rotation of the particle is the dominant mechanism; on the other hand, for μ 0 H > 22 mT, both mechanisms are present within the size distribution. This highlights the importance of taking the field intensity into account to calculate relaxation times when analysing the relaxation mechanisms of magnetic colloids subjected to AC fields., Competing Interests: The authors declare no competing financial or non-financial interest., (This journal is © The Royal Society of Chemistry.)

Magnetically induced catalysis can be promoted taking advantage of optimal heating properties from the magnetic nanoparticles to be employed. However, when unprotected, these heating agents that are usually air-sensitive, get sintered under the harsh catalytic conditions. In this context, we present, to the best of our knowledge, the first example of air-stable magnetic nanoparticles that: 1) show excellent performance as heating agents in the CO 2 methanation catalyzed by Ni/SiRAlOx, with CH 4 yields above 95 %, and 2) do not sinter under reaction conditions. To attain both characteristics we demonstrate, first the exchange-coupled magnetic approach as an alternative and effective way to tune the magnetic response and heating efficiency, and second, the chemical stability of cuboctahedron-shaped core-shell hard CoFe 2 O 4 -soft Fe 3 O 4 nanoparticles., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A main goal of molecular electronics is to relate the performance of devices to the structure and electronic state of molecules. Among the variety of possibilities that organic, organometallic and coordination chemistries offer to tune the energy levels of molecular components, spin crossover phenomenon is a perfect candidate for elaboration of molecular switches. The reorganization of the electronic state population of the molecules associated to the spin crossover can indeed lead to a significant change in conductivity. However, molecular spin crossover is very sensitive to the environment and can disappear once the molecules are integrated into devices. Here, we show that the association of ultra-small 1.2 nm platinum nanoparticles with Fe II triazole-based spin crossover coordination polymers leads to self-assemblies, extremely well organized at the sub-3 nm scale. The quasi-perfect alignment of nanoparticles observed by transmission electron microscopy, in addition to specific signature in infrared spectroscopy, demonstrates the coordination of the long-chain molecules with the nanoparticles. Spin crossover is confirmed in such assemblies by X-ray absorption spectroscopic measurements and shows unambiguous characteristics both in magnetic and charge transport measurements. Coordinating polymers are therefore ideal candidates for the elaboration of robust, well-organized, hybrid self-assemblies with metallic nanoparticles, while maintaining sensitive functional properties, such as spin crossover.

Heating magnetic nanoparticles with high frequency magnetic fields is a topic of interest for biological applications (magnetic hyperthermia) as well as for heterogeneous catalysis. This study shows why FeC NPs of similar structures and static magnetic properties display radically different heating power (SAR from 0 to 2 kW g-1). By combining results from Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and static and time-dependent high-frequency magnetic measurements, we propose a model describing the heating mechanism in FeC nanoparticles. Using, for the first time, time-dependent high-frequency hysteresis loop measurements, it is shown that in the samples displaying the larger heating powers, the hysteresis is strongly time dependent. More precisely, the hysteresis area increases by a factor 10 on a timescale of a few tens of seconds. This effect is directly related to the ability of the nanoparticles to form chains under magnetic excitation, which depends on the presence or not of strong dipolar couplings. These differences are due to different ligand concentrations on the surface of the particles. As a result, this study allows the design of a scalable synthesis of nanomaterials displaying a controllable and reproducible SAR.

In order to understand the properties involved in the heating performance of magnetic nanoparticles during hyperthermia treatments, a systematic study of different γ-Fe₂O₃ and Fe₃O₄ nanoparticles has been done. High-frequency hysteresis loops at 50 kHz carried out on particles with sizes ranging from 6 to 350 nm show susceptibility χ increases from 9 to 40 for large particles and it is almost field independent for the smaller ones. This suggests that the applied field induces chain ordering in large particles but not in the smaller ones due to the competition between thermal and dipolar energy. The specific absorption rate (SAR) calculated from hysteresis losses at 60 mT and 50 kHz ranges from 30 to 360 W/g Fe , depending on particle size, and the highest values correspond to particles ordered in chains. This enhanced heating efficiency is not a consequence of the intrinsic properties like saturation magnetization or anisotropy field but to the spatial arrangement of the particles., Competing Interests: The authors declare no conflict of interest.

The present manuscript reports the use of hybrid magneto-plasmonic nanoparticles (HMPNPs) based on iron oxide nanoparticles and Au nanorods as colloidal nanoheaters. The individual synthesis of the magnetic and plasmonic components allowed optimizing their features for heating performance separately, before they were hybridized. Besides, a detailed characterization and finite element simulations were carried out to explain the interaction effects observed between the phases of the HMPNPs. The study also analyzed the heating power of these nanostructures when they were excited with infrared light and AC magnetic fields, and compared this with the heating power of their plasmonic and magnetic components. In the latter case, the AC magnetization curves revealed that the magnetic dipolar interactions increase the amount of heat released by the hybrid nanostructures.

Therapeutic strategies using drugs which cause Lysosomal Cell Death have been proposed for eradication of resistant cancer cells. In this context, nanotherapy based on Magnetic Intra-Lysosomal Hyperthermia (MILH) generated by magnetic nanoparticles (MNPs) that are grafted with ligands of receptors overexpressed in tumors appears to be a very promising therapeutic option. However, mechanisms whereby MILH induces cell death are still elusive. Herein, using Gastrin-grafted MNPs specifically delivered to lysosomes of tumor cells from different cancers, we provide evidences that MILH causes cell death through a non-apoptotic signaling pathway. The mechanism of cell death involves a local temperature elevation at the nanoparticle periphery which enhances the production of reactive oxygen species through the lysosomal Fenton reaction. Subsequently, MILH induces lipid peroxidation, lysosomal membrane permeabilization and leakage of lysosomal enzymes into the cytosol, including Cathepsin-B which activates Caspase-1 but not apoptotic Caspase-3. These data highlight the clear potential of MILH for the eradication of tumors overexpressing receptors., (Copyright © 2017 Elsevier B.V. All rights reserved.)