Commentary on the clinical and preclinical dosage limits of interstitially administered magnetic fluids for therapeutic hyperthermia based on current practice and efficacy models

Transformer for low concentration image denoising in magnetic particle imaging

Objective.Magnetic particle imaging (MPI) is an emerging tracer-basedin vivoimaging technology. The use of MPI at low superparamagnetic iron oxide nanoparticle concentrations has the potential to be a promising area of clinical application due to the inherent safety for humans. However, low tracer concentrations reduce the signal-to-noise ratio of the magnetization signal, leading to severe noise artifacts in the reconstructed MPI images. Hardware improvements have high complexity, while traditional methods lack robustness to different noise levels, making it difficult to improve the quality of low concentration MPI images.Approach.Here, we propose a novel deep learning method for MPI image denoising and quality enhancing based on a sparse lightweight transformer model. The proposed residual-local transformer structure reduces model complexity to avoid overfitting, in which an information retention block facilitates feature extraction capabilities for the image details. Besides, we design a noisy concentration dataset to train our model. Then, we evaluate our method with both simulated and real MPI image data.Main results.Simulation experiment results show that our method can achieve the best performance compared with the existing deep learning methods for MPI image denoising. More importantly, our method is effectively performed on the real MPI image of samples with an Fe concentration down to 67μgFeml-1.Significance.Our method provides great potential for obtaining high quality MPI images at low concentrations.

Iron Oxide Nanoparticles: Parameters for Optimized Photoconversion Efficiency in Synergistic Cancer Treatment

Photothermal therapy (PTT) can overcome cancer treatment resistance by enhancing the cell membrane permeability, facilitating drug accumulation, and promoting drug release within the tumor tissue. Iron oxide nanoparticles (IONPs) have emerged as effective agents for PTT due to their unique properties and biocompatibility. Approved for the treatment of anemia, as MRI contrast agents, and as magnetic hyperthermia mediators, IONPs also offer excellent light-to-heat conversion and can be manipulated using external magnetic fields for targeted accumulation in specific tissue. Optimizing parameters such as the laser wavelength, power density, shape, size, iron oxidation state, functionalization, and concentration is crucial for IONPs' effectiveness. In addition to PTT, IONPs enhance other cancer treatment modalities. They improve tumor oxygenation, enhancing the efficacy of radiotherapy and photodynamic therapy. IONPs can also trigger ferroptosis, a programmed cell death pathway mediated by iron-dependent lipid peroxidation. Their magneto-mechanical effect allows them to exert a mechanical force on cancer cells to destroy tumors, minimizing the damage to healthy tissue. This review outlines strategies for the management of the photothermal performance and PTT efficiency with iron oxide nanoparticles, as well as synergies with other cancer therapies.

Comparative studies on the cytotoxic effects induced by iron oxide nanoparticles in cancerous and noncancerous human lung cells subjected to an alternating magnetic field

The cytotoxic effects of water-based ferrofluids composed of iron oxide nanoparticles, including magnetite (Fe3O4) and maghemite (γ-Fe2O3), ranging from 15 to 100 nm, were examined on various lung cancer cells including adenocarcinomic human alveolar basal epithelial cells (A549), nonsmall lung squamous cell carcinoma (H1703), small cell lung cancer cells (DMS 114), and normal bronchial epithelial cells (BEAS-2B). The cytotoxic effect was evaluated both with and without exposure to an alternating magnetic field (AMF). The studies revealed that neither AMF nor iron oxide nanoparticles when tested individually, produced cytotoxic effects on either cancerous or noncancerous cells. However, when applied together, they led to a significant decrease in cell viability and proliferative capacity due to the enhanced effects of magnetic fluid hyperthermia (MFH). The most pronounced effects were found for maghemite (<50 nm) when subjected to an AMF. Notably, A549 cells exhibited the highest resistance to the proposed hyperthermia treatment. BEAS-2B cells demonstrated susceptibility to magnetized iron oxide nanoparticles, similar to the response observed in lung cancer cells. The studies provide evidence that MFH is a promising strategy as a standalone treatment for different types of lung cancer cells. Nevertheless, to prevent any MFH-triggered adverse effects on normal lung cells, targeted magnetic ferrofluids should be designed.

Solving the MPI reconstruction problem with automatically tuned regularization parameters

In the field of medical imaging, magnetic particle imaging (MPI) poses a promising non-ionizing tomographic technique with high spatial and temporal resolution. In MPI, iterative solvers are used to reconstruct the particle distribution out of the measured voltage signal based on a system matrix. The amount of regularization needed to reconstruct an image of good quality differs from measurement to measurement, depending on the MPI system and the measurement settings. Finding the right choice for the three major parameters controlling the regularization is commonly done by hand and requires time and experience. In this work, we study the reduction to a single regularization parameter and propose a method that enables automatic reconstruction. The method is qualitatively and quantitatively validated on several MPI data sets showing promising results.

Gold and Iron Oxide Nanoparticle Assemblies on Turnip Yellow Mosaic Virus for In-Solution Photothermal Experiments

The ability to construct three-dimensional architectures via nanoscale engineering is important for emerging applications in sensors, catalysis, controlled drug delivery, microelectronics, and medical diagnostics nanotechnologies. Because of their well-defined and highly organized symmetric structures, viral plant capsids provide a 3D scaffold for the precise placement of functional inorganic particles yielding advanced hierarchical hybrid nanomaterials. In this study, we used turnip yellow mosaic virus (TYMV), grafting gold nanoparticles (AuNP) or iron oxide nanoparticles (IONP) onto its outer surface. It is the first time that such an assembly was obtained with IONP. After purification, the resulting nano-biohybrids were characterized by different technics (dynamic light scattering, transmission electron microcopy, X-ray photoelectron spectroscopy…), showing the robustness of the architectures and their colloidal stability in water. In-solution photothermal experiments were then successfully conducted on TYMV-AuNP and TYMV-IONP, the related nano-biohybrids, evidencing a net enhancement of the heating capability of these systems compared to their free NP counterparts. These results suggest that these virus-based materials could be used as photothermal therapeutic agents.

Saline bolus for negative contrast perfusion imaging in magnetic particle imaging

Objective.Magnetic particle imaging (MPI) is capable of high temporal resolution measurements of the spatial distribution of magnetic nanoparticles and therefore well suited for perfusion imaging, which is an important tool in medical diagnosis. Perfusion imaging in MPI usually requires a fresh bolus of tracer material to capture the key signal dynamics. Here, we propose a method to decouple the imaging sequence from the injection of additional tracer material, without further increasing the administered iron dose in the body with each image.Approach.A bolus of physiological saline solution without any particles (negative contrast) diminishes the steady-state concentration of a long-circulating tracer during passage. This depression in the measured concentration contributes to the required contrast dynamics. The presence of a long-circulating tracer is therefore a prerequisite to obtain the negative contrast. As a quantitative tracer based imaging method, the signal is linear in the tracer concentration for any location that contains nanoparticles and zero in the surrounding tissue which does not provide any intrinsic signal. After tracer injection, the concentration over time (positive contrast) can be utilized to calculate dynamic diagnostic parameters like perfusion parameters in vessels and organs. Every acquired perfusion image thus requires a new bolus of tracer with a sufficiently large iron dose to be visible above the background.Main results.Perfusion parameters are calculated based on the time response of the proposed negative bolus and compared to a positive bolus. Results from phantom experiments show that normalized signals from positive and negative boli are concurrent and deviations of calculated perfusion maps are low.Significance.Our method opens up the possibility to increase the total monitoring time of a future patient by utilizing a positive-negative contrast sequence, while minimizing the iron dose per acquired image.

iMPI: portable human-sized magnetic particle imaging scanner for real-time endovascular interventions

Minimally invasive endovascular interventions have become an important tool for the treatment of cardiovascular diseases such as ischemic heart disease, peripheral artery disease, and stroke. X-ray fluoroscopy and digital subtraction angiography are used to precisely guide these procedures, but they are associated with radiation exposure for patients and clinical staff. Magnetic Particle Imaging (MPI) is an emerging imaging technology using time-varying magnetic fields combined with magnetic nanoparticle tracers for fast and highly sensitive imaging. In recent years, basic experiments have shown that MPI has great potential for cardiovascular applications. However, commercially available MPI scanners were too large and expensive and had a small field of view (FOV) designed for rodents, which limited further translational research. The first human-sized MPI scanner designed specifically for brain imaging showed promising results but had limitations in gradient strength, acquisition time and portability. Here, we present a portable interventional MPI (iMPI) system dedicated for real-time endovascular interventions free of ionizing radiation. It uses a novel field generator approach with a very large FOV and an application-oriented open design enabling hybrid approaches with conventional X-ray-based angiography. The feasibility of a real-time iMPI-guided percutaneous transluminal angioplasty (PTA) is shown in a realistic dynamic human-sized leg model.

Paclitaxel-Loaded Lipid-Coated Magnetic Nanoparticles for Dual Chemo-Magnetic Hyperthermia Therapy of Melanoma

Melanoma is the most aggressive and metastasis-prone form of skin cancer. Conventional therapies include chemotherapeutic agents, either as small molecules or carried by FDA-approved nanostructures. However, systemic toxicity and side effects still remain as major drawbacks. With the advancement of nanomedicine, new delivery strategies emerge at a regular pace, aiming to overcome these challenges. Stimulus-responsive drug delivery systems might considerably reduce systemic toxicity and side-effects by limiting drug release to the affected area. Herein, we report the development of paclitaxel-loaded lipid-coated manganese ferrite magnetic nanoparticles (PTX-LMNP) as magnetosomes synthetic analogs, envisaging the combined chemo-magnetic hyperthermia treatment of melanoma. PTX-LMNP physicochemical properties were verified, including their shape, size, crystallinity, FTIR spectrum, magnetization profile, and temperature profile under magnetic hyperthermia (MHT). Their diffusion in porcine ear skin (a model for human skin) was investigated after intradermal administration via fluorescence microscopy. Cumulative PTX release kinetics under different temperatures, either preceded or not by MHT, were assessed. Intrinsic cytotoxicity against B16F10 cells was determined via neutral red uptake assay after 48 h of incubation (long-term assay), as well as B16F10 cells viability after 1 h of incubation (short-term assay), followed by MHT. PTX-LMNP-mediated MHT triggers PTX release, allowing its thermal-modulated local delivery to diseased sites, within short timeframes. Moreover, half-maximal PTX inhibitory concentration (IC50) could be significantly reduced relatively to free PTX (142,500×) and Taxol® (340×). Therefore, the dual chemo-MHT therapy mediated by intratumorally injected PTX-LMNP stands out as a promising alternative to efficiently deliver PTX to melanoma cells, consequently reducing systemic side effects commonly associated with conventional chemotherapies.

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 g_Fe/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.

Magnetic Nanomaterials for Arterial Embolization and Hyperthermia of Parenchymal Organs Tumors: A Review

Magnetic hyperthermia (MH), proposed by R. K. Gilchrist in the middle of the last century as local hyperthermia, has nowadays become a recognized method for minimally invasive treatment of oncological diseases in combination with chemotherapy (ChT) and radiotherapy (RT). One type of MH is arterial embolization hyperthermia (AEH), intended for the presurgical treatment of primary inoperable and metastasized solid tumors of parenchymal organs. This method is based on hyperthermia after transcatheter arterial embolization of the tumor’s vascular system with a mixture of magnetic particles and embolic agents. An important advantage of AEH lies in the double effect of embolotherapy, which blocks blood flow in the tumor, and MH, which eradicates cancer cells. Consequently, only the tumor undergoes thermal destruction. This review introduces the progress in the development of polymeric magnetic materials for application in AEH.

Individual particle heating of interacting magnetic nanoparticles at nonzero temperature

Interaction phenomena have become a hot topic in nanotechnology due to their influence on the performance of magnetic nanostructures for biomedical applications. Hysteresis loops give a good account of the particles' magnetic behaviour, providing valuable clues on subsequent improvements. Nevertheless, the individual hysteresis loops of these systems are also influenced by any potential energy exchanged between the particles, and in contrast to non-interacting particles, are no longer a good measure for the local heat generated by each particle. As of today, there is no method capable of analysing the heat dissipation resulting from the nanoscale magnetisation dynamics in its full generality, i.e. in the presence of interactions and at nonzero temperature (allowing for thermally induced switching), and therefore the means of exploiting these dynamics remain hampered by a lack of understanding. In this work we address this problem by proposing and validating an equation that can be used to resolve the individual heat dissipation of interacting nanoparticles at nonzero temperature. After assessing this equation for different model systems, we have found that the proportion of heat dissipated in each individual particle tends to become more uniformly distributed for larger fields. Our results might have implications for magnetic particle hyperthermia where one of the most long-standing challenges is to achieve a homogeneous therapeutic temperature distribution in the target region during a treatment. Although tackling this issue involves a number of aspects related to the tissues involved, the injected nanoparticles, and the applied magnetic field, we believe that a more homogeneous heating of the particles inside the tumour will help to overcome this challenge.

Deep-tissue localization of magnetic field hyperthermia using pulse sequencing

OBJECTIVE

Deep-tissue localization of thermal doses is a long-standing challenge in magnetic field hyperthermia (MFH), and remains a limitation of the clinical application of MFH to date. Here, we show that pulse sequencing of MFH leads to a more persistent inhibition of tumor growth and less systemic impact than continuous MFH, even when delivering the same thermal dose.

METHODS

We used an in vivo orthotopic murine model of pancreatic PANC-1 cancer, which was designed with a view to the forthcoming 'NoCanTher' clinical study, and featured MFH alongside systemic chemotherapy (SyC: gemcitabine and nab-paclitaxel). In parallel, in silico thermal modelling was implemented.

RESULTS

Tumor volumes 27 days after the start of MFH/SyC treatment were 53% (of the initial volume) in the pulse MFH group, compared to 136% in the continuous MFH group, and 337% in the non-treated controls. Systemically, pulse MFH led to ca. 50% less core-temperature increase in the mice for a given injected dose of magnetic heating agent, and inflicted lower levels of the stress marker, as seen in the blood-borne neutrophil-to-lymphocyte ratio (1.7, compared to 3.2 for continuous MFH + SyC, and 1.2 for controls).

CONCLUSION

Our data provided insights into the influence of pulse sequencing on the observed biological outcomes, and validated the nature of the improved thermal dose localization, alongside significant lowering of the overall energy expenditure entailed in the treatment.

Magnetic particle imaging for artifact-free imaging of intracranial flow diverter stents: A phantom study

PURPOSE

Magnetic Particle Imaging (MPI) is a new, background- and radiation-free tomographic imaging method that enables near real-time imaging of superparamagnetic iron-oxide nanoparticles (SPIONs) with high temporal and spatial resolution. This phantom study aims to investigate the potential of MPI for visualization of the stent lumen in intracranial flow diverters (FD).

METHODS

Nitinol FD of different dimensions (outer diameter: 3.5 mm, 4.0 mm, 5.5 mm; total length: 22-40 mm) were scanned in vascular phantoms in a custom-built MPI scanner (in-plane resolution: ~ 2 mm, field of view: 65 mm length, 29 mm diameter). Phantoms were filled with diluted (1:50) SPION tracer agent Ferucarbotran (10 µmol (Fe)/ml; NaCL). Each phantom was measured in 32 different projections (overall acquisition time per image: 3200 ms, 5averages). After image reconstruction from raw data, two radiologists assessed image quality using a 5-point Likert scale. The signal intensity profile was measured using a semi-automatic evaluation tool.

RESULTS

MPI visualized the lumen of all FD without relevant differences between the stented vessel phantom and the reference phantom. At 3.5 mm image quality was slightly inferior to the larger diameters. The FD themselves neither generated an MPI signal nor did they lead to relevant imaging artifacts. Ratings of both radiologists showed no significant difference, interrater reliability was good (ICC 0.84). A quantitative evaluation of the signal intensity profile did not reveal any significant differences (p > 0.05) either.

CONCLUSION

MPI visualizes the lumen of nitinol FD stents in vessel phantoms without relevant stent-induced artifacts.

Nonequilibrium Dynamics of Magnetic Nanoparticles with Applications in Biomedicine

Magnetic nanoparticles are currently the focus of investigation for a wide range of biomedical applications that fall into the categories of imaging, sensing, and therapeutics. A deep understanding of nanoparticle magnetization dynamics is fundamental to optimization and further development of these applications. Here, a summary of theoretical models of nanoparticle dynamics is presented, and computational nonequilibrium models are outlined, which currently represent the most sophisticated methods for modeling nanoparticle dynamics. Nanoparticle magnetization response is explored in depth; the effect of applied field amplitude, as well as nanoparticle size, on the resulting rotation mechanism and timescale is investigated. Two applications in biomedicine, magnetic particle imaging and magnetic fluid hyperthermia, are highlighted.

Mitigation of magnetic particle hyperthermia side effects by magnetic field controls

Objective: In magnetic particle hyperthermia, a promising least-invasive cancer treatment, malignant regions in proximity with magnetic nanoparticles undergo heat stress, while unavoidably surrounding healthy tissues may also suffer from heat either directly or indirectly by the induced eddy currents, due to the developed electric fields as well. Here, we propose a facile upgrade of a typical magnetic particle hyperthermia protocol, to selectively mitigate eddy currents' heating without compromising the beneficial role of heating in malignant regions.Method: The key idea is to apply the external magnetic field intermittently (in an ON/OFF pulse mode), instead of the continuous field mode typically applied. The parameters of the intermittent field mode, such as time intervals (ON time: 25-100 s, OFF time: 50-200 s, Duty Cycle:16-100%) and field amplitude (30-70 mT) are optimized based on evaluation on healthy tissue and cancer tissue phantoms. The goal is to sustain in cancer tissue phantom the maximum temperature increase (preferably within 4-8°C above body temperature of 37°C), while in the healthy tissue phantom temperature variation is suppressed far below the 4°C dictating the eddy current mitigation.Results: Optimum conditions of intermittent field (ON/OFF: 50/100 in s, Duty Cycle: 33%, magnetic field: 45mT) are then examined in ex-vivo samples verifying the successful suppression of eddy currents. Simultaneously, a well-elaborated theoretical approach provides a rapid calculation of temperature increase and, furthermore, the ability to quickly simulate a variety of duty cycle times and field controls may save experimental time.Conclusion: Eventually, the application of an intermittent field mode in a magnetic particle hyperthermia protocol, succeeds in eddy current mitigation in surrounding tissues and allows for the application of larger field amplitudes that may augment hyperthermia efficiency without objecting typical biomedical applicability field constraints such as Brezovich criterion.

Whither Magnetic Hyperthermia? A Tentative Roadmap

The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia.

Near real-time magnetic particle imaging for visual assessment of vascular stenosis in a phantom model

PURPOSE

This study aimed to investigate the potential of magnetic particle imaging (MPI) to quantify artificial stenoses in vessel phantoms in near real-time.

METHODS

Custom-made stenosis phantoms with different degrees of stenosis (0%, 25%, 50%, 75%, and 100%; length 40 mm, inner diameter 8 mm, Polyoxymethylene) were filled with diluted Ferucarbotran (superparamagnetic iron-oxide nanoparticle (SPION) tracer agent, 500 mmol (Fe)/l). A traveling wave MPI scanner (spatial resolution ~ 2 mm, gradient strength ~ 1.5 T/m, field of view: 65 mm length and 29 mm diameter, frequencies f₁ = 1050 Hz and f₂ = 12150 Hz) was used to acquire images of the phantoms (200 ms total acquisition time per image, 10 averages). Standardized grey scaling was used for comparability. All measured stenoses (n = 80) were graded manually using a dedicated software tool.

RESULTS

MPI allowed for accurate visualization of stenoses at a frame rate of 5frames per second. Less severe stenoses were detected more precisely than higher-grade stenoses and came with smaller standard deviations. In particular, the 0%, 25%, 50%, 75%, and 100% stenosis phantom were measured as 3.7 ± 2.7% (mean ± standarddeviation), 18.6 ± 1.8%, 52.8 ± 3.7%, 77.8 ± 14.8% and 100 ± 0%. Geometrical distortions occurred around the center of the high-grade stenosis and led to higher standard deviations compared to lower grade stenoses. In the frame of this study the MPI signal depended linearly on the SPION concentration down to 0.05 mmol (Fe)/l.

CONCLUSION

Near real-time MPI accurately visualized and quantified different stenosis grades in vascular phantoms.

In vivo magnetic nanoparticle hyperthermia: a review on preclinical studies, low-field nano-heaters, noninvasive thermometry and computer simulations for treatment planning

Magnetic nanoparticle hyperthermia (MNH) is a promising nanotechnology-based cancer thermal therapy that has been approved for clinical use, together with radiation therapy, for treating brain tumors. Almost ten years after approval, few new clinical applications had appeared, perhaps because it cannot benefit from the gold standard noninvasive MRI thermometry technique, since static magnetic fields inhibit heat generation. This might limit its clinical use, in particular as a single therapeutic modality. In this article, we review the in vivo MNH preclinical studies, discussing results of the last two decades with emphasis on safety as a clinical criteria, the need for low-field nano-heaters and noninvasive thermal dosimetry, and the state of the art of computational modeling for treatment planning using MNH. Limitations to more effective clinical use are discussed, together with suggestions for future directions, such as the development of ultrasound-based, computed tomography-based or magnetic nanoparticle-based thermometry to achieve greater impact on clinical translation of MNH.

Temperature Sensitivity of Magnetic Nanoparticle Hyperthermia Using IR Thermography

Magnetite nanoparticles are extensively studied for their applications in magnetic nanoparticle hyperthermia. However, existing methods involve invasive methods for monitoring the thermal profile while the heat generated by the magnetite nanoparticles is utilized for cancer therapy. Tumor diagnosis utilizing thermography for monitoring the thermal profile is in the early stage of development since the temperature sensitivity is influenced by various experimental factors. Magnetite nanoparticles embedded in agar matrix which mimics the human tissues and their heating characteristics were investigated using infrared thermography. The magnetite nanoparticles with an average particle size of 10[Formula: see text]nm were subjected to heating in an applied frequency of 500[Formula: see text]kHz. The influence of concentration, area and depth on the heating characteristics of the tumor phantoms were deduced from the thermography images. The parameters that influence the therapeutical sensitivity while using infrared thermography for magnetic nanoparticle hyperthermia, have been studied for potential applications in theranostics.

The impact of data selection and fitting on SAR estimation for magnetic nanoparticle heating

BACKGROUND

Magnetic fluid heating has great potential in the fields of thermal medicine and cryopreservation. However, variations among experimental parameters, analysis methods and experimental uncertainty make quantitative comparisons of results among laboratories difficult. Herein, we focus on the impact of calculating the specific absorption rate (SAR) using Time-Rise and Box-Lucas fitting. Time-Rise assumes adiabatic conditions, which is experimentally unachievable, but can be reasonably assumed (quasi-adiabatic) only for specific and limited evaluation times when heat loss is negligible compared to measured heating rate. Box-Lucas, on the other hand, accounts for heat losses but requires longer heating.

METHODS

Through retrospective analysis of data obtained from two laboratories, we demonstrate measurement time is a critical parameter to consider when calculating SAR. Volumetric SAR were calculated using the two methods and compared across multiple iron-oxide nanoparticles.

RESULTS

We observed the lowest volumetric SAR variation from both fitting methods between 1-10 W/mL, indicating an ideal SAR range for heating measurements. Furthermore, our analysis demonstrates that poorly chosen fitting method can generate reproducible but inaccurate SAR.

CONCLUSION

We provide recommendations to select measurement time for data analysis with either Modified Time-Rise or Box-Lucas method, and suggestions to enhance experimental precision and accuracy when conducting heating experiments.

Shell-mediated control of surface chemistry of highly stoichiometric magnetite nanoparticles

Magnetite (Fe3O4) nanoparticles are one of the most studied nanomaterials for different nanotechnological and biomedical applications. However, Fe3O4 nanomaterials gradually oxidize to maghemite (γ-Fe2O3) under conventional environmental conditions leading to changes in their functional properties that determine their performance in many applications. Here we propose a novel strategy to control the surface chemistry of monodisperse 12 nm magnetite nanoparticles by means of a 3 nm-thick Zn-ferrite epitaxial coating in core/shell nanostructures. We have carried out a combined Mössbauer spectroscopy, dc magnetometry, X-ray photoelectron spectroscopy and spatially resolved electron energy loss spectroscopy study on iron oxide and Fe3O4/Zn0.6Fe2.4O4 core/shell nanoparticles aged under ambient conditions for 6 months. Our results reveal that while the aged iron oxide nanoparticles consist of a mixture of γ-Fe2O3 and Fe3O4, the Zn-ferrite-coating preserves a highly stoichiometric Fe3O4 core. Therefore, the aged core/shell nanoparticles present a sharp Verwey transition, an increased saturation magnetization and the possibility of tuning the effective anisotropy through exchange-coupling at the core/shell interface. The inhibition of the oxidation of the Fe3O4 cores can be accounted for in terms of the chemical nature of the shell layer and an epitaxial crystal symmetry matching between the core and the shell.

Energy Conversion and Biocompatibility of Surface Functionalized Magnetite Nanoparticles with Phosphonic Moieties

Magnetite nanoparticles (MNPs) were synthesized using two distinctly different approaches, co-precipitation (CP) and thermal decomposition (TD), and further surface functionalized with organophosphonic ligands containing different numbers of phosphonic groups. We have shown that it is possible to fabricate flower-like assemblies of MNPs through TD at lower temperatures, whereas CP MNPs formed agglomerates of particles with broad size distribution and irregular shapes. The effect of the organophosphonic ligands on the heating efficiency of the TD and CP MNPs under dual mode stimulation (simultaneous action of AMF and NIR laser radiation) was studied for the first time. It was found that in the case of the cost-effective CP MNP synthesis surface functionalization with chosen phosphonic ligands leads to higher heating efficiency upon laser stimulation, whereas better performance of TD MNPs was found under the action of AMF due to the significant difference of nanoparticle properties. The biocompatibility of surface functionalized MNPs with organophosphonic ligands was evaluated through thorough studies of the metabolic activity of MNPs in normal human foreskin fibroblasts as well as oxidative stress induction and oxidation stress response which has not been previously reported for most of the organophosphonic moieties used in this study.

Radiobiological Implications of Nanoparticles Following Radiation Treatment

Materials with a high atomic number (Z) are shown to cause an increase in the level of cell kill by ionizing radiation when introduced into tumor cells. This study uses in vitro experiments to investigate the differences in radiosensitization between two cell lines (MCF-7 and U87) and three commercially available nanoparticles (gold, gadolinium, and iron oxide) irradiated by 6 MV X-rays. To assess cell survival, clonogenic assays are carried out for all variables considered, with a concentration of 0.5 mg mL-1 for each nanoparticle material used. This study demonstrates differences in cell survival between nanoparticles and cell line. U87 shows the greatest enhancement with gadolinium nanoparticles (2.02 ± 0.36), whereas MCF-7 cells have higher enhancement with gold nanoparticles (1.74 ± 0.08). Mass spectrometry, however, shows highest elemental uptake with iron oxide and U87 cells with 4.95 ± 0.82 pg of iron oxide per cell. A complex relationship between cellular elemental uptake is demonstrated, highlighting an inverse correlation with the enhancement, but a positive relation with DNA damage when comparing the same nanoparticle between the two cell lines.

Heat Generation in Single Magnetic Nanoparticles under Near-Infrared Irradiation

Heat generation by pointlike structures is an appealing concept for its implications in nanotechnology and biomedicine. The way to pump energy that excites heat locally and the synthesis of nanostructures that absorb such energy are key issues in this endeavor. High-frequency alternating magnetic or near-infrared optical fields are used to induce heat in iron oxide nanoparticles, a combined solution that is being exploited in hyperthermia treatments. However, the temperature determination around a single iron oxide nanoparticle remains a challenge. We study the heat released from iron oxide nanostructures under near-infrared illumination on a one-by-one basis by optical tweezers. To measure the temperature, we follow the medium viscosity changes around the trapped particle as a function of the illuminating power, thus avoiding the use of thermal probes. Our results help interpret temperature, a statistical parameter, in the nanoscale and the concept of heat production by nanoparticles under thermal agitation.

Iron Nanoparticles for Low-Power Local Magnetic Hyperthermia in Combination with Immune Checkpoint Blockade for Systemic Antitumor Therapy

Magnetic hyperthermia (MHT) utilizing heat generated by magnetic nanoparticles under alternating magnetic field (AMF) is an effective local tumor ablation method but can hardly treat metastatic tumors. In this work, we discover that pure iron nanoparticles (FeNPs) with high magnetic saturation intensity after being modified by biocompatible polymers are stable in aqueous solution and could be employed as a supereffective MHT agent to generate sufficient heating under a low-power AFM. Effective MHT ablation of tumors is then achieved, using either locally injected FeNPs or intravenously injected FeNPs with the help of locally applied tumor-focused constant magnetic field to enhance the tumor accumulation of those nanoparticles. We further demonstrate that the combination of FeNP-based MHT with local injection of nanoadjuvant and systemic injection of anticytotoxic T-lymphocyte antigen-4 (anti-CTLA4) checkpoint blockade would result in systemic therapeutic responses to inhibit tumor metastasis. A robust immune memory effect to prevent tumor recurrence is also observed after the combined MHT-immunotherapy. This work not only highlights that FeNPs with appropriate surface modification could act as a supereffective MHT agent but also presents the great promises of combining MHT with immunotherapy to achieve long-lasting systemic therapeutic outcome after local treatment.

Combining Bulk Temperature and Nanoheating Enables Advanced Magnetic Fluid Hyperthermia Efficacy on Pancreatic Tumor Cells

Many efforts are made worldwide to establish magnetic fluid hyperthermia (MFH) as a treatment for organ-confined tumors. However, translation to clinical application hardly succeeds as it still lacks of understanding the mechanisms determining MFH cytotoxic effects. Here, we investigate the intracellular MFH efficacy with respect to different parameters and assess the intracellular cytotoxic effects in detail. For this, MiaPaCa-2 human pancreatic tumor cells and L929 murine fibroblasts were loaded with iron-oxide magnetic nanoparticles (MNP) and exposed to MFH for either 30 min or 90 min. The resulting cytotoxic effects were assessed via clonogenic assay. Our results demonstrate that cell damage depends not only on the obvious parameters bulk temperature and duration of treatment, but most importantly on cell type and thermal energy deposited per cell during MFH treatment. Tumor cell death of 95% was achieved by depositing an intracellular total thermal energy with about 50% margin to damage of healthy cells. This is attributed to combined intracellular nanoheating and extracellular bulk heating. Tumor cell damage of up to 86% was observed for MFH treatment without perceptible bulk temperature rise. Effective heating decreased by up to 65% after MNP were internalized inside cells.

Specific T cell induction using iron oxide based nanoparticles as subunit vaccine adjuvant

Metal-based nanoparticles (NPs) stimulate innate immunity; however, they have never been demonstrated to be capable of aiding the generation of specific cellular immune responses. Therefore, our objective was to evaluate whether iron oxide-based NPs have adjuvant properties in generating cellular Th1, Th17 and TCD8 (Tc1) immune responses. For this purpose, a fusion protein (CMX) composed of Mycobacterium tuberculosis antigens was used as a subunit vaccine. Citrate-coated MnFe₂O₄ NPs were synthesized by co-precipitation and evaluated by transmission electron microscopy. The vaccine was formulated by homogenizing NPs with the recombinant protein, and protein corona formation was determined by dynamic light scattering and field-emission scanning electron microscopy. The vaccine was evaluated for the best immunization route and strategy using subcutaneous and intranasal routes with 21-day intervals between immunizations. When administered subcutaneously, the vaccine generated specific CD4⁺IFN-γ⁺ (Th1) and CD8⁺IFN-γ⁺ responses. Intranasal vaccination induced specific Th1, Th17 (CD4⁺IL-17⁺) and Tc1 responses, mainly in the lungs. Finally, a mixed vaccination strategy (2 subcutaneous injections followed by one intranasal vaccination) induced a Th1 (in the spleen and lungs) and splenic Tc1 response but was not capable of inducing a Th17 response in the lungs. This study shows for the first time a subunit vaccine with iron oxide based NPs as an adjuvant that generated cellular immune responses (Th1, Th17 and TCD8), thereby exhibiting good adjuvant qualities. Additionally, the immune response generated by the subcutaneous administration of the vaccine diminished the bacterial load of Mtb challenged animals, showing the potential for further improvement as a vaccine against tuberculosis.