Ever-Evolving Identity of Magnetic Nanoparticles within Human Cells: The Interplay of Endosomal Confinement, Degradation, Storage, and Neocrystallization

Biotransformation and biological fate of magnetic iron oxide nanoparticles for biomedical research and clinical applications

Safe implementation of nanotechnology-based products in biomedical applications necessitates an extensive understanding of the (bio)transformations that nanoparticles undergo in living organisms. The long-term fate in the body is a crucial consideration because it governs potential risks for human health. To accurately predict the life cycle of nanoparticles, their fate after administration into the body-including their (bio)transformations, persistence, and biodegradation-needs to be thoroughly evaluated. Magnetic iron oxide nanoparticles (MIONPs) can enter the body through various routes, including inhalation, ingestion, dermal absorption, and injection. Microscale and nanoscale studies are performed to observe nanomaterial biotransformations and their effect on clinically relevant properties. Researchers are utilizing high-resolution TEM for nanoscale monitoring of the nanoparticles while microscale follow-up approaches comprise quantification tools at the whole organism level and the molecular level. Nanoparticle-cell interactions, including cellular uptake and intracellular trafficking, are key to understanding nanoparticle accumulation in cells and organs. Prolonged accumulation may induce cell stress and nanoparticle toxicity, often mediated through oxidative stress and inflammation. In this review article, the journey of nanoparticles in the body is depicted and their biotransformations and final fate are discussed. Immunohistochemical techniques are particularly valuable in tracking nanoparticle distribution within tissues and assessing their impact at the cellular level. A thorough description of a wide range of characterization techniques is provided to unveil the fate and biotransformations of clinically relevant nanoparticles and to assist in their design for successful biomedical applications.

Biotransformation of iron oxide nanoparticles and their impact on biokinetics in rats following intratracheal instillation

Understanding the biokinetics of inhaled nanomaterials is essential for evaluating their potential adverse effects, yet current analytical methods may not account for biotransformation-where nanoparticles are transformed into new particle types. This study compared the biokinetics of partially soluble Fe2O3 and poorly soluble TiO2 to investigate how biotransformation influences lung clearance kinetics. Test nanoparticles (140 µg/rat) were instilled into the lungs of rats, and quantitative and qualitative assessments were performed on samples collected from the lungs on days 0, 1, 7, 14, 28, and 90 post-instillation. Notably, this study focused on the biokinetics of particulate forms within the lungs to specifically address particokinetics. Fe2O3 exhibited biphasic clearance kinetics, with rapid clearance in the early phase (days 0-14; half-life of 13 days) and slow clearance in the late phase (days 14-90; half-life 123 days). This biphasic pattern was attributed to the erosion of Fe2O3 into smaller, nanometer-sized particles, approximately 40 % of which persisted in the lungs for over 3 months. These retained particles showed reduced oxidative potential and were sequestered in ferritin protein, mitigating potential toxicity. In contrast, TiO2 exhibited a monophasic clearance pattern with a half-life of 88 days and did not exhibit particle degradation. These findings underscore the critical role of biotransformation in understanding the long-term safety and toxicity of inhaled nanomaterials, highlighting the need for comprehensive studies to assess their biological fate and potential risks. Further research should focus on potential adverse effects due to particle overload, interactions with biomolecules, and disruptions in metal homeostasis.

Gemcitabine and miRNA34a mimic codelivery with magnetic nanoparticles enhanced anti-tumor effect against pancreatic cancer

Pancreatic ductal adenocarcinoma is a highly aggressive cancer with a low survival rate. Thus, efforts are needed to develop more effective treatments. Herein, we propose utilizing magnetic nanoparticles (MNP) for the concurrent delivery of gemcitabine and miRNA34a mimic to target pancreatic cancer cells. The MNP were functionalized with disulfide bonds to selectively release their cargo inside tumor cells. The incorporation of the miRNA34a mimic increased the sensitivity of cells to gemcitabine, especially in BxPC-3 cells. Additionally, the miRNA34a sequence was modified with locked nucleic acids (LNA) to increase stability. The resulting LNA34a showed a stronger cytotoxic effect when combined with gemcitabine, even in PANC-1 cells, which are resistant to the drug. Notably, the modified MNP exhibited less toxicity than their free counterparts when incubated with HaCaT cells, a model of healthy keratinocytes. Additionally, the combined delivery of miRNA34a mimics and gemcitabine using MNP elicited a synergistic cytotoxic effect against pancreatic cancer cells through magnetic hyperthermia. The intratumoral administration of the modified MNP in subcutaneous xenografts of BxPC-3 cells resulted in a sustained increase in temperature when an alternating magnetic field was applied. Notably, the treatment with the MNP functionalized with GEM and LNA34a led to significant changes in the expression of NOTCH1 and NOTCH2 in the tumor, which are direct targets of miRNA34a, as well as HSP70, which is related to the cellular response to stressors like heat.

Multimodal Profiling of Iron Heterogeneity at the Nanoscale

Life is inherently heterogeneous, and visualizing this heterogeneity in the spatial distribution of biometals offers valuable insights into various biological processes. While biometal mapping provides superior spatial resolution compared to other bioanalytical techniques, it alone cannot fully explain the functional roles of biometals in health and disease. In this study, we introduced a novel method using specially designed sample grids to facilitate beam-, X-ray-, and ion-beam-based imaging of biometals on the same tissue section. This innovative approach aligns and integrates nanoscale-resolved iron profiles across spatial, chemical, and isotopic dimensions. By combining these analyses, we achieved unprecedented spatial resolution and detail, revealing the complex regulatory framework of iron homeostasis in liver tissues following iron overload. These findings demonstrate that enhancing both the information content and spatial resolution of biometal analysis can overcome current limitations, providing new insights into the molecular mechanisms underlying biometal functions.

Harnessing stimuli-responsive biomaterials for advanced biomedical applications

Cell behavior is intricately intertwined with the in vivo microenvironment and endogenous pathways. The ability to guide cellular behavior toward specific goals can be achieved by external stimuli, notably electricity, light, ultrasound, and magnetism, simultaneously harnessed through biomaterial-mediated responses. These external triggers become focal points within the body due to interactions with biomaterials, facilitating a range of cellular pathways: electrical signal transmission, biochemical cues, drug release, cell loading, and modulation of mechanical stress. Stimulus-responsive biomaterials hold immense potential in biomedical research, establishing themselves as a pivotal focal point in interdisciplinary pursuits. This comprehensive review systematically elucidates prevalent physical stimuli and their corresponding biomaterial response mechanisms. Moreover, it delves deeply into the application of biomaterials within the domain of biomedicine. A balanced assessment of distinct physical stimulation techniques is provided, along with a discussion of their merits and limitations. The review aims to shed light on the future trajectory of physical stimulus-responsive biomaterials in disease treatment and outline their application prospects and potential for future development. This review is poised to spark novel concepts for advancing intelligent, stimulus-responsive biomaterials.

Substrate softness increases magnetic microdiscs-induced cytotoxicity

Cytotoxicity of nanoparticles is primarily assessed on cells grown in plastic culture plates, a mechanical environment that is a million times stiffer than most of the human tissues. Here we question whether nanoparticles cytotoxicity is sensitive to the stiffness of the extracellular environment. To this end, we compare the metabolic activity, the proliferation and death rates, and the motility of a glioblastoma cancer cell line and a fibroblast cell line exposed to gold-coated Ni80Fe20 microdiscs when grown on a glass substrate or on a soft substrate whose mechanical properties are close to physiology. Our main result is that cells grown on soft substrates take up more microdiscs which results in greater toxic effects, but also that toxicity at similar particle load is more pronounced on soft substrates especially at large concentration of nanoparticles. These results suggest that both microdiscs uptake and their intracellular processing differ between soft and rigid substrates.

The preparation methods and types of cell sheets engineering

Cell therapy has emerged as a viable approach for treating damaged organs or tissues, particularly with advancements in stem cell research and regenerative medicine. The innovative technique of cell sheet engineering offers the potential to create a cell-dense lamellar structure that preserves the extracellular matrix (ECM) secreted by cells, along with the cell-matrix and intercellular junctions formed during in vitro cultivation. In recent years, significant progress has been made in developing cell sheet engineering technology. A variety of novel materials and methods were utilized for enzyme-free cell detachment during the cell sheet formation process. The complexity of cell sheet structures increased to meet advanced usage demands. This review aims to provide an overview of the preparation methods and types of cell sheets, thereby enhancing the understanding of this rapidly evolving technology and offering a fresh perspective on the development and future application of cell sheet engineering.

Biomaterials functionalized with magnetic nanoparticles for tissue engineering: Between advantages and challenges

The integration of magnetic nanoparticles (MNPs) into biomaterials offers exciting opportunities for tissue engineering as they enable better control over cell guidance, release of bioactive factors and tissue maturation. Despite their potential, challenges such as the heterogeneity of MNPs, their cytotoxicity and the need for precise control of MNP`s properties hinder their widespread application. Overcoming these challenges will require new interdisciplinary efforts and technological advances, including the development of mathematical tools and additional elaborations to ensure the biocompatibility of MNPs.

Programming an Enhanced Uptake and the Intracellular Fate of Magnetic Microbeads

This study compares two kinds of magnetic microbeads with different surface features and cell entry pathways, aiming to provide insights into how to program their cell uptake and intracellular fate. It is found that a rougher surface enhances the cell uptake of the microbeads, regardless of whether they are pulled by a magnetic field gradient or adsorbed by the cell membrane. However, the entry route affects the intracellular localization of the microbeads: The magnetically dragged microbeads reach the cytoplasm, while the adsorbed microbeads stay in the late endosomes and lysosomes. This suggests that different strategies can be used to target different cellular compartments with magnetic microbeads. Moreover, it is demonstrated that the cells containing the microbeads can be moved and regrown at specific locations by applying a magnetic field gradient, showing the potential of these magnetic microbeads for cell delivery and manipulation.

Emergence of magnetic nanoparticles in photothermal and ferroptotic therapies

With their distinctive physicochemical features, nanoparticles have gained recognition as effective multifunctional tools for biomedical applications, with designs and compositions tailored for specific uses. Notably, magnetic nanoparticles stand out as first-in-class examples of multiple modalities provided by the iron-based composition. They have long been exploited as contrast agents for magnetic resonance imaging (MRI) or as anti-cancer agents generating therapeutic hyperthermia through high-frequency magnetic field application, known as magnetic hyperthermia (MHT). This review focuses on two more recent applications in oncology using iron-based nanomaterials: photothermal therapy (PTT) and ferroptosis. In PTT, the iron oxide core responds to a near-infrared (NIR) excitation and generates heat in its surrounding area, rivaling the efficiency of plasmonic gold-standard nanoparticles. This opens up the possibility of a dual MHT + PTT approach using a single nanomaterial. Moreover, the iron composition of magnetic nanoparticles can be harnessed as a chemotherapeutic asset. Degradation in the intracellular environment triggers the release of iron ions, which can stimulate the production of reactive oxygen species (ROS) and induce cancer cell death through ferroptosis. Consequently, this review emphasizes these emerging physical and chemical approaches for anti-cancer therapy facilitated by magnetic nanoparticles, combining all-in-one functionalities.

Magnetic-Based Strategies for Regenerative Medicine and Tissue Engineering

The fabrication of biological substitutes to repair, replace, or enhance tissue- and organ-level functions is a long-sought goal of tissue engineering (TE). However, the clinical translation of TE is hindered by several challenges, including the lack of suitable mechanical, chemical, and biological properties in one biomaterial, and the inability to generate large, vascularized tissues with a complex structure of native tissues. Over the past decade, a new generation of "smart" materials has revolutionized the conventional medical field, transforming TE into a more accurate and sophisticated concept. At the vanguard of scientific development, magnetic nanoparticles (MNPs) have garnered extensive attention owing to their significant potential in various biomedical applications owing to their inherent properties such as biocompatibility and rapid remote response to magnetic fields. Therefore, to develop functional tissue replacements, magnetic force-based TE (Mag-TE) has emerged as an alternative to conventional TE strategies, allowing for the fabrication and real-time monitoring of tissues engineered in vitro. This review addresses the recent studies on the use of MNPs for TE, emphasizing the in vitro, in vivo, and clinical applications. Future perspectives of Mag-TE in the fields of TE and regenerative medicine are also discussed.

Photothermia at the nanoscale induces ferroptosis via nanoparticle degradation

The Fe(II)-induced ferroptotic cell death pathway is an asset in cancer therapy, yet it calls into question the biocompatibility of magnetic nanoparticles. In the latter, Fe(II) is sequestered within the crystal structure and is released only upon nanoparticle degradation, a transition that is not well understood. Here, we dissect the chemical environment necessary for nanoparticle degradation and subsequent Fe(II) release. Importantly, temperature acts as an accelerator of the process and can be triggered remotely by laser-mediated photothermal conversion, as evidenced by the loss of the nanoparticles' magnetic fingerprint. Remarkably, the local hot-spot temperature generated at the nanoscale can be measured in operando, in the vicinity of each nanoparticle, by comparing the photothermal-induced nanoparticle degradation patterns with those of global heating. Further, remote photothermal irradiation accelerates degradation inside cancer cells in a tumor spheroid model, with efficiency correlating with the endocytosis progression state of the nanoparticles. High-throughput imaging quantification of Fe2+ release, ROS generation, lipid peroxidation and cell death at the spheroid level confirm the synergistic thermo-ferroptotic therapy due to the photothermal degradation at the nanoparticle level.

The role of tumor model in magnetic targeting of magnetosomes and ultramagnetic liposomes

The combined passive and active targeting of tumoral tissue remains an active and relevant cancer research field. Here, we exploit the properties of two highly magnetic nanomaterials, magnetosomes and ultramagnetic liposomes, in order to magnetically target prostate adenocarcinoma tumors, implanted orthotopically or subcutaneously, to take into account the role of tumor vascularization in the targeting efficiency. Analysis of organ biodistribution in vivo revealed that, for all conditions, both nanomaterials accumulate mostly in the liver and spleen, with an overall low tumor retention. However, both nanomaterials were more readily identified in orthotopic tumors, reflecting their higher tumor vascularization. Additionally, a 2- and 3-fold increase in nanomaterial accumulation was achieved with magnetic targeting. In summary, ultramagnetic nanomaterials show promise mostly in the targeting of highly-vascularized orthotopic murine tumor models.

Influence of magnetic nanoparticle biotransformation on contrasting efficiency and iron metabolism

Magnetic nanoparticles are widely used in biomedicine for MRI imaging and anemia treatment. The aging of these nanomaterials in vivo may lead to gradual diminishing of their contrast properties and inducing toxicity. Here, we describe observation of the full lifecycle of 40-nm magnetic particles from their injection to the complete degradation in vivo and associated impact on the organism. We found that in 2 h the nanoparticles were eliminated from the bloodstream, but their initial biodistribution changed over time. In 1 week, a major part of the nanoparticles was transferred to the liver and spleen, where they degraded with a half-life of 21 days. MRI and a magnetic spectral approach revealed preservation of contrast in these organs for more than 1 month. The particle degradation led to the increased number of red blood cells and blood hemoglobin level due to released iron without causing any toxicity in tissues. We also observed an increase in gene expression level of Fe-associated proteins such as transferrin, DMT1, and ferroportin in the liver in response to the iron particle degradation. A deeper understanding of the organism response to the particle degradation can bring new directions to the field of MRI contrast agent design.

In Vivo Cellular Magnetic Imaging: Labeled vs. Unlabeled Cells

Superparamagnetic iron oxide (SPIO)-labeling of cells has been applied for magnetic resonance imaging (MRI) cell tracking for over 30 years, having resulted in a dozen or so clinical trials. SPIO nanoparticles are biodegradable and can be broken down into elemental iron, and hence the tolerance of cells to magnetic labeling has been overall high. Over the years, however, single reports have accumulated demonstrating that the proliferation, migration, adhesion and differentiation of magnetically labeled cells may differ from unlabeled cells, with inhibition of chondrocytic differentiation of labeled human mesenchymal stem cells (hMSCs) as a notable example. This historical perspective provides an overview of some of the drawbacks that can be encountered with magnetic labeling. Now that magnetic particle imaging (MPI) cell tracking is emerging as a new in vivo cellular imaging modality, there has been a renaissance in the formulation of SPIO nanoparticles this time optimized for MPI. Lessons learned from the occasional past pitfalls encountered with SPIO-labeling of cells for MRI may expedite possible future clinical translation of (combined) MRI/MPI cell tracking.

Remote Magnetic Microengineering and Alignment of Spheroids into 3D Cellular Fibers

Developing in vitro models that recapitulate the in vivo organization of living cells in a 3D microenvironment is one of the current challenges in the field of tissue engineering. In particular for anisotropic tissues where alignment of precursor cells is required for them to create functional structures. Herein, a new method is proposed that allows aligning in the direction of a uniform magnetic field both individual cells (muscle, stromal, and stem cells) or spheroids in a thermoresponsive collagen hydrogel. In an all‐in‐one approach, spheroids are generated at high throughput by magnetic engineering using microfabricated micromagnets and are used as building blocks to create 3D anisotropic tissue structures of different scales. The magnetic cells and spheroids alignment process is optimized in terms of magnetic cell labeling, concentration, and size. Anisotropic structures are induced to form fibers in the direction of the magnetic alignment, with the respective roles of the magnetic field, the mechanical stretching of hydrogel or co‐culture of the aligned cells with non‐magnetic stromal cells, being investigated. Over days, spheroids fuse into 3D tubular structures, oriented in the direction of the magnetic alignment. Moreover, in the case of the muscle cells model, multinucleated cells can be observed within the fibers.

Emerging Magnetic Fabrication Technologies Provide Controllable Hierarchically-Structured Biomaterials and Stimulus Response for Biomedical Applications

Multifunctional nanocomposites which exhibit well-defined physical properties and encode spatiotemporally-controlled responses are emerging as components for advanced responsive systems. For biomedical applications magnetic nanocomposite materials have attracted significant attention due to their ability to respond to spatially and temporally varying magnetic fields. The current state-of-the-art in development and fabrication of magnetic hydrogels toward biomedical applications is described. There is accelerating progress in the field due to advances in manufacturing capabilities. Three categories can be identified: i) Magnetic hydrogelation, DC magnetic fields are used during solidification/gelation for aligning particles; ii) additive manufacturing of magnetic materials, 3D printing technologies are used to develop spatially-encoded magnetic properties, and more recently; iii) magnetic additive manufacturing, magnetic responses are applied during the printing process to develop increasingly complex structural arrangement that may recapitulate anisotropic tissue structure and function. The magnetic responsiveness of conventionally and additively manufactured magnetic hydrogels are described along with recent advances in soft magnetic robotics, and the categorization is related to final architecture and emergent properties. Future challenges and opportunities, including the anticipated role of combinatorial approaches in developing 4D-responsive functional materials for tackling long-standing problems in biomedicine including production of 3D-specified responsive cell scaffolds are discussed.

Bacterial Magnetosomes Release Iron Ions and Induce Regulation of Iron Homeostasis in Endothelial Cells

Magnetosomes (MAGs) extracted from magnetotactic bacteria are well-defined membrane-enveloped single-domain magnetic nanoparticles. Due to their superior magnetic and structural properties, MAGs constitute potential materials that can be manipulated via genetic and chemical engineering for use in biomedical and biotechnological applications. However, the long-term effects exerted by MAGs on cells are of concern in the context of in vivo applications. Meanwhile, it remains relatively unclear which mechanisms are employed by cells to process and degrade MAGs. Hence, a better understanding of MAGs' degradation and fundamental signal modulations occurring throughout this process is essential. In the current study, we investigated the potential actions of MAGs on endothelial cells over a 10-day period. MAGs were retained in cells and found to gradually gather in the lysosome-like vesicles. Meanwhile, iron-ion release was observed. Proteomics further revealed a potential cellular mechanism underlying MAGs degradation, in which a group of proteins associated with vesicle biogenesis, and lysosomal enzymes, which participate in protein hydrolysis and lipid degradation, were rapidly upregulated. Moreover, the released iron triggered the regulation of the iron metabolic profiles. However, given that the levels of cell oxidative damage were relatively stable, the released iron ions were handled by iron metabolic profiles and incorporated into normal metabolic routes. These results provide insights into the cell response to MAGs degradation that may improve their in vivo applications.

Optomagnetic nanofluids for controlled brain hyperthermia: a critical study

Optomagnetic nanofluids (OMNFs) are colloidal dispersions of nanoparticles (NPs) with combined magnetic and optical properties. They are especially appealing in biomedicine since they can be used as minimally invasive platforms for controlled hyperthermia treatment of otherwise difficultly accessible tumors such as intracranial ones. On the one hand, magnetic NPs act as heating mediators when subjected to alternating magnetic fields or light irradiation. On the other hand, suitably tailored luminescent NPs can provide a precise and remote thermal readout in real time. The combination of heating and thermometric properties allows, in principle, to precisely monitor the increase in the temperature of brain tumors up to the therapeutic level, without causing undesired collateral damage. In this work we demonstrate that this view is an oversimplification since it ignores the presence of relevant interactions between magnetic (γ-Fe₂O₃ nanoflowers) and luminescent nanoparticles (Ag₂S NPs) that result in a detrimental alteration of their physicochemical properties. The magnitude of such interactions depends on the interparticle distance and on the surface properties of nanoparticles. Experiments performed in mouse brains (phantoms and ex vivo) revealed that OMNFs cannot induce relevant heating under alternating magnetic fields and fail to provide reliable temperature reading. In contrast, we demonstrate that the use of luminescent nanofluids (containing only Ag₂S NPs acting as both photothermal agents and nanothermometers) stands out as a better alternative for thermally monitored hyperthermia treatment of brain tumors in small animal models.

Proteomics unite traditional toxicological assessment methods to evaluate the toxicity of iron oxide nanoparticles

Iron oxide nanoparticles (IONPs) are the first generation of nanomaterials approved by the Food and Drug Administration for use as imaging agents and for the treatment of iron deficiency in chronic kidney disease. However, several IONPs-based imaging agents have been withdrawn because of toxic effects and the poor understanding of the underlying mechanisms. This study aimed to evaluate IONPs toxicity and to elucidate the underlying mechanism after intravenous administration in rats. Seven-week-old rats were intravenously administered IONPs at doses of 0, 10, 30, and 90 mg/kg body weight for 14 consecutive days. Toxicity and molecular perturbations were evaluated using traditional toxicological assessment methods and proteomics approaches, respectively. The administration of 90 mg/kg IONPs induced mild toxic effects, including abnormal clinical signs, lower body weight gain, changes in serum biochemical and hematological parameters, and increased organ coefficients in the spleen, liver, heart, and kidneys. Toxicokinetics, tissue distribution, histopathological, and transmission electron microscopy analyses revealed that the spleen was the primary organ for IONPs elimination from the systemic circulation and that the macrophage lysosomes were the main organelles of IONPs accumulation after intravenous administration. We identified 197 upregulated and 75 downregulated proteins in the spleen following IONPs administration by proteomics. Mechanically, the AKT/mTOR/TFEB signaling pathway facilitated autophagy and lysosomal activation in splenic macrophages. This is the first study to elucidate the mechanism of IONPs toxicity by combining proteomics with traditional methods for toxicity assessment.

Quantitative Comparison of the Light-to-Heat Conversion Efficiency in Nanomaterials Suitable for Photothermal Therapy

Functional colloidal nanoparticles capable of converting between various energy types are finding an increasing number of applications. One of the relevant examples concerns light-to-heat-converting colloidal nanoparticles that may be useful for localized photothermal therapy of cancers. Unfortunately, quantitative comparison and ranking of nanoheaters are not straightforward as materials of different compositions and structures have different photophysical and chemical properties and may interact differently with the biological environment. In terms of photophysical properties, the most relevant information to rank these nanoheaters is the light-to-heat conversion efficiency, which, along with information on the absorption capacity of the material, can be used to directly compare materials. In this work, we evaluate the light-to-heat conversion properties of 17 different nanoheaters belonging to different groups (plasmonic, semiconductor, lanthanide-doped nanocrystals, carbon nanocrystals, and metal oxides). We conclude that the light-to-heat conversion efficiency alone is not meaningful enough as many materials have similar conversion efficiencies─in the range of 80-99%─while they significantly differ in their extinction coefficient. We therefore constructed their qualitative ranking based on the external conversion efficiency, which takes into account the conventionally defined light-to-heat conversion efficiency and its absorption capacity. This ranking demonstrated the differences between the samples more meaningfully. Among the studied systems, the top-ranking materials were black porous silicon and CuS nanocrystals. These results allow us to select the most favorable materials for photo-based theranostics and set a new standard in the characterization of nanoheaters.

Laser Synthesized Core-Satellite Fe-Au Nanoparticles for Multimodal In Vivo Imaging and In Vitro Photothermal Therapy

Hybrid multimodal nanoparticles, applicable simultaneously to the noninvasive imaging and therapeutic treatment, are highly demanded for clinical use. Here, Fe-Au core-satellite nanoparticles prepared by the method of pulsed laser ablation in liquids were evaluated as dual magnetic resonance imaging (MRI) and computed tomography (CT) contrast agents and as sensitizers for laser-induced hyperthermia of cancer cells. The biocompatibility of Fe-Au nanoparticles was improved by coating with polyacrylic acid, which provided excellent colloidal stability of nanoparticles with highly negative ζ-potential in water (−38 ± 7 mV) and retained hydrodynamic size (88 ± 20 nm) in a physiological environment. The ferromagnetic iron cores offered great contrast in MRI images with r₂ = 11.8 ± 0.8 mM⁻¹ s⁻¹ (at 1 T), while Au satellites showed X-ray attenuation in CT. The intravenous injection of nanoparticles enabled clear tumor border visualization in mice. Plasmonic peak in the Fe-Au hybrids had a tail in the near-infrared region (NIR), allowing them to cause hyperthermia under 808 nm laser exposure. Under NIR irradiation Fe-Au particles provided 24.1 °C/W heating and an IC₅₀ value below 32 µg/mL for three different cancer cell lines. Taken together, these results show that laser synthesized Fe-Au core-satellite nanoparticles are excellent theranostic agents with multimodal imaging and photothermal capabilities.

Vitrification and Rewarming of Magnetic Nanoparticle-Loaded Rat Hearts

To extend the preservation of donor hearts beyond the current 4-6 h, this paper explores heart cryopreservation by vitrification-cryogenic storage in a glass-like state. While organ vitrification is made possible by using cryoprotective agents (CPA) that inhibit ice during cooling, failure occurs during convective rewarming due to slow and non-uniform rewarming which causes ice crystallization and/or cracking. Here an alternative, "nanowarming", which uses silica-coated iron oxide nanoparticles (sIONPs) perfusion loaded through the vasculature is explored, that allows a radiofrequency coil to rewarm the organ quickly and uniformly to avoid convective failures. Nanowarming has been applied to cells and tissues, and a proof of principle study suggests it is possible in the heart, but proper physical and biological characterization especially in organs is still lacking. Here, using a rat heart model, controlled machine perfusion loading and unloading of CPA and sIONPs, cooling to a vitrified state, and fast and uniform nanowarming without crystallization or cracking is demonstrated. Further, nanowarmed hearts maintain histologic appearance and endothelial integrity superior to convective rewarming and indistinguishable from CPA load/unload control hearts while showing some promising organ-level (electrical) functional activity. This work demonstrates physically successful heart vitrification and nanowarming and that biological outcomes can be expected to improve by reducing or eliminating CPA toxicity during loading and unloading.

Small-angle X-ray scattering to quantify the incorporation and analyze the disposition of magnetic nanoparticles inside cells

Access to detailed information on cells loaded with nanoparticles with nanoscale precision is of a long-standing interest in many areas of nanomedicine. In this context, designing a single experiment able to provide statistical mean data from a large number of living unsectioned cells concerning information on the nanoparticle size and aggregation inside cell endosomes and accurate nanoparticle cell up-take is of paramount importance. Small-angle X-ray scattering (SAXS) is presented here as a tool to achieve such relevant data. Experiments were carried out in cultures of B16F0 murine melanoma and A549 human lung adenocarcinoma cell lines loaded with various iron oxide nanostructures displaying distinctive structural characteristics. Five systems of water-dispersible magnetic nanoparticles (MNP) of different size, polydispersity and morphology were analyzed, namely, nearly monodisperse MNP with 11 and 13 nm mean size coated with meso-2,3-dimercaptosuccinic acid, more polydisperse 6 nm colloids coated with citric acid and two nanoflowers (NF) systems of 24 and 27 nm in size resulting from the aggregation of 8 nm MNP. Up-take was determined for each system using B16F0 cells. Here we show that SAXS pattern provides high resolution information on nanoparticles disposition inside endosomes of the cytoplasm through the structure factor analysis, on nanoparticles size and dispersity after their incorporation by the cell and on up-take quantification from the extrapolation of the intensity in absolute scale to null scattering vector. We also report on the cell culture preparation to reach sensitivity for the observation of MNP inside cell endosomes using high brightness SAXS synchrotron source. Our results show that SAXS can become a valuable tool for analyzing MNP in cells and tissues.

In Vivo Assimilation of CuS, Iron Oxide and Iron Oxide@CuS Nanoparticles in Mice: A 6-Month Follow-Up Study

Nanoparticles (NPs) are at the leading edge of nanomedicine, and determining their biosafety remains a mandatory precondition for biomedical applications. Herein, we explore the bioassimilation of copper sulfide NPs reported as powerful photo-responsive anticancer therapeutic agents. The nanoparticles investigated present a hollow shell morphology, that can be left empty (CuS NPs) or be filled with an iron oxide flower-like core (iron oxide@CuS NPs), and are compared with the iron oxide nanoparticles only (iron oxide NPs). CuS, iron oxide@CuS and iron oxide NPs were injected in 6-week-old mice, at doses coherent with an antitumoral treatment. Cu and Fe were quantified in the liver, spleen, kidneys, and lungs over 6 months, including the control animals, thus providing endogenous Cu and Fe levels in the first months after animal birth. After intravenous NPs administration, 77.0 ± 3.9% of the mass of Cu injected, and 78.6 ± 3.8% of the mass of Fe, were detected in the liver. In the spleen, we found 3.3 ± 0.6% of the injected Cu and 3.8 ± 0.6% for the Fe. No negative impact was observed on organ weight, nor on Cu or Fe homeostasis in the long term. The mass of the two metals returned to the control values within three months, a result that was confirmed by transmission electron microscopy and histology images. This bioassimilation with no negative impact comforts the possible translation of these nanomaterials into clinical practice.

Magnetic Compression of Tumor Spheroids Increases Cell Proliferation In Vitro and Cancer Progression In Vivo

A growing tumor is submitted to ever-evolving mechanical stress. Endoscopic procedures add additional constraints. However, the impact of mechanical forces on cancer progression is still debated. Herein, a set of magnetic methods is proposed to form tumor spheroids and to subject them to remote deformation, mimicking stent-imposed compression. Upon application of a permanent magnet, the magnetic tumor spheroids (formed from colon cancer cells or from glioblastoma cells) are compressed by 50% of their initial diameters. Such significant deformation triggers an increase in the spheroid proliferation for both cell lines, correlated with an increase in the number of proliferating cells toward its center and associated with an overexpression of the matrix metalloproteinase-9 (MMP-9). In vivo peritoneal injection of the spheroids made from colon cancer cells confirmed the increased aggressiveness of the compressed spheroids, with almost a doubling of the peritoneal cancer index (PCI), as compared with non-stimulated spheroids. Moreover, liver metastasis of labeled cells was observed only in animals grafted with stimulated spheroids. Altogether, these results demonstrate that a large compression of tumor spheroids enhances cancer proliferation and metastatic process and could have implications in clinical procedures where tumor compression plays a role.

Assessing the parameters modulating optical losses of iron oxide nanoparticles under near infrared irradiation

Heating mediated by iron oxide nanoparticles subjected to near infrared irradiation has recently gained lots of interest. The high optical loss values reported in combination with the optical technologies already existing in current clinical practices, have made optical heating mediated by iron oxide nanoparticles an attractive choice for treating internal or skin tumors. However, the identification of the relevant parameters and the influence of methodologies for quantifying the optical losses released by iron oxide nanoparticles are not fully clear. Here, we report on a systematic study of different intrinsic (size, shape, crystallinity, and iron oxidation state) and extrinsic (aggregation, concentration, intracellular environment and irradiation conditions) parameters involved in the photothermal conversion of iron oxide nanoparticles under near infrared irradiation. We have probed the temperature increments to determine the specific loss power of iron oxide nanoparticles with different sizes and shapes dispersed in colloidal suspensions or inside live breast cancer cells. Our results underline the relevance of crystal surface defects, aggregation, concentration, magnetite abundance, excitation wavelength and density power on the modulation of the photothermal conversion. Contrary to plasmonic or magnetic losses, no significant influence of nanoparticle size nor shape was observed on the optical losses released by the studied iron oxide nanoparticles. Interestingly, no significant differences of measured temperature increments and specific loss power values were either observed when nanoparticles were inside live cells or in colloidal dispersion. Our findings highlight the advantages of optical heat losses released by iron oxide nanoparticles for therapeutic applications.

Magnetic Patterning of Tissue Spheroids Using Polymer Microcapsules Containing Iron Oxide Nanoparticles

Magnetic tissue engineering is one of the rapidly emerging and promising directions of tissue engineering and biofabrication where the magnetic field is employed as temporal removal support or scaffold. Iron oxide nanoparticles are used to label living cells and provide the desired magnetic properties. Recently, polymer microcapsules loaded with iron oxide nanoparticles have been proposed as a novel approach to designing magnetic materials with high local concentrations. These microcapsules can be readily internalized and retained intracellularly for a long time in various types of cells. The low cytotoxicity of these microcapsules was previously shown in 2D cell culture. This paper has demonstrated that cells containing these nontoxic nanomaterials can form viable 3D tissue spheroids for the first time. The spheroids retained labeled fluorescent microcapsules with magnetic nanoparticles without a detectable cytotoxic effect. The high concentration of packed nanoparticles inside the microcapsules enables the evident magnetic properties of the labeled spheroids to be maintained. Finally, magnetic spheroids can be effectively used for magnetic patterning and biofabrication of tissue-engineering constructs.

Bioinspired Virus-like Fe3O4/Au@C Nanovector for Programmable Drug Delivery via Hierarchical Targeting

Bioinspired strategies have recently emerged as novel approaches for designing a functionalized nanovector with enhanced tumor targeting and therapeutic efficacy. Herein, a virus-like Fe₃O₄/Au@C nanovector is described for programmable drug delivery via hierarchical targeting. Specifically, the virus-like Fe₃O₄/Au@C nanovector is synthesized via a simple hydrothermal process, and then the spiky surface of which is camouflaged via doxorubicin (DOX)-conjugated polyethylene glycol (PEG), constructing an innovative virus-like core/spherical shell biomimetic nanomedicine (Fe₃O₄/Au@C-DOX-PEG), which is conducive to improve bioavailability and reduce adverse effects. After systemic administration, the as-prepared nanomedicine is capable of facilitating effective tumor accumulation and deep tumor penetration with the assistance of an external magnetic field and endogenous pH stimuli. Simultaneously, in response to the acidic tumor microenvironment, Fe₃O₄/Au@C-DOX nanocomposites are released and exhibit excellent performance in cellular internalization through a virus-mimetic rough surface. Furthermore, the in vivo experiments identify that the unique nanomedicine is bestowed with an effective targeting tumor, prominent antitumor efficacy, and reduced systemic toxicity. Such a bioinspired hierarchical targeting nanoplatform holds promising potential for enhanced chemotherapeutic intracellular delivery and tumor theranostics.

Construction of oxygen vacancy assisted Z-scheme BiO2-x/BiOBr heterojunction for LED light pollutants degradation and bacteria inactivation

It is well known that the most important task of photocatalytic technology is to synthesize photocatalysts with compact heterojunction structure and high redox ability. To achieve the goal, a novel Z-scheme BiO_2-x/BiOBr heterojunction containing oxygen vacancy was synthesized by an in-situ generation process. Several techniques, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have verified the BiO_2-x/BiOBr heterojunction. XPS and electron spin resonance (ESR) reveals the presence of oxygen vacancy in the BiO_2-x/BiOBr composite. As expected, the BiO_2-x/BiOBr composite showed good performance in removing Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Rhodamine B (RhB) and tetracycline (TC). The effects of inorganic ions, pH value and water matrix were investigated with many details. The active species and proposed mechanism were revealed by trapping experiment and related characterizations. The synergistic effect of oxygen vacancy and Z-scheme heterojunction makes the BiO_2-x/BiOBr composite possess excellent photocatalytic activity.

Selective Magnetic Nanoheating: Combining Iron Oxide Nanoparticles for Multi-Hot-Spot Induction and Sequential Regulation

The contactless heating capacity of magnetic nanoparticles (MNPs) has been exploited in fields such as hyperthermia cancer therapy, catalysis, and enzymatic thermal regulation. Herein, we propose an advanced technology to generate multiple local temperatures in a single-pot reactor by exploiting the unique nanoheating features of iron oxide MNPs exposed to alternating magnetic fields (AMFs). The heating power of the MNPs depends on their magnetic features but also on the intensity and frequency conditions of the AMF. Using a mixture of diluted colloids of MNPs we were able to generate a multi-hot-spot reactor in which each population of MNPs can be selectively activated by adjusting the AMF conditions. The maximum temperature reached at the surface of each MNP was registered using independent fluorescent thermometers that mimic the molecular link between enzymes and MNPs. This technology paves the path for the implementation of a selective regulation of multienzymatic reactions.

Massive Intracellular Remodeling of CuS Nanomaterials Produces Nontoxic Bioengineered Structures with Preserved Photothermal Potential

Despite efforts in producing nanoparticles with tightly controlled designs and specific physicochemical properties, these can undergo massive nano-bio interactions and bioprocessing upon internalization into cells. These transformations can generate adverse biological outcomes and premature loss of functional efficacy. Hence, understanding the intracellular fate of nanoparticles is a necessary prerequisite for their introduction in medicine. Among nanomaterials devoted to theranostics is copper sulfide (CuS), which provides outstanding optical properties along with easy synthesis and low cost. Herein, we performed a long-term multiscale study on the bioprocessing of hollow CuS nanoparticles (CuS NPs) and rattle-like iron oxide nanoflowers@CuS core-shell hybrids (IONF@CuS NPs) when inside stem cells and cancer cells, cultured as spheroids. In the spheroids, both CuS NPs and IONF@CuS NPs are rapidly dismantled into smaller units (day 0 to 3), and hair-like nanostructures are generated (day 9 to 21). This bioprocessing triggers an adaptation of the cellular metabolism to the internalized metals without impacting cell viability, differentiation, or oxidative stress response. Throughout the remodeling, a loss of IONF-derived magnetism is observed, but, surprisingly, the CuS photothermal potential is preserved, as demonstrated by a full characterization of the photothermal conversion across the bioprocessing process. The maintained photothermal efficiency correlated well with synchrotron X-ray absorption spectroscopy measurements, evidencing a similar chemical phase for Cu but not for Fe over time. These findings evidence that the intracellular bioprocessing of CuS nanoparticles can reshape them into bioengineered nanostructures without reducing the photothermal function and therapeutic potential.

The Potential Application of Magnetic Nanoparticles for Liver Fibrosis Theranostics

Liver fibrosis is a major cause of morbidity and mortality worldwide due to chronic liver damage and leading to cirrhosis, liver cancer, and liver failure. To date, there is no effective and specific therapy for patients with hepatic fibrosis. As a result of their various advantages such as biocompatibility, imaging contrast ability, improved tissue penetration, and superparamagnetic properties, magnetic nanoparticles have a great potential for diagnosis and therapy in various liver diseases including fibrosis. In this review, we focus on the molecular mechanisms and important factors for hepatic fibrosis and on potential magnetic nanoparticles-based therapeutics. New strategies for the diagnosis of liver fibrosis are also discussed, with a summary of the challenges and perspectives in the translational application of magnetic nanoparticles from bench to bedside.

Principles and Applications of Single Particle Tracking in Cell Research

It is a tough challenge for many decades to decipher the complex relationships between cell behaviors and cellular physical properties. Single particle tracking (SPT) with high spatial and temporal resolution has been applied extensively in cell research to understand physicochemical properties of cells and their bio-functions by tracking endogenous or exogenous probes. This review describes the fundamental principles of SPT as well as its applications in intracellular mechanics, membrane dynamics, organelles distribution, and processes of internalization and transport. Finally, challenges and future directions of SPT are also discussed.