Ultracompact Iron Oxide Nanoparticles with a Monolayer Coating of Succinylated Heparin: A New Class of Renal-Clearable and Nontoxic T1 Agents for High-Field MRI

Iron oxide nanoparticle-based nanocomposites in biomedical application

Iron-oxide-based biomagnetic nanocomposites, recognized for their significant properties, have been utilized in MRI and cancer treatment for several decades. The expansion of clinical applications is limited by the occurrence of adverse effects. These limitations are largely attributed to suboptimal material design, resulting in agglomeration, reduced magnetic relaxivity, and inadequate functionality. To address these challenges, various synthesis methods and modification strategies have been used to tailor the size, shape, and properties of iron oxide nanoparticle (FeONP)-based nanocomposites. The resulting modified nanocomposites exhibit significant potential for application in diagnostic, therapeutic, and theranostic contexts, including MRI, drug delivery, and anticancer and antimicrobial activity. Yet, their biosafety profile must be rigorously evaluated. Such efforts will facilitate the broader clinical translation of FeONP-based nanocomposites in biomedical applications.

Exceedingly Small Magnetic Iron Oxide Nanoparticles for T1 -Weighted Magnetic Resonance Imaging and Imaging-Guided Therapy of Tumors

Magnetic iron oxide nanoparticles (MIONs) based T2 -weighted magnetic resonance imaging (MRI) contrast agents (CAs) are liver-specific with good biocompatibility, but have been withdrawn from the market and replaced with Eovist (Gd-EOB-DTPA) due to their inherent limitations (e.g., susceptibility to artifacts, high magnetic moment, dark signals, long processing time of T2 imaging, and long waiting time for patients after administration). Without the disadvantages of Gd-chelates and MIONs, the recently emerging exceedingly small MIONs (ES-MIONs) (<5 nm) are promising T1 CAs for MRI. However, there are rare review articles focusing on ES-MIONs for T1 -weighted MRI. Herein, the recent progress of ES-MIONs, including synthesis methods (the current basic synthesis methods and improved methods), surface modifications (artificial polymers, natural polymers, zwitterions, and functional protein), T1 -MRI visual strategies (structural remodeling, reversible self-assemblies, metal ions doped, T1 /T2 dual imaging modes, and PET/MRI strategy), and imaging-guided cancer therapy (chemotherapy, gene therapy, ferroptosis therapy, photothermal therapy, photodymatic therapy, radiotherapy, immuotherapy, sonodynamic therapy, and multimode therapy), is summarized. The detailed description of synthesis methods and applications of ES-MIONs in this review is anticipated to attract extensive interest from researchers in different fields and promote their participation in the establishment of ES-MIONs based nanoplatforms for tumor theranostics.

O2-Generating Fluorescent Carbon Dot-Decorated MnO2 Nanosheets for "Off/On" MR/Fluorescence Imaging and Enhanced Photodynamic Therapy

Imaging-guided photodynamic therapy (PDT) has emerged as a promising protocol for cancer theragnostic. However, facile preparation of such a theranostic system for simultaneously achieving tumor location, real-time monitoring, and high-performance reactive oxygen species generation is highly desirable but remains challenging. Herein, we developed a reasonable tumor-targeting strategy based on carbon dots (CDs)-decorated MnO2 nanosheets (HA-MnO2-CDs) with an active magnetic resonance (MR)/fluorescence imaging and enhanced PDT effect. Under light irradiation, the addition of HA-MnO2-CDs increased the production of 1O2 by 2.5 times compared with CDs, providing favorable conditions for the PDT treatment effect on breast cancer. Moreover, HA-MnO2-CDs exhibited excellent performance in producing O2 in the presence of endogenous H2O2, which alleviated hypoxia in tumors and improved the therapeutic effect of PDT. In the presence of glutathione (GSH), the degraded MnO2 nanosheets released CDs and Mn2+ from HA-MnO2-CDs, restoring their fluorescence imaging function and increasing T1 relaxivity (r1) by 23 times. In vivo fluorescence and MR imaging suggested the excellent tumor-targeting property of HA-MnO2-CDs. By combining the complementary properties of nanoprobes and tumor microenvironments, the in vivo PDT therapeutic effect was significantly improved under the action of HA-MnO2-CDs. Overall, our reasonably designed HA-MnO2-CDs may inspire the future development of the next generation of high-performance tumor-responsive diagnostic and therapeutic agents to further enhance the targeted therapy effect of tumors.

Coating influence on inner shell water exchange: An underinvestigated major contributor to SPIONs relaxation properties

Superparamagnetic iron oxide nanoparticles (SPIONs) are heavily studied as potential MRI contrast enhancing agents. Every year, novel coatings are reported which yield large increases in relaxivity compared to similar particles. However, the reason for the increased performance is not always well understood mechanistically. In this review, we attempt to relate these advances back to fundamental models of relaxivity, developed for chelated metal ions, primarily gadolinium. We focus most closely on the three-shell model which considers the relaxation of surface-bound, entrained, and bulk water molecules as three distinct contributions to total relaxation. Because SPIONs are larger, more complex, and entrain significantly more water than gadolinium-based contrast agents, we consider how to adapt the application of classical models to SPIONs in a predictive manner. By carefully considering models and previous results, a qualitative model of entrained water interactions emerges, based primarily on the contributions of core size, coating thickness, density, and hydrophilicity.

Recent advances of Pluronic-based copolymers functionalization in biomedical applications

The design of polymeric biocompatible nanomaterials for biological and medical applications has received special attention in recent years. Among different polymers, the triblock type copolymers (EO)_x(PO)_y(EO)_x or Pluronics® stand out due its favorable characteristics such as biocompatibility, low tissue adhesion, thermosensitivity, and structural capacity to produce different types of macro and nanostructures, e.g. micelles, vesicles, nanocapsules, nanospheres, and hydrogels. However, Pluronic itself is not the "magic bullet" and its functionalization via chemical synthesis following biologically oriented design rules is usually required aiming to improve its properties. Therefore, this paper presents some of the main publications on new methodologies for synthetic modifications and applications of Pluronic-based nanoconstructs in the biomedical field in the last 15 years. In general, the polymer modifications aim to improve physical-chemical properties related to the micellization process or physical entrapment of drug cargo, responsive stimuli, active targeting, thermosensitivity, gelling ability, and hydrogel formation. Among these applications, it can be highlighted the treatment of malignant neoplasms, infectious diseases, wound healing, cellular regeneration, and tissue engineering. Functionalized Pluronic has also been used for various purposes, including medical diagnosis, medical imaging, and even miniaturization, such as the creation of lab-on-a-chip devices. In this context, this review discusses the main scientific contributions to the designing, optimization, and improvement of covalently functionalized Pluronics aiming at new strategies focused on the multiple areas of the biomedical field.

Magnetic Iron Oxide Nanoparticles for Brain Imaging and Drug Delivery

Central nervous system (CNS) disorders affect as many as 1.5 billion people globally. The limited delivery of most imaging and therapeutic agents into the brain is a major challenge for treatment of CNS disorders. With the advent of nanotechnologies, controlled delivery of drugs with nanoparticles holds great promise in CNS disorders for overcoming the blood-brain barrier (BBB) and improving delivery efficacy. In recent years, magnetic iron oxide nanoparticles (MIONPs) have stood out as a promising theranostic nanoplatform for brain imaging and drug delivery as they possess unique physical properties and biodegradable characteristics. In this review, we summarize the recent advances in MIONP-based platforms as imaging and drug delivery agents for brain diseases. We firstly introduce the methods of synthesis and surface functionalization of MIONPs with emphasis on the inclusion of biocompatible polymers that allow for the addition of tailored physicochemical properties. We then discuss the recent advances in in vivo imaging and drug delivery applications using MIONPs. Finally, we present a perspective on the remaining challenges and possible future directions for MIONP-based brain delivery systems.

Immune-regulating camouflaged nanoplatforms: A promising strategy to improve cancer nano-immunotherapy

Although nano-immunotherapy has advanced dramatically in recent times, there remain two significant hurdles related to immune systems in cancer treatment, such as (namely) inevitable immune elimination of nanoplatforms and severely immunosuppressive microenvironment with low immunogenicity, hampering the performance of nanomedicines. To address these issues, several immune-regulating camouflaged nanocomposites have emerged as prevailing strategies due to their unique characteristics and specific functionalities. In this review, we emphasize the composition, performances, and mechanisms of various immune-regulating camouflaged nanoplatforms, including polymer-coated, cell membrane-camouflaged, and exosome-based nanoplatforms to evade the immune clearance of nanoplatforms or upregulate the immune function against the tumor. Further, we discuss the applications of these immune-regulating camouflaged nanoplatforms in directly boosting cancer immunotherapy and some immunogenic cell death-inducing immunotherapeutic modalities, such as chemotherapy, photothermal therapy, and reactive oxygen species-mediated immunotherapies, highlighting the current progress and recent advancements. Finally, we conclude the article with interesting perspectives, suggesting future tendencies of these innovative camouflaged constructs towards their translation pipeline.

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Various immune-regulating camouflaged nanoplatforms are emphasized.

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Immunotherapeutic applications of camouflaged nanoplatforms are systematically summarized.

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ICD-induced therapeutic modalities based on these nanoplatforms are discussed.

Fluorescently-tagged magnetic protein nanoparticles for high-resolution optical and ultra-high field magnetic resonance dual-modal cerebral angiography

Extremely small paramagnetic iron oxide nanoparticles (FeMNPs) (<5 nm) can enhance positive magnetic resonance imaging (MRI) contrast by shortening the longitudinal relaxation time of water (T₁), but these nanoparticles experience rapid renal clearance. Here, magnetic protein nanoparticles (MPNPs) are synthesized from protein-conjugated citric acid coated FeMNPs (c-FeMNPs) without loss of the T₁ MRI properties and tagged with fluorescent dye (f-MPNPs) for optical cerebrovascular imaging. The c-FeMNPs shows average size 3.8 ± 0.7 nm with T₁ relaxivity (r₁) of 1.86 mM^-1 s^-1 and transverse/longitudinal relaxivity ratio (r₂/r₁) of 2.53 at 11.7 T. The f-MPNPs show a higher r₁ value of 2.18 mM^-1 s^-1 and r₂/r₁ ratio of 2.88 at 11.7 T, which generates excellent positive MRI contrast. In vivo cerebral angiography with f-MPNPs enables detailed microvascular contrast enhancement for differentiation of major blood vessels of murine brain, which corresponds well with whole brain three-dimensional time-of-flight MRI angiograms (17 min imaging time with 60 ms repetition time and 40 μm isotropic voxels). The real-time fluorescence angiography enables unambiguous detection of brain capillaries with diameter < 40 μm. Biodistribution examination revealed that f-MPNPs were safely cleared by the organs like the liver, spleen, and kidneys within a day after injection. Blood biochemical assays demonstrated no risk of iron overload in both rats and mice. With hybrid neuroimaging technologies (e.g., MRI-optical) on the rise, f-MPNPs built on this platform can generate exciting neuroscience applications.

Heparin-Superparamagnetic Iron Oxide Nanoparticles for Theranostic Applications

In this study, superparamagnetic iron oxide nanoparticles (SPIONs) were engineered with an organic coating composed of low molecular weight heparin (LMWH) and bovine serum albumin (BSA), providing heparin-based nanoparticle systems (LMWH@SPIONs). The purpose was to merge the properties of the heparin skeleton and an inorganic core to build up a targeted theranostic nanosystem, which was eventually enhanced by loading a chemotherapeutic agent. Iron oxide cores were prepared via the co-precipitation of iron salts in an alkaline environment and oleic acid (OA) capping. Dopamine (DA) was covalently linked to BSA and LMWH by amide linkages via carbodiimide coupling. The following ligand exchange reaction between the DA-BSA/DA-LMWH and OA was conducted in a biphasic system composed of water and hexane, affording LMWH@SPIONs stabilized in water by polystyrene sulfonate (PSS). Their size and morphology were investigated via dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. The LMWH@SPIONs’ cytotoxicity was tested, showing marginal or no toxicity for samples prepared with PSS at concentrations of 50 µg/mL. Their inhibitory activity on the heparanase enzyme was measured, showing an effective inhibition at concentrations comparable to G4000 (N-desulfo-N-acetyl heparin, a non-anticoagulant and antiheparanase heparin derivative; Roneparstat). The LMWH@SPION encapsulation of paclitaxel (PTX) enhanced the antitumor effect of this chemotherapeutic on breast cancer cells, likely due to an improved internalization of the nanoformulated drug with respect to the free molecule. Lastly, time-domain NMR (TD-NMR) experiments were conducted on LMWH@SPIONs obtaining relaxivity values within the same order of magnitude as currently used commercial contrast agents.

Continuous preparation of a nontoxic magnetic fluid as a dual-mode contrast agent for MRI

Ultrasmall nanoparticle contrast agents provide dual-mode MRI. However, the application of ultrasmall nanoparticle contrast agents is limited by low manufacturing outputs and cumbersome preparation processes. Herein, we report a novel continuous-flow coprecipitation method for the preparation of the Fe₃O₄ nanoparticles magnetic fluid (CFCPFe) coated with ultrasmall cysteine-terminated polymethacrylic acid (Cys-PMAA). The preparation process is more coherent, simpler, and less expensive. Compared with magnetic fluids prepared by the conventional method (Cys-PMAA@Fe₃O₄), CFCPFe has smaller particle sizes (3.27 ± 0.93 nm). Moreover, CFCPFe demonstrates excellent stability for >180 days with different pH values (pH = 2-12) and salt concentrations (up to 2 mol/L). In addition, HEK293T cytotoxicity tests, hemolysis tests, and H&E tissue sections show excellent in vitro and in vivo biocompatibility. In vitro magnetic resonance imaging (MRI) at 1.5 T shows that the r₂ value (50.51 mM^-1·s^-1) of CFCPFe is slightly lower than that of Combidex (r₂ = 65 mM^-1·s^-1) and that the r₁ value (9.54 mM^-1·s^-1) is 2.7 times higher than that of Gd-DTPA (r₁ = 3.5 mM^-1·s^-1). Finally, in vivo imaging shows that CFCPFe reaches the tumor region of the mouse liver cancer model, and a small tumor can be observed in dual-mode imaging. This work offers an effective method for the preparation of a low-cost, stable, and biocompatible ultrasmall contrast agent exhibiting a strong magnetic-imaging effect for dual-mode imaging.

Ultrasmall superparamagnetic iron oxide nanoparticles: A next generation contrast agent for magnetic resonance imaging

As a research hotspot, the development of magnetic resonance imaging (MRI) contrast agents has attracted great attention over the past decades for improving the accuracy of diagnosis. Ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles with core diameter smaller than 5.0 nm are expected to become a next generation of contrast agents owing to their excellent MRI performance, long blood circulation time upon proper surface modification, renal clearance capacity, and remarkable biosafety profile. On top of these merits, USPIO nanoparticles are used for developing not only T₁ contrast agents, but also T₂ /T₁ switchable contrast agents via assembly/disassembly approaches. In recent years, as a new type of contrast agents, USPIO nanoparticles have shown considerable applications in the diagnosis of various diseases such as vascular pathological changes and inflammations apart from malignant tumors. In this review, we are focusing on the state-of-the-art developments and the latest applications of USPIO nanoparticles as MRI contrast agents to discuss their advantages and future prospects. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Progress and prospects of magnetic iron oxide nanoparticles in biomedical applications: A review

Nanoscience has been considered as one of the most substantial research in modern science. The utilization of nanoparticle (NP) materials provides numerous advantages in biomedical applications due to their unique properties. Among various types of nanoparticles, the magnetic nanoparticles (MNPs) of iron oxide possess intrinsic features, which have been efficiently exploited for biomedical purposes including drug delivery, magnetic resonance imaging, Magnetic-activated cell sorting, nanobiosensors, hyperthermia, and tissue engineering and regenerative medicine. The size and shape of nanostructures are the main factors affecting the physicochemical features of superparamagnetic iron oxide nanoparticles, which play an important role in the improvement of MNP properties, and can be controlled by appropriate synthesis strategies. On the other hand, the proper modification and functionalization of the surface of iron oxide nanoparticles have significant effects on the improvement of physicochemical and mechanical features, biocompatibility, stability, and surface activity of MNPs. This review focuses on popular methods of fabrication, beneficial surface coatings with regard to the main required features for their biomedical use, as well as new applications.

Imaging Constructs: The Rise of Iron Oxide Nanoparticles

Over the last decade, an important challenge in nanomedicine imaging has been the work to design multifunctional agents that can be detected by single and/or multimodal techniques. Among the broad spectrum of nanoscale materials being investigated for imaging use, iron oxide nanoparticles have gained significant attention due to their intrinsic magnetic properties, low toxicity, large magnetic moments, superparamagnetic behaviour and large surface area-the latter being a particular advantage in its conjunction with specific moieties, dye molecules, and imaging probes. Tracers-based nanoparticles are promising candidates, since they combine synergistic advantages for non-invasive, highly sensitive, high-resolution, and quantitative imaging on different modalities. This study represents an overview of current advancements in magnetic materials with clinical potential that will hopefully provide an effective system for diagnosis in the near future. Further exploration is still needed to reveal their potential as promising candidates from simple functionalization of metal oxide nanomaterials up to medical imaging.