Iron Oxide Nanoparticles as T1 Contrast Agents for Magnetic Resonance Imaging: Fundamentals, Challenges, Applications, and Prospectives

Core-shell hybrid liposomes: Transforming imaging diagnostics and therapeutic strategies

For the last few years, researchers and industry have intensified efforts to develop a diverse array of diagnostic and therapeutic approaches to fight diseases such as cancer, diabetes, and viral infections. Among the emerging technologies, hybrid liposomes (HLs) stand out for their ability to address key limitations of conventional liposomes and deliver multifunctional solutions more effectively. While several novel nanosystems, including polymerlipid conjugates and inorganic nanoparticles (NPs), have shown great potential in the preclinical and clinical phases for the diagnosis and treatment of diseases, particularly cancer, HLs can integrate the best of both worlds, combining drug delivery properties with imaging capabilities. HLs, particularly those with core-shell structures, can surpass conventional liposomes by offering improved physicochemical properties, multifunctionality, and the capacity to overcome critical delivery challenges. The integration of natural and synthetic polymers has rapidly emerged as a preferred strategy in the development of HLs, providing significant advantages, such as enhanced stability, stimuli-responsive drug release, prolonged circulation, and improved therapeutic efficacy. Additionally, the customizable structure of HLs allows the incorporation of diverse materials, such as metals, ligands, and functional lipids, improving diagnosis and enhancing targeted delivery and cellular uptake far beyond what conventional liposomes offer. This review provides a critical and updated analysis of core-shell structure exhibiting HLs, with a focus on their preparation, characterization, and functional enhancements. We also examine in vitro/in vivo outcomes in imaging diagnosis and drug delivery while addressing the current barriers to clinical translation and future prospects for these versatile nanoplatforms.

Molecular imaging-guided diagnosis and treatment integration for brain diseases

In practical clinical scenarios, improved diagnostic methods have been developed for the precise visualization of molecular targets using molecular imaging in brain diseases. Recently, the introduction of innovative molecular imaging modalities across both macroscopic and mesoscopic dimensions, with remarkable specificity and spatial resolution, has expanded the scope of applications beyond diagnostic testing, with the potential to guide therapeutic interventions, offering real-time feedback in the context of brain therapy. The molecular imaging-guided integration of diagnosis and treatment holds the potential to revolutionize disease management by enabling the real-time monitoring of treatment responses and therapy adjustments. Given the vibrant and ever-evolving nature of this field, this review provides an integrated picture on molecular image-guided diagnosis and treatment integration for brain diseases involving the basic concepts, significant breakthroughs, and recent trends. In addition, based on the current achievements, some critical challenges are also discussed.

Diagnostics of brain tumor in the early stage: current status and future perspectives

Early diagnosis of brain tumors is challenging due to their complexity and delicate structure. Conventional imaging techniques like MRI, CT, and PET are unable to provide detailed visualization of early-stage brain tumors. Early-stage detection of brain tumors is vital for enhancing patient outcomes and survival rates. So far, several scientists have dedicated their efforts to innovating advanced diagnostic probes to efficiently cross the BBB and selectively target brain tumors for optimal imaging. The integration of these techniques presents a viable pathway for non-invasive, accurate, and early-stage tumor identification. Herein, we provide a timely update on the various imaging probes and potential challenges for the diagnosis of early-stage brain tumors. Furthermore, this review highlights the significance of integrating advanced imaging probes for improving the early detection of brain tumors, ultimately enhancing treatment outcomes. Hopefully, this review will stimulate the interest of researchers to accelerate the development of new imaging probes and even their clinical translation for improving the early diagnosis of brain tumors.

Multielement Doping Engineered Iron Oxide Nanoparticles: Enabling the Shift from Negative to Positive MRI Contrast for Enhanced Diagnostic Precision

Contrast-enhanced magnetic resonance imaging (CE-MRI) is a crucial tool for the diagnosis and management of various diseases globally. Iron oxide nanoparticles with sizes less than 5 nm are expected to address the long-term toxicity and brain accumulation issues associated with clinical gadolinium-based T1 contrast agents (GBCAs) due to their non-toxicity and biodegradability. However, synthesizing sub-5-nanometer particles presents significant challenges that complicate their clinical translation. Herein, traditional iron oxide-based negative (T2) agents into positive (T1) agents are transformed and an all-in-one multielement doping strategy is developed. Multiple elements into iron oxide crystals are introduced to form multielement doping engineered iron oxide nanoparticles (MDE-IONPs) and their surfaces with flexible hydrophilic ligands are subsequently modified. It is shown that Ni (II) and Gd (III) doping engineered nanoparticles can effectively enhance imaging efficacy, reducing clearance rates, and enabling controlled synthesis. Ultimately, the implementation of Ni (II) and Gd (III) co-engineering yield longitudinal relaxivity of up to 14.7 mM-1s-1 even for particles as large as 9 nm, an improvement of approximately 300% over GBCAs. Combined with the stability, biosafety, both in vitro and in vivo results suggest that all-in-one multielement doping is a favorable strategy for advancing the development of next-generation safe MRI contrast agents.

Time-resolved T1 and T2 contrast for enhanced accuracy in MRI tumor detection

Stimuli-responsive contrast agents (CAs) have shown great promise in enhancing magnetic resonance imaging (MRI) for more accurate tumor diagnosis. However, current CAs still face challenges in achieving high accuracy due to their low specificity and contrast signals being confounded by potential endogenous MRI artifacts. Herein, an extremely small iron oxide nanoparticle (ESIONP)-based smart responsive MRI contrast agent (LESPH) is proposed, which is meticulously designed with sequential dual biochemical stimuli-initiated, time-resolved T1 and T2 contrast presentation, ensuring high tumor specificity while minimizing interference from endogenous artifacts. LESPH is constructed using emulsion solvent evaporation by assembling poly(2-(hexamethyleneimino) ethyl methacrylate) terminally conjugated with a disulfide bond-linked catechol group (DSPH)-modified ESIONPs, with lauryl betaine serving as a surfactant. When LESPH undergoes sequential responses to the weak acidity and high-concentration glutathione (GSH) in the tumor microenvironment, it experiences an extremely rapid transition from sparse ESIONP assemblies to dispersed ESIONPs, followed by a slower transition to closely aggregated ones, concomitantly providing distinguishable brightening and darkening contrast enhancement at the tumor location on different time scales. By virtue of its sequential dual responsiveness and time-resolved distinguishable contrast enhancements, LESPH successfully detects tumors with extremely high accuracy, providing a novel paradigm for the precise medical diagnosis of cancer.

Ultrasmall maghemite nanoparticles as MRI contrast agent: Unique combination of aggregation stability, low toxicity, and tumor visualization

Iron oxide nanoparticles are a promising candidate for the dual-mode MRI contrast agent, however most of them have limited circulation time and predominant negative contrast. We developed citric acid stabilized superparamagnetic maghemite nanoparticles (CA-SPMNs) with size 3.2 ± 0.7 nm with intense positive contrast. Co-precipitation reactions under well-controlled conditions in the automatic chemical reactor have carried out the synthesis. We found an encouraging correlation between aggregate formation kinetics in biological media and in vitro cytotoxicity results and in vivo circulation time. A cytotoxicity test showed the mouse fibroblast viability over 80 % for iron doses exceeding 1 mg/mL. CA-SPMNs have a low r2/r1 ratio, exhibiting positive contrast. Using in vivo MRI we demonstrated that CA-SPMNs circulate in the blood for 12-24 h, enabling blood vessel and tumor visualization, and partial renal clearance. Finally, CA-SPMNs show promise as effective MRI contrast agents, enabling differentiation between normal and pathological tissues.

Topology-dependent T2 relaxivity in Fe3O cluster-based MOFs for enhanced tumor monitoring via MRI

Metal-organic frameworks (MOFs) are crystalline porous materials with tunable structures, where metal ions or clusters serve as magnetic centers and organic ligands offer spatial separation. These characteristics, combined with their diverse topologies, make MOFs promising candidates for contrast agents (CAs) in magnetic resonance imaging (MRI). Herein we synthesized four MOFs based on the same triangular Fe3O clusters with different topologies: MIL-101(Fe) (moo net), MIL-100(Fe) (mtn net), MIL-59(Fe) (pcu net), and MIL-88B(Fe) (acs net). To clarify the relationship between topologies and T2 relaxivities, the MOFs were tailored into uniform, nanoscale spherical morphologies. Notably, the value of T2 relaxivity for MIL-88B(Fe) with acs topology is nearly three times that for MIL-101(Fe) with moo topology at 7.0 T. By comparing the magnetic properties of Fe3O molecular clusters and Ga-doped MIL-88B(Fe), our analysis demonstrated the significant advantage of MOFs with fixed arrays, adjustable components and diverse topologies in enhancing magnetic relaxation. Cellular MRI experiments further revealed that MIL-88B(Fe) could differentiate between M1 and M2 macrophages, highlighting its potential for monitoring tumor progression. These findings offer valuable insights into how MOF topology can be strategically utilized to enhance T2 relaxivities for MRI applications.

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.

Nitroxide radical contrast agents for safe magnetic resonance imaging: progress, challenges, and perspectives

Magnetic resonance imaging (MRI) is considered one of the most valuable diagnostic technologies in the 21st century. To enhance the image contrast of anatomical features, MRI contrast agents have been widely used in clinical MRI diagnosis, especially those based on gadolinium, manganese, and iron oxide. However, these metal-based MRI contrast agents show potential toxicity to patients, which urges researchers to develop novel MRI contrast agents that can replace metal-based MRI contrast agents. Metal-free nitroxide radical contrast agents (NRCAs) effectively overcome the shortcomings of metal-based contrast agents and also have many advantages, including good biocompatibility, prolonged systemic circulation time, and easily functionalized structures. Importantly, since NRCAs acquire MRI signals with standard tissue water 1H relaxation mechanisms, they have great potential to realize clinical translation among many metal-free MRI contrast agents. At present, NRCAs have been proposed as an effective substitute for metal-based MRI contrast agents. Herein, this review first briefly introduces NRCAs, including their composition, classification, mechanism of action, application performances and advantages. Then, this review highlights the progress of NRCAs, including small molecule-based NRCAs and polymer-based NRCAs. Finally, this review also discusses the challenges and future perspectives of NRCAs.

Facile construction of manganese-based contrast agent with high T 1 relaxivity for magnetic resonance imaging via flash technology-based self-assembly

To address the limitations of low relaxivity and physiological toxicity in commercial gadolinium-based contrast agents for magnetic resonance imaging (MRI), a novel manganese chelate macromolecular system was developed using a flash nanopreparation technique. Herein, the approach applying an instantaneous fluid device incorporated gallic acid, dopamine and Mn2+ to perform in situ polymerization of dopamine and covalent binding with albumin in a nanoconfined environment. This controllable self-assembly process characterized by its scalability and reproducibility was suitable for industrial-scale production. Under optimized flow rates and material ratios, the synthesized ultrasmall protein-based system, Mn-GA@BSA@DA, exhibited excellent aqueous dispersion with an average size of approximately 18 nm, allowing for long-term lyophilized powder storage. More importantly, the nanosystem demonstrated superior MRI-T 1 relaxivity, significantly surpassing that of clinical gadopentetate dimeglumine, with a high value around 18.5 mM-1 s-1 and a low r 2/r 1 ratio (<5 at 3.0 T). Furthermore, this Mn-GA@BSA@DA contrast agent was endowed with tumor-targeting effects and a long MRI monitoring window period for the liver, gallbladder and renal tubules. The metal chelation within the nanoagent minimizes Mn2+ release; importantly, the antioxidant components, gallic acid and dopamine, significantly inhibit the Fenton reaction-induced toxicity, enhancing biocompatibility. Therefore, this study presents a simple and scalable production technique for a kind of MRI-T 1-weighted contrast agent with high relaxivity and biocompatibility, offering a promising alternative to commercial Gd chelates.

Graphdiyne biomaterials: from characterization to properties and applications

Graphdiyne (GDY), the sole synthetic carbon allotrope with sp-hybridized carbon atoms, has been extensively researched that benefit from its pore structure, fully conjugated surfaces, wide band gaps, and more reactive C≡C bonds. In addition to the intrinsic features of GDY, engineering at the nanoscale, including metal/transition metal ion modification, chemical elemental doping, and other biomolecular modifications, endowed GDY with a broader functionality. This has led to its involvement in biomedical applications, including enzyme catalysis, molecular assays, targeted drug delivery, antitumor, and sensors. These promising research developments have been made possible by the rational design and critical characterization of GDY biomaterials. In contrast to other research areas, GDY biomaterials research has led to the development of characterization techniques and methods with specific patterns and some innovations based on the integration of materials science and biology, which are crucial for the biomedical applications of GDY. The objective of this review is to provide a comprehensive overview of the biomedical applications of GDY and the characterization techniques and methods that are essential in this process. Additionally, a general strategy for the biomedical research of GDY will be proposed, which will be of limited help to researchers in the field of GDY or nanomedicine.

Advanced Carriers for Precise Delivery and Therapeutic Mechanisms of Traditional Chinese Medicines: Integrating Spatial Multi-Omics and Delivery Visualization

The complex composition of traditional Chinese medicines (TCMs) has posed challenges for in-depth study and global application, despite their abundance of bioactive compounds that make them valuable resources for disease treatment. To overcome these obstacles, it is essential to modernize TCMs by focusing on precise disease treatment. This involves elucidating the structure-activity relationships within their complex compositions, ensuring accurate in vivo delivery, and monitoring the delivery process. This review discusses the research progress of TCMs in precision disease treatment from three perspectives: spatial multi-omics technology for precision therapeutic activity, carrier systems for precise in vivo delivery, and medical imaging technology for visualizing the delivery process. The aim is to establish a novel research paradigm that advances the precision therapy of TCMs.

Click Chemistry-Based Bioconjugation of Iron Oxide Nanoparticles

Superparamagnetic iron oxide nanoparticles (SPIONs) exhibit unique properties for diverse biomedical applications, including drug delivery and diagnostic imaging. Actively targeted SPIONs enhance delivery to diseased sites, reducing side effects and enhancing treatment efficacy. However, the development of reproducible functionalization protocols is challenged by the erratic behavior of nanoparticles in suspensions, such as agglomeration and sedimentation. In this study, a functionalization method is developed and systematically optimized to attach the Fc-region of antibodies onto silica-coated SPIONs via click chemistry, ensuring controlled ligand orientation on the particle surface. The synthesis and successive modifications of silica-coated SPIONs with organic moieties are presented resulting in the final click conjugation with antibodies targeting intercellular adhesion molecule 1 (ICAM1). This protein is upregulated on epithelial cell surfaces during gastrointestinal inflammation. Thermogravimetric analysis and infrared spectroscopy confirm successful SPION functionalization after each modification step. Cell viability assessment indicates no adverse effects of bioconjugated particles. Quantitative elemental analysis reveals significantly higher iron concentration in inflammation-induced Caco-2 cells exposed to ICAM1-modified particles compared to non-conjugated counterparts. Furthermore, laser scanning confocal microscopy of these cells suggests surface interaction and internalization of bioconjugated SPIONs, underscoring their potential for targeted imaging and therapy in inflammatory diseases.

Insights into Non-Metallic Magnetic Resonance Imaging Contrast Agents: Advances and Perspectives

Traditional metal-based magnetic resonance imaging contrast agents (MRI CAs), such as gadolinium, iron, and manganese, have made significant advancements in diagnosing major diseases. However, their potential toxicity due to long-term accumulation in the brain and bones raises safety concerns. In contrast, non-metallic MRI CAs, which can produce a nuclear magnetic resonance effect, show great promise in MRI applications due to their adaptable structure and function, good biocompatibility, and excellent biodegradability. Nevertheless, the development of non-metallic MRI CAs is slow due to the inherent low magnetic sensitivity of organic compounds, their rapid metabolism, and susceptibility to reduction. Designing effective multifunctional organic compounds for high-sensitivity MRI remains a challenge. In this discussion, the mechanisms of various non-metallic MRI CAs are explored and an overview of their current status, highlighting both their advantages and potential drawbacks, is provided. The key strategies for creating high-performance MRI CAs are summarized and how different synthetic approaches affect the performance of non-metallic MRI Cas is evaluated. Last, the challenges and future prospects for these promising non-metallic MRI CAs are addressed.

Magnetically driven bionic nanorobots enhance chemotherapeutic efficacy and the tumor immune response via precise targeting

We developed magnetically driven bionic drug-loaded nanorobots (MDNs) to accurately target tumors and deliver chemotherapy agents using a customized three-dimensional (3D) magnetic manipulation platform (MMP) system to precisely control their movement mode. MDNs were based on polyethylene glycol-modified homogeneous ultrasmall iron oxide nanoparticles (7.02 ± 0.18 nm). Doxorubicin (12% ± 2% [w/w]) was encapsulated in MDNs by an imide bond. MDNs could imitate the movement mode of a school of wild herrings (e.g., re-dispersion/arrangement/vortex/directional movement) to adapt to the changing and complex physiological environment through the 3D MMP system. MDNs overcame blood flow resistance and biological barriers using optimized magnetic driving properties according to in vivo imaging (magnetic resonance imaging and fluorescence) and histopathology. The performance of fabricated MDNs was verified through cells and tumor-bearing mouse models. The MDNs showed high efficiency of drug delivery and targeting at the tumor site (>10-fold), lower toxicity than free doxorubicin (5 mg/kg body weight), activated immune response in the tumor site, and significantly lengthened survival for mice. The synergistic interaction between MDNs and the 3D MMP system underscores the immense potential of this drug delivery system, indicating a potential revolution in the field of tumor chemotherapy.

Iron(III)-Quercetin Complex: In Vivo Acute Toxicity and Biodistribution of Novel MRI Agent

Background

The iron(III)-quercetin complex, known as "IronQ", is an innovative MRI contrast agent composed of one Fe(III) ion and two quercetin molecules. IronQ is efficiently internalized by cells, enabling T1-weighted MRI tracking. It has demonstrated therapeutic benefits in reducing inflammation in an intracerebral hemorrhage (ICH) mouse model and offers a safer alternative to gadolinium-based agents by avoiding cytotoxicity and genotoxicity. These properties make IronQ a promising candidate for safe and effective MRI contrast enhancement.

Purpose

This study aims to further the development of IronQ as an MRI contrast agent by investigating its biodistribution, pharmacokinetics, and acute toxicity in a preclinical animal model.

Methods

The relaxivity of IronQ was measured in water and whole blood phantoms. Acute toxicity was evaluated in Sprague Dawley rats administered single intraperitoneal doses of IronQ (75, 150, and 225 µmol Fe/kg BW) over a 14-day period. Pharmacokinetic studies were performed at a dose of 150 µmol Fe/kg BW, with blood iron content analyzed using ICP-OES. For in vivo biodistribution, SD rats were administered an intravenous dose of IronQ (225 µmol Fe/kg BW), followed by MR imaging using a 1.5 T scanner and subsequent tissue-ICP analysis.

Results

The longitudinal relaxivity (r1) of IronQ was measured to be 2.17 mm⁻¹s⁻¹ in ultrapure water and 3.56 mm⁻¹s⁻¹ in whole blood. Acute toxicity studies showed no mortality, morbidity, or significant biochemical changes, with histopathology confirming no irreversible organ damage. Pharmacokinetics revealed peak blood iron content at 1.1 hours post-administration and clearance within 24 hours. MRI demonstrated enhanced T1 signal intensity, particularly in the liver and kidney.

Conclusion

These findings provide valuable insights into the safety, pharmacokinetics, and imaging efficacy of IronQ, highlighting its potential as a robust and biocompatible MRI contrast agent.

PEGylated Ultrasmall Iron Oxide Nanoparticles as MRI Contrast Agents for Vascular Imaging and Real-Time Monitoring

Accurate imaging evaluations of pre- and post-treatment of cardiovascular diseases are pivotal for effective clinical interventions and improved patient outcomes. However, current imaging methods lack real-time monitoring capabilities with a high contrast and resolution during treatments. This study introduces PEGylated ultrasmall iron oxide nanoparticles (PUSIONPs), which have undergone comprehensive safety evaluations, boasting an r1 value of 6.31 mM-1 s-1, for contrast-enhanced magnetic resonance angiography (MRA). Systematic comparisons against common clinical methods in rabbits reveal that PUSIONPs-enhanced MRA exhibited improved vascular contrast, clearer vascular boundaries, and superior vessel resolution. Moreover, owing to their nanosize, PUSIONPs demonstrate significantly prolonged blood circulation compared to small molecular contrast agents such as Magnevist and Ultravist. This extended circulation enables captivating real-time monitoring of thrombolysis treatment for up to 4 h in rabbit models postsingle contrast agent injection. Additionally, in larger animal models such as beagles and Bama minipigs, PUSIONPs-enhanced MRA also showcases superior contrast effects, boundary delineation, and microvessel visualization, underscoring their potential to transform cardiovascular imaging, particularly in real-time monitoring and high-resolution visualization during treatment processes.

Improving Stroke Treatment Using Magnetic Nanoparticle Sensors to Monitor Brain Thrombus Extraction

(1) Background: Mechanical thrombectomy (MT) successfully treats ischemic strokes by extracting the thrombus, or clot, using a stent retriever to pull it through the blood vessel. However, clot slippage and/or fragmentation can occur. Real-time feedback to a clinician about attachment between the stent and clot could enable more complete removal. We propose a system whereby antibody-targeted magnetic nanoparticles (NPs) are injected via a microcatheter to coat the clot, oscillating magnetic fields excite the particles, and a small coil attached to the catheter picks up a signal that determines the proximity of the clot to the stent. (2) Methods: We used existing simulation code to model the signal from NPs distributed on a hemispherical clot with three orthogonally applied magnetic fields. An in vitro apparatus was built that applied fields and read out signals from a 1.5 mm pickup coil at a variable distance and orientation angle from a sample of 100 nm iron oxide core/shell NPs. (3) Results: Our simulations suggest that the sum of the voltages induced in the pickup coil from three orthogonal applied fields could localize a clot to within 180 µm, regardless of the exact orientation of the pickup coil, with further precision added via rotation-correction formulae. Our experimental system validated simulations; we estimated an in vitro distance recovery precision of 41 µm with a pickup coil 1 mm from the clot. (4) Conclusions: Magnetic NP sensing could be a safe and real-time method to estimate whether a clot is attached to the stent retriever during MT.

Nanoparticle Contrast Agents for Dark-Field X-ray Imaging

The poor soft tissue contrast of X-ray CT necessitates contrast agent use to improve diagnosis across disease applications, yet their poor detection sensitivity requires high injected doses, which restrict use in at-risk populations. Dark-field X-ray imaging is emerging as a more sensitive alternative to traditional attenuation-based imaging, leveraging scattered radiation to produce contrast. Yet aside from large, short-lived microbubbles, the alternate physics of dark-field detection has yet to be exploited for contrast agent development. Here we demonstrate that high-Z nanoparticles can provide a new means to producing dark-field image contrast, promoting scatter via a higher rather than lower electron density compared to microbubbles, increasing detection sensitivity compared to attenuation-based detection of a clinical iodine-based agent at an equivalent X-ray dose. As the use of dark-field X-ray imaging expands into more common clinical usage, this will support the development of a new class of nanoparticulate contrast agents.

Innovative applications of advanced nanomaterials in cerebrovascular imaging

Cerebrovascular imaging is essential for the diagnosis, treatment, and prognosis of cerebrovascular disease, including stroke, aneurysms, and vascular malformations. Conventional imaging techniques such as MRI, CT, DSA and ultrasound have their own strengths and limitations, particularly in terms of resolution, contrast and safety. Recent advances in nanotechnology offer new opportunities for improved cerebrovascular imaging. Nanomaterials, including metallic nanoparticles, magnetic nanoparticles, quantum dots, carbon-based nanomaterials, and polymer nanoparticles, show great potential due to their unique physical, chemical, and biological properties. This review summarizes recent advances in advanced nanomaterials for cerebrovascular imaging and their applications in various imaging techniques, and discusses challenges and future research directions. The aim is to provide valuable insights for researchers to facilitate the development and clinical application of these innovative nanomaterials in cerebrovascular imaging.

A Single-Chain Peptide Probe Targeting Pathological Collagen for Precise Staging of Hepatic Fibrosis by MR Imaging

Hepatic fibrosis, a chronic liver response to injury with potential severe outcomes like cirrhosis and liver cancer, necessitates urgent noninvasive diagnostic techniques to halt disease progression. We herein for the first time developed a single-chain peptide probe targeting pathological collagen for in vivo magnetic resonance imaging (MRI) of hepatic fibrosis. The novel (GhypO)10 probe, distinguished by its unique monomeric conformation achieved through Pro to (2S,4S)-hydroxyproline (hyp) substitution and subsequent disruption of hydrogen bonding, exhibits selectivity for pathological collagen over its intact counterpart in connective tissues. Fluorescence imaging of liver specimens from fibrotic models displayed a discernible relationship between pathological collagen levels and fibrosis stage. Moreover, T1-weighted MR images post Gd-GhypO administration revealed progressive signal enhancement congruent with fibrosis severity, corroborated by a corresponding increase in the contrast-to-noise ratio (ΔCNR). Biodistribution analysis indicates that Gd-GhypO has low Gd retention in the main organs 24 h postinjection, ensuring the probe's safety for molecular imaging. The Gd-GhypO probe therefore emerges as a potent tool for the precise, noninvasive delineation of hepatic fibrosis stages, offering significant implications for the diagnosis and management of liver fibrosis.

Research progress of nitroxide radical-based MRI contrast agents: from structure design to application

Magnetic resonance imaging (MRI) remains a cornerstone of diagnostic imaging, offering unparalleled insights into anatomical structures and pathological conditions. Gadolinium-based contrast agents have long been the standard in MRI enhancement, yet concerns over nephrogenic systemic fibrosis have spurred interest in metal-free alternatives. Nitroxide radical-based MRI contrast agents (NO-CAs) have emerged as promising candidates, leveraging their biocompatibility and imaging capabilities. This review summaries the latest advancements in NO-CAs, focusing on synthesis methodologies, influencing effects of structures of NO-CAs on relaxation efficiency and their applications across various clinical contexts. Comprehensive discussions encompass small molecular, polymeric, and nano-sized NO-CAs, detailing their unique properties and potential clinical utilities. Despite challenges, NO-CAs represent a dynamic area of research poised to revolutionize MRI diagnostics. This review serves as a critical resource for researchers and practitioners seeking to navigate the evolving landscape of MRI contrast agents.

Advancements in Iron Oxide Nanoparticles for Multimodal Imaging and Tumor Theranostics

The emergence of nanomedicine offers renewed promise in the diagnosis and treatment of diseases. Due to their unique physical and chemical properties, iron oxide nanoparticles (IONPs) exhibit widespread application in the diagnosis and treatment of various ailments, particularly tumors. IONPs have magnetic resonance (MR) T1/T2 imaging capabilities due to their different sizes. In addition, IONPs also have biocatalytic activity (nanozymes) and magnetocaloric effects. They are widely used in chemodynamic therapy (CDT), magnetic hyperthermia treatment (MHT), photodynamic therapy (PDT), and drug delivery. This review outlines the synthesis, modification, and biomedical applications of IONPs, emphasizing their role in enhancing diagnostic imaging (including single-mode and multimodal imaging) and their potential in cancer therapies (including chemotherapy, radiotherapy, CDT, and PDT). Furthermore, we briefly explore the challenges in the clinical application of IONPs, such as surface modification and protein adsorption, and put forward opinions on the clinical transformation of IONPs.

Artificially Engineered Nanoprobes for Ultrasensitive Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a noninvasive and radiation-free technique used for soft tissue. However, there are some limitations of the MRI modality, such as low sensitivity and poor image resolution. Artificially engineered magnetic nanoprobes have been extensively explored as a versatile platform for ultrasensitive MRI contrast agents due to their unique physiochemical characteristics and tunable magnetic properties. In this review, the emphasis is on recent progress in MRI nanoprobes with different structures and elements, including gadolinium-, iron-, manganese-based and metal-free nanoprobes. The key influencing factors and advanced engineering strategies for modulating the relaxation ratio of MRI nanoprobes are systematically condensed. Furthermore, the widespread and noninvasive visualization applications of MRI nanoprobes for real time monitoring of major organs and accurate disease diagnosing, such as cerebrovascular, ischemia, Alzheimer's disease, liver fibrosis, whole-body tumors, inflammation, as well as multi-mode imaging applications are summarized. Finally, the challenges and prospects for the future development of MRI nanoprobes are discussed, and promising strategies are specifically emphasized for improving biocompatibility, precisely engineering of optimal size, AI-driven prediction and design, and multifunctional self-assembly to enhance diagnostics. This review will provide new inspiration for artificial engineering and nanotechnology-based molecular probes for medical diagnosis and therapy with ultrasensitive MRI.

Nanomedicine and clinical diagnostics part I: applications in conventional imaging (MRI, X-ray/CT, and ultrasound)

Integrating nanotechnologies in diagnostic imaging presents a promising step forward compared to traditional methods, which carry certain limitations. Conventional imaging routes, such as X-ray/computed tomography and magnetic resonance imaging, derive significant advantages from nanoparticles (NPs), which allow researchers and clinicians to overcome some of the limitations of traditional imaging agents. In this literature review, we explore recent advancements in nanomaterials being applied in conventional diagnostic imaging techniques by exploring relevant reviews and original research papers (e.g. experimental models and theoretical model studies) in the literature. Collectively, there are numerous nanomaterials currently being examined for use in conventional imaging modalities, and each imaging technique has unique NPs with properties that can be manipulated to answer an array of clinical questions specific to that imaging modality. There are still challenges to consider, including getting regulatory approval for clinical research and routine use about long-term biocompatibility, which collectively emphasize the need for continued research to facilitate the integration of nanotechnology into routine clinical practice. Most importantly, there is a continued need for strong, collaborative efforts between researchers, biomedical engineers, clinicians, and industry stakeholders, which are necessary to bridge the persistent gap between translational ideas and implementation in clinical settings.

Metal Nanoparticles for Simultaneous Use in AC Magnetic Field Hyperthermia and Magnetic Resonance Imaging

Magnetic nanoparticles (MNPs) are produced for both diagnosis and treatment due to their simultaneous availability in magnetic resonance imaging (MRI) and magnetic hyperthermia (MHT). Extensive investigations focus on developing MNPs for individual MHT or MRI applications, but the development of MNPs for theragnostic applications has received very little attention. In this study, through efficient examination of synthesis conditions such as metal precursors, reaction parameters, and solvent choices, we aimed to optimize MNP production for effective utilization for MHT and MRI simultaneously. MNPs were synthesized by thermal decomposition under 17 different conditions and deeply characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The heating efficiency of MNPs under an alternating current (AC) magnetic field was quantified, while MRI performance was evaluated through agar phantom experiments. Our findings highlight the crucial role of benzyl ether in metal ion reduction and size control. Metal-doped iron oxide MNPs displayed promise for MHT, whereas Mn-doped iron oxide MNPs exhibited enhanced MRI capabilities. Consequently, five engineered MNPs were considered potential candidates for further studies, demonstrating their dual ability in MRI and MHT.

Nanoparticles Perspective in Skin Tissue Engineering: Current Concepts and Future Outlook

Nanotechnology seems to provide solutions to the unresolved complications in skin tissue engineering. According to the broad function of nanoparticles, this review article is intended to build a perspective for future success in skin tissue engineering. In the present review, recent studies were reviewed, and essential benefits and challenging issues regarding the application of nanoparticles in skin tissue engineering were summarized. Previous studies indicated that nanoparticles can play essential roles in the improvement of engineered skin. Bio-inspired design of an engineered skin structure first needs to understand the native tissue and mimic that in laboratory conditions. Moreover, a fundamental comprehension of the nanoparticles and their related effects on the final structure can guide researchers in recruiting appropriate nanoparticles. Attention to essential details, including the designation of nanoparticle type according to the scaffold, how to prepare the nanoparticles, and what concentration to use, is critical for the application of nanoparticles to become a reality. In conclusion, nanoparticles were applied to promote scaffold characteristics and angiogenesis, improve cell behavior, provide antimicrobial conditions, and cell tracking.

Size-Dependent Oxygen Vacancy of Iron Oxide Nanoparticles

Prior research has highlighted the reduction of iron oxide nanoparticle (IONPs) sizes to the "ultra-small" dimension as a pivotal approach in developing T1-MRI contrast agents, and the enhancement in T1 contrast performance with the reducing size is usually attributed to the increased specific surface area and weakened magnetization. Nonetheless, as the size decreases, the variation in surface defects, particularly oxygen vacancy (VO) defects, significantly impacts the T1 imaging efficacy. In this study, the VO on IONPs is meticulously investigated through XPS, Raman, and EPR spectroscopy. As the nanoparticle size decreased, the VO concentration rose initially but subsequently declined, with the peak concentration observed in the size of 8.27 nm. Further insights gained from synchrotron XAS analysis and DFT calculations indicate that both surface tension and phase transition in IONPs contribute to alterations in the Fe─O bond length, thereby influencing the VO formation energy across varying nanoparticle sizes. The MRI tests reveal that the VO in IONPs serve as pivotal sites for the attachment of water molecules to iron ions, and IONPs with fewer VO exhibited a deterioration in T1-MRI contrast effects. This research may provide a deeper understanding of the relationship between T1 contrast performance and the size of IONPs.

Iron Oxide Nanoparticle-Based T1 Contrast Agents for Magnetic Resonance Imaging: A Review

This review highlights recent progress in utilizing iron oxide nanoparticles (IONPs) as a safer alternative to gadolinium-based contrast agents (GBCAs) for magnetic resonance imaging (MRI). It consolidates findings from multiple studies, discussing current T1 contrast agents (CAs), the synthesis techniques for IONPs, the theoretical principles for designing IONP-based MRI CAs, and the key factors that impact their T1 contrast efficacy, such as nanoparticle size, morphology, surface modifications, valence states, and oxygen vacancies. Furthermore, we summarize current strategies to achieve IONP-based responsive CAs, including self-assembly/disassembly and distance adjustment. This review also evaluates the biocompatibility, organ accumulation, and clearance pathways of IONPs for clinical applications. Finally, the challenges associated with the clinical translation of IONP-based T1 CAs are included.

Shedding light on vascular imaging: the revolutionary role of nanotechnology

Vascular dysfunction, characterized by changes in anatomy, hemodynamics, and molecular expressions of vasculatures, is closely linked to the onset and development of diseases, emphasizing the importance of its detection. In clinical practice, medical imaging has been utilized as a significant tool in the assessment of vascular dysfunction, however, traditional imaging techniques still lack sufficient resolution for visualizing the complex microvascular systems. Over the past decade, with the rapid advancement of nanotechnology and the emergence of corresponding detection facilities, engineered nanomaterials offer new alternatives to traditional contrast agents. Compared with conventional small molecule counterparts, nanomaterials possess numerous advantages for vascular imaging, holding the potential to significantly advance related technologies. In this review, the latest developments in nanotechnology-assisted vascular imaging research across different imaging modalities, including contrast-enhanced magnetic resonance (MR) angiography, susceptibility-weighted imaging (SWI), and fluorescence imaging in the second near-infrared window (NIR-II) are summarized. Additionally, the advancements of preclinical and clinical studies related to these nanotechnology-enhanced vascular imaging approaches are outlined, with subsequent discussion on the current challenges and future prospects in both basic research and clinical translation.

A switchable magnetic resonance imaging nanoplatform for in situ microRNA imaging

Aberrant microRNA (miRNA) expression is associated with various types of carcinogenesis, making miRNA a promising candidate for diagnostic and therapeutic biomarkers. However, in situ miRNA diagnostics remains a significant challenge owing to the various biological barriers. Herein, we report a novel miRNA imaging probe consisting of PEG-polylysine-PNIPAM polymer matrix-modified small Fe3O4 (PAA-Fe3O4-DNA@PPP) nanoparticles with an improved circulatory half-life, efficient tissue permeability, and enhanced tumor accumulation, for in situ miRNA magnetic resonance imaging (MRI). In this strategy, we employed large size PAA-Fe3O4-DNA@PPP to improve circulatory time and utilized PEG-polylysine-PNIPAM as a GSH-responsive moiety to dissociate PAA-Fe3O4-DNA@PPP and release small size PAA-Fe3O4-DNA for enhanced tumor permeability. Specifically, the target miRNA acts as a cross-linker for PAA-Fe3O4-DNA, forming larger assemblies that not only amplify the MRI signal for detection but also enhance retention for prolonged observation. Both the in vitro and in vivo results validate that the imaging probe exhibits an enhanced MRI signal with 3.69-fold amplification for tumor interior miRNA detection, allowing the dynamic changes in miRNA to be monitored by the probe. Given its long circulation, efficient penetration, and enhanced tumor accumulation, the PAA-Fe3O4-DNA@PPP probe holds great promise for in situ miRNA imaging and spatial genomics analysis in situ.

Enhancing Magnetic Hyperthermia Efficiency in Pd/Fe-Oxide Hybrid Nanoparticles through Mn-Doping

Multifunctional, biocompatible magnetic materials, such as iron oxide nanoparticles (IONPs), hold great potential for biomedical applications including diagnostics (e.g., MRI) and cancer therapy. In particular, they can play a crucial role in advancing cancer thermotherapy by generating heat when administered intratumorally and when exposed to an alternating magnetic field. This heat application is often combined with radio- (chemo)therapy and/or imaging. Consequently, the design of materials for such a multimodal approach requires hybrid nanoparticles that retain their magnetic properties while integrating additional functionalities. This work introduces synthesis and investigation of magnetically enhanced nanoparticles with a palladium core (envisioned for future radiolabeling with therapeutic 103Pd) and a magnetic iron oxide shell containing paramagnetic manganese (Pd/Fe|(nMn)-oxide, n = 0.25 and 0.5). Doping the iron oxide lattice with Mn significantly increases magnetic saturation, boosting specific loss power up to 1.7 times compared to that of undoped analogs. Interestingly, higher Mn-content in Pd/Fe|(0.5Mn)-oxide leads to a pronounced Mn outer rim, enhancing the heating efficiency at 346 kHz and 23 mT and contributing to the water exchange on the surface of the paramagnetically doped nanoparticles, resulting in additional T 1 MRI contrast. The enhanced magnetic properties of the hybrid Pd/Fe|Mn-oxide nanoparticles enable effective therapeutic outcomes with injection of only small quantities of the material, offering great potential for effective cancer treatment strategies that combine hyperthermia/thermal ablation with radiotherapy while allowing for real-time monitoring via MRI.

Bismuth drug-inspired ultra-small dextran coated bismuth oxide nanoparticles for targeted computed tomography imaging of inflammatory bowel disease

Bismuth (Bi)-based computed tomography (CT) imaging contrast agents (CAs) hold significant promise for diagnosing gastrointestinal diseases due to their cost-effectiveness, heightened sensitivity, and commendable biocompatibility. Nevertheless, substantial challenges persist in achieving an easy synthesis process, remarkable water solubility, and effective targeting ability for the potential clinical transformation of Bi-based CAs. Herein, we show Bi drug-inspired ultra-small dextran coated bismuth oxide nanoparticles (Bi2O3-Dex NPs) for targeted CT imaging of inflammatory bowel disease (IBD). Bi2O3-Dex NPs are synthesized through a simple alkaline precipitation reaction using bismuth salts and dextran as the template. The Bi2O3-Dex NPs exhibit ultra-small size (3.4 nm), exceptional water solubility (over 200 mg mL-1), high Bi content (19.75 %), excellent biocompatibility and demonstrate higher X-ray attenuation capacity compared to clinical iohexol. Bi2O3-Dex NPs not only enable clear visualization of the GI tract outline and intestinal loop structures in CT imaging but also specifically target and accumulate at the inflammatory site in colitis mice after oral administration, facilitating a precise diagnosis and enabling targeted CT imaging of IBD. Our study introduces a novel and clinically promising strategy for synthesizing high-performance Bi2O3-Dex NPs for diagnosing gastrointestinal diseases.

Elucidating the Dynamics of Biodegradation and Biosynthesis of Magnetic Nanoparticles in Human Stem Cells

Iron oxide nanoparticles, due to their magnetic properties, are versatile tools for biomedical applications serving both diagnostic and therapeutic roles. Their performance is intricately intertwined with their fate in the demanding biological environment. Once inside cells, these nanoparticles can be degraded, implying a loss of magnetic efficacy, but also transformed into neo-synthesized magnetic nanoparticles, potentially restoring functionality. This study aims to delineate biological features governing these processes. Magnetic nanoparticles are internalized in human mesenchymal stem cells (hMSCs), and their biotransformations are investigated from nano- to micro-scale using electron microscopy (STEM-HAADF, HRTEM, SAED), a benchtop magnetic sensor, and fine structural characterizations (synchrotron XRD, VSM). Results evidence a delicate equilibrium between the biodegradation and biosynthesis of magnetic nanoparticles, with biotransformation kinetics depending on cell density at magnetic labeling and on spatial cell configuration (monolayers vs spheroids). The biotransformed nanoparticles, composed of magnetite or maghemite, are localized within endosomal/lysosomal compartments and associated with the recruitment of ferritin proteins.

Drug delivery for age-related bone diseases: From therapeutic targets to common and emerging therapeutic strategies

With the accumulation of knowledge on aging, people have gradually realized that among the many factors that cause individual aging, the accumulation of aging cells is an essential cause of organ degeneration and, ultimately, age-related diseases. Most cells present in the bone microenvironment gradually age over time, leading to an imbalance of osteogenesis, osteoclastogenesis, adipogenesis, and chondrogenesis. This imbalance contributes to age-related bone loss and the development of age-related bone diseases, such as osteoporosis. Bone aging can prolong the lifespan and delay the development of age-related diseases. Nanoparticles have controllable and stable physical and chemical properties and can precisely target different tissues and organs. By preparing multiple easily modified and biocompatible nanoparticles as different drug delivery carriers, specifically targeting various diseased tissues for controlled-release and sustained-release administration, the delivery efficiency of drugs can be significantly improved, and the toxicity and side effects of drugs can be substantially reduced, thereby improving the therapeutic effect of age-related bone diseases. In addition, other novel anti-aging strategies (such as stem cell exosomes) also have significant scientific and practical significance in anti-aging research on age-related bone diseases. This article reviews the research progress of various nano-drug-loaded particles and emerging anti-aging methods for treating age-related bone diseases, offering new insights and directions for precise targeted clinical therapies.

In vitro and in vivo evaluation of biohybrid tissue-engineered vascular grafts with transformative 1H/19F MRI traceable scaffolds

Biohybrid tissue-engineered vascular grafts (TEVGs) promise long-term durability due to their ability to adapt to hosts' needs. However, the latter calls for sensitive non-invasive imaging approaches to longitudinally monitor their functionality, integrity, and positioning. Here, we present an imaging approach comprising the labeling of non-degradable and degradable TEVGs' components for their in vitro and in vivo monitoring by hybrid 1H/19F MRI. TEVGs (inner diameter 1.5 mm) consisted of biodegradable poly(lactic-co-glycolic acid) (PLGA) fibers passively incorporating superparamagnetic iron oxide nanoparticles (SPIONs), non-degradable polyvinylidene fluoride scaffolds labeled with highly fluorinated thermoplastic polyurethane (19F-TPU) fibers, a smooth muscle cells containing fibrin blend, and endothelial cells. 1H/19F MRI of TEVGs in bioreactors, and after subcutaneous and infrarenal implantation in rats, revealed that PLGA degradation could be faithfully monitored by the decreasing SPIONs signal. The 19F signal of 19F-TPU remained constant over weeks. PLGA degradation was compensated by cells' collagen and α-smooth-muscle-actin deposition. Interestingly, only TEVGs implanted on the abdominal aorta contained elastin. XTT and histology proved that our imaging markers did not influence extracellular matrix deposition and host immune reaction. This concept of non-invasive longitudinal assessment of cardiovascular implants using 1H/19F MRI might be applicable to various biohybrid tissue-engineered implants, facilitating their clinical translation.

Nanoassemblies with Gd-chelating lipids (GMO@DTPA-BSA-Gd) as a potential new type of high molecular weight contrast agents

Self-assembled lipid nanoparticles containing Gd-chelating lipids are a new type of positive magnetic resonance imaging contrast agents (MRI CAs). High molecular weight imposes reduced molecular reorientation (τr) and corresponding longer reorientation correlation times (τc), finally resulting in overall high relaxivity (r1) of such contrast agents. Therefore, we report nanoassemblies based on two types of amphiphile molecules: glyceryl monooleate (GMO) as a matrix embedded with DTPA-bis(stearylamide) and its gadolinium salt (DTPA-BSA-Gd) as a Gd-chelating lipid, stabilized by surfactant Pluronic F127 molecules. The loading of DTPA-BSA-Gd into the GMO matrix was investigated at low (5% w/w) and high (30, 40, 50% w/w) contents. Small angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) results show that although the nanoassembly of both amphiphile molecules within the nanoparticle is disturbed in terms of the formed phases, this composition ensures their colloidal stability. In nanoparticles with low DTPA-BSA-Gd contents, the assembly results in a cubic diamond phase that is co-existing with a fraction of liposomes. For high DTPA-BSA-Gd contents, swelling of the structure occurs such that the initially formed primitive cubic phase transforms toward a lamellar phase in the nanoassemblies. Results from inductively coupled plasma mass spectrometry (ICP-MS) indicate that for almost all systems, the loading efficiency (LE) of DTPA-BSA-Gd is high (reaching up to approx. 85%), and the nanoassembly provides strong entrapment of Gd3+ ions, which are then efficiently uptaken by cells. Moreover, the higher the surfactant content, the higher the LE. The viability studies demonstrate that the prepared nanoassemblies preserve high biocompatibility towards both cancer (HeLa) and normal cells (MSU 1.1). Nuclear magnetic resonance relaxometry studies (NMR relaxometry) followed by MRI on the prepared nanoassembly dispersions proved that the formation of GMO@DTPA-BSA-Gd nanoassemblies, considered as high molecular weight CAs, results in high relaxivity parameters (e.g., r1 = 19.72 mM-1 s-1 for 2GMO-40DTPA-10F127) that are superior to commercially developed ones (e.g., Magnevist or Gadovist). These comprehensive studies imply that a high degree of internal ordering of nanoassemblies with a higher content of Gd-chelating lipid is not a decisive factor in determining the increase in relaxivity, thus confirming their potential as positive MRI CAs.

Macrophage tracking with USPIO imaging and T2 mapping predicts immune rejection of transplanted stem cells

To develop a clinical imaging method for monitoring macrophage migration to the defect site after implantation of various stem cells and evaluating immune responses in the context of knee arthritis, T2 mapping was correlated with CD68-positive cell densities in defects and the bone marrow. This study, which was approved by the Institutional Animal Care and Use Committee, used 32 New Zealand white rabbits preloaded with ultrasmall superparamagnetic iron oxide particles (USPIOs). They were divided into groups that received different stem cell implants after osteochondral defect induction. T2 imaging was performed using a 3.0 T MR scanner, and the data were analysed via one-way ANOVA, with CD68 expression assessed via immunohistochemistry. After implantation, the T2 signal intensity increased across groups, with subgroup D1 (implantation of rat bone marrow stem cells (BMSCs)) showing the lowest T2 value early and the steepest increase in T2 values. Notable differences in CD68-positive cell density were found between Subgroup D1 and the other groups and between Subgroups A1 and C1 post-surgery. A moderate negative correlation was observed between T2 signals and CD68-positive cell density in defects (r = -0.468, p = 0.001), whereas a weak correlation was detected in the bone marrow (r = 0.096, p = 0.313). A significant link was identified between CD68-positive cell density in the bone marrow and in defects (r = -0.255, p = 0.001). This study revealed significant differences in immune responses to stem cells from different origin tissues in the context of cartilage repair. Adipose-derived stem cells (ADSCs) were found to be more likely to provoke immune rejection than were BMSCs in the repair of femoral condyle cartilage defects. Compared with allogeneic transplants, xenogeneic mesenchymal stem cell transplants were associated with prolonged immune rejection. T2 mapping technology was effective in predicting the density of CD68-positive cells, providing a valuable tool for immune monitoring in stem cell therapy.

Nanotheranostics in Breast Cancer Bone Metastasis: Advanced Research Progress and Future Perspectives

Breast cancer is the leading cause of cancer-related morbidity and mortality among women worldwide, with bone being the most common site of all metastatic breast cancer. Bone metastases are often associated with pain and skeletal-related events (SREs), indicating poor prognosis and poor quality of life. Most current therapies for breast cancer bone metastasis primarily serve palliative purposes, focusing on pain management, mitigating the risk of bone-related complications, and inhibiting tumor progression. The emergence of nanodelivery systems offers novel insights and potential solutions for the diagnosis and treatment of breast cancer-related bone metastasis. This article reviews the recent advancements and innovative applications of nanodrug delivery systems in the context of breast cancer bone metastasis and explores future directions in nanotheranostics.

Engineering Protein-Nanoparticle Hybrids as Targeted Contrast Agents

Iron oxide nanoparticles (IONPs) have shown great promise in biomedical applications, particularly as MRI contrast agents due to their magnetic properties and biocompatibility. Although several IONPs have been approved by regulatory agencies as MRI contrast agents, their primary application as negative contrast agents limits their usage. Additionally, there is an emerging need for the development of molecular contrast agents that can specifically target biomarkers, enabling more accurate and sensitive diagnostics. To address these challenges, we exploited the engineerability of proteins to stabilize IONPs with tailored magnetic properties, creating protein-stabilized iron oxide nanoparticles (Prot-IONPs) and leveraged the chemical diversity of proteins to functionalize Prot-IONPs with targeting moieties. As a proof-of-concept, we used alendronate (Ald) to target atherosclerotic plaques in the aorta. Simple protein functionalization allowed targeting while maintaining the stability and relaxation properties of the Prot-IONPs. Prot-IONPs-Ald successfully enabled positive contrast imaging of atherosclerotic plaques in vivo in an atherosclerotic mouse model (ApoE-/- mice on a high-fat diet). This study demonstrates the potential of engineering protein-nanoparticle hybrids as versatile platforms for developing targeted in vivo MRI contrast agents.

Quantitative in Vivo Molecular MRI

Molecular magnetic resonance imaging (MRI) combines chemistry, chemical biology, and imaging techniques to track molecular events non-invasively. Quantitative molecular MRI aims to provide meaningful, reproducible numerical measurements of molecular processes or biochemical targets within the body. In this review, the classifications of molecular MRI probes based on their signal-generating mechanism and functionality are first described. From there, the primary considerations for in vitro characterization and in vivo validation of molecular MRI probes, including how to avoid pitfalls and biases are discussed. Then, recommendations on imaging acquisition protocols and analysis methods to establish quantitative relationships between MRI signal change induced by the probes and the molecular processes of interest are provided. Finally, several representative case studies are highlighted that incorporate these features. Quantitative molecular MRI is a multidisciplinary research area incorporating expertise in chemical biology, inorganic chemistry, molecular probes, imaging physics, drug development, pathobiology, and medicine. The purpose of this review is to provide guidance to chemists developing MR imaging probes and methods in terms of in vitro and in vivo validation to accelerate the translation of these new quantitative tools for non-invasive imaging of biological processes.

Biomineralization Synthesis of HoMn Nanoparticles for Ultrahigh-Field-Tailored and T1-T2 Dual-Mode MRI-Guided Cancer Theranostics

Ultrahigh field magnetic resonance imaging (UHF-MRI) (≥7 T) can dramatically boost image resolution and signal-to-noise ratio, which have distinct advantages in multifunctional imaging. However, their research and application are currently limited by the absence of high-field contrast agents (CAs) and the low sensitivity and accuracy of T1/T2 single-modality CAs. Therefore, the development of T1-T2 dual-mode CAs that respond to UHF-MRI and nanoformulations with therapeutic sensitization can bring ideas for the integrated application of precise and synchronous tumor theranostics. Herein, we present a biomimetic mineralization strategy for synthesizing holmium/manganese oxide-bovine serum albumin-photosensitizer chlorin e6 nanohybrids. The hybrid nanoparticles exhibited better tumor accumulation, a suitable time imaging window, and excellent pH-response T1-T2 dual-mode UHF-MRI performance. The antitumor effect comes from the amelioration of the hypoxic tumor microenvironment to promote the synergistic effect of photodynamic therapy and radiotherapy, along with negligible acute toxicity. Undoubtedly, this work not only provides a different perspective for developing multifunctional nanotherapeutics but also promotes the potential clinical exploitation and translation of UHF CAs.

Chitosan-modified manganese oxide-conjugated methotrexate nanoparticles delivering 5-aminolevulinic acid as a dual-modal T1-T2* MRI contrast agent in U87MG cell detection

OBJECTIVE

Glioblastoma multiforme is a highly aggressive form of brain cancer, and early diagnosis plays a pivotal role in improving patient survival rates. In this regard, molecular magnetic resonance imaging has emerged as a promising imaging modality due to its exceptional sensitivity to minute tissue changes and the ability to penetrate deep into the brain. This study aimed to assess the efficacy of a novel contrast agent in detecting gliomas during MRI scans.

MATERIALS AND METHODS

The contrast agent utilized modified chitosan coating on manganese oxide nanoparticles. The modification included adding methotrexate and 5-aminolevulinic acid (MnO2/CS@5-ALA-MTX) to target cells with overexpressed folate receptors and breaking down excess hydrogen peroxide in tumor tissue, resulting in enhanced signal intensity in T1-weighted MR images but diminished signal intensity in T2*-weighted MR images.

RESULTS

The nanosystem was characterized and evaluated in MR imaging, safety, and ability to target cells both in vivo and in vitro. MTX-free nanoparticles (MnO2/CS@5-ALA NPs) had no obvious cytotoxicity on cell lines U87MG and NIH3T3 after 24/48 h at a concentration of up to 160 µgr/mL (cell viability more than 80%). In this system, methotrexate enables tumor targeting and the MnO2/5-ALA improves T1-T2*-weighted MRI. In addition, MRI scans of mice with M109 carcinoma indicated significant tumor uptake and NP capacity to improve the positive contrast effect.

CONCLUSION

This developed MnO2/CS@5-ALA-MTX nanoparticle system may exhibit great potential in the accurate diagnosis of folate receptor over-expressing cancers such as glioblastoma.

Enhancing organ and vascular contrast in preclinical ultra-low field MRI using superparamagnetic iron oxide nanoparticles

Superparamagnetic iron oxide nanoparticles (SPIONs) are characterized by their exceptional susceptibility and relaxivity at ultra-low field (ULF) regimes, make them a promising contrast agent (CA) for ULF MRI. Despite their distinct advantages, the translation of these properties into clinically valuable image contrast in ULF MRI remains underexplored. In this study, we investigate the use of SPIONs to generate in vivo MRI contrast at 6.5 mT within the organs and vascular system of rodents. This investigation includes comprehensive SPION characterization and phantom imaging experiments to validate the utility of SPIONs to produce positive image contrast and to facilitate phase-sensitive imaging at ULF. Optimized balanced steady-state free precession (bSSFP) and spoiled gradient echo (SPGR) MRI sequences are used to generate in vivo contrast by leveraging the distinctive properties of SPIONs at ULF. Imaging studies in rodents reveal positive organ contrast attainable in magnitude images, and MRI phase maps can be used to visualize the vascular system. This work demonstrates the effectiveness of SPIONs in enhancing preclinical organ and vascular imaging at ULF; it bridges the gap between the study of the distinctive physical properties of SPIONs and the demonstration of in vivo image contrast.

Application of H2N-Fe3O4 Nanoparticles for Prostate Cancer Magnetic Resonance Imaging in an Animal Model

This paper presents the efficacy of a contrast agent based on H2N-Fe3O4 nanoparticles for the detection of prostate cancer in an animal model using a preclinical 9.4 T MRI system. The relaxivities r1 and r2 of the nanoparticles were 6.31 mM-1s-1 and 8.33 mM-1s-1, respectively. Nanoparticles injected in a concentration of 2 mg Fe/mL decreased the tumor-relative T1 relaxation across all animals from 100 to 76 ± 26, 85 ± 27, 89 ± 20, and 97 ± 16 12 min 1 h, 2 h, and 24 h post injection, respectively. The corresponding T1 decrease in muscle tissues was 90 ± 20, 94 ± 23, 99 ± 12, and 99 ± 14. The relative T2 changes in the tumor were 82 ± 17, 89 ± 19, 97 ± 14, and 99 ± 8 12 min, 1 h, 2 h, and 24 h post injection, respectively, while, for muscle tissues, these values were 95 ± 11, 95 ± 8, 97 ± 6, and 95 ± 10 at the corresponding time points. The differences in the relative T1 and T2 were only significant 12 min after injection (p < 0.05), although a decrease was visible at each time point, but it was statistically insignificant (p > 0.05). The results showed the potential application of H2N-Fe3O4 nanoparticles as contrast agents for enhanced prostate cancer MRI.

Thermochemistry of Solid-State Formation, Structure, Optical, and Luminescent Properties of Complex Oxides Eu2MeO6 (Me-Mo, W), Eu2W2O9: A Combined Experimental and DFT Study

Complex oxides Eu2MeO6 (Me-Mo, W), Eu2W2O9 were obtained by a solid-phase reaction between binary oxides. The thermodynamic and kinetic mechanisms of the reaction processes were established using a variety of physical-chemical methods. All compounds obtained in this work crystallize in the low-symmetry monoclinic system, forming complex framework structures, which determine a set of very valuable physical-chemical properties. Comparison of experimental Kubelka-Munk functions and DFT- calculated absorption spectra shows adequate agreement and reveals the origin of the fundamental absorption. In addition, the deficiency in DFT calculations in the part of mutual contribution of CTBs of Mo-O and W-O, from one side, and Eu-O contributions, from the other side, is reported. Calculations of absorption spectra are shown to be superior to band structure analysis in the determination of optical band gaps. Additionally, luminescent properties of Eu2MeO6 and Eu2W2O9 compounds were investigated. These studies provide a better understanding of the electronic and optical properties of the compounds Eu2MeO6 and Eu2W2O9, along with their potential applications in various areas.

Targeted delivery of cisplatin magnetic nanoparticles for diagnosis and treatment of nasopharyngeal carcinoma

Rapid advances in nanotechnology are paving the way for innovative breakthroughs in overcoming the current limitations in the clinical treatment of cancer and other prevalent diseases plaguing mankind. Magnetic nanoparticles composed of iron oxide (Fe3O4) are a novel class of nanoparticles that are receiving increasing attention in the field of cancer therapy. To address the inherent limitations, bare Fe3O4 can be functionalized, polymerized, assembled, or combined with other functional materials to produce a range of smart nanoplatforms suitable for tumor therapy. In this paper, we present a unique multifunctional therapeutic nanoplatform centered on aldehyde-oxidized sodium alginate-stabilized iron oxide nanoparticles (NPs) designed for T2-weighted magnetic resonance (MR) imaging. Sodium alginate oxide and ferric oxide nanoparticles were prepared respectively, and the two particles were mixed in a certain molar ratio to form a complex, which was coupled to target polypeptide GE11 by Schiff base reaction, and finally supported by cisplatin through coordination complexation. The prepared magnetic nanoparticles (hereinafter referred to as GE11-CDDP-ASA@Fe3O4) have an average diameter of 152.9 nm, and have good colloidal stability and cytocompatibility. The distinctive structure and composition of GE11-CDDP-ASA@Fe3O4 contribute to its excellent MRI imaging performance, positioning it as a nano platform suitable for enhancing the efficacy of combination therapy in tumor treatment. This is of great significance for translational nanomedicine applications.

Nitroxide radical conjugated ovalbumin theranostic nanosystem for enhanced dendritic cell-based immunotherapy and T1 magnetic resonance imaging

Melanoma, known for its aggressive metastatic nature, presents a formidable challenge in cancer treatment, where conventional therapies often fall short. This study introduces a pioneering approach utilizing metal-free nanosystem as tumor vaccines, spotlighting their potential in revolutionizing melanoma treatment. This work employed organic nitroxides, specifically 4-carboxy-TEMPO, in combination with chitosan (CS), to create a novel nanocomposite material - the CS-TEMPO-OVA nanovaccines. This composition not only improves biocompatibility and extends blood circulation time of TEMPO but also marks a significant departure from traditional gadolinium-based contrast agents in MRI technology, addressing safety concerns. CS-TEMPO-OVA nanovaccines demonstrate excellent biocompatibility at both the cellular and organoid level. They effectively stimulate bone marrow-derived dendritic cells (BMDCs), which in turn promote the maturation and activation of T cells. This ultimately leads to a strong production of essential cytokines. These nanovaccines serve a dual purpose as both therapeutic and preventive. By inducing an immune response, activating cytotoxic T cells, and promoting macrophage M1 polarization, they effectively inhibit melanoma growth and enhance survival in mouse models. When combined with αPD-1, the CS-TEMPO-OVA nanovaccines significantly bolster the infiltration of cytotoxic T lymphocytes (CTLs) within tumors, sparking a powerful systemic antitumor response that effectively curbs tumor metastasis. The ability of these nanovaccines to control both primary (subcutaneous) and metastatic B16-OVA tumors highlights their remarkable efficacy. Furthermore, the CS-TEMPO-OVA nanovaccine can be administered in vivo via both intravenous and intramuscular routes, both of which effectively enhance the T1 contrast of magnetic resonance imaging in tumor tissue. This study offers invaluable insights into the integrated application of these nanovaccines in both clinical diagnostics and treatment, marking a significant stride in cancer research and patient care.

Fe2+-Dominated Relaxometric Properties of Iron Oxide Nanoparticles as MRI Contrast Agents

Iron oxide nanoparticles (IONPs) have garnered significant interest as magnetic resonance imaging (MRI) contrast agents due to their exceptional magnetic properties and biocompatibility. Toward more precise diagnosis of diseases, the relaxometric properties of IONPs have become a key research focus. Despite extensive studies on structural factors such as size, morphology, surface modification, crystalline phase, and aggregation state, the correlation between the intrinsic structure and relaxometric behavior remains unclear, particularly for ultrasmall IONPs. To address this issue, we carefully compared IONPs with identical size, shape, and surface modification and found out strong correlations among the content of Fe2+ ions, oxygen vacancies, and the relaxometric properties. By optimizing the reaction system, ultrasmall IONPs showing outstanding relaxometric performance, with longitudinal relaxivity up to 9.0 mM-1 s-1 and transverse relaxivity up to 28.5 mM-1 s-1, were successfully obtained. These results underscore the pivotal role of Fe2+ in the relaxometric properties of IONP-based MRI contrast agents.