NMR Relaxation of Water in Nanostructures: Analysis of Ferromagnetic Cobalt-Ferrite Polyelectrolyte Nanocomposites

Magnetically driven preparation of 1-D nano-necklaces capable of MRI relaxation enhancement

We report a novel magnetically-facilitated approach to produce 1-D 'nano-necklace' arrays composed of 0-D magnetic nanoparticles, which are assembled and coated with an oxide layer to produce semi-flexible core@shell type structures. These 'nano-necklaces' demonstrate good MRI relaxation properties despite their coating and permanent alignment, with low field enhancement due to structural and magnetocrystalline anisotropy.

An NMR relaxometry approach for quantitative investigation of the transchelation of gadolinium ions from GBCAs to a competing macromolecular chelator

Gadolinium-based contrast agents (GBCAs) have been used in clinical Magnetic Resonance Imaging (MRI) for more than 30 years. However, there is increasing evidence that their dissociation in vivo leads to long-term depositions of gadolinium ions in the human body. In vitro experiments provide critical insights into kinetics and thermodynamic equilibria of underlying processes, which give hints towards the in vivo situation. We developed a time-resolved MRI relaxometry-based approach that exploits distinct relaxivities of Gd3+ in different molecular environments. Its applicability to quantify the transmetallation of GBCAs, the binding of Gd3+ to competing chelators, and the combined transchelation process is demonstrated. Exemplarily, the approach is applied to investigate two representative GBCAs in the presence of Zn2+ and heparin, which is used as a model for a macromolecular and physiologically occurring chelator. Opposing indirect impacts of heparin on increasing the kinetic stability but reducing the thermodynamic stability of GBCAs are observed. The relaxivity of resulting Gd-heparin complexes is shown to be essentially increased compared to that of the parent GBCAs so that they might be one explanation for observed long-term MRI signal enhancement in vivo. In forthcoming studies, the presented method could help to identify the most potent Gd-complexing macromolecular species.

Superparamagnetic cobalt ferrite nanoparticles as T2 contrast agent in MRI: in vitro study

Superparamagnetic cobalt ferrite nanoparticles (CoFe₂O₄) possess favourite advantages for theranostic applications. Most of previous studies reported that CoFe₂O₄ magnetic nanoparticles (MNPs) are suitable candidates for induction of hyperthermia and transfection agents for drug delivery. The present study synthesized and investigated the potential use of CoFe₂O₄ as a contrast agent in magnetic resonance imaging (MRI) by using a conventional MRI system. The CoFe₂O₄ were synthesized using co-precipitation method and characterized by TEM, XRD, FTIR, EDX and VSM techniques. Relaxivities r₁ and r₂ of CoFe₂O₄ were then calculated using a 1.5 Tesla clinical magnetic field. The cytotoxicity of CoFe₂O₄ was evaluated by the MTT assay. Finally, the optimal concentrations of MNPs for MRI uses were calculated through the analysis of T₂ weighted imaging cell phantoms. The superparamagnetic CoFe2O4 NPs with an average stable size of 10.45 nm were synthesized. Relaxivity r₁,₂ calculations resulted in suitable r₂ and r₂/ r₁ with values of 58.6 and 51 that confirmed the size dependency on relaxivity values. The optimal concentration of MNPs for MR image acquisition was calculated as 0.154 mM. Conclusion: CoFe₂O₄ synthesized in this study could be considered as a suitable T₂ weighted contrast agent because of its high r₂/r₁ value.

Exploring precision polymers to fine-tune magnetic resonance imaging properties of iron oxide nanoparticles

The use of bio-polymers as stabilising agents for iron oxide-based negative magnetic resonance imaging (MRI) contrast agents has become popular in recent years, however the wide polydispersity of biologically-derived and commercially available polymers limits the ability to produce truly tuneable and reproducible behaviour, a major challenge in this area. In this work, stable colloids of iron oxide nanoparticles were prepared utilising precision-engineered bio-polymer mimics, poly(2-acrylamido-2-methylpropane sodium sulfonate) (P(AMPS)) polymers, with controlled narrow polydispersity molecular weights, as templating stabilisers. In addition to producing magnetic colloids with excellent MRI contrast capabilities (r₂ values reaching 434.2 mM^-1 s^-1 at 25 °C and 23 MHz, several times higher than similar commercial analogues), variable field relaxometry provided unexpected important insights into the dynamic environment of the hydrated materials, and hence their exceptional MRI behaviour. Thanks to the polymer's templating backbone and flexible conformation in aqueous suspension, nanocomposites appear to behave as "multi-core" clustered species, enhancing interparticle interactions whilst retaining water diffusion, boosting relaxation properties at low frequency. This clustering behaviour, evidenced by small-angle X-ray scattering, and strong relaxometric response, was fine-tuned using the well-defined molecular weight polymer species with precise iron to polymer ratios. By also showing negligible haemolytic activity, these nanocomposites exhibit considerable potential for MRI diagnostics.

Supramolecular and biomacromolecular enhancement of metal-free magnetic resonance imaging contrast agents

Many contrast agents for magnetic resonance imaging are based on gadolinium, however side effects limit their use in some patients. Organic radical contrast agents (ORCAs) are potential alternatives, but are reduced rapidly in physiological conditions and have low relaxivities as single molecule contrast agents. Herein, we use a supramolecular strategy where cucurbit[8]uril binds with nanomolar affinities to ORCAs and protects them against biological reductants to create a stable radical in vivo. We further overcame the weak contrast by conjugating this complex on the surface of a self-assembled biomacromolecule derived from the tobacco mosaic virus.

Magnetically activated adhesives: towards on-demand magnetic triggering of selected polymerisation reactions

We demonstrate a new strategy to inhibit and trigger polymerisation of an adhesive formulation, utilising colloidal core@shell CoFe₂O₄@MnO₂ magnetic nanoparticles.

On-demand initiation of chemical reactions is becoming increasingly popular in many areas. The use of a magnetic field to trigger reactions is an intriguing concept, with vast potential in both research and industrial settings, though it remains a challenge as yet unsolved. Here we report the first example of on-demand magnetic activation of a polymerisation process using an anaerobic adhesive formulation as an example of this new approach toward triggering polymerisation reactions using an external magnetic field. Our strategy involves the use of a colloidal system comprising functional methacrylate ester monomers, peroxide and Cu^II-salt as polymerisation initiators and magnetic nanoparticles coated with an oxidising shell. This unique combination prevents reduction of the reactive transition metal (Cu^II) ion by the metal substrates (steel or aluminium) to be joined – hence inhibiting the redox radical initiated cationic polymerisation reaction and efficiently preventing adhesion. The polymerisation and corresponding adhesion process can be triggered by removal of the functional magnetic particles using a permanent external magnet either prior to formulation application or at the joint to be adhered, enabling the polymerisation to proceed through Cu^II-mediated reduction. This new approach enables on-demand magnetically-triggered reaction initiation and holds potential for a range of useful applications in chemistry, materials science and relevant industrial manufacturing.

Heparin-stabilised iron oxide for MR applications: a relaxometric study

Superparamagnetic nanoparticles have strong potential in biomedicine and have seen application as clinical magnetic resonance imaging (MRI) contrast agents, though their popularity has plummeted in recent years, due to low efficacy and safety concerns, including haemagglutination. Using an in situ procedure, we have prepared colloids of magnetite nanoparticles, exploiting the clinically approved anti-coagulant, heparin, as a templating stabiliser. These colloids, stable over several days, produce exceptionally strong MRI contrast capabilities particularly at low fields, as demonstrated by relaxometric investigations using nuclear magnetic resonance dispersion (NMRD) techniques and single field r₁ and r₂ relaxation measurements. This behaviour is due to interparticle interactions, enhanced by the templating effect of heparin, resulting in strong magnetic anisotropic behaviour which closely maps particle size. The nanocomposites have also reliably prevented protein-adsorption triggered thrombosis typical of non-stabilised nanoparticles, showing great potential for in vivo MRI diagnostics.

Microwave-assisted synthesis of highly crystalline, multifunctional iron oxide nanocomposites for imaging applications

We report a single-step, microwave-assisted approach for the preparation of multifunctional magnetic nanocomposites. We demonstrate the link between synthetic methodology and the functionality of the nanocomposites as biomedical imaging agents.

New approach for understanding experimental NMR relaxivity properties of magnetic nanoparticles: focus on cobalt ferrite

Relaxivities r₁ and r₂ of cobalt ferrite magnetic nanoparticles (MNPs) have been investigated in the aim of improving the models of NMR relaxation induced by magnetic nanoparticles.

Environmentally responsive MRI contrast agents

Biomedical imaging techniques can provide a vast amount of anatomical information, enabling diagnosis and the monitoring of disease and treatment profile. MRI uniquely offers convenient, non-invasive, high resolution tomographic imaging. A considerable amount of effort has been invested, across several decades, in the design of non toxic paramagnetic contrast agents capable of enhancing positive MRI signal contrast. Recently, focus has shifted towards the development of agents capable of specifically reporting on their local biochemical environment, where a switch in image contrast is triggered by a specific stimulus/biochemical variable. Such an ability would not only strengthen diagnosis but also provide unique disease-specific biochemical insight. This feature article focuses on recent progress in the development of MRI contrast switching with molecular, macromolecular and nanoparticle-based agents.

Magnetic core-shell nanoparticles for drug delivery by nebulization

BACKGROUND

Aerosolized therapeutics hold great potential for effective treatment of various diseases including lung cancer. In this context, there is an urgent need to develop novel nanocarriers suitable for drug delivery by nebulization. To address this need, we synthesized and characterized a biocompatible drug delivery vehicle following surface coating of Fe3O4 magnetic nanoparticles (MNPs) with a polymer poly(lactic-co-glycolic acid) (PLGA). The polymeric shell of these engineered nanoparticles was loaded with a potential anti-cancer drug quercetin and their suitability for targeting lung cancer cells via nebulization was evaluated.

RESULTS

Average particle size of the developed MNPs and PLGA-MNPs as measured by electron microscopy was 9.6 and 53.2 nm, whereas their hydrodynamic swelling as determined using dynamic light scattering was 54.3 nm and 293.4 nm respectively. Utilizing a series of standardized biological tests incorporating a cell-based automated image acquisition and analysis procedure in combination with real-time impedance sensing, we confirmed that the developed MNP-based nanocarrier system was biocompatible, as no cytotoxicity was observed when up to 100 μg/ml PLGA-MNP was applied to the cultured human lung epithelial cells. Moreover, the PLGA-MNP preparation was well-tolerated in vivo in mice when applied intranasally as measured by glutathione and IL-6 secretion assays after 1, 4, or 7 days post-treatment. To imitate aerosol formation for drug delivery to the lungs, we applied quercitin loaded PLGA-MNPs to the human lung carcinoma cell line A549 following a single round of nebulization. The drug-loaded PLGA-MNPs significantly reduced the number of viable A549 cells, which was comparable when applied either by nebulization or by direct pipetting.

CONCLUSION

We have developed a magnetic core-shell nanoparticle-based nanocarrier system and evaluated the feasibility of its drug delivery capability via aerosol administration. This study has implications for targeted delivery of therapeutics and poorly soluble medicinal compounds via inhalation route.

Preparation of multifunctional nanoparticles and their assemblies

This article describes the synthesis of multifunctional nanoparticulate systems and a range of organic reactions for modifying the surface functionalities of these particles and their composites. The reactions include surface silanization, amine-azide conversion, azide-alkyne 'click' chemistry, thiol and amine click chemistry and amide coupling. In addition, we discuss a number of relevant nanoparticle preparations to exemplify the interrelationship of these reactions. This system can readily be adapted to produce a wide range of composites with different features, such as fluorescence, magnetism, plasmon resonance and multiple biofunctionalities.

Location-tuned relaxivity in Gd-doped mesoporous silica nanoparticles

In tuning the sub-particle localisation of Gd(III) binding macrocycles within a mesoporous scaffold, nanoparticle contrast agents of unprecedented relaxivity and low Gd(III) loadings can be realised.