Exosomes released by breast cancer cells under mild hyperthermic stress possess immunogenic potential and modulate polarization in vitro in macrophages.

Macrophages play a dual role in tumor initiation and progression, with both tumor-promoting and tumor-suppressive effects; hence, it is essential to understand the distinct responses of macrophages to tumor progression and therapy. Mild hyperthermia has gained importance as a therapeutic regimen against cancer due to its immunogenic nature, efficacy, and potential synergy with other therapies, yet the response of macrophages to molecular signals from hyperthermic cancer cells has not yet been clearly defined. Due to limited response rate of breast cancer to conventional therapeutics the development, and understanding of alternative therapies like hyperthermia is pertinent. In order to determine conditions corresponding to mild thermal dose, cytotoxicity of different hyperthermic temperatures and treatment durations were tested in normal murine macrophages and breast cancer cell lines. Examination of exosome release in hyperthermia-treated cancer cells revealed enhanced efflux and a larger size of exosomes released under hyperthermic stress. Exposure of naïve murine macrophages to exosomes released from 4T1 and EMT-6 cells posthyperthermia treatment, led to an increased expression of specific macrophage activation markers. Further, exosomes released by hyperthermia-treated cancer cells had increased content of heat shock protein 70 (Hsp70). Together, these results suggest a potential immunogenic role for exosomes released from cancer cells treated with mild hyperthermia.

Combining magnetic particle imaging and magnetic fluid hyperthermia for localized and image-guided treatment.

Magnetic fluid hyperthermia (MFH) has been widely investigated as a treatment tool for cancer and other diseases. However, focusing traditional MFH to a tumor deep in the body is not feasible because the in vivo wavelength of 300 kHz very low frequency (VLF) excitation fields is longer than 100 m. Recently we demonstrated that millimeter-precision localized heating can be achieved by combining magnetic particle imaging (MPI) with MFH. In principle, real-time MPI imaging can also guide the location and dosing of MFH treatments. Hence, the combination of MPI imaging plus real time localized MPI-MFH could soon permit closed-loop high-resolution hyperthermia treatment. In this review, we will discuss the fundamentals of localized MFH (e.g. physics and biosafety limitations), hardware implementation, MPI real-time guidance, and new research directions on MPI-MFH. We will also discuss how the scale up to human-sized MPI-MFH scanners could proceed.

Longitudinal evaluation of tumor microenvironment in rat focal brainstem glioma using diffusion and perfusion MRI.

BACKGROUND: Brainstem gliomas are aggressive and difficult to treat. Growth of these tumors may be characterized with MRI methods. PURPOSE: To visualize longitudinal changes in tumor volume, vascular leakiness, and tissue microstructure in an animal model of brainstem glioma. STUDY TYPE: Prospective animal model. ANIMAL MODEL: Male Sprague-Dawley rats (n = 9) were imaged with 9L gliosarcoma cells infused into the pontine reticular formation of the brainstem. The MRI tumor microenvironment was studied at 3 and 10 days postimplantation of tumor cells. FIELD STRENGTH/SEQUENCE: Diffusion tensor imaging (DTI) and dynamic contrast-enhanced (DCE)-MRI were performed at 4.7T using spin-echo multislice echo planar imaging and gradient echo multislice imaging, respectively. ASSESSMENT: Tumor leakiness was assessed by the forward volumetric transfer constant, Ktrans , estimated from DCE-MRI data. Tumor structure was evaluated with fractional anisotropy (FA) obtained from DTI. Tumor volumes, delineated by a T1 map, T2 -weighted image, FA, and DCE signal enhancement were compared. STATISTICAL TESTS: Changes in the assessed parameters within and across the groups (ie, rats 3 and 10 days post tumor cell implantation) were evaluated with Wilcoxon rank-sum tests. RESULTS: Day 3 tumors were visible mainly on contrast-enhanced images, while day 10 tumors were visible in both contrast-enhanced and diffusion-weighted images. Mean Ktrans at day 10 was 41% lower than at day 3 (P = 0.23). In day 10 tumors, FA was regionally lower in the tumor compared to normal tissue (P = 0.0004), and tumor volume, segmented based on FA map, was significantly smaller (P ≤ 0.05) than that obtained from other contrasts. DATA CONCLUSION: Contrast-enhanced MRI was found to be more sensitive in detecting early-stage tumor boundaries than other contrasts. Areas of the tumor outlined by DCE-MRI and DTI were significantly different. Over the observed period of tumor growth, average vessel leakiness decreased with tumor progression. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;49:1322-1332.

Salmonella enterica Serovar Typhimurium Alters the Extracellular Proteome of Macrophages and Leads to the Production of Proinflammatory Exosomes.

Salmonella enterica serovar Typhimurium is a Gram-negative bacterium, which can invade and survive within macrophages. Pathogenic salmonellae induce the secretion of specific cytokines from these phagocytic cells and interfere with the host secretory pathways. In this study, we describe the extracellular proteome of human macrophages infected with S Typhimurium, followed by analysis of canonical pathways of proteins isolated from the extracellular milieu. We demonstrate that some of the proteins secreted by macrophages upon S Typhimurium infection are released via exosomes. Moreover, we show that infected macrophages produce CD63+ and CD9+ subpopulations of exosomes at 2 h postinfection. Exosomes derived from infected macrophages trigger the Toll-like receptor 4-dependent release of tumor necrosis factor alpha (TNF-α) from naive macrophages and dendritic cells, but they also stimulate secretion of such cytokines as RANTES, IL-1ra, MIP-2, CXCL1, MCP-1, sICAM-1, GM-CSF, and G-CSF. Proinflammatory effects of exosomes are partially attributed to lipopolysaccharide, which is encapsulated within exosomes. In summary, we show for the first time that proinflammatory exosomes are formed in the early phase of macrophage infection with S Typhimurium and that they can be used to transfer cargo to naive cells, thereby leading to their stimulation.

Stability and Mobility of Magnetic Nanoparticles in Biological Environments Determined from Dynamic Magnetic Susceptibility Measurements.

Low tumor accumulation following systemic delivery remains a key challenge for advancing many cancer nanomedicines. One obstacle in engineering nanoparticles for high tumor accumulation is a lack of techniques to monitor their stability and mobility in situ. One way to monitor the stability and mobility of magnetic nanoparticles biological fluids in situ is through dynamic magnetic susceptibility measurements (DMS), which under certain conditions provide a measure of the particle's rotational diffusivity. For magnetic nanoparticles modified to have commonly used biomedical surface coatings, we describe a systematic comparison of DMS measurements in whole blood and tumor tissue explants. DMS measurements clearly demonstrated that stability and mobility changed over time and from one medium to another for each different coating. It was found that nanoparticles coated with covalently grafted, dense layers of PEG were the only ones to show good stability and mobility in all settings tested. These studies illustrate the utility of DMS measurements to estimate the stability and mobility of nanoparticles in situ, and which can provide insights that lead to engineering better nanoparticles for in vivo use.

Processing-Size Correlations in the Preparation of Magnetic Alginate Microspheres Through Emulsification and Ionic Crosslinking.

Magnetic alginate microspheres are biocompatible due to their alginate matrix, and motion-controllable by applied magnetic fields due to their magnetic character. Therefore, they have the potential of being used as vessels to a broad variety of materials, including drugs and therapeutic agents, facilitating entry to biological systems in a relatively non-invasive manner. Here, magnetic alginate microspheres were prepared through an emulsification and ionic cross-linking process, where a mixture of alginate and iron oxide magnetic nanoparticles was initially dispersed in a continuous phase, followed by gelation of this dispersed phase into microspheres by cross-linking the dispersion with calcium ions. The resulting magnetic alginate microspheres were found to be superparamagnetic and to respond to applied magnetic fields by chain formation. The effect of shear rate, alginate concentration, and magnetic nanoparticle concentration on microsphere size was investigated with the aim to control the size of microspheres with respect to process and formulation parameters. Two of these parameters, shear rate and alginate concentration, were used to correlate experimental results with a theoretical model for the case where the dispersed phase is more viscous than the continuous phase.

Breakdown of the Stokes-Einstein Relation for the Rotational Diffusivity of Polymer Grafted Nanoparticles in Polymer Melts.

We report observations of breakdown of the Stokes-Einstein relation for the rotational diffusivity of polymer-grafted spherical nanoparticles in polymer melts. The rotational diffusivity of magnetic nanoparticles coated with poly(ethylene glycol) dispersed in poly(ethylene glycol) melts was determined through dynamic magnetic susceptibility measurements of the collective rotation of the magnetic nanoparticles due to imposed time-varying magnetic torques. These measurements clearly demonstrate the existence of a critical molecular weight for the melt polymer, below which the Stokes-Einstein relation accurately describes the rotational diffusivity of the polymer-grafted nanoparticles and above which the Stokes-Einstein relation ceases to apply. This critical molecular weight was found to correspond to a chain contour length that approximates the hydrodynamic diameter of the nanoparticles.

Nanoscale thermal phenomena in the vicinity of magnetic nanoparticles in alternating magnetic fields.

Magnetic nanoparticles can be made to dissipate heat to their immediate surroundings in response to an applied alternating magnetic field. This property, combined with the biocompatibility of iron oxide nanoparticles and the ability of magnetic fields to penetrate deep in the body, makes magnetic nanoparticles attractive in a range of biomedical applications where thermal energy is used either directly to achieve a therapeutic effect or indirectly to actuate the release of a therapeutic agent. Although the concept of bulk heating of fluids and tissues using energy dissipated by magnetic nanoparticles has been well accepted and applied for several decades, many new and exciting biomedical applications of magnetic nanoparticles take advantage of heat effects that are confined to the immediate nanoscale vicinity of the nanoparticles. Until recently the existence of these nanoscale thermal phenomena had remained controversial. In this short review we summarize some of the recent developments in this field and emerging applications for nanoscale thermal phenomena in the vicinity of magnetic nanoparticles in alternating magnetic fields.

Theoretical Predictions for Spatially-Focused Heating of Magnetic Nanoparticles Guided by Magnetic Particle Imaging Field Gradients.

Magnetic nanoparticles in alternating magnetic fields (AMFs) transfer some of the field's energy to their surroundings in the form of heat, a property that has attracted significant attention for use in cancer treatment through hyperthermia and in developing magnetic drug carriers that can be actuated to release their cargo externally using magnetic fields. To date, most work in this field has focused on the use of AMFs that actuate heat release by nanoparticles over large regions, without the ability to select specific nanoparticle-loaded regions for heating while leaving other nanoparticle-loaded regions unaffected. In parallel, magnetic particle imaging (MPI) has emerged as a promising approach to image the distribution of magnetic nanoparticle tracers in vivo, with sub-millimeter spatial resolution. The underlying principle in MPI is the application of a selection magnetic field gradient, which defines a small region of low bias field, superimposed with an AMF (of lower frequency and amplitude than those normally used to actuate heating by the nanoparticles) to obtain a signal which is proportional to the concentration of particles in the region of low bias field. Here we extend previous models for estimating the energy dissipation rates of magnetic nanoparticles in uniform AMFs to provide theoretical predictions of how the selection magnetic field gradient used in MPI can be used to selectively actuate heating by magnetic nanoparticles in the low bias field region of the selection magnetic field gradient. Theoretical predictions are given for the spatial decay in energy dissipation rate under magnetic field gradients representative of those that can be achieved with current MPI technology. These results underscore the potential of combining MPI and higher amplitude/frequency actuation AMFs to achieve selective magnetic fluid hyperthermia (MFH) guided by MPI.

Optimization of synthesis and peptization steps to obtain iron oxide nanoparticles with high energy dissipation rates.

Magnetic Fluid Hyperthermia (MFH) uses heat generated by magnetic nanoparticles exposed to alternating magnetic fields to cause a temperature increase in tumors to the hyperthermia range (43-47 °C), inducing apoptotic cancer cell death. As with all cancer nanomedicines, one of the most significant challenges with MFH is achieving high nanoparticle accumulation at the tumor site. This motivates development of synthesis strategies that maximize the rate of energy dissipation of iron oxide magnetic nanoparticles, preferable due to their intrinsic biocompatibility. This has led to development of synthesis strategies that, although attractive from the point of view of chemical elegance, may not be suitable for scale-up to quantities necessary for clinical use. On the other hand, to date the aqueous co-precipitation synthesis, which readily yields gram quantities of nanoparticles, has only been reported to yield sufficiently high specific absorption rates after laborious size selective fractionation. This work focuses on improvements to the aqueous co-precipitation of iron oxide nanoparticles to increase the specific absorption rate (SAR), by optimizing synthesis conditions and the subsequent peptization step. Heating efficiencies up to 1,048 W/gFe (36.5 kA/m, 341 kHz; ILP = 2.3 nH·m2·kg-1) were obtained, which represent one of the highest values reported for iron oxide particles synthesized by co-precipitation without size-selective fractionation. Furthermore, particles reached SAR values of up to 719 W/gFe (36.5 kA/m, 341 kHz; ILP = 1.6 nH·m2·kg-1) when in a solid matrix, demonstrating they were capable of significant rates of energy dissipation even when restricted from physical rotation. Reduction in energy dissipation rate due to immobilization has been identified as an obstacle to clinical translation of MFH. Hence, particles obtained with the conditions reported here have great potential for application in nanoscale thermal cancer therapy.

Magnetic fluid hyperthermia: advances, challenges, and opportunity.

Though the concepts of magnetic fluid hyperthermia (MFH) were originally proposed over 50 years ago, the technique has yet to be successfully translated into routine clinical application. Significant challenges must be addressed if the field is to progress and realise its potential as an option for treatment of diseases such as cancer. These challenges include determining the optimum fields and frequencies that maximise the effectiveness of MFH without significant detrimental off-target effects on healthy tissue, achieving sufficient concentrations of magnetic nanoparticles (MNPs) within the target tumour, and developing a better mechanistic understanding of MNP-mediated energy deposition and its effects on cells and tissue. On the other hand, emerging experimental evidence indicates that local thermal effects indeed occur in the vicinity of energy-dissipating MNPs. These findings point to the opportunity of engineering MNPs for the selective destruction of cells and/or intracellular structures without the need for a macroscopic tissue temperature rise, in what we here call magnetically mediated energy delivery (MagMED).

Role of viscosity in influencing the glass-forming ability of organic molecules from the undercooled melt state.

PURPOSE: Understanding the critical factors governing the crystallization tendency of organic compounds is vital when assessing the feasibility of an amorphous formulation to improve oral bioavailability. The objective of this study was to investigate potential links between viscosity and crystallization tendency for organic compounds from the undercooled melt state. METHODS: Steady shear rate viscosities of numerous compounds were measured using standard rheometry as a function of temperature through the undercooled melt regime. Data for each compound were fit to the Vogel-Tamman-Fulcher (VTF) equation; kinetic fragility via strength parameter (D) was determined. RESULTS: Compounds with high crystallization tendencies exhibited lower melt viscosities than compounds with low crystallization tendencies. A correlation was observed between rate of change in viscosity with temperature and crystallization tendency, with slowly crystallizing compounds exhibiting larger increases in viscosity as temperature decreased below T(m). Calculated strength parameters indicated all compounds were kinetically fragile liquids; thus, kinetic fragility may not accurately assess glass-forming ability from undercooled melt state. CONCLUSIONS: A link was observed between the viscosity of a compound through the undercooled melt regime and its resultant crystallization tendency, indicating viscosity is a critical parameter to fully understand crystallization tendency of organic compounds.

Hyperthermia induced by magnetic nanoparticles improves the effectiveness of the anticancer drug cis-diamminedichloroplatinum.

The cytotoxic enhancement of cisplatin by magnetic fluid hyperthermia (MFH) was investigated in human colon adenocarcinoma cells (Caco-2). A nanoparticle platform based on iron oxide functionalized with carboxymethyl dextran was employed to produce heat at the nanoscale. To assess the synergistic effect of hyperthermia and the anticancer drug cis-Diamminedichloroplatinum, commonly known as cisplatin (CIS), cell viability was measured 24, 48, and 72 hours after three different combined hyperthermia and CIS exposure sequences. These included CIS incubation prior to hyperthermia or magnetic fluid hyperthermia, CIS exposure only during hyperthermia or MFH, and additional CIS incubation following hyperthermia or MFH. Additional incubation of CIS after hyperthermia treatment appears to be more effective than prior CIS incubation for both hyperthermia treatments. Viability data also indicated that MFH combined with CIS is significantly more effective than hot water hyperthermia at the same temperature. A CIS concentration an order of magnitude lower than the calculated IC50 was found to be very effective in reducing cell viability. Such dramatic differences suggest that MFH may enhance the passive transport of CIS.

Perfusion, cryopreservation, and nanowarming of whole hearts using colloidally stable magnetic cryopreservation agent solutions.

Nanowarming of cryopreserved organs perfused with magnetic cryopreservation agents (mCPAs) could increase donor organ utilization by extending preservation time and avoiding damage caused by slow and nonuniform rewarming. Here, we report formulation of an mCPA containing superparamagnetic iron oxide nanoparticles (SPIONs) that are stable against aggregation in the cryopreservation agent VS55 before and after vitrification and nanowarming and that achieve high-temperature rise rates of up to 321°C/min under an alternating magnetic field. These SPIONs and mCPAs have low cytotoxicity against primary cardiomyocytes. We demonstrate successful perfusion of whole rat hearts with the mCPA and removal using Custodiol HTK solution, even after vitrification, cryostorage in liquid nitrogen for 1 week, and nanowarming under an alternating magnetic field. Quantification of SPIONs in the hearts using magnetic particle imaging demonstrates that the formulated mCPAs are suitable for perfusion, vitrification, and nanowarming of whole organs with minimal residual iron in tissues.

Fundamental solutions to the bioheat equation and their application to magnetic fluid hyperthermia.

Methods of predicting temperature profiles during local hyperthermia treatment are very important to avoid damage to healthy tissue. With this aim, fundamental solutions of Pennes' bioheat equation are derived in rectangular, cylindrical, and spherical coordinates. The medium is idealised as isotropic with effective thermal properties. Temperature distributions due to space- and time-dependent heat sources are obtained by the solution method presented. Applications of the fundamental solutions are addressed with emphasis on a particular problem of Magnetic Fluid Hyperthermia (MFH) consisting of a thin shell of magnetic nanoparticles in the outer surface of a spherical solid tumour. It is observed from the solution of this particular problem that the temperature profiles are strongly dependent on the distribution of the magnetic nanoparticles within the tissue. An almost uniform temperature profile is obtained inside the tumour with little penetration of therapeutic temperatures to the outer region of healthy tissue. The fundamental solutions obtained can be used to develop boundary element methods to predict temperature profiles with more complicated geometries.

Chemiluminescence from the Ba((3)P)+N(2)O-->BaO(A (1)Sigma(+))+N(2) reaction: Collision energy effects on the product rotational alignment and energy release.

Both fully dispersed unpolarized and polarized chemiluminescence spectra from the Ba((3)P)+N(2)O reaction have been recorded under hyperthermal laser-ablated atomic beam-Maxwellian gas conditions at three specific average collision energies E(c) in the range of 4.82-7.47 eV. A comprehensive analysis of the whole data series suggests that the A (1)Sigma(+)-->X (1)Sigma(+) band system dominates the chemiluminescence. The polarization results revealed that the BaO(A (1)Sigma(+)) product rotational alignment is insensitive to its vibrational state upsilon(') at E(c)=4.82 eV but develops into an strong negative correlation between product rotational alignment and upsilon(') at 7.47 eV. The results are interpreted in terms of a direct mechanism involving a short-range, partial electron transfer from Ba((3)P) to N(2)O which is constrained by the duration of the collision, so that the reaction has a larger probability to occur when the collision time is larger than the time needed for N(2)O bending. The latter in turn determines that, at any given E(c), collinear reactive intermediates are preferentially involved when the highest velocity components of the corresponding collision energy distributions are sampled. Moreover, the data at 4.82 eV suggest that a potential barrier to reaction which favors charge transfer to bent N(2)O at chiefly coplanar geometries is operative for most of the reactive trajectories that sample the lowest velocity components. Such a barrier would arise from the relevant ionic-covalent curve crossings occurring in the repulsive region of the covalent potential Ba((3)P)cdots, three dots, centeredN(2)O((1)Sigma(+)); from this crossing the BaO(A (1)Sigma(+)) product may be reached through mixings in the exit channel with potential energy surfaces leading most likely to the spin-allowed b (3)Pi and a (3)Sigma(+) products. The variation with increasing E(c) of both the magnitude of the average BaO(A (1)Sigma(+)) rotational alignment and the BaO(A (1)Sigma(+)) rovibrational excitation, as obtained from spectral simulations of the unpolarized chemiluminescence spectra, consistently points to additional dynamic factors, most likely the development of induced repulsive energy release as the major responsible for the angular momentum and energy disposal at the two higher E(c) studied. The results of a simplified version of the direct interaction with product repulsion-distributed as in photodissociation model do not agree with the observed average product rotational alignments, showing that a more realistic potential energy surface model will be necessary to explain the present results.

Computational predictions of enhanced magnetic particle imaging performance by magnetic nanoparticle chains.

The magnetic particle imaging (MPI) performance of collections of chains of magnetic nanoparticles with Néel and Brownian relaxation mechanisms was studied by carrying out simulations based on the Landau-Lifshitz-Gilbert equation and rotational Brownian dynamics, respectively. The effect of magnetic dipole-dipole interactions within chains on the time-domain average magnetic dipole moment and corresponding dynamic hysteresis loops, harmonic spectra, and point spread functions (PSFs) of the particle chains was evaluated. The results show that interactions within chains lead to 'square-like' dynamic hysteresis loops and enhanced MPI performance, compared to chains of non-interacting nanoparticles. For nanoparticles with the Brownian relaxation mechanism, subjected to a superimposed alternating and ramping magnetic field mimicking the magnetic field in MPI applications, we studied the dependence of x-space MPI performance of particle chains on parameters such as the amplitude of the alternating magnetic field, surface-to-surface separation between nanoparticles, solvent viscosity, and the number of nanoparticles in a chain. The results illustrate that magnetic dipole-dipole interactions within a chain contribute to enhanced MPI performance, and also suggest that there exist optimal values of the above parameters that lead to the best x-space MPI performance, i.e. maximum peak signal intensity and smallest full-width-at-half-maximum in PSFs.

In vitro Ultrasonic Potentiation of 2-Phenylethynesulfonamide/Magnetic Fluid Hyperthermia Combination Treatments for Ovarian Cancer.

BACKGROUND: Magnetic Fluid Hyperthermia (MFH) is a promising adjuvant for chemotherapy, potentiating the action of anticancer agents. However, drug delivery to cancer cells must be optimized to improve the overall therapeutic effect of drug/MFH combination treatments. PURPOSE: The aim of this work was to demonstrate the potentiation of 2-phenylethynesulfonamide (PES) at various combination treatments with MFH, using low-intensity ultrasound as an intracellular delivery enhancer. METHODS: The effect of ultrasound (US), MFH, and PES was first evaluated individually and then as combination treatments. Definity® microbubbles and polyethylene glycol (PEG)-coated iron oxide nanoparticles were used to induce cell sonoporation and MFH, respectively. Assessment of cell membrane permeabilization was evaluated via fluorescence microscopy, iron uptake by cells was quantified by UV-Vis spectroscopy, and cell viability was determined using automatic cell counting. RESULTS: Notable reductions in cancer cell viability were observed when ultrasound was incorporated. For example, the treatment US+PES reduced cell viability by 37% compared to the non-toxic effect of the drug. Similarly, the treatment US+MFH using mild hyperthermia (41°C), reduced cell viability by an additional 18% when compared to the effect of MH alone. Significant improvements were observed for the combination of US+PES+MFH with cell viability reduced by an additional 26% compared to the PES+MFH group. The improved cytotoxicity was attributed to enhanced drug/nanoparticle intracellular delivery, with iron uptake values nearly twice those achieved without ultrasound. Various treatment schedules were examined, and all of them showed substantial cell death, indicating that the time elapsed between sonoporation and magnetic field exposure was not significant. CONCLUSION: Superior cancer cell-killing patterns took place when ultrasound was incorporated thus demonstrating the in vitro ultrasonic potentiation of PES and mild MFH. This work demonstrated that ultrasound is a promising non-invasive enhancer of PES/MFH combination treatments, aiming to establish a sono-thermo-chemotherapy in the treatment of ovarian cancer.

Effects of particle diameter and magnetocrystalline anisotropy on magnetic relaxation and magnetic particle imaging performance of magnetic nanoparticles.

The dynamic magnetization of immobilized spherical single-domain magnetic nanoparticles (MNPs) with uniaxial or cubic magnetocrystalline anisotropy was studied computationally by executing simulations based on the Landau-Lifshitz-Gilbert (LLG) equation. For situations when a static magnetic field was suddenly applied and then removed, the effects of particle diameter and anisotropy (considering both type of symmetry and characteristic energy) on the characteristic magnetic relaxation time were studied parametrically. The results, for both anisotropy symmetries, show that when a static magnetic field is suddenly turned on or off the MNPs undergo a successive two-step or combined one-step relaxation. Whether a MNP relaxes with one or two steps when the field is turned on is determined by the competition between the energy of the applied magnetic field, the magnetic anisotropy energy, and thermal energy. When the applied magnetic field is suddenly turned off, our results show good agreement with theoretical predictions for the cases of [Formula: see text] and [Formula: see text], where [Formula: see text] represents the magnetic anisotropy energy barrier, [Formula: see text] is the Boltzmann constant and [Formula: see text] represents the absolute temperature. For the case of an applied alternating magnetic field (AMF) that is typical of magnetic particle imaging (MPI) applications, the effects of particle diameter and anisotropy symmetry were studied in terms of time-domain magnetization dynamics, dynamic hysteresis loops, harmonic spectra, and x-space point spread functions (PSFs). Results illustrate that the type of magnetocrystalline anisotropy (uniaxial versus cubic) has a significant effect on the MPI performance of the nanoparticles. These computational studies provide insight into the role of particle diameter and magnetic anisotropy on the performance of MNPs for applications in magnetorelaxometry and MPI.

The clearance and biodistribution of magnetic composite nanoparticles in healthy and osteoarthritic rat knees.

Intra-articular injections are the most direct route for administering osteoarthritis (OA) therapies, yet how drug carriers distribute within the joint remains understudied. To this end, we developed a magnetic composite nanoparticle that can be tracked with fluorescence in vivo via an in vivo imaging system (IVIS), and quantified ex vivo via electron paramagnetic resonance (EPR) spectroscopy. Using this particle, the effects of age and OA pathogenesis on particle clearance and distribution were evaluated in the medial meniscus transection model of OA (5-, 10-, and 15-month old male Lewis rats). At 9 weeks after meniscus transection, composite nanoparticles were injected and joint clearance was assessed via IVIS. At 2 weeks after injection, animals were euthanized and particle distribution was quantified ex vivo via EPR spectroscopy. IVIS and EPR spectroscopy data indicate a predominant amount of particles remained in the joint after 14 days. EPR spectroscopy data suggests particles cleared more slowly from OA knees than from the contralateral control, with particles clearing more slowly from 15-month old rats than from 5- and 10-month old rats. This study demonstrates the importance of including both age and OA as factors when evaluating nanoparticles for intra-articular drug delivery.