Spatially selective delivery of living magnetic microrobots through torque-focusing

Rotating magnetic fields enable biomedical microrobots to overcome physiological barriers and promote extravasation and accumulation in tumors. Nevertheless, targeting deeply situated tumors requires suppression of off-target actuation in healthy tissue. Here, we investigate a control strategy for applying spatially selective torque density to microrobots by combining rotating fields with magnetostatic selection fields. Taking magnetotactic bacteria as diffuse torque-based actuators, we numerically model off-target torque suppression, indicating the feasibility of centimeter to millimeter resolution for human applications. We study focal torque application in vitro, observing off-target suppression of actuation-dependent effects such as colonization of bacteria in tumor spheroids. We then design and construct a mouse-scale torque-focusing apparatus capable of maneuvering the focal point. Applying this system to a mouse tumor model increased accumulation of intravenously injected bacteria within tumors receiving focused actuation compared to non-actuated or globally actuated groups. This control scheme combines the advantages of torque-based actuation with spatial targeting.

Magnetically controlled cyclic microscale deformation of in vitro cancer invasion models

Mechanical cues play an important role in the metastatic cascade of cancer. Three-dimensional (3D) tissue matrices with tunable stiffness have been extensively used as model systems of the tumor microenvironment for physiologically relevant studies. Tumor-associated cells actively deform these matrices, providing mechanical cues to other cancer cells residing in the tissue. Mimicking such dynamic deformation in the surrounding tumor matrix may help clarify the effect of local strain on cancer cell invasion. Remotely controlled microscale magnetic actuation of such 3D in vitro systems is a promising approach, offering a non-invasive means for in situ interrogation. Here, we investigate the influence of cyclic deformation on tumor spheroids embedded in matrices, continuously exerted for days by cell-sized anisotropic magnetic probes, referred to as μRods. Particle velocimetry analysis revealed the spatial extent of matrix deformation produced in response to a magnetic field, which was found to be on the order of 200 μm, resembling strain fields reported to originate from contracting cells. Intracellular calcium influx was observed in response to cyclic actuation, as well as an influence on cancer cell invasion from 3D spheroids, as compared to unactuated controls. Furthermore, RNA sequencing revealed subtle upregulation of certain genes associated with migration and stress, such as induced through mechanical deformation, for spheroids exposed to actuation vs. controls. Localized actuation at one side of a tumor spheroid tended to result in anisotropic invasion toward the μRods causing the deformation. In summary, our approach offers a strategy to test and control the influence of non-invasive micromechanical cues on cancer cell invasion and metastasis.

Inductive sensing of magnetic microrobots under actuation by rotating magnetic fields

The engineering space for magnetically manipulated biomedical microrobots is rapidly expanding. This includes synthetic, bioinspired, and biohybrid designs, some of which may eventually assume clinical roles aiding drug delivery or performing other therapeutic functions. Actuating these microrobots with rotating magnetic fields (RMFs) and the magnetic torques they exert offers the advantages of efficient mechanical energy transfer and scalable instrumentation. Nevertheless, closed-loop control still requires a complementary noninvasive imaging modality to reveal position and trajectory, such as ultrasound or X-rays, increasing complexity and posing a barrier to use. Here, we investigate the possibility of combining actuation and sensing via inductive detection of model microrobots under field magnitudes ranging from 100 s of microtesla to 10 s of millitesla rotating at 1 to 100 Hz. A prototype apparatus accomplishes this using adjustment mechanisms for both phase and amplitude to finely balance sense and compensation coils, suppressing the background signal of the driving RMF by 90 dB. Rather than relying on frequency decomposition to analyze signals, we show that, for rotational actuation, phase decomposition is more appropriate. We demonstrate inductive detection of a micromagnet placed in two distinct viscous environments using RMFs with fixed and time-varying frequencies. Finally, we show how magnetostatic selection fields can spatially isolate inductive signals from a micromagnet actuated by an RMF, with the resolution set by the relative magnitude of the selection field and the RMF. The concepts developed here lay a foundation for future closed-loop control schemes for magnetic microrobots based on simultaneous inductive sensing and actuation.

Engineering Responsive Ultrasound Contrast Agents Through Crosslinked Networks on Lipid-Shelled Microbubbles

Ultrasound imaging with contrast agents, especially with lipid-shelled microbubbles, has become a vital tool in clinical diagnostics. Efforts to adapt these agents for molecular imaging have typically focused on targeted binding. More recently, crosslinking the lipid shell to alter its mechanical properties, followed by decrosslinking upon exposure to a stimulus, has been shown as a promising approach for imaging soluble molecular targets. Nevertheless, a systematic study of the influence of crosslinker concentration and structure on the mechanical properties of microbubbles has not been undertaken. An improved understanding of the role of these parameters is necessary to more effectively design contrast agents that detect proteases, an informative class of soluble disease markers. Here, the influence of crosslinker parameters on the acoustic properties of microbubbles, developing a model of crosslinker network formation on microbubble shells that explains the experimental observations, are studied. By incorporating cleavable elements that respond to UV light or proteolysis, kinetically resolved acoustic detection of these stimuli and the relevance of crosslinker design are demonstrated. The framework established in this study can be readily adapted to other protease-cleavable units and provides a basis for the future development of responsive ultrasound contrast agents for molecular imaging of proteolytic activity.

3D magnetically controlled spatiotemporal probing and actuation of collagen networks from a single cell perspective

Cells continuously sense and react to mechanical cues from their surrounding matrix, which consists of a fibrous network of biopolymers that influences their fate and behavior. Several powerful methods employing magnetic control have been developed to assess the micromechanical properties within extracellular matrix (ECM) models hosting cells. However, many of these are limited to in-plane sensing and actuation, which does not allow the matrix to be probed within its full 3D context. Moreover, little attention has been given to factors specific to the model ECM systems that can profoundly influence the cells contained there. Here we present methods to spatiotemporally probe and manipulate extracellular matrix networks at the scale relevant to cells using magnetic microprobes (μRods). Our techniques leverage 3D magnetic field generation, physical modeling, and image analysis to examine and apply mechanical stimuli to fibrous collagen matrices. We determined shear moduli ranging between hundreds of Pa to tens of kPa and modeled the effects of proximity to rigid surfaces and local fiber densification. We analyzed the spatial extent and dynamics of matrix deformation produced in response to magnetic torques on the order of 10 pNm, deflecting fibers over an area spanning tens of micrometers. Finally, we demonstrate 3D actuation and pose extraction of fluorescently labelled μRods.

Magnetothermal nanoparticle technology alleviates parkinsonian-like symptoms in mice

Deep brain stimulation (DBS) has long been used to alleviate symptoms in patients suffering from psychiatric and neurological disorders through stereotactically implanted electrodes that deliver current to subcortical structures via wired pacemakers. The application of DBS to modulate neural circuits is, however, hampered by its mechanical invasiveness and the use of chronically implanted leads, which poses a risk for hardware failure, hemorrhage, and infection. Here, we demonstrate that a wireless magnetothermal approach to DBS (mDBS) can provide similar therapeutic benefits in two mouse models of Parkinson's disease, the bilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and in the unilateral 6-hydroxydopamine (6-OHDA) model. We show magnetothermal neuromodulation in untethered moving mice through the activation of the heat-sensitive capsaicin receptor (transient receptor potential cation channel subfamily V member 1, TRPV1) by synthetic magnetic nanoparticles. When exposed to an alternating magnetic field, the nanoparticles dissipate heat, which triggers reversible firing of TRPV1-expressing neurons. We found that mDBS in the subthalamic nucleus (STN) enables remote modulation of motor behavior in healthy mice. Moreover, mDBS of the STN reversed the motor deficits in a mild and severe parkinsonian model. Consequently, this approach is able to activate deep-brain circuits without the need for permanently implanted hardware and connectors.

Capillary Microfluidics for Monitoring Medication Adherence

Medication adherence is a medical and societal issue worldwide, with approximately half of patients failing to adhere to prescribed treatments. The goal of this Minireview is to examine how recent work on microfluidics for point-of-care diagnostics may be used to enhance adherence to medication. It specifically focuses on capillary microfluidics since these devices are self-powered, easy to use, and well established for diagnostics and drug monitoring. Considering that an improvement in medication adherence can have a much larger effect than the development of new medical treatments, it is long overdue for the research communities working in chemistry, biology, pharmacology, and material sciences to consider developing technologies to enhance medication adherence. For these reasons, this Minireview is not meant to be exhaustive but rather to provide a quick starting point for researchers interested in joining this complex but intriguing and exciting field of research.

The Tumor Proteolytic Landscape: A Challenging Frontier in Cancer Diagnosis and Therapy

In recent decades, dysregulation of proteases and atypical proteolysis have become increasingly recognized as important hallmarks of cancer, driving community-wide efforts to explore the proteolytic landscape of oncologic disease. With more than 100 proteases currently associated with different aspects of cancer development and progression, there is a clear impetus to harness their potential in the context of oncology. Advances in the protease field have yielded technologies enabling sensitive protease detection in various settings, paving the way towards diagnostic profiling of disease-related protease activity patterns. Methods including activity-based probes and substrates, antibodies, and various nanosystems that generate reporter signals, i.e., for PET or MRI, after interaction with the target protease have shown potential for clinical translation. Nevertheless, these technologies are costly, not easily multiplexed, and require advanced imaging technologies. While the current clinical applications of protease-responsive technologies in oncologic settings are still limited, emerging technologies and protease sensors are poised to enable comprehensive exploration of the tumor proteolytic landscape as a diagnostic and therapeutic frontier. This review aims to give an overview of the most relevant classes of proteases as indicators for tumor diagnosis, current approaches to detect and monitor their activity in vivo, and associated therapeutic applications.

Production losses five months after outbreak with a recombinant of two PRRSV vaccine strains in 13 Danish sow herds

Background

In July 2019, a PRRSV-negative boar station was infected with a recombinant of two PRRSV vaccine strains, which subsequently spread to at least 36 herds that had received semen from the boar station. In the following months, all the infected herds reported reduced productivity. The aim of the present study was to evaluate the impact of the PRRS outbreak.

Results

Production data were collected from 13 of the herds. The average levels of farrowings/week, liveborns/litter, stillborns/litter, pre-weaning mortality and weaned pigs/litter were compared for the five-month period after infection and the preceding 7 months before infection with the new variant of PRRSV-1. Twelve herds experienced a decrease in farrowings/week (0.1-10.8% fewer farrowings/week), and all herds experienced fewer liveborns (0.8-4.8 fewer liveborns/litter) and more stillborns (0.6-2.6 more stillborns/litter). Pre-weaning mortality nearly doubled in half of the herds. Overall, the 13 herds were missing 2.4-6.5 pigs/litter at weaning during the 5 months after infection compared to the seven preceding months before infection.

Conclusion

In this study, the impact of this new PRRSV-1 variant on productivity exceeded that typically seen in Danish herds infected with PRRSV-1.

Magnetothermal Multiplexing for Selective Remote Control of Cell Signaling

Magnetic nanoparticles have garnered sustained research interest for their promise in biomedical applications including diagnostic imaging, triggered drug release, cancer hyperthermia, and neural stimulation. Many of these applications make use of heat dissipation by ferrite nanoparticles under alternating magnetic fields, with these fields acting as an externally administered stimulus that is either present or absent, toggling heat dissipation on and off. Here, we motivate and demonstrate an extension of this concept, magnetothermal multiplexing, in which exposure to alternating magnetic fields of differing amplitude and frequency can result in selective and independent heating of magnetic nanoparticle ensembles. The differing magnetic coercivity of these particles, empirically characterized by a custom high amplitude alternating current magnetometer, informs the systematic selection of a multiplexed material system. This work culminates in a demonstration of magnetothermal multiplexing for selective remote control of cellular signaling in vitro.

Transgene-free remote magnetothermal regulation of adrenal hormones

The field of bioelectronic medicines seeks to modulate electrical signaling within peripheral organs, providing temporally precise control of physiological functions. This is usually accomplished with implantable devices, which are often unsuitable for interfacing with soft and highly vascularized organs. Here, we demonstrate an alternative strategy for modulating peripheral organ function, which relies on the endogenous expression of a heat-sensitive cation channel, transient receptor potential vanilloid family member 1 (TRPV1), and heat dissipation by magnetic nanoparticles (MNPs) in remotely applied alternating magnetic fields. We use this approach to wirelessly control adrenal hormone secretion in genetically intact rats. TRPV1-dependent calcium influx into the cells of adrenal cortex and medulla is sufficient to drive rapid release of corticosterone and (nor)epinephrine. As altered levels of these hormones have been correlated with mental conditions such as posttraumatic stress disorder and major depression, our approach may facilitate the investigation of physiological and psychological impacts of stress.

Remotely controlled chemomagnetic modulation of targeted neural circuits

Connecting neural circuit output to behaviour can be facilitated by the precise chemical manipulation of specific cell populations^1,2. Engineered receptors exclusively activated by designer small molecules enable manipulation of specific neural pathways^3,4. However, their application to studies of behaviour has thus far been hampered by a trade-off between the low temporal resolution of systemic injection versus the invasiveness of implanted cannulae or infusion pumps². Here, we developed a remotely controlled chemomagnetic modulation-a nanomaterials-based technique that permits the pharmacological interrogation of targeted neural populations in freely moving subjects. The heat dissipated by magnetic nanoparticles (MNPs) in the presence of alternating magnetic fields (AMFs) triggers small-molecule release from thermally sensitive lipid vesicles with a 20 s latency. Coupled with the chemogenetic activation of engineered receptors, this technique permits the control of specific neurons with temporal and spatial precision. The delivery of chemomagnetic particles to the ventral tegmental area (VTA) allows the remote modulation of motivated behaviour in mice. Furthermore, this chemomagnetic approach activates endogenous circuits by enabling the regulated release of receptor ligands. Applied to an endogenous dopamine receptor D1 (DRD1) agonist in the nucleus accumbens (NAc), a brain area involved in mediating social interactions, chemomagnetic modulation increases sociability in mice. By offering a temporally precise control of specified ligand-receptor interactions in neurons, this approach may facilitate molecular neuroscience studies in behaving organisms.

Magnetic Strategies for Nervous System Control

Magnetic fields pass through tissue undiminished and without producing harmful effects, motivating their use as a wireless, minimally invasive means to control neural activity. Here, we review mechanisms and techniques coupling magnetic fields to changes in electrochemical potentials across neuronal membranes. Biological magnetoreception, although incompletely understood, is discussed as a potential source of inspiration. The emergence of magnetic properties in materials is reviewed to clarify the distinction between biomolecules containing transition metals and ferrite nanoparticles that exhibit significant net moments. We describe recent developments in the use of magnetic nanomaterials as transducers converting magnetic stimuli to forms readily perceived by neurons and discuss opportunities for multiplexed and bidirectional control as well as the challenges posed by delivery to the brain. The variety of magnetic field conditions and mechanisms by which they can be coupled to neuronal signaling cascades highlights the desirability of continued interchange between magnetism physics and neurobiology.

Practical methods for generating alternating magnetic fields for biomedical research

Alternating magnetic fields (AMFs) cause magnetic nanoparticles (MNPs) to dissipate heat while leaving surrounding tissue unharmed, a mechanism that serves as the basis for a variety of emerging biomedical technologies. Unfortunately, the challenges and costs of developing experimental setups commonly used to produce AMFs with suitable field amplitudes and frequencies present a barrier to researchers. This paper first presents a simple, cost-effective, and robust alternative for small AMF working volumes that uses soft ferromagnetic cores to focus the flux into a gap. As the experimental length scale increases to accommodate animal models (working volumes of 100s of cm³ or greater), poor thermal conductivity and volumetrically scaled core losses render that strategy ineffective. Comparatively feasible strategies for these larger volumes instead use low loss resonant tank circuits to generate circulating currents of 1 kA or greater in order to produce the comparable field amplitudes. These principles can be extended to the problem of identifying practical routes for scaling AMF setups to humans, an infrequently acknowledged challenge that influences the extent to which many applications of MNPs may ever become clinically relevant.

Magnetically Actuated Protease Sensors for in Vivo Tumor Profiling

Targeted cancer therapies require a precise determination of the underlying biological processes driving tumorigenesis within the complex tumor microenvironment. Therefore, new diagnostic tools that capture the molecular activity at the disease site in vivo are needed to better understand tumor behavior and ultimately maximize therapeutic responses. Matrix metalloproteinases (MMPs) drive multiple aspects of tumorigenesis, and their activity can be monitored using engineered peptide substrates as protease-specific probes. To identify tumor specific activity profiles, local sampling of the tumor microenvironment is necessary, such as through remote control of probes, which are only activated at the tumor site. Alternating magnetic fields (AMFs) provide an attractive option to remotely apply local triggering signals because they penetrate deep into the body and are not likely to interfere with biological processes due to the weak magnetic properties of tissue. Here, we report the design and evaluation of a protease-activity nanosensor that can be remotely activated at the site of disease via an AMF at 515 kHz and 15 kA/m. Our nanosensor was composed of thermosensitive liposomes containing functionalized protease substrates that were unveiled at the target site by remotely triggered heat dissipation of coencapsulated magnetic nanoparticles (MNPs). This nanosensor was combined with a unique detection assay to quantify the amount of cleaved substrates in the urine. We applied this spatiotemporally controlled system to determine tumor protease activity in vivo and identified differences in substrate cleavage profiles between two mouse models of human colorectal cancer.

High-Performance Ferrite Nanoparticles through Nonaqueous Redox Phase Tuning

From magnetic resonance imaging to cancer hyperthermia and wireless control of cell signaling, ferrite nanoparticles produced by thermal decomposition methods are ubiquitous across biomedical applications. While well-established synthetic protocols allow for precise control over the size and shape of the magnetic nanoparticles, structural defects within seemingly single-crystalline materials contribute to variability in the reported magnetic properties. We found that stabilization of metastable wüstite in commonly used hydrocarbon solvents contributed to significant cation disorder, leading to nanoparticles with poor hyperthermic efficiencies and transverse relaxivities. By introducing aromatic ethers that undergo radical decomposition upon thermolysis, the electrochemical potential of the solvent environment was tuned to favor the ferrimagnetic phase. Structural and magnetic characterization identified hallmark features of nearly defect-free ferrite nanoparticles that could not be demonstrated through postsynthesis oxidation with nearly 500% increase in the specific loss powers and transverse relaxivity times compared to similarly sized nanoparticles containing defects. The improved crystallinity of the nanoparticles enabled rapid wireless control of intracellular calcium. Our work demonstrates that redox tuning during solvent thermolysis can generate potent theranostic agents through selective phase control in ferrites and can be extended to other transition metal oxides relevant to memory and electrochemical storage devices.

Targeted Magnetic Nanoparticles for Remote Magnetothermal Disruption of Amyloid-β Aggregates

Remotely triggered hysteretic heat dissipation by magnetic nanoparticles (MNPs) selectively attached to targeted proteins can be used to break up self-assembled aggregates. This magnetothermal approach is applied to the amyloid-β (Aβ) protein, which forms dense, insoluble plaques characteristic of Alzheimer's disease. Specific targeting of dilute MNPs to Aβ aggregates is confirmed via transmission electron microscopy (TEM) and is found to be consistent with a statistical model of MNP distribution on the Aβ substrates. MNP composition and size are selected to achieve efficient hysteretic power dissipation at physiologically safe alternating magnetic field (AMF) conditions. Dynamic light scattering, fluorescence spectroscopy, and TEM are used to characterize the morphology and size distribution of aggregates before and after exposure to AMF. A dramatic reduction in aggregate size from microns to tens of nanometers is observed, suggesting that exposure to an AMF effectively destabilizes Aβ deposits decorated with targeted MNPs. Experiments in primary hippocampal neuronal cultures indicate that the magnetothermal disruption of aggregates reduces Aβ cytotoxicity, which may enable future applications of this approach for studies of protein disaggregation in physiological environments.

Maximizing hysteretic losses in magnetic ferrite nanoparticles via model-driven synthesis and materials optimization

This article develops a set of design guidelines for maximizing heat dissipation characteristics of magnetic ferrite MFe2O4 (M = Mn, Fe, Co) nanoparticles in alternating magnetic fields. Using magnetic and structural nanoparticle characterization, we identify key synthetic parameters in the thermal decomposition of organometallic precursors that yield optimized magnetic nanoparticles over a wide range of sizes and compositions. The developed synthetic procedures allow for gram-scale production of magnetic nanoparticles stable in physiological buffer for several months. Our magnetic nanoparticles display some of the highest heat dissipation rates, which are in qualitative agreement with the trends predicted by a dynamic hysteresis model of coherent magnetization reversal in single domain magnetic particles. By combining physical simulations with robust scalable synthesis and materials characterization techniques, this work provides a pathway to a model-driven design of magnetic nanoparticles tailored to a variety of biomedical applications ranging from cancer hyperthermia to remote control of gene expression.

Soccer players under regular training show oxidative stress but an improved plasma antioxidant status

Physical activity is known to induce oxidative stress in individuals subjected to intense exercise. In this study, we investigated the lipoprotein profile and the plasma antioxidant status in a group of soccer players engaged in a regular training programme. As was expected for aerobic exercise, high-density lipoprotein-cholesterol (HDL-C) and HDL3-C levels were significantly increased in the sportsmen (P<0.05). Total plasma antioxidant capacity was 25% higher in sportsmen than in controls (P<0.005). Accordingly, plasma hydrosoluble antioxidant levels (ascorbic acid and uric acid) were found to be significantly elevated in the soccer players (P<0.005). In addition, these subjects showed high concentrations of alpha-tocopherol in plasma compared with controls (P<0.005). Furthermore, an increase in plasma superoxide dismutase activity was also observed in relation to exercise (P<0.01). The elevation in plasma activities of antioxidant enzymes and the higher levels of free radical scavengers of low molecular mass may compensate the oxidative stress caused by physical activity. High levels of high-density lipoprotein in plasma may offer additional protection by inhibiting low-density lipoprotein oxidation and thus liposoluble antioxidant consumption. Therefore, soccer players under regular training show an improved plasma antioxidant status in comparison to sedentary controls.