Control of smooth muscle α-actin (SMA) up-regulation in HBMSCs using remote magnetic particle mechano-activation

An "All-in-One" Strategy to Reconstruct Temporomandibular Joint Osteoarthritic Microenvironment Using γ-Fe2O3@TA@ALN Nanoparticles

Current clinical strategies for the treatment of temporomandibular joint osteoarthritis (TMJOA) primarily target cartilage biology, overlooking the synergetic effect of various cells and inorganic components in shaping the arthritic microenvironment, thereby impeding the effectiveness of existing therapeutic options for TMJOA. Here, γ-Fe2O3@TA@ALN magnetic nanoparticles (γ-Fe2O3@TA@ALN MNPs) composed of γ-Fe2O3, tannic acid (TA), and alendronate sodium (ALN) are engineered to reconstruct the osteoarthritic microenvironment and mitigate TMJOA progression. γ-Fe2O3@TA@ALN MNPs can promote chondrocytes' proliferation, facilitate chondrogenesis and anisotropic organization, enhance lubrication and reduce cartilage wear, and encourage cell movement. Magnetic-responsive γ-Fe2O3@TA@ALN MNPs also exhibit pH sensitivity, which undergoes decomposition within acidic environment to release ALN on demand. Under a 0.2 T static magnetic field, γ-Fe2O3@TA@ALN MNPs accelerate the synthesis of cartilage-specific proteins, and suppress catabolic-related genes expression and reactive oxygen species generation, affording additional protection to TMJ cartilage. In TMJOA mouse models, articular injection of γ-Fe2O3@TA@ALN MNPs effectively alleviates cartilage degeneration and subchondral bone loss in short and long terms, offering promising avenues for the development of therapeutic interventions for TMJOA.

Magnetogenetics as a promising tool for controlling cellular signaling pathways

Magnetogenetics emerges as a transformative approach for modulating cellular signaling pathways through the strategic application of magnetic fields and nanoparticles. This technique leverages the unique properties of magnetic nanoparticles (MNPs) to induce mechanical or thermal stimuli within cells, facilitating the activation of mechano- and thermosensitive proteins without the need for traditional ligand-receptor interactions. Unlike traditional modalities that often require invasive interventions and lack precision in targeting specific cellular functions, magnetogenetics offers a non-invasive alternative with the capacity for deep tissue penetration and the potential for targeting a broad spectrum of cellular processes. This review underscores magnetogenetics' broad applicability, from steering stem cell differentiation to manipulating neuronal activity and immune responses, highlighting its potential in regenerative medicine, neuroscience, and cancer therapy. Furthermore, the review explores the challenges and future directions of magnetogenetics, including the development of genetically programmed magnetic nanoparticles and the integration of magnetic field-sensitive cells for in vivo applications. Magnetogenetics stands at the forefront of cellular manipulation technologies, offering novel insights into cellular signaling and opening new avenues for therapeutic interventions.

Advanced 3D Magnetic Scaffolds for Tumor-Related Bone Defects

The need for bone substitutes is a major challenge as the incidence of serious bone disorders is massively increasing, mainly attributed to modern world problems, such as obesity, aging of the global population, and cancer incidence. Bone cancer represents one of the most significant causes of bone defects, with reserved prognosis regarding the effectiveness of treatments and survival rate. Modern therapies, such as hyperthermia, immunotherapy, targeted therapy, and magnetic therapy, seem to bring hope for cancer treatment in general, and bone cancer in particular. Mimicking the composition of bone to create advanced scaffolds, such as bone substitutes, proved to be insufficient for successful bone regeneration, and a special attention should be given to control the changes in the bone tissue micro-environment. The magnetic manipulation by an external field can be a promising technique to control this micro-environment, and to sustain the proliferation and differentiation of osteoblasts, promoting the expression of some growth factors, and, finally, accelerating new bone formation. By incorporating stimuli responsive nanocarriers in the scaffold's architecture, such as magnetic nanoparticles functionalized with bioactive molecules, their behavior can be rigorously controlled under external magnetic driving, and stimulates the bone tissue formation.

Immobilization of Wnt Fragment Peptides on Magnetic Nanoparticles or Synthetic Surfaces Regulate Wnt Signaling Kinetics

Wnt signaling plays an important role in embryogenesis and adult stem cell homeostasis. Its diminished activation is implicated in osteoporosis and degenerative neural diseases. However, systematic administration of Wnt-signaling agonists carries risk, as aberrantly activated Wnt/β-catenin signaling is linked to cancer. Therefore, technologies for local modulation and control of Wnt signaling targeted to specific sites of disease or degeneration have potential therapeutic value in the treatment of degenerative diseases. We reported a facile approach to locally activate the canonical Wnt signaling cascade using nanomagnetic actuation or ligand immobilized platforms. Using a human embryonic kidney (HEK293) Luc-TCF/LEF reporter cell line, we demonstrated that targeting the cell membrane Wnt receptor, Frizzled 2, with peptide-tagged magnetic nanoparticles (MNPs) triggered canonical Wnt signaling transduction when exposed to a high-gradient, time-varying magnetic field, and the induced TCF/LEF signal transduction was shown to be avidity-dependent. We also demonstrated that the peptide retained signaling activity after functionalization onto glass surfaces, providing a versatile platform for drug discovery or recreation of the cell niche. In conclusion, these results showed that peptide-mediated Wnt signaling kinetics depended not only on ligand concentration but also on the presentation method of the ligand, which may be further modulated by magnetic actuation. This has important implications when designing future therapeutic platforms involving Wnt mimetics.

Engineered Magnetic Nanocomposites to Modulate Cellular Function

Magnetic nanoparticles (MNPs) have various applications in biomedicine, including imaging, drug delivery and release, genetic modification, cell guidance, and patterning. By combining MNPs with polymers, magnetic nanocomposites (MNCs) with diverse morphologies (core-shell particles, matrix-dispersed particles, microspheres, etc.) can be generated. These MNCs retain the ability of MNPs to be controlled remotely using external magnetic fields. While the effects of these biomaterials on the cell biology are still poorly understood, such information can help the biophysical modulation of various cellular functions, including proliferation, adhesion, and differentiation. After recalling the basic properties of MNPs and polymers, and describing their coassembly into nanocomposites, this review focuses on how polymeric MNCs can be used in several ways to affect cell behavior. A special emphasis is given to 3D cell culture models and transplantable grafts, which are used for regenerative medicine, underlining the impact of MNCs in regulating stem cell differentiation and engineering living tissues. Recent advances in the use of MNCs for tissue regeneration are critically discussed, particularly with regard to their prospective involvement in human therapy and in the construction of advanced functional materials such as magnetically operated biomedical robots.

Biophysical Approaches for Applying and Measuring Biological Forces

Over the past decades, increasing evidence has indicated that mechanical loads can regulate the morphogenesis, proliferation, migration, and apoptosis of living cells. Investigations of how cells sense mechanical stimuli or the mechanotransduction mechanism is an active field of biomaterials and biophysics. Gaining a further understanding of mechanical regulation and depicting the mechanotransduction network inside cells require advanced experimental techniques and new theories. In this review, the fundamental principles of various experimental approaches that have been developed to characterize various types and magnitudes of forces experienced at the cellular and subcellular levels are summarized. The broad applications of these techniques are introduced with an emphasis on the difficulties in implementing these techniques in special biological systems. The advantages and disadvantages of each technique are discussed, which can guide readers to choose the most suitable technique for their questions. A perspective on future directions in this field is also provided. It is anticipated that technical advancement can be a driving force for the development of mechanobiology.

Magnetomechanical force: an emerging paradigm for therapeutic applications

Mechanical forces, which play an profound role in cell fate regulation, have prompted the rapid development and popularization of mechanobiology. More recently, magnetic fields in combination with intelligent materials featuring...

Non-Heating Alternating Magnetic Field Nanomechanical Stimulation of Biomolecule Structures via Magnetic Nanoparticles as the Basis for Future Low-Toxic Biomedical Applications

The review discusses the theoretical, experimental and toxicological aspects of the prospective biomedical application of functionalized magnetic nanoparticles (MNPs) activated by a low frequency non-heating alternating magnetic field (AMF). In this approach, known as nano-magnetomechanical activation (NMMA), the MNPs are used as mediators that localize and apply force to such target biomolecular structures as enzyme molecules, transport vesicles, cell organelles, etc., without significant heating. It is shown that NMMA can become a biophysical platform for a family of therapy methods including the addressed delivery and controlled release of therapeutic agents from transport nanomodules, as well as selective molecular nanoscale localized drugless nanomechanical impacts. It is characterized by low system biochemical and electromagnetic toxicity. A technique of 3D scanning of the NMMA region with the size of several mm to several cm over object internals has been described.

Optical Imaging of Magnetic Particle Cluster Oscillation and Rotation in Glycerol

Magnetic particles have been evaluated for their biomedical applications as a drug delivery system to treat asthma and other lung diseases. In this study, ferromagnetic barium hexaferrite (BaFe12O19) and iron oxide (Fe3O4) particles were suspended in water or glycerol, as glycerol can be 1000 times more viscous than water. The particle concentration was 2.50 mg/mL for BaFe12O19 particle clusters and 1.00 mg/mL for Fe3O4 particle clusters. The magnetic particle cluster cross-sectional area ranged from 15 to 1000 μμm2, and the particle cluster diameter ranged from 5 to 45 μμm. The magnetic particle clusters were exposed to oscillating or rotating magnetic fields and imaged with an optical microscope. The oscillation frequency of the applied magnetic fields, which was created by homemade wire spools inserted into an optical microscope, ranged from 10 to 180 Hz. The magnetic field magnitudes varied from 0.25 to 9 mT. The minimum magnetic field required for particle cluster rotation or oscillation in glycerol was experimentally measured at different frequencies. The results are in qualitative agreement with a simplified model for single-domain magnetic particles, with an average deviation from the model of 1.7 ± 1.3. The observed difference may be accounted for by the fact that our simplified model does not include effects on particle cluster motion caused by randomly oriented domains in multi-domain magnetic particle clusters, irregular particle cluster size, or magnetic anisotropy, among other effects.

Magnetic Forces Enable Control of Biological Processes In Vivo

Similar to mechanical forces that can induce profound biological effects, magnetic fields can have a broad range of implications to biological systems, from magnetoreception that allows an organism to detect a magnetic field to perceive direction, altitude, or location, to the use of heating induced by magnetic field for altering neuron activity. This review focuses on the application of magnetic forces generated by magnetic iron oxide nanoparticles (MIONs), which can also provide imaging contrast and mechanical/thermal energy in response to an external magnetic field, a special feature that distinguishes MIONs from other nanomaterials. The magnetic properties of MIONs offer unique opportunities for enabling control of biological processes under different magnetic fields. Here, we describe the approaches of utilizing the forces generated by MIONs under an applied magnetic field to control biological processes and functions, including the targeting of drug molecules to a specific tissue, increasing the vessel permeability for improving drug delivery, and activating a particular viral vector for spatial control of genome editing in vivo. The opportunities of using nanomagnets for a broad range of biomedical applications are briefly discussed.

Remote triggering of TGF-β/Smad2/3 signaling in human adipose stem cells laden on magnetic scaffolds synergistically promotes tenogenic commitment

Injuries affecting load bearing tendon tissues are a significant clinical burden and efficient treatments are still unmet. Tackling tendon regeneration, tissue engineering strategies aim to develop functional substitutes that recreate native tendon milieu. Tendon mimetic scaffolds capable of remote magnetic responsiveness and functionalized magnetic nanoparticles (MNPs) targeting cellular mechanosensitive receptors are potential instructive tools to mediate mechanotransduction in guiding tenogenic responses. In this work, we combine magnetically responsive scaffolds and targeted Activin A type II receptor in human adipose stem cells (hASCs), under alternating magnetic field (AMF), to synergistically facilitate external control over signal transduction. The combination of remote triggering TGF-β/Smad2/3 using MNPs tagged hASCs, through magnetically actuated scaffolds, stimulates overall expression of tendon related genes and the deposition of tendon related proteins, in comparison to non-stimulated conditions. Moreover, the phosphorylation of Smad2/3 proteins and their nuclear co-localization was also more evident. Overall, biophysical stimuli resulting from magnetic scaffolds and magnetically triggered cells under AMF stimulation modulate the mechanosensing response of hASCs towards tenogenesis, holding therapeutic promise. STATEMENT OF SIGNIFICANCE: The concept of magnetically-assisted tissue engineering may assist the development of innovative solutions to treat tendon disorders upon remote control of biological processes as cell migration or differentiation. Herein, we originally combine a fibrous aligned superparamagnetic scaffold, based on a biodegradable polymeric blend of starch and poly-ɛ-caprolactone incorporating magnetic nanoparticles (MNPs), and human adipose stem cells (hASCs) labelled with MNPs functionalized with anti-activin receptor type IIA (ActRIIA). Constructs were stimulated using alternating magnetic field (AMF), to activate the ActRIIA and subsequent induction of TGF-β signaling, through Smad2/3 phosphorylation cascade, enhancing the expression of tendon-related markers. Altogether, these findings contribute with powerful bio-magnetic approaches to activate key tenogenic pathways, envisioning future translation of magnetic biomaterials into regenerative platforms for tendon repair.

Magnetic Mechanoactivation of Wnt Signaling Augments Dopaminergic Differentiation of Neuronal Cells

Wnt signaling is a key developmental pathway that regulates dopaminergic progenitor cell proliferation and differentiation during neuronal development. This makes Wnt signaling an important therapeutic target for neurodegenerative conditions such as Parkinson's disease. Wnt signaling can be modulated using peptides such as UM206, which bind to the Wnt receptor Frizzled. Previous work has demonstrated remote activation of the Wnt pathway through Frizzled using peptide-functionalized magnetic nanoparticles (MNPs) with magnetic field stimulation. Using this technology, Wnt signaling is remotely activated in the neuronal cell line SH-SY5Y, and the phenotypic response to stimulation is assessed. Results indicate β-catenin translocalization and activation of TCF/LEF responsive transcription in response to MNP and magnetic fields, which result in dopaminergic marker expression when synergistically combined with differentiation factors retinoic acid and the phorbol ester phorbol 12-myristate 13-acetate. This approach is translated into ex vivo postnatal rat brain slices modeling the developing nigrostriatal pathway. Dopaminergic marker expression is maintained in MNP-labeled SH-SY5Y cells after injection and magnetic stimulation. These results demonstrate the translational value of remote control of signal transduction for controlling neuronal precursor cell behavior and highlight the potential applications for controlled cell differentiation as part of cell therapies for neurodegenerative disease.

Magnetic biomaterials and nano-instructive tools as mediators of tendon mechanotransduction

Tendon tissues connect muscle to bone allowing the transmission of forces resulting in joint movement. Tendon injuries are prevalent in society and the impact on public health is of utmost concern. Thus, clinical options for tendon treatments are in demand, and tissue engineering aims to provide reliable and successful long-term regenerative solutions. Moreover, the possibility of regulating cell fate by triggering intracellular pathways is a current challenge in regenerative medicine. In the last decade, the use of magnetic nanoparticles as nano-instructive tools has led to great advances in diagnostics and therapeutics. Recent advances using magnetic nanomaterials for regenerative medicine applications include the incorporation of magnetic biomaterials within 3D scaffolds resulting in mechanoresponsive systems with unprecedented properties and the use of nanomagnetic actuators to control cell signaling. Mechano-responsive scaffolds and nanomagnetic systems can act as mechanostimulation platforms to apply forces directly to single cells and multicellular biological tissues. As transmitters of forces in a localized manner, the approaches enable the downstream activation of key tenogenic signaling pathways. In this minireview, we provide a brief outlook on the tenogenic signaling pathways which are most associated with the conversion of mechanical input into biochemical signals, the novel bio-magnetic approaches which can activate these pathways, and the efforts to translate magnetic biomaterials into regenerative platforms for tendon repair.

Magnetic Iron Oxide Nanoparticles for Disease Detection and Therapy

Magnetic iron oxide nanoparticles (MIONs) are among the first generation of nanomaterials that have advanced to clinic use. A broad range of biomedical techniques has been developed by combining the versatile nanomagnetism of MIONs with various forms of applied magnetic fields. MIONs can generate imaging contrast and provide mechanical/thermal energy in vivo in response to an external magnetic field, a special feature that distinguishes MIONs from other nanomaterials. These properties offer unique opportunities for nanomaterials engineering in biomedical research and clinical interventions. The past few decades have witnessed the evolution of the applications of MIONs from conventional drug delivery and hyperthermia to the regulation of molecular and cellular processes in the body. Here we review the most recent development in this field, including clinical studies of MIONs and the emerging techniques that may contribute to future innovation in medicine.

Magnetically Assisted Control of Stem Cells Applied in 2D, 3D and In Situ Models of Cell Migration

The success of cell therapy approaches is greatly dependent on the ability to precisely deliver and monitor transplanted stem cell grafts at treated sites. Iron oxide particles, traditionally used in vivo for magnetic resonance imaging (MRI), have been shown to also represent a safe and efficient in vitro labelling agent for mesenchymal stem cells (MSCs). Here, stem cells were labelled with magnetic particles, and their resulting response to magnetic forces was studied using 2D and 3D models. Labelled cells exhibited magnetic responsiveness, which promoted localised retention and patterned cell seeding when exposed to magnet arrangements in vitro. Directed migration was observed in 2D culture when adherent cells were exposed to a magnetic field, and also when cells were seeded into a 3D gel. Finally, a model of cell injection into the rodent leg was used to test the enhanced localised retention of labelled stem cells when applying magnetic forces, using whole body imaging to confirm the potential use of magnetic particles in strategies seeking to better control cell distribution for in vivo cell delivery.

In Situ Observation of Chymotrypsin Catalytic Activity Change Actuated by Nonheating Low-Frequency Magnetic Field

Magnetomechanical modulation of biochemical processes is a promising instrument for bioengineering and nanomedicine. This work demonstrates two approaches to control activity of an enzyme, α-chymotrypsin immobilized on the surface of gold-coated magnetite magnetic nanoparticles (GM-MNPs) using a nonheating low-frequency magnetic field (LF MF). The measurement of the enzyme reaction rate was carried out in situ during exposure to the magnetic field. The first approach involves α-chymotrypsin-GM-MNPs conjugates, in which the enzyme undergoes mechanical deformations with the reorientation of the MNPs under LF MF (16-410 Hz frequency, 88 mT flux density). Such mechanical deformations result in conformational changes in α-chymotrypsin structure, as confirmed by infrared spectroscopy and molecular modeling, and lead to a 63% decrease of enzyme initial activity. The second approach involves an α-chymotrypsin-GM-MNPs/trypsin inhibitor-GM-MNPs complex, in which the activity of the enzyme is partially inhibited. In this case the reorientation of MNPs in the field leads to disruption of the enzyme-inhibitor complex and an almost 2-fold increase of enzyme activity. The results further demonstrate the utility of magnetomechanical actuation at the nanoscale for the remote modulation of biochemical reactions.

Triggering the activation of Activin A type II receptor in human adipose stem cells towards tenogenic commitment using mechanomagnetic stimulation

Stem cell therapies hold potential to stimulate tendon regeneration and homeostasis, which is maintained in response to the native mechanical environment. Activins are members of the mechano-responsive TGF-β superfamily that participates in the regulation of several downstream biological processes. Mechanosensitive membrane receptors such as activin can be activated in different types of stem cells via magnetic nanoparticles (MNPs) through remote magnetic actuation resulting in cell differentiation. In this work, we target the Activin receptor type IIA (ActRIIA) in human adipose stem cells (hASCs), using anti-ActRIIA functionalized MNPs, externally activated through a oscillating magnetic bioreactor. Upon activation, the phosphorylation of Smad2/3 is induced allowing translocation of the complex to the nucleus, regulating tenogenic transcriptional responses. Our study demonstrates the potential remote activation of MNPs tagged hASCs to trigger the Activin receptor leading to tenogenic differentiation. These results may provide insights toward tendon regeneration therapies.

Magnetic forces enable controlled drug delivery by disrupting endothelial cell-cell junctions

The vascular endothelium presents a major transport barrier to drug delivery by only allowing selective extravasation of solutes and small molecules. Therefore, enhancing drug transport across the endothelial barrier has to rely on leaky vessels arising from disease states such as pathological angiogenesis and inflammatory response. Here we show that the permeability of vascular endothelium can be increased using an external magnetic field to temporarily disrupt endothelial adherens junctions through internalized iron oxide nanoparticles, activating the paracellular transport pathway and facilitating the local extravasation of circulating substances. This approach provides a physically controlled drug delivery method harnessing the biology of endothelial adherens junction and opens a new avenue for drug delivery in a broad range of biomedical research and therapeutic applications.

The transportation of large molecules through the vascular endothelium presents a major challenge for in vivo drug delivery. Here, the authors demonstrate the potential of using external magnetic fields and magnetic nanoparticles to enhance the local extravasation of circulating large molecules.

Emerging translational research on magnetic nanoparticles for regenerative medicine

Regenerative medicine, which replaces or regenerates human cells, tissues or organs, to restore or establish normal function, is one of the fastest-evolving interdisciplinary fields in healthcare. Over 200 regenerative medicine products, including cell-based therapies, tissue-engineered biomaterials, scaffolds and implantable devices, have been used in clinical development for diseases such as diabetes and inflammatory and immune diseases. To facilitate the translation of regenerative medicine from research to clinic, nanotechnology, especially magnetic nanoparticles have attracted extensive attention due to their unique optical, electrical, and magnetic properties and specific dimensions. In this review paper, we intend to summarize current advances, challenges, and future opportunities of magnetic nanoparticles for regenerative medicine.

Autonomous magnetic labelling of functional mesenchymal stem cells for improved traceability and spatial control in cell therapy applications

Mesenchymal stem cells (MSCs) represent a valuable resource for regenerative medicine treatments for orthopaedic repair and beyond. Following developments in isolation, expansion and differentiation protocols, efforts to promote clinical translation of emerging cellular strategies now seek to improve cell delivery and targeting. This study shows efficient live MSC labelling using silica‐coated magnetic particles (MPs), which enables 3D tracking and guidance of stem cells. A procedure developed for the efficient and unassisted particle uptake was shown to support MSC viability and integrity, while surface marker expression and MSC differentiation capability were also maintained. In vitro, MSCs showed a progressive decrease in labelling over increasing culture time, which appeared to be linked to the dilution effect of cell division, rather than to particle release, and did not lead to detectable secondary particle uptake. Labelled MSC populations demonstrated magnetic responsiveness in vitro through directed migration in culture and, when seeded onto a scaffold, supporting MP‐based approaches to cell targeting. The potential of these silica‐coated MPs for MRI cell tracking of MSC populations was validated in 2D and in a cartilage repair model following cell delivery. These results highlight silica‐coated magnetic particles as a simple, safe and effective resource to enhance MSC targeting for therapeutic applications and improve patient outcomes. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Exploring the Potential of Starch/Polycaprolactone Aligned Magnetic Responsive Scaffolds for Tendon Regeneration

The application of magnetic nanoparticles (MNPs) in tissue engineering (TE) approaches opens several new research possibilities in this field, enabling a new generation of multifunctional constructs for tissue regeneration. This study describes the development of sophisticated magnetic polymer scaffolds with aligned structural features aimed at applications in tendon tissue engineering (TTE). Tissue engineering magnetic scaffolds are prepared by incorporating iron oxide MNPs into a 3D structure of aligned SPCL (starch and polycaprolactone) fibers fabricated by rapid prototyping (RP) technology. The 3D architecture, composition, and magnetic properties are characterized. Furthermore, the effect of an externally applied magnetic field is investigated on the tenogenic differentiation of adipose stem cells (ASCs) cultured onto the developed magnetic scaffolds, demonstrating that ASCs undergo tenogenic differentiation synthesizing a Tenascin C and Collagen type I rich matrix under magneto-stimulation conditions. Finally, the developed magnetic scaffolds were implanted in an ectopic rat model, evidencing good biocompatibility and integration within the surrounding tissues. Together, these results suggest that the effect of the magnetic aligned scaffolds structure combined with magnetic stimulation has a significant potential to impact the field of tendon tissue engineering toward the development of more efficient regeneration therapies.

Coupling the magnetic and heat dissipative properties of Fe3O4 particles to enable applications in catalysis, drug delivery, tissue destruction and remote biological interfacing

As interest in nanomaterials continues to grow, and the scope of their applications widens, one subset of materials has set itself apart: magnetic nanoparticles (MNPs).

Multidimensional nanomaterials for the control of stem cell fate

Current stem cell therapy suffers low efficiency in giving rise to differentiated cell lineages, which can replace the original damaged cells. Nanomaterials, on the other hand, provide unique physical size, surface chemistry, conductivity, and topographical microenvironment to regulate stem cell differentiation through multidimensional approaches to facilitate gene delivery, cell-cell, and cell-ECM interactions. In this review, nanomaterials are demonstrated to work both alone and synergistically to guide selective stem cell differentiation. From three different nanotechnology families, three approaches are shown: (1) soluble microenvironmental factors; (2) insoluble physical microenvironment; and (3) nano-topographical features. As regenerative medicine is heavily invested in effective stem cell therapy, this review is inspired to generate discussions in the potential clinical applications of multi-dimensional nanomaterials.

Towards nanomedicines of the future: Remote magneto-mechanical actuation of nanomedicines by alternating magnetic fields

The paper describes the concept of magneto-mechanical actuation of single-domain magnetic nanoparticles (MNPs) in super-low and low frequency alternating magnetic fields (AMFs) and its possible use for remote control of nanomedicines and drug delivery systems. The applications of this approach for remote actuation of drug release as well as effects on biomacromolecules, biomembranes, subcellular structures and cells are discussed in comparison to conventional strategies employing magnetic hyperthermia in a radio frequency (RF) AMF. Several quantitative models describing interaction of functionalized MNPs with single macromolecules, lipid membranes, and proteins (e.g. cell membrane receptors, ion channels) are presented. The optimal characteristics of the MNPs and an AMF for effective magneto-mechanical actuation of single molecule responses in biological and bio-inspired systems are discussed. Altogether, the described studies and phenomena offer opportunities for the development of novel therapeutics both alone and in combination with magnetic hyperthermia.

Advanced cell therapies: targeting, tracking and actuation of cells with magnetic particles

Regenerative medicine would greatly benefit from a new platform technology that enabled measurable, controllable and targeting of stem cells to a site of disease or injury in the body. Superparamagnetic iron-oxide nanoparticles offer attractive possibilities in biomedicine and can be incorporated into cells, affording a safe and reliable means of tagging. This review describes three current and emerging methods to enhance regenerative medicine using magnetic particles to guide therapeutic cells to a target organ; track the cells using MRI and assess their spatial localization with high precision and influence the behavior of the cell using magnetic actuation. This approach is complementary to the systemic injection of cell therapies, thus expanding the horizon of stem cell therapeutics.

Remote activation of the Wnt/β-catenin signalling pathway using functionalised magnetic particles

Wnt signalling pathways play crucial roles in developmental biology, stem cell fate and tissue patterning and have become an attractive therapeutic target in the fields of tissue engineering and regenerative medicine. Wnt signalling has also been shown to play a role in human Mesenchymal Stem Cell (hMSC) fate, which have shown potential as a cell therapy in bone and cartilage tissue engineering. Previous work has shown that biocompatible magnetic nanoparticles (MNP) can be used to stimulate specific mechanosensitive membrane receptors and ion channels in vitro and in vivo. Using this strategy, we determined the effects of mechano-stimulation of the Wnt Frizzled receptor on Wnt pathway activation in hMSC. Frizzled receptors were tagged using anti-Frizzled functionalised MNP (Fz-MNP). A commercially available oscillating magnetic bioreactor (MICA Biosystems) was used to mechanically stimulate Frizzled receptors remotely. Our results demonstrate that Fz-MNP can activate Wnt/β-catenin signalling at key checkpoints in the signalling pathway. Immunocytochemistry indicated nuclear localisation of the Wnt intracellular messenger β-catenin after treatment with Fz-MNP. A Wnt signalling TCF/LEF responsive luciferase reporter transfected into hMSC was used to assess terminal signal activation at the nucleus. We observed an increase in reporter activity after treatment with Fz-MNP and this effect was enhanced after mechano-stimulation using the magnetic array. Western blot analysis was used to probe the mechanism of signalling activation and indicated that Fz-MNP signal through an LRP independent mechanism. Finally, the gene expression profiles of stress response genes were found to be similar when cells were treated with recombinant Wnt-3A or Fz-MNP. This study provides proof of principle that Wnt signalling and Frizzled receptors are mechanosensitive and can be remotely activated in vitro. Using magnetic nanoparticle technology it may be possible to modulate Wnt signalling pathways and thus control stem cell fate for therapeutic purposes.

Magnetically shaped cell aggregates: from granular to contractile materials

In recent decades, significant advances have been made in the description and modelling of tissue morphogenesis. By contrast, the initial steps leading to the formation of a tissue structure, through cell-cell adhesion, have so far been described only for small numbers of interacting cells. Here, through the use of remote magnetic forces, we succeeded at creating cell aggregates of half million cells, instantaneously and for several cell types, not only those known to form spheroids. This magnetic compaction gives access to the cell elasticity, found in the range of 800 Pa. The magnetic force can be removed at any time, allowing the cell mass to evolve spontaneously thereafter. The dynamics of contraction of these cell aggregates just after their formation (or, in contrast, their spreading for non-interacting monocyte cells) provides direct information on cell-cell interactions and allows retrieving the adhesion energy, in between 0.05 and 2 mJ m(-2), depending on the cell type tested, and in the case of cohesive aggregates. Thus, we show, by probing a large number of cell types, that cell aggregates behave like complex materials, undergoing a transition from a wet granular to contractile network, and that this transition is controlled by cell-cell interactions.

Receptor-targeted, magneto-mechanical stimulation of osteogenic differentiation of human bone marrow-derived mesenchymal stem cells

Mechanical cues are employed to promote stem cell differentiation and functional tissue formation in tissue engineering and regenerative medicine. We have developed a Magnetic Force Bioreactor (MFB) that delivers highly targeted local forces to cells at a pico-newton level, utilizing magnetic micro- and nano-particles to target cell surface receptors. In this study, we investigated the effects of magnetically targeting and actuating specific two mechanical-sensitive cell membrane receptors-platelet-derived growth factor receptor α (PDGFRα) and integrin ανβ3. It was found that a higher mineral-to-matrix ratio was obtained after three weeks of magneto-mechanical stimulation coupled with osteogenic medium culture by initially targeting PDGFRα compared with targeting integrin ανβ3 and non-treated controls. Moreover, different initiation sites caused a differentiated response profile when using a 2-day-lagged magneto-mechanical stimulation over culture periods of 7 and 12 days). However, both resulted in statistically higher osteogenic marker genes expression compared with immediate magneto-mechanical stimulation. These results provide insights into important parameters for designing appropriate protocols for ex vivo induced bone formation via magneto-mechanical actuation.