Selective activation of mechanosensitive ion channels using magnetic particles

Magnetic nanoparticle-based approaches to locally target therapy and enhance tissue regeneration in vivo

Magnetic-based systems utilizing superparamagnetic nanoparticles and a magnetic field gradient to exert a force on these particles have been used in a wide range of biomedical applications. This review is focused on drug targeting applications that require penetration of a cellular barrier as well as strategies to improve the efficacy of targeting in these biomedical applications. Another focus of this review is regenerative applications utilizing tissue engineered scaffolds prepared with the aid of magnetic particles, the use of remote actuation for release of bioactive molecules and magneto-mechanical cell stimulation, cell seeding and cell patterning.

Magnetic poly(ε-caprolactone)/iron-doped hydroxyapatite nanocomposite substrates for advanced bone tissue engineering

In biomedicine, magnetic nanoparticles provide some attractive possibilities because they possess peculiar physical properties that permit their use in a wide range of applications. The concept of magnetic guidance basically spans from drug delivery and hyperthermia treatment of tumours, to tissue engineering, such as magneto-mechanical stimulation/activation of cell constructs and mechanosensitive ion channels, magnetic cell-seeding procedures, and controlled cell proliferation and differentiation. Accordingly, the aim of this study was to develop fully biodegradable and magnetic nanocomposite substrates for bone tissue engineering by embedding iron-doped hydroxyapatite (FeHA) nanoparticles in a poly(ε-caprolactone) (PCL) matrix. X-ray diffraction analyses enabled the demonstration that the phase composition and crystallinity of the magnetic FeHA were not affected by the process used to develop the nanocomposite substrates. The mechanical characterization performed through small punch tests has evidenced that inclusion of 10 per cent by weight of FeHA would represent an effective reinforcement. The inclusion of nanoparticles also improves the hydrophilicity of the substrates as evidenced by the lower values of water contact angle in comparison with those of neat PCL. The results from magnetic measurements confirmed the superparamagnetic character of the nanocomposite substrates, indicated by a very low coercive field, a saturation magnetization strictly proportional to the FeHA content and a strong history dependence in temperature sweeps. Regarding the biological performances, confocal laser scanning microscopy and AlamarBlue assay have provided qualitative and quantitative information on human mesenchymal stem cell adhesion and viability/proliferation, respectively, whereas the obtained ALP/DNA values have shown the ability of the nanocomposite substrates to support osteogenic differentiation.

Multifunctional ferromagnetic disks for modulating cell function

In this work, we focus on the methods for controlling cell function with ferromagnetic disk-shaped particles. We will first review the history of magnetically assisted modulation of cell behavior and applications of magnetic particles for studying physical properties of a cell. Then, we consider the biological applications of the microdisks such as the method for induction of cancer cell apoptosis, controlled drug release, hyperthermia and MRI imaging.

Orthopaedic applications of nanoparticle-based stem cell therapies

Stem cells have tremendous applications in the field of regenerative medicine and tissue engineering. These are pioneering fields that aim to create new treatments for disease that currently have limited therapies or cures. A particularly popular avenue of research has been the regeneration of bone and cartilage to combat various orthopaedic diseases. Magnetic nanoparticles (MNPs) have been applied to aid the development and translation of these therapies from research to the clinic. This review highlights contemporary research for the applications of iron-oxide-based MNPs for the therapeutic implementation of stem cells in orthopaedics. These MNPs comprise of an iron oxide core, coated with a choice of biological polymers that can facilitate the uptake of MNPs by cells through improving endocytic activity. The combined use of these oxides and the biological polymer coatings meet biological requirements, effectively encouraging the use of MNPs in regenerative medicine. The association of MNPs with stem cells can be achieved via the process of endocytosis resulting in the internalisation of these particles or the attachment to cell surface receptors. This allows for the investigation of migratory patterns through various tracking studies, the targeting of particle-labelled cells to desired locations via the application of an external magnetic field and, finally, for activation stem cells to initiate various cellular responses to induce the differentiation. Characterisation of cell localisation and associated tissue regeneration can therefore be enhanced, particularly for in vivo applications. MNPs have been shown to have the potential to stimulate differentiation of stem cells for orthopaedic applications, without limiting proliferation. However, careful consideration of the use of active agents associated with the MNP is suggested, for differentiation towards specific lineages. This review aims to broaden the knowledge of current applications, paving the way to translate the in vitro and in vivo work into further orthopaedic clinical studies.

The promotion of in vitro vessel-like organization of endothelial cells in magnetically responsive alginate scaffolds

One of the major challenges in engineering thick, complex tissues such as cardiac muscle, is the need to pre-vascularize the engineered tissue in vitro to enable its efficient integration with host tissue upon implantation. Herein, we explored new magnetic alginate composite scaffolds to provide means of physical stimulation to cells. Magnetite-impregnated alginate scaffolds seeded with aortic endothelial cells stimulated during the first 7 days out of a total 14 day experimental course showed significantly elevated metabolic activity during the stimulation period. Expression of proliferating cell nuclear antigen (PCNA) indicated that magnetically stimulated cells had a lower proliferation index as compared to the non-stimulated cells. This suggests that the elevated metabolic activity could instead be related to cell migration and re-organization. Immunostaining and confocal microscopy analyses supported this observation showing that on day 14 in magnetically stimulated scaffolds without supplementation of any growth factors, cellular vessel-like (loop) structures, known as indicators of vasculogenesis and angiogenesis were formed as compared to cell sheets or aggregates observed in the non-stimulated (control) scaffolds. This work is the first step in our understanding of how to accurately control cellular organization to form tissue engineered constructs, which together with additional molecular signals could lead to a creation of an efficient pre-vascularized tissue construct with potential applicability for transplantation.

Magnetic nanoparticles for the manipulation of proteins and cells

In the rapidly developing areas of nanobiotechnology, magnetic nanoparticles (MNPs) are one type of the most well-established nanomaterials because of their biocompatibility and the potential applications as alternative contrast enhancing agents for magnetic resonance imaging (MRI). While the development of MNPs as alternative contrast agents for MRI application has moved quickly to testing in animal models and clinical trials, other applications of biofunctional MNPs have been explored extensively at the stage of qualitative or conceptual demonstration. In this critical review, we summarize the development of two straightforward applications of biofunctional MNPs--manipulating proteins and manipulating cells--in the last five years or so and hope to provide a relatively comprehensive assessment that may help the future developments. Specifically, we start with the examination of the strategy for the surface functionalization of MNPs because the applications of MNPs essentially depend on the molecular interactions between the functional molecules on the MNPs and the intended biological targets. Then, we discuss the use of MNPs for manipulating proteins since protein interactions are critical for biological functions. Afterwards, we evaluate the development of the use of MNPs to manipulate cells because the response of MNPs to a magnetic field offers a unique way to modulate cellular behavior in a non-contact or "remote" mode (i.e. the magnet exerts force on the cells without direct contact). Finally, we provide a perspective on the future directions and challenges in the development of MNPs for these two applications. By reviewing the examples of the design and applications of biofunctional MNPs, we hope that this article will provide a reference point for the future development of MNPs that address the present challenges and lead to new opportunities in nanomedicine and nanobiotechnology (137 references).

Magnetically enhanced nucleic acid delivery. Ten years of magnetofection-progress and prospects

Nucleic acids carry the building plans of living systems. As such, they can be exploited to make cells produce a desired protein, or to shut down the expression of endogenous genes or even to repair defective genes. Hence, nucleic acids are unique substances for research and therapy. To exploit their potential, they need to be delivered into cells which can be a challenging task in many respects. During the last decade, nanomagnetic methods for delivering and targeting nucleic acids have been developed, methods which are often referred to as magnetofection. In this review we summarize the progress and achievements in this field of research. We discuss magnetic formulations of vectors for nucleic acid delivery and their characterization, mechanisms of magnetofection, and the application of magnetofection in viral and nonviral nucleic acid delivery in cell culture and in animal models. We summarize results that have been obtained with using magnetofection in basic research and in preclinical animal models. Finally, we describe some of our recent work and end with some conclusions and perspectives.

More than a feeling: discovering, understanding, and influencing mechanosensing pathways

The ability of cells to extract biophysical information from their extracellular environment and convert it to biochemical signals is known as mechanotransduction. Here we detail three passive, 'inside-out' mechanotransduction mechanisms with an emphasis on the mechanosensing pathways involved in creating these signal: Rho/ROCK, stretch-activated channels, and 'Molecular Strain Gauges.' We also examine how molecular tools have been used to perturb these pathways to better understand their interconnectivity. However, perturbing pathways may have unintended confounding effects, which must also be addressed. By discovering and understanding mechanosensitive pathways, the ability to influence them for clinical applications increases.

Controlled differentiation of human bone marrow stromal cells using magnetic nanoparticle technology

Targeting and differentiating stem cells at sites of injury and repair is an exciting and promising area for disease treatment and reparative medicine. We have investigated remote magnetic field activation of magnetic nanoparticle-tagged mechanosensitive receptors on the cell membrane of human bone marrow stromal cells (HBMSCs) for use in osteoprogenitor cell delivery systems and activation of differentiation in vitro and in vivo toward an osteochondral lineage. HBMSC-labeled with magnetic beads coated with antibodies or peptides to the transmembrane ion channel stretch activated potassium channel (TREK-1) or arginine–glycine–aspartic acid were cultured in monolayer or encapsulated into polysaccharide alginate/chitosan microcapsules. Upregulation in gene expression was measured in magnetic particle-labeled HBMSCs in response to TREK-1 activation over a short period (7 days) with an increase in mRNA levels of Sox9, core binding factor alpha1 (Cbfa1), and osteopontin. Magnetic particle-labeled HBMSCs encapsulated into alginate chitosan capsules were exposed to magnetic forces both in vitro and in vivo intermittently for 21 days. After 21 days the encapsulated, magnetic particle-labeled HBMSCs in vivo were viable as evidenced by extensive cell tracker green fluorescence. The mechanical stimulation of HBMSCs labeled with TREK-1 magnetic nanoparticle receptors enhanced expression of type-1 collagen in vitro with increases in proteoglycan matrix, core binding factor alpha1 (Cbfa1) and collagen synthesis, and extracellular matrix production and elevated the expression of type-1 and type-2 collagen in vivo. Additionally, the magnetically remote stimulation of HBMSCs labeled with magnetic nanoparticle arginine–glycine–aspartic acid considerably enhanced proteoglycan and collagen synthesis and extracellular matrix production and elevated the expression of type-1 and type-2 collagen in vivo and in vitro. Osteogenic mechanosensitive receptor manipulation by magnetic nanotechnology can induce the differentiation of osteoprogenitor cell populations toward an osteogenic lineage. These cell manipulation strategies offer tremendous therapeutic opportunities in soft and hard tissue repair.

Remote control of ion channels and neurons through magnetic-field heating of nanoparticles

Recently, optical stimulation has begun to unravel the neuronal processing that controls certain animal behaviours. However, optical approaches are limited by the inability of visible light to penetrate deep into tissues. Here, we show an approach based on radio-frequency magnetic-field heating of nanoparticles to remotely activate temperature-sensitive cation channels in cells. Superparamagnetic ferrite nanoparticles were targeted to specific proteins on the plasma membrane of cells expressing TRPV1, and heated by a radio-frequency magnetic field. Using fluorophores as molecular thermometers, we show that the induced temperature increase is highly localized. Thermal activation of the channels triggers action potentials in cultured neurons without observable toxic effects. This approach can be adapted to stimulate other cell types and, moreover, may be used to remotely manipulate other cellular machinery for novel therapeutics.

Iron oxide-based nanomagnets in nanomedicine: fabrication and applications

Iron oxide-based nanomagnets have attracted a great deal of attention in nanomedicine over the past decade. Down to the nanoscale, superparamagnetic iron oxide nanoparticles can only be magnetized in the presence of an external magnetic field, which makes them capable of forming stable colloids in a physio-biological medium. Their superparamagnetic property, together with other intrinsic properties, such as low cytotoxicity, colloidal stability, and bioactive molecule conjugation capability, makes such nanomagnets ideal in both in-vitro and in-vivo biomedical applications. In this review, a chemical, physical, and biological synthetic approach to prepare iron oxide-based nanomagnets with different physicochemical properties was illustrated and compared. The growing interest in iron oxide-based nanomagnets with multifunctionalities was explored in cancer diagnostics and treatment, focusing on their combined roles in a magnetic resonance contrast agent, hyperthermia, and magnetic force assisted drug delivery. Iron oxides as magnetic carriers in gene therapy were reviewed with a focus on the sophisticated design and construction of magnetic vectors. Finally, the iron oxide-based nanomagnet also represents a very promising tool in particle/cell interfacing in controlling cellular functionalities, such as adhesion, proliferation, differentiation, and cell patterning, in stem cell therapy and tissue engineering applications.

pH sensitive CdS-iron oxide fluorescent-magnetic nanocomposites

There has been great interest in the use of nanoparticles for imaging, particularly in multimodal applications (e.g., combination of MRI and fluorescence). Yet creating particles with multiple functionalities has been challenging. Here, we report the synthesis of pH sensitive, fluorescent-magnetic, nanocomposites created through a simple aqueous procedure. Separately synthesized superparamagnetic iron oxide nanoparticles and mercaptopropionic acid (MPA)-coated CdS quantum dots were crosslinked using 3-mercaptopropyl trimethoxysilane (MPS) as a bifunctional linker to yield CdS-iron oxide conjugates. Conjugates formed clusters of 0.1-1.0 microm diameter, with the smallest observed particle diameter approximately 50 nm. Particle solubility and photoluminescent (PL) intensity were sensitive to solution pH, with the highest PL intensity and stability obtained at pH values < 3.0 and MPS:Cd:Fe ratios of 1:10:1. pH sensitivity is believed to result from changes in nanoparticle solubility within the silica-based matrix. Given these unique properties, this material might find application in separation, pH sensitive detection (e.g., endosomal tracking) and biosensing.