A tiny touch: activation of cell signaling pathways with magnetic nanoparticles

Chitosan/MWCNTs nanocomposite coating on 3D printed scaffold of poly 3-hydroxybutyrate/magnetic mesoporous bioactive glass: A new approach for bone regeneration

The utilization of 3D printing has become increasingly common in the construction of composite scaffolds. In this study, magnetic mesoporous bioactive glass (MMBG) was incorporated into polyhydroxybutyrate (PHB) to construct extrusion-based 3D printed scaffold. After fabrication of the PHB/MMBG composite scaffolds, they were coated with chitosan (Cs) and chitosan/multi-walled carbon nanotubes (Cs/MWCNTs) solutions utilizing deep coating method. FTIR was conducted to confirm the presence of Cs and MWCNTs on the scaffolds' surface. The findings of mechanical analysis illustrated that presence of Cs/MWCNTs on the composite scaffolds increases compressive young modulus significantly, from 16.5 to 42.2 MPa. According to hydrophilicity evaluation, not only MMBG led to decrease the contact angle of pure PHB but also scaffolds surface modification utilization of Cs and MWCNTs, the contact angle decreased significantly from 82.34° to 54.15°. Furthermore, investigation of cell viability, cell metabolism and inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) and interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β) proved that the scaffolds not only do not stimulate the immune system, but also polarize macrophage cells from M1 phase to M2 phase. The present study highlights the suitability of 3D printed scaffold PHB/MMBG with Cs/MWCNTs coating for bone tissue engineering.

Construction and interpretation of high-order image information based on NV optical magnetic vector detection

Tensor imaging can provide more comprehensive information about spatial physical properties, but it is a high-dimensional physical quantity that is difficult to observe directly. This paper proposes a fast-transform magnetic tensor imaging method based on the NV magnetic detection technique. The Euler deconvolution interprets the magnetic tensor data to obtain the target three-dimensional (3D) boundary information. Fast magnetic vector imaging was performed using optical detection of magnetic resonance (ODMR) to verify the method's feasibility. The complete tensor data was obtained based on the transformation of the vector magnetic imaging data, which was subsequently solved, and the contour information of the objective was restored. In addition, a fast magnetic moment judgment model and an angular transformation model of the observation space are developed in this paper to reduce the influence of the magnetic moment direction on the results and to help interpret the magnetic tensor data. Finally, the experiment realizes the localization, judgment of magnetic moment direction, and 3D boundary identification of a micron-sized tiny magnet with a spatial resolution of 10 µm, a model accuracy of 90.1%, and a magnetic moment direction error of 4.2°.

Hydrogel Composite Magnetic Scaffolds: Toward Cell-Free In Situ Bone Tissue Engineering

Reconstruction of critical sized bone defects in the oral and maxillofacial region continues to be clinically challenging despite the significant development of osteo-regenerative materials. Among 3D biomaterials, hydrogels and hydrogel composites have been explored for bone regeneration, however, their inferior clinical performance in comparison to autografts is mainly attributed to variable rates of degradation and lack of vascularization. In this study, we report hydrogel composite magnetic scaffolds formed from calcium carbonate, poly(vinyl alcohol) (PVA), and magnetic nanoparticles (MNPs), using PVA as matrix and calcium carbonate particles in vaterite phase as filler, to enhance the cross-linking of matrix and porosity with MNPs that can target and regulate cell signaling pathways to control cell behavior and improve the osteogenic and angiogenic potential. The physical and mechanical properties were evaluated, and cytocompatibility was investigated by culturing human osteoblast-like cells onto the scaffolds. The vaterite phase due to its higher solubility in comparison to calcium phosphates, combined with the freezing-thawing process of PVA, yielded porous scaffolds that exhibited adequate thermal stability, favorable water-absorbing capacity, excellent mineralization ability, and cytocompatibility. An increasing concentration from 1, 3, and 6 wt % MNPs in the scaffolds showed a statistically significant increase in compressive strength and modulus of the dry specimens that exhibited brittle fracture. However, the hydrated specimens were compressible and showed a slight decrease in compressive strength with 6% MNPs, although this value was higher compared to that of the scaffolds with no MNPs.

Hope for bone regeneration: The versatility of iron oxide nanoparticles

Although bone tissue has the ability to heal itself, beyond a certain point, bone defects cannot rebuild themselves, and the challenge is how to promote bone tissue regeneration. Iron oxide nanoparticles (IONPs) are a magnetic material because of their excellent properties, which enable them to play an active role in bone regeneration. This paper reviews the application of IONPs in bone tissue regeneration in recent years, and outlines the mechanisms of IONPs in bone tissue regeneration in detail based on the physicochemical properties, structural characteristics and safety of IONPs. In addition, a bibliometric approach has been used to analyze the hot spots and trends in the field in order to identify future directions. The results demonstrate that IONPs are increasingly being investigated in bone regeneration, from the initial use as magnetic resonance imaging (MRI) contrast agents to later drug delivery vehicles, cell labeling, and now in combination with stem cells (SCs) composite scaffolds. In conclusion, based on the current research and development trends, it is more inclined to be used in bone tissue engineering, scaffolds, and composite scaffolds.

Incorporation of Superparamagnetic Iron Oxide Nanoparticles into Collagen Formulation for 3D Electrospun Scaffolds

Nowadays, there is an ever-increasing interest in the development of systems able to guide and influence cell activities for bone regeneration. In this context, we have explored for the first time the combination of type-I collagen and superparamagnetic iron oxide nanoparticles (SPIONs) to design magnetic and biocompatible electrospun scaffolds. For this purpose, SPIONs with a size of 12 nm were obtained by thermal decomposition and transferred to an aqueous medium via ligand exchange with dimercaptosuccinic acid (DMSA). The SPIONs were subsequently incorporated into type-I collagen solutions to prove the processability of the resulting hybrid formulation by means of electrospinning. The optimized method led to the fabrication of nanostructured scaffolds composed of randomly oriented collagen fibers ranging between 100 and 200 nm, where SPIONs resulted distributed and embedded into the collagen fibers. The SPIONs-containing electrospun structures proved to preserve the magnetic properties of the nanoparticles alone, making these matrices excellent candidates to explore the magnetic stimuli for biomedical applications. Furthermore, the biological assessment of these collagen scaffolds confirmed high viability, adhesion, and proliferation of both pre-osteoblastic MC3T3-E1 cells and human bone marrow-derived mesenchymal stem cells (hBM-MSCs).

Iron Oxide Nanoparticles in Regenerative Medicine and Tissue Engineering

In recent years, many promising nanotechnological approaches to biomedical research have been developed in order to increase implementation of regenerative medicine and tissue engineering in clinical practice. In the meantime, the use of nanomaterials for the regeneration of diseased or injured tissues is considered advantageous in most areas of medicine. In particular, for the treatment of cardiovascular, osteochondral and neurological defects, but also for the recovery of functions of other organs such as kidney, liver, pancreas, bladder, urethra and for wound healing, nanomaterials are increasingly being developed that serve as scaffolds, mimic the extracellular matrix and promote adhesion or differentiation of cells. This review focuses on the latest developments in regenerative medicine, in which iron oxide nanoparticles (IONPs) play a crucial role for tissue engineering and cell therapy. IONPs are not only enabling the use of non-invasive observation methods to monitor the therapy, but can also accelerate and enhance regeneration, either thanks to their inherent magnetic properties or by functionalization with bioactive or therapeutic compounds, such as drugs, enzymes and growth factors. In addition, the presence of magnetic fields can direct IONP-labeled cells specifically to the site of action or induce cell differentiation into a specific cell type through mechanotransduction.

Microphysiological models of the central nervous system with fluid flow

There are over 1,000 described neurological and neurodegenerative disorders affecting nearly 100 million Americans - roughly one third of the U.S. population. Collectively, treatment of neurological conditions is estimated to cost $800 billion every year. Lowering this societal burden will require developing better model systems in which to study these diverse disorders. Microphysiological systems are promising tools for modeling healthy and diseased neural tissues to study mechanisms and treatment of neuropathology. One major benefit of microphysiological systems is the ability to incorporate biophysical forces, namely the forces derived from biological fluid flow. Fluid flow in the central nervous system (CNS) is a complex but important element of physiology, and pathologies as diverse as traumatic or ischemic injury, cancer, neurodegenerative disease, and natural aging have all been found to alter flow pathways. In this review, we summarize recent advances in three-dimensional microphysiological systems for studying the biology and therapy of CNS disorders and highlight the ability and growing need to incorporate biological fluid flow in these miniaturized model systems.

Creating Structured Hydrogel Microenvironments for Regulating Stem Cell Differentiation

The development of distinct biomimetic microenvironments for regulating stem cell behavior and bioengineering human tissues and disease models requires a solid understanding of cell-substrate interactions, adhesion, and its role in directing cell behavior, and other physico-chemical cues that drive cell behavior. In the past decade, innovative developments in chemistry, materials science, microfabrication, and associated technologies have given us the ability to manipulate the stem cell microenvironment with greater precision and, further, to monitor effector impacts on stem cells, both spatially and temporally. The influence of biomaterials and the 3D microenvironment's physical and biochemical properties on mesenchymal stem cell proliferation, differentiation, and matrix production are the focus of this review chapter. Mechanisms and materials, principally hydrogel and hydrogel composites for bone and cartilage repair that create "cell-supportive" and "instructive" biomaterials, are emphasized. We begin by providing an overview of stem cells, their unique properties, and their challenges in regenerative medicine. An overview of current fabrication strategies for creating instructive substrates is then reviewed with a focused discussion of selected fabrication methods with an emphasis on bioprinting as a critical tool in creating novel stem cell-based biomaterials. We conclude with a critical assessment of the current state of the field and offer our view on the promises and potential pitfalls of the approaches discussed.

Does Pharmacodynamics of Drugs Change After Presenting them as Nanoparticles Like their Pharmacokinetics?

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Nowadays, the breakthrough in different medical branches makes it feasible to designate new methods of drug delivery to achieve the most cost-effective and the least unpleasant consequenceimposing solutions to overcome a wide range of diseases.

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Nanoparticle (NP) drugs entered the therapeutic system, especially in cancer chemotherapy. These drugs are quite well-known for two traits of being long-acting and less toxic. For a long time, it has been investigated how NPs will change the kinetics of drugs. However, there are a few studies that inclined their attention to how NPs affect the dynamics of drugs. In this review, the latter point will mainly be discussed in an example-based manner. Besides, other particular features of NPs will be briefly noted.

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NPs are capable of affecting the biologic system as much as a drug. Moreover, NPs could arise a wide variety of effects by triggering their own receptors. NPs are able to change a receptor function and manipulate its downstream signaling cascade.

Nongenetic engineering strategies for regulating receptor oligomerization in living cells

Nongenetic strategies for regulating receptor oligomerization in living cells based on DNA, protein, small molecules and physical stimuli.

Energy-Mediated Machinery Drives Cellular Mechanical Allostasis

Allostasis is a fundamental biological process through which living organisms achieve stability via physiological or behavioral changes to protect against internal and external stresses, and ultimately better adapt to the local environment. However, an full understanding of cellular-level allostasis is far from developed. By employing an integrated micromechanical tool capable of applying controlled mechanical stress on an individual cell and simultaneously reporting dynamic information of subcellular mechanics, individual cell allostasis is observed to occur through a biphasic process; cellular mechanics tends to restore to a stable state through a mechanoadaptative process with excitative biophysical activity followed by a decaying adaptive phase. Based on these observations, it is found that cellular allostasis occurs through a complex balance of subcellular energy and cellular mechanics; upon a transient and local physical stimulation, cells trigger an allostatic state that maximizes energy and overcomes a mechanical "energy barrier" followed by a relaxation state that reaches its mechanobiological stabilization and energy minimization. Discoveries of energy-driven cellular machinery and conserved mechanotransductive pathways underscore the critical role of force-sensitive cytoskeleton equilibrium in cellular allostasis. This highlight the biophysical origin of cellular mechanical allostasis, providing subcellular methods to understand the etiology and progression of certain diseases or aging.

An in vitro correlation of metastatic capacity and dual mechanostimulation

Cells are under the influence of multiple forms of mechanical stimulation in vivo. For example, a cell is subjected to mechanical forces from tissue stiffness, shear and tensile stress and transient applied strain. Significant progress has been made in understanding the cellular mechanotransduction mechanisms in response to a single mechanical parameter. However, our knowledge of how a cell responds to multiple mechanical inputs is currently limited. In this study, we have tested the cellular response to the simultaneous application of two mechanical inputs: substrate compliance and transient tugging. Our results suggest that cells within a multicellular spheroid will restrict their response to a single mechanical input at a time and when provided with two mechanical inputs simultaneously, one will dominate. In normal and non-metastatic mammary epithelial cells, we found that they respond to applied stimulation and will override substrate compliance cues in favor of the applied mechanical stimulus. Surprisingly, however, metastatic mammary epithelial cells remain non-responsive to both mechanical cues. Our results suggest that, within our assay system, metastatic progression may involve the down-regulation of multiple mechanotransduction pathways.

Nanoparticle-Cell Interaction: A Cell Mechanics Perspective

Progress in the field of nanoparticles has enabled the rapid development of multiple products and technologies; however, some nanoparticles can pose both a threat to the environment and human health. To enable their safe implementation, a comprehensive knowledge of nanoparticles and their biological interactions is needed. In vitro and in vivo toxicity tests have been considered the gold standard to evaluate nanoparticle safety, but it is becoming necessary to understand the impact of nanosystems on cell mechanics. Here, the interaction between particles and cells, from the point of view of cell mechanics (i.e., bionanomechanics), is highlighted and put in perspective. Specifically, the ability of intracellular and extracellular nanoparticles to impair cell adhesion, cytoskeletal organization, stiffness, and migration are discussed. Furthermore, the development of cutting-edge, nanotechnology-driven tools based on the use of particles allowing the determination of cell mechanics is emphasized. These include traction force microscopy, colloidal probe atomic force microscopy, optical tweezers, magnetic manipulation, and particle tracking microrheology.

Magnetically actuated mechanical stimuli on Fe3O4/mineralized collagen coatings to enhance osteogenic differentiation of the MC3T3-E1 cells

Mechanical stimuli at the bone-implant interface are considered to activate the mechanotransduction pathway of the cell to improve the initial osseointegration establishment and to guarantee clinical success of the implant. However, control of the mechanical stimuli at the bone-implant interface still remains a challenge. In this study, we have designed a strategy of a magnetically responsive coating on which the mechanical stimuli is controlled because of coating deformation under static magnetic field (SMF). The iron oxide nanoparticle/mineralized collagen (IOP-MC) coatings were electrochemically codeposited on titanium substrates in different quantities of IOPs and distributions; the resulting coatings were verified to possess swelling behavior with flexibility same as that of hydrogel. The relative quantity of IOP to collagen and the IOP distribution in the coatings were demonstrated to play a critical role in mediating cell behavior. The cells present on the outer layer of the distributed IOP-MC (O-IOP-MC) coating with a mass ratio of 0.67 revealed the most distinct osteogenic differentiation activity being promoted, which could be attributed to the maximized mechanical stimuli with exposure to SMF. Furthermore, the enhanced osteogenic differentiation of the stimulated MC3T3-E1 cells originated from magnetically actuated mechanotransduction signaling pathway, embodying the upregulated expression of osteogenic-related and mechanotransduction-related genes. This work therefore provides a promising strategy for implementing mechanical stimuli to activate mechanotransduction on the bone-implant interface and thus to promote osseointegration.

STATEMENT OF SIGNIFICANCE

The magnetically actuated coating is designed to produce mechanical stimuli to cells for promoting osteogenic differentiation based on the coating deformation. Iron oxide nanoparticles (IOPs) were incorporated into the mineralized collagen coatings (MC) forming the composite coatings (IOP-MC) with spatially distributed IOPs, and the IOP-MC coatings with outer distributed IOPs (O-IOPs-MC) shows the maximized mechanical stimuli to cells with enhanced osteogenic differentiation under static magnetic field. The upregulated expression of the associated genes reveals that the enabled mechanotransduction signaling pathway is responsible for the promoted cellular osteogenic differentiation. This work therefore provides a promising strategy for implementing mechanical stimuli to activate mechanotransduction on the bone-implant interface to promote osseointegration.

Mechanic stress generated by a time-varying electromagnetic field on bone surface

Bone cells sense mechanical load, which is essential for bone growth and remodeling. In a fracture, this mechanism is compromised. Electromagnetic stimulation has been widely used to assist in bone healing, but the underlying mechanisms are largely unknown. A recent hypothesis suggests that electromagnetic stimulation could influence tissue biomechanics; however, a detailed quantitative understanding of EM-induced biomechanical changes in the bone is unavailable. This paper used a muscle/bone model to study the biomechanics of the bone under EM exposure. Due to the dielectric properties of the muscle/bone interface, a time-varying magnetic field can generate both compressing and shear stresses on the bone surface, where many mechanical sensing cells are available for cellular mechanotransduction. I calculated these stresses and found that the shear stress is significantly greater than the compressing stress. Detailed parametric analysis suggests that both the compressing and shear stresses are dependent on the geometrical and electrical properties of the muscle and the bone. These stresses are also functions of the orientation of the coil and the frequency of the magnetic field. It is speculated that the EM field could apply biomechanical influence to fractured bone, through the fine-tuning of the controllable field parameters. Graphical abstract Mechanic stress on bone surface in a time-varying magnetic field.

Advances in Magnetic Nanoparticles for Biomedical Applications

Magnetic nanoparticles (NPs) are emerging as an important class of biomedical functional nanomaterials in areas such as hyperthermia, drug release, tissue engineering, theranostic, and lab-on-a-chip, due to their exclusive chemical and physical properties. Although some works can be found reviewing the main application of magnetic NPs in the area of biomedical engineering, recent and intense progress on magnetic nanoparticle research, from synthesis to surface functionalization strategies, demands for a work that includes, summarizes, and debates current directions and ongoing advancements in this research field. Thus, the present work addresses the structure, synthesis, properties, and the incorporation of magnetic NPs in nanocomposites, highlighting the most relevant effects of the synthesis on the magnetic and structural properties of the magnetic NPs and how these effects limit their utilization in the biomedical area. Furthermore, this review next focuses on the application of magnetic NPs on the biomedical field. Finally, a discussion of the main challenges and an outlook of the future developments in the use of magnetic NPs for advanced biomedical applications are critically provided.

Nanoscale Mechanical Stimulation Method for Quantifying C. elegans Mechanosensory Behavior and Memory

Withdrawal escape response of C. elegans to nonlocalized vibration is a useful behavioral paradigm to examine mechanisms underlying mechanosensory behavior and its memory-dependent change. However, there are very few methods for investigating the degree of vibration frequency, amplitude and duration needed to induce behavior and memory. Here, we establish a new system to quantify C. elegans mechanosensory behavior and memory using a piezoelectric sheet speaker. In the system, we can flexibly change the vibration properties at a nanoscale displacement level and quantify behavioral responses under each vibration property. This system is an economic setup and easily replicated in other laboratories. By using the system, we clearly detected withdrawal escape responses and confirmed habituation memory. This system will facilitate the understanding of physiological aspects of C. elegans mechanosensory behavior in the future.

Mechanical determination of particle–cell interactions and the associated biomedical applications

Mechanical determination of particle–cell interactions and the associated biomedical applications.

Quantum dots modulate intracellular Ca2+ level in lung epithelial cells

While adverse effects of nanoparticles on lung health have previously been proposed, few studies have addressed the direct effects of nanoparticle exposure on the airway epithelium. In this work, we examine the response of the pulmonary airway to nanoparticles by measuring intracellular Ca²⁺ concentration ([Ca²⁺]_i) in the Calu-3 epithelial layer stimulated by 3-mercaptopropionic-acid (3MPA) coated CdSe-CdS/ZnS core-multishell quantum dots (QDs). Simultaneous transient transepithelial electrical resistance (TEER) decrease and global [Ca²⁺]_i increase in Calu-3 epithelial layer, accompanied by cell displacements, contraction, and expansion, were observed under QD deposition. This suggests that a QD-induced global [Ca²⁺]_i increase in the Calu-3 epithelial layer caused the transient TEER decrease. The [Ca²⁺]_i increase was marked and rapid in the apical region, while [Ca²⁺]_i decreased in the basolateral region of the epithelial layer. TEER transient response and extracellular Ca²⁺ entry induced by QD deposition were completely inhibited in cells treated with stretched-activated (SA) inhibitor GdCl₃ and store-operated calcium entry (SOCE) inhibitor BTP2 and in cells immersed in Ca²⁺-free medium. The voltage-gated calcium channel (VGCC) inhibitor nifedipine decreased, stabilized, and suppressed the TEER response, but did not affect the [Ca²⁺]_i increase, due to QD deposition. This demonstrates that the Ca²⁺ influx activated by QDs’ mechanical stretch occurs through activation of both SA and SOCE channels. QD-induced [Ca²⁺]_i increase occurred in the Calu-3 epithelial layer after culturing for 15 days, while significant TEER drop only occurred after 23 days. This work provides a new perspective from which to study direct interactions between airway epithelium and nanoparticles and may help to reveal the pathologies of pulmonary disease.

Superparamagnetic Iron Oxide Nanoparticle-Mediated Forces Enhance the Migration of Schwann Cells Across the Astrocyte-Schwann Cell Boundary In vitro

Schwann cells (SCs) are one of the most promising cellular candidates for the treatment of spinal cord injury. However, SCs show poor migratory ability within the astrocyte-rich central nervous system (CNS) environment and exhibit only limited integration with host astrocytes. Our strategy for improving the therapeutic potential of SCs was to magnetically drive SCs to migrate across the astrocyte-SC boundary to intermingle with astrocytes. SCs were firstly magnetized with poly-L-lysine-coated superparamagnetic iron oxide nanoparticles (SPIONs). Internalization of SPIONs showed no effect upon the migration of SCs in the absence of a magnetic field (MF). In contrast, magnetized SCs exhibited enhanced migration along the direction of force in the presence of a MF. An inverted coverslip assay showed that a greater number of magnetized SCs migrated longer distances onto astrocytic monolayers under the force of a MF compared to other test groups. More importantly, a confrontation assay demonstrated that magnetized SCs intermingled with astrocytes under an applied MF. Furthermore, inhibition of integrin activation reduced the migration of magnetized SCs within an astrocyte-rich environment under an applied MF. Thus, SPION-mediated forces could act as powerful stimulants to enhance the migration of SCs across the astrocyte-SC boundary, via integrin-mediated mechanotransduction, and could represent a vital way of improving the therapeutic potential of SCs for spinal cord injuries.

A cell-based biosensor for nanomaterials cytotoxicity assessment in three dimensional cell culture

Nanoparticles (NPs) are widely used in consumer and medicinal products. The high prevalence of nanoparticles in the environment raises concerns regarding their effects on human health, but there is limited knowledge about how NPs interact with cells or tissues. Because the European Union has called for a substantial reduction of animal experiments for scientific purposes (Directive 2010/63), increased efforts are required to develop in vitro models to evaluate potentially hazardous agents. Here, we describe a new cell-based biosensor for the evaluation of NPs cytotoxicity. The new biosensor is based on transgenic human hepatoblastoma cells (HepG2) that express a secreted form of alkaline phosphatase (SEAP) as a reporter protein whose expression is induced upon activation of a stress response pathway controlled by the transcription regulator nuclear factor-κB (NF-κB). The NF-κB_HepG2 sensor cells were cultured in a Matrigel-based three dimensional environment to simulate the in vivo situation. The new biosensor cells offer the advantage of generating fast and reproducible readout at lower concentrations and shorter incubation time than conventional viability assays, avoid possible interaction between nanomaterials and assay compounds, therefore, minimize generation of false positive or negative results and indicate mechanism of toxicity through NF-κB signaling.

Magnetically actuated tissue engineered scaffold: insights into mechanism of physical stimulation

Providing the right stimulatory conditions resulting in efficient tissue promoting microenvironment in vitro and in vivo is one of the ultimate goals in tissue development for regenerative medicine. It has been shown that in addition to molecular signals (e.g. growth factors) physical cues are also required for generation of functional cell constructs. These cues are particularly relevant to engineering of biological tissues, within which mechanical stress activates mechano-sensitive receptors, initiating biochemical pathways which lead to the production of functionally mature tissue. Uniform magnetic fields coupled with magnetizable nanoparticles embedded within three dimensional (3D) scaffold structures remotely create transient physical forces that can be transferrable to cells present in close proximity to the nanoparticles. This study investigated the hypothesis that magnetically responsive alginate scaffold can undergo reversible shape deformation due to alignment of scaffold's walls in a uniform magnetic field. Using custom made Helmholtz coil setup adapted to an Atomic Force Microscope we monitored changes in matrix dimensions in situ as a function of applied magnetic field, concentration of magnetic particles within the scaffold wall structure and rigidity of the matrix. Our results show that magnetically responsive scaffolds exposed to an externally applied time-varying uniform magnetic field undergo a reversible shape deformation. This indicates on possibility of generating bending/stretching forces that may exert a mechanical effect on cells due to alternating pattern of scaffold wall alignment and relaxation. We suggest that the matrix structure deformation is produced by immobilized magnetic nanoparticles within the matrix walls resulting in a collective alignment of scaffold walls upon magnetization. The estimated mechanical force that can be imparted on cells grown on the scaffold wall at experimental conditions is in the order of 1 pN, which correlates well with reported threshold to induce mechanotransduction effects on cellular level. This work is our next step in understanding of how to accurately create proper stimulatory microenvironment for promotion of cellular organization to form mature tissue engineered constructs.

A soft, stretchable and conductive biointerface for cell mechanobiology

In mechanobiology the study of cell response to mechanical stimuli is fundamental, and the involved processes (i.e., mechanotransduction) need to be investigated by interfacing (mechanically and electrically) with the cells in dynamic and non-invasive natural-like conditions. In this work, we present a novel soft, stretchable and conductive biointerface that allows both cell mechanical stimulation and dynamic impedance recording. The biointerface stretchability and conductivity, jointly to the biocompatibility and transparency needed to perform cell culture studies, were obtained by exploiting the formation of wrinkles on the surface of a 90 nm thick conductive layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) on a pre-stretched 130 μm thick poly(dimethylsiloxane) (PDMS) substrate. Cell adhesion and proliferation of SH-SY5Y human neuroblastoma cells were evaluated, and cell differentiation on the corrugated surface was assessed. We demonstrate how the biointerface remains conductive when applying uniaxial strain up to 10%, and when cell culturing is performed. Finally, a reduction of about 30% of the relative impedance variation signal was measured, with respect to the control, as a result of the mechanical stimulation of cells.

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.

Extracellular Stiffness Modulates the Expression of Functional Proteins and Growth Factors in Endothelial Cells

Angiogenesis, the formation of blood vessels from pre-existing ones, is of vital importance during the early stages of bone healing. Extracellular stiffness plays an important role in regulating endothelial cell behavior and angiogenesis, but how this mechanical cue affects proliferation kinetics, gene regulation, and the expression of proteins implicated in angiogenesis and bone regeneration remains unclear. Using collagen-coated polyacrylamide (PAAm) hydrogels, human umbilical vein endothelial cells (HUVECs) are exposed to an environment that mimics the elastic properties of collagenous bone, and cellular proliferation and gene and protein expressions are assessed. The proliferation and gene expression of HUVECs are not differentially affected by culture on 3 or 30 kPa PAAm hydrogels, henceforth referred to as low and high stiffness gels, respectively. Although the proliferation and gene transcript levels remain unchanged, significant differences are found in the expressions of functional proteins and growth factors implicated both in the angiogenic and osteogenic processes. The down-regulation of the vascular endothelial growth factor receptor-2 protein with concomitant over-expression of caveolin-1, wingless-type 2, bone morphogenic protein 2, and basic fibroblast growth factor on the high stiffness PAAm hydrogel suggests that rigidity has a pro-angiogenic effect with inherent benefits for bone regeneration.

Magnetic Nanocomposite Scaffold-Induced Stimulation of Migration and Odontogenesis of Human Dental Pulp Cells through Integrin Signaling Pathways

Magnetism is an intriguing physical cue that can alter the behaviors of a broad range of cells. Nanocomposite scaffolds that exhibit magnetic properties are thus considered useful 3D matrix for culture of cells and their fate control in repair and regeneration processes. Here we produced magnetic nanocomposite scaffolds made of magnetite nanoparticles (MNPs) and polycaprolactone (PCL), and the effects of the scaffolds on the adhesion, growth, migration and odontogenic differentiation of human dental pulp cells (HDPCs) were investigated. Furthermore, the associated signaling pathways were examined in order to elucidate the molecular mechanisms in the cellular events. The magnetic scaffolds incorporated with MNPs at varying concentrations (up to 10%wt) supported cellular adhesion and multiplication over 2 weeks, showing good viability. The cellular constructs in the nanocomposite scaffolds played significant roles in the stimulation of adhesion, migration and odontogenesis of HDPCs. Cells were shown to adhere to substantially higher number when affected by the magnetic scaffolds. Cell migration tested by in vitro wound closure model was significantly enhanced by the magnetic scaffolds. Furthermore, odontogenic differentiation of HDPCs, as assessed by the alkaline phosphatase activity, mRNA expressions of odontogenic markers (DMP-1, DSPP,osteocalcin, and ostepontin), and alizarin red staining, was significantly stimulated by the magnetic scaffolds. Signal transduction was analyzed by RT-PCR, Western blotting, and confocal microscopy. The magnetic scaffolds upregulated the integrin subunits (α1, α2, β1 and β3) and activated downstream pathways, such as FAK, paxillin, p38, ERK MAPK, and NF-κB. The current study reports for the first time the significant impact of magnetic scaffolds in stimulating HDPC behaviors, including cell migration and odontogenesis, implying the potential usefulness of the magnetic scaffolds for dentin-pulp tissue engineering.

Physical Stimuli-Induced Chondrogenic Differentiation of Mesenchymal Stem Cells Using Magnetic Nanoparticles

Chondrogenic commitments of mesenchymal stem cells (MSCs) require 3D cellular organization. Furthermore, recent progresses in bioreactor technology have contributed to the development of various biophysical stimulation platforms for efficient cartilage tissue formation. Here, an approach is reported to drive 3D cellular organization and enhance chondrogenic commitment of bone-marrow-derived human mesenchymal stem cells (BM-hMSCs) via magnetic nanoparticle (MNP)-mediated physical stimuli. MNPs isolated from Magnetospirillum sp. AMB-1 are endocytosed by the BM-hMSCs in a highly efficient manner. MNPs-incorporated BM-hMSCs are pelleted and then subjected to static magnetic field and/or magnet-derived shear stress. Magnetic-based stimuli enhance level of sulfated glycosaminoglycan (sGAG) and collagen synthesis, and facilitate the chondrogenic differentiation of BM-hMSCs. In addition, both static magnetic field and magnet-derived shear stress applied for the chondrogenic differentiation of BM-hMSCs do not show increament of hypertrophic differentiation. This MNP-mediated physical stimulation platform demonstrates a promising strategy for efficient cartilage tissue engineering.

The interplay of cell-cell and cell-substrate adhesion in collective cell migration

Collective cell migration often involves notable cell-cell and cell-substrate adhesions and highly coordinated motion of touching cells. We focus on the interplay between cell-substrate adhesion and cell-cell adhesion. We show that the loss of cell-surface contact does not significantly alter the dynamic pattern of protrusions and retractions of fast migrating amoeboid cells (Dictyostelium discoideum), but significantly changes their ability to adhere to other cells. Analysis of the dynamics of cell shapes reveals that cells that are adherent to a surface may coordinate their motion with neighbouring cells through protrusion waves that travel across cell-cell contacts. However, while shape waves exist if cells are detached from surfaces, they do not couple cell to cell. In addition, our investigation of actin polymerization indicates that loss of cell-surface adhesion changes actin polymerization at cell-cell contacts. To further investigate cell-cell/cell-substrate interactions, we used optical micromanipulation to form cell-substrate contact at controlled locations. We find that both cell-shape dynamics and cytoskeletal activity respond rapidly to the formation of cell-substrate contact.

From mechanical stimulation to biological pathways in the regulation of stem cell fate

Mechanical stimuli are important in directing the fate of stem cells; the effects of mechanical stimuli reported in recent research are reviewed here. Stem cells normally undergo two fundamental processes: proliferation, in which their numbers multiply, and differentiation, in which they transform into the specialized cells needed by the adult organism. Mechanical stimuli are well known to affect both processes of proliferation and differentiation, although the complete pathways relating specific mechanical stimuli to stem cell fate remain to be elucidated. We identified two broad classes of research findings and organized them according to the type of mechanical stress (compressive, tensile or shear) of the stimulus. Firstly, mechanical stress of any type activates stretch-activated channels (SACs) on the cell membrane. Activation of SACs leads to cytoskeletal remodelling and to the expression of genes that regulate the basic growth, survival or apoptosis of the cells and thus regulates proliferation. Secondly, mechanical stress on cells that are physically attached to an extracellular matrix (ECM) initiates remodelling of cell membrane structures called integrins. This second process is highly dependent on the type of mechanical stress applied and result into various biological responses. A further process, the Wnt pathway, is also implicated: crosstalk between the integrin and Wnt pathways regulates the switch from proliferation to differentiation and finally regulates the type of differentiation. Therefore, the stem cell differentiation process involves different signalling molecules and their pathways and most likely depends upon the applied mechanical stimulation.

Thermal potentiation of chemotherapy by magnetic nanoparticles

Clinical studies have demonstrated the effectiveness of hyperthermia as an adjuvant for chemotherapy and radiotherapy. However, significant clinical challenges have been encountered, such as a broader spectrum of toxicity, lack of patient tolerance, temperature control and significant invasiveness. Hyperthermia induced by magnetic nanoparticles in high-frequency oscillating magnetic fields, commonly termed magnetic fluid hyperthermia, is a promising form of heat delivery in which thermal energy is supplied at the nanoscale to the tumor. This review discusses the mechanisms of heat dissipation of iron oxide-based magnetic nanoparticles, current methods and challenges to deliver heat in the clinic, and the current work related to the use of magnetic nanoparticles for the thermal-chemopotentiation of therapeutic drugs.

The role of mechanics in actin stress fiber kinetics

The dynamic responses of actin stress fibers within a cell's cytoskeleton are central to the development and maintenance of healthy tissues and organs. Disturbances to these underlie a broad range of pathologies. Because of the importance of these responses, extensive experiments have been conducted in vitro to characterize actin cytoskeleton dynamics of cells cultured upon two-dimensional substrata, and the first experiments have been conducted for cells within three-dimensional tissue models. Three mathematical models exist for predicting the dynamic behaviors observed. Surprisingly, despite differing viewpoints on how actin stress fibers are stabilized or destabilized, all of these models are predictive of a broad range of available experimental data. Coarsely, the models of Kaunas and co-workers adopt a strategy whereby mechanical stretch can hasten the depolymerization actin stress fibers that turn over constantly, while the models of Desphande and co-workers adopt a strategy whereby mechanical stress is required to activate the formation of stress fibers and subsequently stabilize them. In three-dimensional culture, elements of both approaches appear necessary to predict observed phenomena, as embodied by the model of Lee et al. After providing a critical review of existing models, we propose lines of experimentation that might be able to test the different principles underlying their kinetic laws.

Mechanobiology: a new frontier for human pluripotent stem cells

Research on human pluripotent stem cells (hPSCs) has expanded rapidly over the last two decades, owing to the promises of hPSCs for applications in regenerative medicine, disease modeling, and developmental biology studies. While most studies of hPSCs have so far focused on identifying extrinsic soluble factors, intracellular signaling pathways, and transcriptional networks that are involved in regulating hPSC self-renewal and differentiation, a few promising studies have emerged in recent years to reveal some unique mechano-sensitive and -responsive properties of hPSCs and the effect of the physical aspects of the local cellular microenvironment on regulating hPSC behaviors. This Frontier Review is to highlight these recent studies of mechanobiology in hPSCs and to discuss the impact of advancing our understanding of mechanoregulation of hPSC behaviors on improving survival, self-renewal and differentiation of hPSCs using well-controlled synthetic micro/nanoscale cell culture tools.

Vitronectin absorbed on nanoparticles mediate cell viability/proliferation and uptake by 3T3 Swiss albino mouse fibroblasts: in vitro study

We study the interaction of 3T3 Swiss albino mouse fibroblasts with polymeric nanoparticles (NPs) and investigate cellular behaviour in terms of viability/cytotoxicity, cell cycle, NPs uptake, MAP kinase (ERK1/2), and focal adhesion kinase (FAK) activation. After incubation of NPs with cell culture media, western blot analysis showed that Vitronectin is retained by NPs, while Fibronectin is not detected. From cytotoxicity studies (MTT and BrdU methods) an LD50 of about 1.5 mg/mL results for NPs. However, NPs in the range 0.01-0.30 mg/mL are able to trigger a statistically significant increase in proliferation and cell cycle progression in dose and time depending manner. Also, biochemical evaluation of ERK1/2 and FAK clearly shows an increasing phosphorylation in a dose and time depending manner. Finally, we found by transmission electron microscopy that NPs are internalised by cells. Competitively blocking VN-integrin receptors with echistatin (1 μg/mL) results in a decrease of viability/proliferation, cell cycle progression, cellular uptake, and FAK/ERK activation showing the involvement of Vitronectin receptors in signal transduction. In conclusion, our results show that cell surface NPs interactions are mediated by absorbed plasma proteins (i.e., Vitronectin) that represent an external stimuli, switched to the nucleus by FAK enzyme, which in turn modulate fibroblasts viability/proliferation.

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.

Balancing forces: architectural control of mechanotransduction. Nat Rev Mol Cell Biol. 2011;12:308-319. [PMID: 21508987 DOI: 10.1038/nrm3112]

All cells exist within the context of a three-dimensional microenvironment in which they are exposed to mechanical and physical cues. These cues can be disrupted through perturbations to mechanotransduction, from the nanoscale-level to the tissue-level, which compromises tensional homeostasis to promote pathologies such as cardiovascular disease and cancer. The mechanisms of such perturbations suggest that a complex interplay exists between the extracellular microenvironment and cellular function. Furthermore, sustained disruptions in tensional homeostasis can be caused by alterations in the extracellular matrix, allowing it to serve as a mechanically based memory-storage device that can perpetuate a disease or restore normal tissue behaviour.

Polystyrene nanoparticles activate ion transport in human airway epithelial cells

BACKGROUND

Over the last decade, nanotechnology has provided researchers with new nanometer materials, such as nanoparticles, which have the potential to provide new therapies for many lung diseases. In this study, we investigated the acute effects of polystyrene nanoparticles on epithelial ion channel function.

METHODS

Human submucosal Calu-3 cells that express cystic fibrosis transmembrane conductance regulator (CFTR) and baby hamster kidney cells engineered to express the wild-type CFTR gene were used to investigate the actions of negatively charged 20 nm polystyrene nanoparticles on short-circuit current in Calu-3 cells by Ussing chamber and single CFTR Clchannels alone and in the presence of known CFTR channel activators by using baby hamster kidney cell patches.

RESULTS

Polystyrene nanoparticles caused sustained, repeatable, and concentration-dependent increases in short-circuit current. In turn, these short-circuit current responses were found to be biphasic in nature, ie, an initial peak followed by a plateau. EC(50) values for peak and plateau short-circuit current responses were 1457 and 315.5 ng/mL, respectively. Short-circuit current was inhibited by diphenylamine-2-carboxylate, a CFTR Cl(-) channel blocker. Polystyrene nanoparticles activated basolateral K(+) channels and affected Cl(-) and HCO(3) (-) secretion. The mechanism of short-circuit current activation by polystyrene nanoparticles was found to be largely dependent on calcium-dependent and cyclic nucleotide-dependent phosphorylation of CFTR Cl(-) channels. Recordings from isolated inside-out patches using baby hamster kidney cells confirmed the direct activation of CFTR Cl(-) channels by the nanoparticles.

CONCLUSION

This is the first study to identify the activation of ion channels in airway cells after exposure to polystyrene-based nanomaterials. Thus, polystyrene nanoparticles cannot be considered as a simple neutral vehicle for drug delivery for the treatment of lung diseases, due to the fact that they may have the ability to affect epithelial cell function and physiological processes on their own.

Recording of mechanosensitive currents using piezoelectrically driven mechanostimulator

Mechanotransduction constitutes the basis of a variety of physiological processes, such as the senses of touch, balance, proprioception and hearing. In vertebrates, mechanosensation is mediated by mechanosensory receptors. The aptitude of these mechanoreceptors for detecting mechanical information relies on the presence of mechanosensitive channels that transform mechanical forces into electrical signals. However, advances in understanding mechanical transduction processes have proven difficult because sensory nerve endings have historically been inaccessible to patch-clamp recording. We report here an in vitro model of mechanotransduction that allows the application of focal force on sensory neuron membrane during whole-cell patch clamping. This technique, called mechano-clamp, provides an opportunity to explore the properties and identities of mechanotransducer channels in mammalian sensory neurons. The protocol-from tissue dissociation to patch-clamp recording-can be completed in 7 h.

Molecular mechanisms of mechanotransduction in mammalian sensory neurons

The somatosensory system mediates fundamental physiological functions, including the senses of touch, pain and proprioception. This variety of functions is matched by a diverse array of mechanosensory neurons that respond to force in a specific fashion. Mechanotransduction begins at the sensory nerve endings, which rapidly transform mechanical forces into electrical signals. Progress has been made in establishing the functional properties of mechanoreceptors, but it has been remarkably difficult to characterize mechanotranducer channels at the molecular level. However, in the past few years, new functional assays have provided insights into the basic properties and molecular identity of mechanotransducer channels in mammalian sensory neurons. The recent identification of novel families of proteins as mechanosensing molecules will undoubtedly accelerate our understanding of mechanotransduction mechanisms in mammalian somatosensation.

Effects of vibration on differentiation of cultured PC12 cells

Different types of physiological-mechanical stress, such as shear stress in vascular endothelial cells or hydrostatic pressure in chondrocytes are well known as regulators of cell function. In this study, the effects of vibration, a type of non-physiological mechanical stimulation, on differentiation of rat pheochromocytoma (PC12) cells are reported. A nano-vibration system was designed to produce nanometer-scale vibration. The frequency and amplitude of the nano-vibrations were monitored by a capacitance displacement sensor connected to an oscilloscope. When PC12 cells exposed to nerve growth factor were subjected to vibration at 10 kHz, differentiation and elongation of their neurites were promoted earlier in the culture. Vibration promoted differentiation of PC12 cells. This approach could therefore also be promising for determining of the effects of the physical environment on cell differentiation.

Nanoparticles: molecular targets and cell signalling

Increasing evidence linking nanoparticles (NPs) with different cellular outcomes necessitate an urgent need for the better understanding of cellular signalling pathways triggered by NPs. Oxidative stress has largely been reported to be implicated in NP-induced toxicity. It could activate a wide variety of cellular events such as cell cycle arrest, apoptosis, inflammation and induction of antioxidant enzymes. These responses occur after the activation of different cellular pathways. In this context, three groups of MAP kinase cascades [ERK (extracellular signal-regulated kinases), p38 mitogen-activated protein kinase and JNK (c-Jun N-terminal kinases)] as well as redox-sensitive transcription factors such as NFκB and Nrf-2 were specially investigated. The ability of NPs to interact with these signalling pathways could partially explain their cytotoxicity. The induction of apoptosis is also closely related to the modulation of signalling pathways induced by NPs. Newly emerged scientific areas of research are the studies on interactions between NPs and biological molecules in body fluids, cellular microenvironment, intracellular components or secreted cellular proteins such as cytokines, growth factors and enzymes and use of engineered NPs to target various signal transduction pathways in cancer therapy. Recently published data present the ability of NPs to interact with membrane receptors leading to a possible aggregation of these receptors. These interactions could lead to a sustained modulation of specific signalling in the target cells or paracrine and even "by-stander" effects of the neighbouring cells or tissues. However, oxidative stress is not sufficient to explain specific mechanisms which could be induced by NPs, and these new findings emphasize the need to revise the paradigm of oxidative stress to explain the effects of NPs.