Mechanisms of Mechanotransduction

Epidermal growth factor receptor and integrins control force-dependent vinculin recruitment to E-cadherin junctions

This study reports novel findings that link E-cadherin (also known as CDH1)-mediated force-transduction signaling to vinculin targeting to intercellular junctions via epidermal growth factor receptor (EGFR) and integrins. These results build on previous findings that demonstrated that mechanically perturbed E-cadherin receptors activate phosphoinositide 3-kinase and downstream integrins in an EGFR-dependent manner. Results of this study show that this EGFR-mediated kinase cascade controls the force-dependent recruitment of vinculin to stressed E-cadherin complexes - a key early signature of cadherin-based mechanotransduction. Vinculin targeting requires its phosphorylation at tyrosine 822 by Abl family kinases (hereafter Abl), but the origin of force-dependent Abl activation had not been identified. We now present evidence that integrin activation, which is downstream of EGFR signaling, controls Abl activation, thus linking E-cadherin to Abl through a mechanosensitive signaling network. These findings place EGFR and integrins at the center of a positive-feedback loop, through which force-activated E-cadherin signals regulate vinculin recruitment to cadherin complexes in response to increased intercellular tension.This article has an associated First Person interview with the first author of the paper.

Heterogeneous Cytoskeletal Force Distribution Delineates the Onset Ca2+ Influx Under Fluid Shear Stress in Astrocytes

Mechanical perturbations increase intracellular Ca²⁺ in cells, but the coupling of mechanical forces to the Ca²⁺ influx is not well understood. We used a microfluidic chamber driven with a high-speed pressure servo to generate defined fluid shear stress to cultured astrocytes, and simultaneously measured cytoskeletal forces using a force sensitive actinin optical sensor and intracellular Ca²⁺. Fluid shear generated non-uniform forces in actinin that critically depended on the stimulus rise time emphasizing the presence of viscoelasticity in the activating sequence. A short (ms) shear pulse with fast rise time (2 ms) produced an immediate increase in actinin tension at the upstream end of the cell with minimal changes at the downstream end. The onset of Ca²⁺ rise began at highly strained areas. In contrast to stimulus steps, slow ramp stimuli produced uniform forces throughout the cells and only a small Ca²⁺ response. The heterogeneity of force distribution is exaggerated in cells having fewer stress fibers and lower pre-tension in actinin. Disruption of cytoskeleton with cytochalasin-D (Cyt-D) eliminated force gradients, and in those cells Ca²⁺ elevation started from the soma. Thus, Ca²⁺ influx with a mechanical stimulus depends on local stress within the cell and that is time dependent due to viscoelastic mechanics.

Biophysical Stimulation for Engineering Functional Skeletal Muscle

Tissue engineering is a promising therapeutic strategy to regenerate skeletal muscle. However, ex vivo cultivation methods typically result in a low differentiation efficiency of stem cells as well as grafts that resemble the native tissues morphologically, but lack contractile function. The application of biomimetic tensile strain provides a potent stimulus for enhancing myogenic differentiation and engineering functional skeletal muscle grafts. We reviewed integrin-dependent mechanisms that potentially link mechanotransduction pathways to the upregulation of myogenic genes. Yet, gaps in our understanding make it challenging to use these pathways to theoretically determine optimal ex vivo strain regimens. A multitude of strain protocols have been applied to in vitro cultures for the cultivation of myogenic progenitors (adipose- and bone marrow-derived stem cells and satellite cells) and transformed murine myoblasts, C2C12s. Strain regimens are characterized by orientation, amplitude, and time-dependent factors (effective frequency, duration, and the rest period between successive strain cycles). Analysis of published data has identified possible minimum/maximum values for these parameters and suggests that uniaxial strains may be more potent than biaxial strains, possibly because they more closely mimic physiologic strain profiles. The application of these biophysical stimuli for engineering 3D skeletal muscle grafts is nontrivial and typically requires custom-designed bioreactors used in combination with biomaterial scaffolds. Consideration of the physical properties of these scaffolds is critical for effective transmission of the applied strains to encapsulated cells. Taken together, these studies demonstrate that biomimetic tensile strain generally results in improved myogenic outcomes in myogenic progenitors and differentiated myoblasts. However, for 3D systems, the optimization of the strain regimen may require the entire system including cells, biomaterials, and bioreactor, to be considered in tandem.

Theoretical framework for analyzing structural compliance properties of proteins

We propose methods for directly analyzing structural compliance (SC) properties of elastic network models of proteins, and we also propose methods for extracting information about motion properties from the SC properties. The analysis of SC properties involves describing the relationships between the applied forces and the deformations. When decomposing the motion according to the magnitude of SC (SC mode decomposition), we can obtain information about the motion properties under the assumption that the lower SC mode motions or the softer motions occur easily. For practical applications, the methods are formulated in a general form. The parts where forces are applied and those where deformations are evaluated are separated from each other for enabling the analyses of allosteric interactions between the specified parts. The parts are specified not only by the points but also by the groups of points (the groups are treated as flexible bodies). In addition, we propose methods for quantitatively evaluating the properties based on the screw theory and the considerations of the algebraic structures of the basic equations expressing the SC properties. These methods enable quantitative discussions about the relationships between the SC mode motions and the motions estimated from two different conformations; they also help identify the key parts that play important roles for the motions by comparing the SC properties with those of partially constrained models. As application examples, lactoferrin and ATCase are analyzed. The results show that we can understand their motion properties through their lower SC mode motions or the softer motions.

Pneumatically actuated cell-stretching array platform for engineering cell patterns in vitro

Cellular response to mechanical stimuli is a well-known phenomenon known as mechanotransduction. It is widely accepted that mechanotransduction plays an important role in cell alignment which is critical for cell homeostasis. Although many approaches have been developed in recent years to study the effect of external mechanical stimuli on cell behaviour, most of them have not explored the ability of mechanical stimuli to engineer cell alignment to obtain patterned cell cultures. This paper introduces a simple, yet effective pneumatically actuated 4 × 2 cell stretching array for concurrently inducing a range of cyclic normal strains onto cell cultures to achieve predefined cell alignment. We utilised a ring-shaped normal strain pattern to demonstrate the growth of in vitro patterned cell cultures with predefined circumferential cellular alignment. Furthermore, to ensure the compatibility of the developed cell stretching platform with general tools and existing protocols, the dimensions of the developed cell-stretching platform follow the standard F-bottom 96-well plate. In this study, we report the principle design, simulation and characterisation of the cell-stretching platform with preliminary observations using fibroblast cells. Our experimental results of cytoskeleton reorganisation such as perpendicular cellular alignment of the cells to the direction of normal strain are consistent with those reported in the literature. After two hours of stretching, the circumferential alignment of fibroblast cells confirms the capability of the developed system to achieve patterned cell culture. The cell-stretching platform reported is potentially a useful tool for drug screening in 2D mechanobiology experiments, tissue engineering and regenerative medicine.

Role of membrane-tension gated Ca2+ flux in cell mechanosensation

Eukaryotic cells are sensitive to mechanical forces they experience from the environment. The process of mechanosensation is complex, and involves elements such as the cytoskeleton and active contraction from myosin motors. Ultimately, mechanosensation is connected to changes in gene expression in the cell, known as mechanotransduction. While the involvement of the cytoskeleton in mechanosensation is known, the processes upstream of cytoskeletal changes are unclear. In this paper, by using a microfluidic device that mechanically compresses live cells, we demonstrate that Ca2+ currents and membrane tension-sensitive ion channels directly signal to the Rho GTPase and myosin contraction. In response to membrane tension changes, cells actively regulate cortical myosin contraction to balance external forces. The process is captured by a mechanochemical model where membrane tension, myosin contraction and the osmotic pressure difference between the cytoplasm and extracellular environment are connected by mechanical force balance. Finally, to complete the picture of mechanotransduction, we find that the tension-sensitive transcription factor YAP family of proteins translocate from the nucleus to the cytoplasm in response to mechanical compression.

Darwinian evolution and cardiovascular remodeling

Mechanotransduction, MT, is an ancient evolutionary legacy existing in every living species and involving complex rearrangements of multiple proteins in response to a mechanical stress. MT includes three different interrelated processes: mechanosensation, mechanotransmission, and mechanoresponse. Each process is specifically adapted to a given tissue and stress. Both cardiac and arterial remodeling involve MT. Physiological or pathological cardiac remodeling, CR, is firstly a beneficial mechanoresponse, MR, which allows the heart to recover to a normal economy, better adapted to the new working conditions. Nevertheless, exercise-induced cardiac remodeling is more a coming-back to normal conditions than a superimposed event. On the longer term, the MR creates fibrosis which accounts, in part, for the reduced cardiac output in the CR. In the hypertension-induced arterial remodeling, arterial MR allows the vessels to maintain a normal circumferential constraint before an augmented arterial pressure. In atherogenesis: (i) The presence of atheroma in several animal species and atherosclerosis in ancient civilizations suggests more basic predispositions. (ii) The atherosclerotic plaques preferably develop at predictable arterial sites of disturbed blood flow showing that MT is involved in the initial steps of atherogenesis.

In Vitro Modeling of Mechanics in Cancer Metastasis

In addition to a multitude of genetic and biochemical alterations, abnormal morphological, structural, and mechanical changes in cells and their extracellular environment are key features of tumor invasion and metastasis. Furthermore, it is now evident that mechanical cues alongside biochemical signals contribute to critical steps of cancer initiation, progression, and spread. Despite its importance, it is very challenging to study mechanics of different steps of metastasis in the clinic or even in animal models. While considerable progress has been made in developing advanced in vitro models for studying genetic and biological aspects of cancer, less attention has been paid to models that can capture both biological and mechanical factors realistically. This is mainly due to lack of appropriate models and measurement tools. After introducing the central role of mechanics in cancer metastasis, we provide an outlook on the emergence of novel in vitro assays and their combination with advanced measurement technologies to probe and recapitulate mechanics in conditions more relevant to the metastatic disease.

Dual αvβ3 and αvβ5 blockade attenuates fibrotic and vascular alterations in a murine model of systemic sclerosis

Systemic sclerosis (SSc) is a connective tissue disorder characterized by fibroblast activation and fibrosis of the skin and internal organs. Alterations in cell-integrin interaction are sufficient to initiate profibrotic processes. SSc fibroblasts express both αvβ3 and αvβ5 integrins and their activation induces myofibroblasts differentiation. The aim of the present study was to evaluate the effect of the anb3 and anb5 inhibitor, cilengitide, on the development of vascular and fibrotic changes in the chronic oxidant stress murine model of systemic sclerosis. SSc was induced in BALB/c mice by daily s.c. injections of HOCl for 6 weeks. Mice were randomized in three arms: HOCl alone (n=8), HOCl + Cilengitide (n=8), or Vehicle alone (n=8). Treatment with cilengitide 20 (mg/kg/i.p./day) was started 4 weeks after the first administration of HOCl and maintained throughout the remaining experimental period (2 weeks). Lung, skin, and heart fibrosis were evaluated by histology while kidney morphology by PAS staining. Collagen type I, focal adhesion kinase (FAK), and a-SMA were evaluated by immunostaining and p-FAK and TGF-β1 by Western blot and gene expression. Both cutaneous and pulmonary fibrosis induced by HOCl were attenuated by cilengitide treatment. Cilengitide administration reduced a-SMA, TGF-β1, and p-FAK expression and the increased deposition of fibrillar collagen in the heart and prevented glomeruli collapse in the kidneys. The inhibition of aνβ3 and aνβ5 integrin signaling prevented systemic fibrosis and renal vascular abnormalities in the reactive oxygen species model of SSc. Integrins aνβ3 and aνβ5 could prove useful as a therapeutic target in SSc.

Developmental finite element analysis of cichlid pharyngeal jaws: Quantifying the generation of a key innovation

Advances in imaging and modeling facilitate the calculation of biomechanical forces in biological specimens. These factors play a significant role during ontogenetic development of cichlid pharyngeal jaws, a key innovation responsible for one of the most prolific species diversifications in recent times. MicroCT imaging of radiopaque-stained vertebrate embryos were used to accurately capture the spatial relationships of the pharyngeal jaw apparatus in two cichlid species (Haplochromis elegans and Amatitlania nigrofasciata) for the purpose of creating a time series of developmental stages using finite element models, which can be used to assess the effects of biomechanical forces present in a system at multiple points of its ontogeny. Changes in muscle vector orientations, bite forces, force on the neurocranium where cartilage originates, and stress on upper pharyngeal jaws are analyzed in a comparative context. In addition, microCT scanning revealed the presence of previously unreported cement glands in A. nigrofasciata. The data obtained provide an underrepresented dimension of information on physical forces present in developmental processes and assist in interpreting the role of developmental dynamics in evolution.

The collective influence of 1, 25-dihydroxyvitamin D3 with physiological fluid shear stress on osteoblasts

1, 25-dihydroxyvitamin D₃ (1, 25 (OH)₂ D₃) and mechanical stimuli in physiological environment contributes greatly to osteoporosis pathogenesis. Wide investigations have been conducted on how 1, 25-dihydroxyvitamin D₃ and mechanical stimuli separately impact osteoblasts. This study reports the collective influences of 1, 25-dihydroxyvitamin D₃ and flow shear stress (FSS) on biological functions of osteoblasts. 1, 25 (OH)₂ D₃ were prepared in various kinds of concentrations (0, 1, 10, 100 nmmol/L), while physiological fluid shear stress (12 dynes/cm²) was produced by using a parallel-plate fluid flow system. 1, 25 (OH)₂ D₃ affects the responses of ROBs to FSS, including the inhibition of NO release and cell proliferation as well as the promotion of PGE₂ release and cell differentiation. These findings provide a possible mechanism by which 1, 25(OH)₂ D₃ influences osteoblasts' responses to FSS, thus most probably providing guidance for the selection of 1, 25(OH)₂ D₃ concentration and mechanical loading in order to produce functional bone tissues in vitro.

Routine clinical anti-platelet agents have limited efficacy in modulating hypershear-mediated platelet activation associated with mechanical circulatory support

INTRODUCTION

Continuous flow ventricular assist devices (cfVADs) continue to be limited by thrombotic complications associated with disruptive flow patterns and supraphysiologic shear stresses. Patients are prescribed complex antiplatelet therapies, which do not fully prevent recurrent thromboembolic events. This is partially due to limited data on antiplatelet efficacy under cfVAD-associated shear conditions.

MATERIALS AND METHODS

We investigated the efficacy of antiplatelet drugs directly acting on three pathways: (1) cyclooxygenase (aspirin), (2) phosphodiesterase (dipyridamole, pentoxifylline, cilostazol), and (3) glycoprotein IIb-IIIa (eptifibatide). Gel-filtered platelets treated with these drugs were exposed for 10min to either constant shear stresses (30dyne/cm² and 70dyne/cm²) or dynamic shear stress profiles extracted from simulated platelet trajectories through a cfVAD (Micromed DeBakey). Platelet activation state (PAS) was measured using a modified prothrombinase-based assay, with drug efficacy quantified based on PAS reduction compared to untreated controls.

RESULTS AND CONCLUSIONS

Significant PAS reduction was observed for all drugs after exposure to 30dyne/cm² constant shear stress, and all drugs but dipyridamole after exposure to the 30th percentile shear stress waveform of the cfVAD. However, only cilostazol was significantly effective after 70dyne/cm² constant shear stress exposure, though no significant reduction was observed upon exposure to median shear stress conditions in the cfVAD. These results, coupled with the persistence of reported clinical thrombotic complication, suggest the need for the development of new classes of drugs that are especially designed to mitigate thrombosis in cfVAD patients, while reducing or eliminating the risk of bleeding.

First-Breath-Induced Type 2 Pathways Shape the Lung Immune Environment

From birth onward, the lungs are exposed to the external environment and therefore harbor a complex immunological milieu to protect this organ from damage and infection. We investigated the homeostatic role of the epithelium-derived alarmin interleukin-33 (IL-33) in newborn mice and discovered the immediate upregulation of IL-33 from the first day of life, closely followed by a wave of IL-13-producing type 2 innate lymphoid cells (ILC2s), which coincided with the appearance of alveolar macrophages (AMs) and their early polarization to an IL-13-dependent anti-inflammatory M2 phenotype. ILC2s contributed to lung quiescence in homeostasis by polarizing tissue resident AMs and induced an M2 phenotype in transplanted macrophage progenitors. ILC2s continued to maintain the M2 AM phenotype during adult life at the cost of a delayed response to Streptococcus pneumoniae infection in mice. These data highlight the homeostatic role of ILC2s in setting the activation threshold in the lung and underline their implications in anti-bacterial defenses.

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The first breath triggers IL-33 induction by AEC2 in lungs of newborn mice

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IL-33 promotes the perinatal expansion and activation of ST2-expressing ILC2s

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ILC2-derived IL-13 polarizes newborn’s AMs into an M2 phenotype

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This homeostatic type 2 pathway delays antibacterial effector responses

Why we need mechanics to understand animal regeneration

Mechanical forces are an important contributor to cell fate specification and cell migration during embryonic development in animals. Similarities between embryogenesis and regeneration, particularly with regards to pattern formation and large-scale tissue movements, suggest similarly important roles for physical forces during regeneration. While the influence of the mechanical environment on stem cell differentiation in vitro is being actively exploited in the fields of tissue engineering and regenerative medicine, comparatively little is known about the role of stresses and strains acting during animal regeneration. In this review, we summarize published work on the role of physical principles and mechanical forces in animal regeneration. Novel experimental techniques aimed at addressing the role of mechanics in embryogenesis have greatly enhanced our understanding at scales from the subcellular to the macroscopic - we believe the time is ripe for the field of regeneration to similarly leverage the tools of the mechanobiological research community.

Low-Intensity Ultrasound Modulates Ca2+ Dynamics in Human Mesenchymal Stem Cells via Connexin 43 Hemichannel

In recent years, ultrasound has gained attention in new biological applications due to its ability to induce specific biological responses at the cellular level. Although the biophysical mechanisms underlying the interaction between ultrasound and cells are not fully understood, many agree on a pivotal role of Ca²⁺ signaling through mechanotransduction pathways. Because Ca²⁺ regulates a vast range of downstream cellular processes, a better understanding of how ultrasound influences Ca²⁺ signaling could lead to new applications for ultrasound. In this study, we investigated the mechanism of ultrasound-induced Ca²⁺ mobilization in human mesenchymal stem cells using 47 MHz focused ultrasound to stimulate single cells at low intensities (~ 110 mW/cm²). We found that ultrasound exposure triggers opening of connexin 43 hemichannels on the plasma membrane, causing release of ATP into the extracellular space. That ATP then binds to G-protein-coupled P₂Y₁ purinergic receptors on the membrane, in turn activating phospholipase C, which evokes production of inositol trisphosphate and release of Ca²⁺ from intracellular stores.

Large Amplitude Oscillatory Shear Rheology of Living Fibroblasts: Path-Dependent Steady States

Mechanical properties of biological cells play a role in cell locomotion, embryonic tissue formation, and tumor migration among many other processes. Cells exhibit a complex nonlinear response to mechanical cues that is not understood. Cells may stiffen as well as soften, depending on the exact type of stimulus. Here we apply large-amplitude oscillatory shear to a monolayer of separated fibroblast cells suspended between two plates. Although we apply identical steady-state excitations, in response we observe different typical regimes that exhibit cell softening or cell stiffening to varying degrees. This degeneracy of the cell response can be linked to the initial paths that the instrument takes to go from cell rest to steady state. A model of cross-linked, force-bearing filaments submitted to steady-state excitation renders the different observed regimes with minor changes in parameters if the filaments are permitted to self-organize and form different spatially organized structures. We suggest that rather than a complex viscoelastic or plastic response, the different observed regimes reflect the emergence of different steady-state cytoskeletal conformations. A high sensitivity of the cytoskeletal rheology and structure to minor changes in parameters or initial conditions enables a cell to respond to mechanical requirements quickly and in various ways with only minor biochemical intervention. Probing path-dependent rheological changes constitutes a possibly very sensitive assessment of the cell cytoskeleton as a possible tool for medical diagnosis. Our observations show that the memory of subtle differences in earlier deformation paths must be taken into account when deciphering the cell mechanical response to large-amplitude deformations.

Receptor-mediated cell mechanosensing

Mechanosensing depicts the ability of a cell to sense mechanical cues, which under some circumstances is mediated by the surface receptors. In this review, a four-step model is described for receptor-mediated mechanosensing. Platelet GPIb, T-cell receptor, and integrins are used as examples to illustrate the key concepts and players in this process.

Mechanosensing describes the ability of a cell to sense mechanical cues of its microenvironment, including not only all components of force, stress, and strain but also substrate rigidity, topology, and adhesiveness. This ability is crucial for the cell to respond to the surrounding mechanical cues and adapt to the changing environment. Examples of responses and adaptation include (de)activation, proliferation/apoptosis, and (de)differentiation. Receptor-mediated cell mechanosensing is a multistep process that is initiated by binding of cell surface receptors to their ligands on the extracellular matrix or the surface of adjacent cells. Mechanical cues are presented by the ligand and received by the receptor at the binding interface; but their transmission over space and time and their conversion into biochemical signals may involve other domains and additional molecules. In this review, a four-step model is described for the receptor-mediated cell mechanosensing process. Platelet glycoprotein Ib, T-cell receptor, and integrins are used as examples to illustrate the key concepts and players in this process.

An Electromagnetically Actuated Double-Sided Cell-Stretching Device for Mechanobiology Research

Cellular response to mechanical stimuli is an integral part of cell homeostasis. The interaction of the extracellular matrix with the mechanical stress plays an important role in cytoskeleton organisation and cell alignment. Insights from the response can be utilised to develop cell culture methods that achieve predefined cell patterns, which are critical for tissue remodelling and cell therapy. We report the working principle, design, simulation, and characterisation of a novel electromagnetic cell stretching platform based on the double-sided axial stretching approach. The device is capable of introducing a cyclic and static strain pattern on a cell culture. The platform was tested with fibroblasts. The experimental results are consistent with the previously reported cytoskeleton reorganisation and cell reorientation induced by strain. Our observations suggest that the cell orientation is highly influenced by external mechanical cues. Cells reorganise their cytoskeletons to avoid external strain and to maintain intact extracellular matrix arrangements.

Theoretical modeling of mechanical homeostasis of a mammalian cell under gravity-directed vector

Translocation of dense nucleus along gravity vector initiates mechanical remodeling of a eukaryotic cell. In our previous experiments, we quantified the impact of gravity vector on cell remodeling by placing an MC3T3-E1 cell onto upward (U)-, downward (D)-, or edge-on (E)- orientated substrate. Our experimental data demonstrate that orientation dependence of nucleus longitudinal translocation is positively correlated with cytoskeletal (CSK) remodeling of their expressions and structures and also is associated with rearrangement of focal adhesion complex (FAC). However, the underlying mechanism how CSK network and FACs are reorganized in a mammalian cell remains unclear. In this paper, we developed a theoretical biomechanical model to integrate the mechanosensing of nucleus translocation with CSK remodeling and FAC reorganization induced by a gravity vector. The cell was simplified as a nucleated tensegrity structure in the model. The cell and CSK filaments were considered to be symmetrical. All elements of CSK filaments and cytomembrane that support the nucleus were simplified as springs. FACs were simplified as an adhesion cluster of parallel bonds with shared force. Our model proposed that gravity vector-directed translocation of the cell nucleus is mechanically balanced by CSK remodeling and FAC reorganization induced by a gravitational force. Under gravity, dense nucleus tends to translocate and exert additional compressive or stretching force on the cytoskeleton. Finally, changes of the tension force acting on talin by microfilament alter the size of FACs. Results from our model are in qualitative agreement with those from experiments.

Mimicking mechanical response of natural tissues. Strain hardening induced by transient reticulation in lactose-modified chitosan (chitlac)

The effect of transient cross-links has been explored on a lactose-modified chitosan, which previously had shown interesting biological features. The presence of galactose side chains and of the polyol spacer resulted particularly appealing for the reticulation by borate ions. The interaction between chitlac and borax was investigated by means of ¹¹B NMR while rheology pointed to a marked non-linear behavior depending on the amount of borax added to the system. The presence of limited amount of cross-linking ion led to dilatant behavior when the steady flow curve was measured. In addition, strain stiffening was noticed on elastic response upon exceeding a critical stress, indicating a transient nature in the formation of the cross-links. The non-linear response of chitlac in the presence of borax compared surprisingly well with the one showed by proteins composing the natural ECM pointing at a possible role of mechanotransduction in the biological significance of the modified chitosan.

Intestinal Stem Cell Niche: The Extracellular Matrix and Cellular Components

The intestinal epithelium comprises a monolayer of polarised columnar cells organised along the crypt-villus axis. Intestinal stem cells reside at the base of crypts and are constantly nourished by their surrounding niche for maintenance, self-renewal, and differentiation. The cellular microenvironment including the adjacent Paneth cells, stromal cells, smooth muscle cells, and neural cells as well as the extracellular matrix together constitute the intestinal stem cell niche. A dynamic regulatory network exists among the epithelium, stromal cells, and the matrix via complex signal transduction to maintain tissue homeostasis. Dysregulation of these biological or mechanical signals could potentially lead to intestinal injury and disease. In this review, we discuss the role of different intestinal stem cell niche components and dissect the interaction between dynamic matrix factors and regulatory signalling during intestinal stem cell homeostasis.

Mechanical forces in the immune system

Leukocytes can completely reorganize their cytoskeletal architecture within minutes. This structural plasticity, which facilitates their migration and communicative function, also enables them to exert a substantial amount of mechanical force against the extracellular matrix and the surfaces of interacting cells. In recent years, it has become increasingly clear that these forces have crucial roles in immune cell activation and subsequent effector responses. Here, I review our current understanding of how mechanical force regulates cell-surface receptor activation, cell migration, intracellular signalling and intercellular communication, highlighting the biological ramifications of these effects in various immune cell types.

Mechanically Loading Cell/Hydrogel Constructs with Low-Intensity Pulsed Ultrasound for Bone Repair

Low-intensity pulsed ultrasound (LIPUS) has been shown to be effective for orthopedic fracture repair and nonunion defects, but the specific mechanism behind its efficacy is still unknown. Previously, we have shown a measurable acoustic radiation force at LIPUS intensities traditionally used for clinical treatment and have applied this force to osteoblastic cells encapsulated in type I collagen hydrogels. Our goal in this study is to provide insight and inform the appropriate design of a cell therapy approach to bone repair in which osteoblasts are embedded in collagen hydrogels, implanted into a bony defect, and then transdermally stimulated using LIPUS-derived acoustic radiation force to enhance bone formation at the earliest time points after bone defect repair. To this end, in this study, we demonstrate the ability to measure local hydrogel deformations in response to LIPUS-induced acoustic radiation force and reveal that hydrogel deformation varies with both LIPUS intensity and hydrogel stiffness. Specifically, hydrogel deformation is positively correlated with LIPUS intensity and this deformation is further increased by reducing the stiffness of the hydrogel. We have also shown that encapsulated osteoblastic cells respond to increases in LIPUS intensity by upregulating both cyclooxygenase 2 and prostaglandin E₂ (PGE₂), both implicated in new bone formation and well-established responses to the application of fluid forces on osteoblast cells. Finally, we demonstrate that combining an increase in LIPUS with a three-dimensional culture environment upregulates both markers beyond their expression noted from either experimental condition alone, suggesting that both LIPUS and hydrogel encapsulation, when combined and modulated appropriately, can enhance osteoblastic response considerably. These studies provide important information toward a clinically relevant cell therapy treatment for bone defects that allows the transdermal application of mechanical loading to bone defects without physically destabilizing the defect site.

Single microtubules and small networks become significantly stiffer on short time-scales upon mechanical stimulation

The transfer of mechanical signals through cells is a complex phenomenon. To uncover a new mechanotransduction pathway, we study the frequency-dependent transport of mechanical stimuli by single microtubules and small networks in a bottom-up approach using optically trapped beads as anchor points. We interconnected microtubules to linear and triangular geometries to perform micro-rheology by defined oscillations of the beads relative to each other. We found a substantial stiffening of single filaments above a characteristic transition frequency of 1–30 Hz depending on the filament’s molecular composition. Below this frequency, filament elasticity only depends on its contour and persistence length. Interestingly, this elastic behavior is transferable to small networks, where we found the surprising effect that linear two filament connections act as transistor-like, angle dependent momentum filters, whereas triangular networks act as stabilizing elements. These observations implicate that cells can tune mechanical signals by temporal and spatial filtering stronger and more flexibly than expected.

Structural Studies of Hydrographenes

As a result of the unique physical and electrical properties, graphene continues to attract the interest of a large segment of the scientific community. Since graphene does not occur naturally, the ability to exfoliate and isolate individual layers of graphene from graphite is an important and challenging process. The interlayer cohesive energy of graphite that results from van der Waals attractions has been determined experimentally to be 61 meV per carbon atom (61 meV/C atom). This requires the development of a method to overcome the strong attractive forces associated with graphite. The exfoliation process that we, and others, have investigated involves electron transfer into bulk graphite from intercalated lithium to yield lithium graphenide. The resulting graphenide can be reacted with various reagents to yield functionalized graphene. As a part of our interest in the functionalization of graphene, we have explored the Birch reduction as a route to hydrographenes. The addition of hydrogen transforms graphene into an insulator, leading to the prediction that important applications will emerge. This Account focuses mainly on the characterization of the hydrographenes that are obtained from different types of graphite including synthetic graphite powder, natural flake graphite, and annealed graphite powder. Analysis by solid state ¹³C NMR spectroscopy proved to be important since it was shown that the hydrographenes are composed of interior, isolated aromatic (predominantly fully substituted benzene) rings surrounded by saturated rings. The expected clusters of benzene rings were not found. NMR spectroscopy also offers strong evidence for the presence of tert-butyl alcohol and ethanol (workup solvent) that could not be removed in vacuo from the samples. These compounds could be observed to move freely within the layers of the hydrographene. High-resolution transmission electron microscopy images revealed a remarkable change in morphology that results when hydrogen is added to the graphenide. The appearance of edge and circular dislocations and increased distances between graphitic layers are most visible in the case of the hydrographenes that are formed from annealed graphite. The repetitive hydrogenation of synthetic graphite powder leads to an increase in the distances between the graphitic layers in the (002) direction from 3.4 Å for the initial graphite to 4.11 Å after the first reduction and to 4.29 Å after a third reduction of the same material. Defect-free graphite is formed when the hydrographenes are heated. The distance between carbon layers decreases from 4.11 to 3.44 Å after heating the samples to 1200 °C. This trend toward the spacing of graphite confirms the reversibility of the functionalization process. The C-H bonds have been broken yielding hydrogen, and the exposed carbon orbitals are in close enough proximity to have reverted to graphite. This Account introduces only a narrow area of materials chemistry, and many applications of graphene and its derivatives can be expected as researchers exploit this burgeoning field.

Traction force and its regulation during cytokinesis in Dictyostelium cells

Cytokinesis is the final stage of cell division. Dictyostelium cells have multiple modes of cytokinesis, including cytokinesis A, B and C. Cytokinesis A is a conventional mode, which depends on myosin II in the contractile ring. Myosin II null cells divide depending on substratum-attachment (cytokinesis B) or in a multi-polar fashion independent of the cell cycle (cytokinesis C). We investigated the traction stress exerted by dividing cells in the three different modes using traction force microscopy. In all cases, the traction forces were directed inward from both poles. Interestingly, the traction stress of cytokinesis A was the smallest of the three modes. Latrunculin B, an inhibitor of actin polymerization, completely diminished the traction stress of dividing cells, but blebbistatin, an inhibitor of myosin II ATPase, increased the traction stress. Myosin II is proposed to contribute to the detachment of cell body from the substratum. When the cell-substratum attachment was artificially strengthened by a poly-lysine coating, wild type cells increased their traction stress in contrast to myosin II null and other cytokinesis-deficient mutant cells, which suggests that wild type cells may increase their own power to conduct their cytokinesis. The cytokinesis-deficient mutants frequently divided unequally, whereas wild type cells divided equally. A traction stress imbalance between two daughter halves was correlated with cytokinesis failure. We discuss the regulation of cell shape changes during cell division through mechanosensing.

Stretch-induced actomyosin contraction in epithelial tubes: Mechanotransduction pathways for tubular homeostasis

Many tissues in our body have a tubular shape and are constantly exposed to various stresses. Luminal pressure imposes tension on the epithelial and myoepithelial or smooth muscle cells surrounding the lumen of the tubes. Contractile forces generated by actomyosin assemblies within these cells oppose the luminal pressure and must be calibrated to maintain tube diameter homeostasis and tissue integrity. In this review, we discuss mechanotransduction pathways that can lead from sensation of cell stretch to activation of actomyosin contractility, providing rapid mechanochemical feedback for proper tubular tissue function.

The arterial microenvironment: the where and why of atherosclerosis

The formation of atherosclerotic plaques in the large and medium sized arteries is classically driven by systemic factors, such as elevated cholesterol and blood pressure. However, work over the past several decades has established that atherosclerotic plaque development involves a complex coordination of both systemic and local cues that ultimately determine where plaques form and how plaques progress. Although current therapeutics for atherosclerotic cardiovascular disease primarily target the systemic risk factors, a large array of studies suggest that the local microenvironment, including arterial mechanics, matrix remodelling and lipid deposition, plays a vital role in regulating the local susceptibility to plaque development through the regulation of vascular cell function. Additionally, these microenvironmental stimuli are capable of tuning other aspects of the microenvironment through collective adaptation. In this review, we will discuss the components of the arterial microenvironment, how these components cross-talk to shape the local microenvironment, and the effect of microenvironmental stimuli on vascular cell function during atherosclerotic plaque formation.

Roles of the cytoskeleton, cell adhesion and rho signalling in mechanosensing and mechanotransduction

All cells sense and respond to various mechanical forces in and mechanical properties of their environment. To respond appropriately, cells must be able to sense the location, direction, strength and duration of these forces. Recent progress in mechanobiology has provided a better understanding of the mechanisms of mechanoresponses underlying many cellular and developmental processes. Various roles of mechanoresponses in development and tissue homeostasis have been elucidated, and many molecules involved in mechanotransduction have been identified. However, the whole picture of the functions and molecular mechanisms of mechanotransduction remains to be understood. Recently, novel mechanisms for sensing and transducing mechanical stresses via the cytoskeleton, cell-substrate and cell-cell adhesions and related proteins have been identified. In this review, we outline the roles of the cytoskeleton, cell-substrate and cell-cell adhesions, and related proteins in mechanosensing and mechanotransduction. We also describe the roles and regulation of Rho-family GTPases in mechanoresponses.

A Bio-Realistic Finite Element Model to Evaluate the Effect of Masticatory Loadings on Mouse Mandible-Related Tissues

Mice are arguably the dominant model organisms for studies investigating the effect of genetic traits on the pathways to mammalian skull and teeth development, thus being integral in exploring craniofacial and dental evolution. The aim of this study is to analyse the functional significance of masticatory loads on the mouse mandible and identify critical stress accumulations that could trigger phenotypic and/or growth alterations in mandible-related structures. To achieve this, a 3D model of mouse skulls was reconstructed based on Micro Computed Tomography measurements. Upon segmenting the main hard tissue components of the mandible such as incisors, molars and alveolar bone, boundary conditions were assigned on the basis of the masticatory muscle architecture. The model was subjected to four loading scenarios simulating different feeding ecologies according to the hard or soft type of food and chewing or gnawing biting movement. Chewing and gnawing resulted in varying loading patterns, with biting type exerting a dominant effect on the stress variations experienced by the mandible and loading intensity correlating linearly to the stress increase. The simulation provided refined insight on the mechanobiology of the mouse mandible, indicating that food consistency could influence micro evolutionary divergence patterns in mandible shape of rodents.

Perceptual evaluation of violins: A psycholinguistic analysis of preference verbal descriptions by experienced musicians

In this paper, how the notion of violin quality is conveyed in spontaneous verbalizations by experienced violinists during preference judgments is investigated. The aims of the study were to better understand how musicians conceptualize violin quality, what aspects of the sound and the playing experience are essential, and what associations are formed between perceptual evaluation and physical description. Upon comparing violins of varying make and age, players were interviewed about their preferences using open-ended questions. Concepts of violin quality were identified and categorized based on the syntactic and linguistic analysis of musicians' responses. While perceived variations in how a violin sounds and feels, and consequently conceptualization structures, rely on the variations in style and expertise of different violinists, the broader semantic categories emerging from sensory descriptions remain common across performers with diverse musical profiles, reflecting a shared perception of physical parameter patterns that allowed the development of a musician-driven framework for understanding how the dynamic behavior of a violin might relate to its perceived quality. Implications for timbre perception and the crossmodal audio-tactile sensation of sound in music performance are discussed.

Regulatory Roles of Fluctuation-Driven Mechanotransduction in Cell Function

Cells in the body are exposed to irregular mechanical stimuli. Here, we review the so-called fluctuation-driven mechanotransduction in which stresses stretching cells vary on a cycle-by-cycle basis. We argue that such mechanotransduction is an emergent network phenomenon and offer several potential mechanisms of how it regulates cell function. Several examples from the vasculature, the lung, and tissue engineering are discussed. We conclude with a list of important open questions.

Simplified preparation and characterization of magnetic hydroxyapatite-based nanocomposites

Authors aimed to provide a magnetic responsiveness to bone-mimicking nano-hydroxyapatite (n-HA). For this purpose, dextran-grafted iron oxide nanoarchitectures (DM) were synthesized by a green-friendly and scalable alkaline co-precipitation method at room temperature and used to functionalize n-HA crystals. Different amounts of DM hybrid structures were added into the nanocomposites (DM/n-HA 1:1, 2:1 and 3:1weight ratio) which were investigated through extensive physicochemical (XRD, ICP, TGA and Zeta-potential), microstructural (TEM and DLS), magnetic (VSM) and biological analyses (MTT proliferation assay). X-ray diffraction patterns have confirmed the n-HA formation in the presence of DM as a co-reagent. Furthermore, the addition of DM during the synthesis does not affect the primary crystallite domains of DM/n-HA nanocomposites. DM/n-HAs have shown a rising of the magnetic moment values by increasing DM content up to 2:1 ratio. However, the magnetic moment value recorded in the DM/n-HA 3:1 do not further increase showing a saturation behaviour. The cytocompatibility of the DM/n-HA was evaluated with respect to the MG63 osteoblast-like cell line. Proliferation assays revealed that viability, carried out in the absence of external magnetic field, was not affected by the amount of DM employed. Interestingly, assays also suggested that the DM/n-HA nanocomposites exhibit a possible shielding effect with respect to the anti-proliferative activity induced by the DM particles alone.

Integrin signaling in atherosclerosis

Atherosclerosis, a chronic lipid-driven inflammatory disease affecting large arteries, represents the primary cause of cardiovascular disease in the world. The local remodeling of the vessel intima during atherosclerosis involves the modulation of vascular cell phenotype, alteration of cell migration and proliferation, and propagation of local extracellular matrix remodeling. All of these responses represent targets of the integrin family of cell adhesion receptors. As such, alterations in integrin signaling affect multiple aspects of atherosclerosis, from the earliest induction of inflammation to the development of advanced fibrotic plaques. Integrin signaling has been shown to regulate endothelial phenotype, facilitate leukocyte homing, affect leukocyte function, and drive smooth muscle fibroproliferative remodeling. In addition, integrin signaling in platelets contributes to the thrombotic complications that typically drive the clinical manifestation of cardiovascular disease. In this review, we examine the current literature on integrin regulation of atherosclerotic plaque development and the suitability of integrins as potential therapeutic targets to limit cardiovascular disease and its complications.

Biophysical Tools to Study Cellular Mechanotransduction

The cell membrane is the interface that volumetrically isolates cellular components from the cell's environment. Proteins embedded within and on the membrane have varied biological functions: reception of external biochemical signals, as membrane channels, amplification and regulation of chemical signals through secondary messenger molecules, controlled exocytosis, endocytosis, phagocytosis, organized recruitment and sequestration of cytosolic complex proteins, cell division processes, organization of the cytoskeleton and more. The membrane's bioelectrical role is enabled by the physiologically controlled release and accumulation of electrochemical potential modulating molecules across the membrane through specialized ion channels (e.g., Na⁺, Ca2+, K⁺ channels). The membrane's biomechanical functions include sensing external forces and/or the rigidity of the external environment through force transmission, specific conformational changes and/or signaling through mechanoreceptors (e.g., platelet endothelial cell adhesion molecule (PECAM), vascular endothelial (VE)-cadherin, epithelial (E)-cadherin, integrin) embedded in the membrane. Certain mechanical stimulations through specific receptor complexes induce electrical and/or chemical impulses in cells and propagate across cells and tissues. These biomechanical sensory and biochemical responses have profound implications in normal physiology and disease. Here, we discuss the tools that facilitate the understanding of mechanosensitive adhesion receptors. This article is structured to provide a broad biochemical and mechanobiology background to introduce a freshman mechano-biologist to the field of mechanotransduction, with deeper study enabled by many of the references cited herein.

Dynamic regulation of nuclear architecture and mechanics-a rheostatic role for the nucleus in tailoring cellular mechanosensitivity

Nuclear architecture, a function of both chromatin and nucleoskeleton structure, is known to change with stem cell differentiation and differs between various somatic cell types. These changes in nuclear architecture are associated with the regulation of gene expression and genome function in a cell-type specific manner. Biophysical stimuli are known effectors of differentiation and also elicit stimuli-specific changes in nuclear architecture. This occurs via the process of mechanotransduction whereby extracellular mechanical forces activate several well characterized signaling cascades of cytoplasmic origin, and potentially some recently elucidated signaling cascades originating in the nucleus. Recent work has demonstrated changes in nuclear mechanics both with pluripotency state in embryonic stem cells, and with differentiation progression in adult mesenchymal stem cells. This review explores the interplay between cytoplasmic and nuclear mechanosensitivity, highlighting a role for the nucleus as a rheostat in tuning the cellular mechano-response.

Magnetic silk fibroin e-gel scaffolds for bone tissue engineering applications

Recently, the incorporation of magnetic nanoparticles into standard scaffolds has emerged as a promising approach for tissue engineering applications. This strategy can promote not only tissue regeneration but also reloading of scaffolds through an external supervising center that adsorbs growth factors, preserving their stability and biological activity. In this study, novel magnetic silk fibroin e-gel scaffolds were prepared by the electrogelation process of concentrated Bombyx mori silk fibroin (8 wt%) aqueous solution. In addition, basic fibroblast growth factor was conjugated physically to human serum albumin = Fe3O4 nanoparticles (71.52 ± 2.3 nm in size) with 97.5% binding yield. Scanning electron microscopy images of the prepared human serum albumin = Fe3O4-basic fibroblast growth factor-loaded silk fibroin e-gel scaffolds showed a three-dimensional porous morphology. In terms of water uptake, basic fibroblast growth factor-conjugated scaffolds had the highest water absorbability among all groups. In vitro cell culture studies showed that both the human serum albumin coating of Fe3O4 nanoparticle surface and basic fibroblast growth factor conjugation had an inductive effect on cell viability. One of the most used markers of bone formation and osteoblast differentiation is alkaline phosphatase activity; human serum albumin = Fe3O4-basic fibroblast growth factor-loaded silk fibroin e-gels showed significantly enhanced alkaline phosphatase activity (p < 0.05). SaOS-2 cells cultured on human serum albumin = Fe3O4-basic fibroblast growth factor-loaded silk fibroin e-gels deposited more calcium compared with those cultured on bare silk fibroin e-gels. These results indicated that the proposed e-gel scaffolds are valuable candidates for magnetic guiding in bone tissue regeneration, and they will present new perspectives for magnetic field application in regenerative medicine.

Biophysical Regulation of Cell Behavior-Cross Talk between Substrate Stiffness and Nanotopography

The stiffness and nanotopographical characteristics of the extracellular matrix (ECM) influence numerous developmental, physiological, and pathological processes in vivo. These biophysical cues have therefore been applied to modulate almost all aspects of cell behavior, from cell adhesion and spreading to proliferation and differentiation. Delineation of the biophysical modulation of cell behavior is critical to the rational design of new biomaterials, implants, and medical devices. The effects of stiffness and topographical cues on cell behavior have previously been reviewed, respectively; however, the interwoven effects of stiffness and nanotopographical cues on cell behavior have not been well described, despite similarities in phenotypic manifestations. Herein, we first review the effects of substrate stiffness and nanotopography on cell behavior, and then focus on intracellular transmission of the biophysical signals from integrins to nucleus. Attempts are made to connect extracellular regulation of cell behavior with the biophysical cues. We then discuss the challenges in dissecting the biophysical regulation of cell behavior and in translating the mechanistic understanding of these cues to tissue engineering and regenerative medicine.

Cell Jamming in the Airway Epithelium

Hallmarks of asthma include chronic airway inflammation, progressive airway remodeling, and airway hyperresponsiveness. The initiation and perpetuation of these processes are attributable at least in part to critical events within the airway epithelium, but the underlying mechanisms remain poorly understood. New evidence now suggests that epithelial cells derived from donors without asthma versus donors with asthma, even in the absence of inflammatory cells or mediators, express modes of collective migration that innately differ not only in the amount of migration but also in the kind of migration. The maturing cell layer tends to undergo a transition from a hypermobile, fluid-like, unjammed phase in which cells readily rearrange, exchange places, and flow, to a quiescent, solid-like, jammed phase in which cells become virtually frozen in place. Moreover, the unjammed phase defines a phenotype that can be perpetuated by the compressive stresses caused by bronchospasm. Importantly, in cells derived from donors with asthma versus donors without asthma, this jamming transition becomes substantially delayed, thus suggesting an immature or dysmature epithelial phenotype in asthma.

Concise Review: Organ Engineering: Design, Technology, and Integration

Engineering complex tissues and whole organs has the potential to dramatically impact translational medicine in several avenues. Organ engineering is a discipline that integrates biological knowledge of embryological development, anatomy, physiology, and cellular interactions with enabling technologies including biocompatible biomaterials and biofabrication platforms such as three-dimensional bioprinting. When engineering complex tissues and organs, core design principles must be taken into account, such as the structure-function relationship, biochemical signaling, mechanics, gradients, and spatial constraints. Technological advances in biomaterials, biofabrication, and biomedical imaging allow for in vitro control of these factors to recreate in vivo phenomena. Finally, organ engineering emerges as an integration of biological design and technical rigor. An overall workflow for organ engineering and guiding technology to advance biology as well as a perspective on necessary future iterations in the field is discussed. Stem Cells 2017;35:51-60.

The dynamic conductance response and mechanics-modulated memristive behavior of the Azurin monolayer under cyclic loads

The conductance of Azurin is found to depend on both the magnitude and duration of mechanical loading, which is defined as mechanical modulated memristive (MMM) behaviour.

Tissue mechanics regulate brain development, homeostasis and disease

All cells sense and integrate mechanical and biochemical cues from their environment to orchestrate organismal development and maintain tissue homeostasis. Mechanotransduction is the evolutionarily conserved process whereby mechanical force is translated into biochemical signals that can influence cell differentiation, survival, proliferation and migration to change tissue behavior. Not surprisingly, disease develops if these mechanical cues are abnormal or are misinterpreted by the cells - for example, when interstitial pressure or compression force aberrantly increases, or the extracellular matrix (ECM) abnormally stiffens. Disease might also develop if the ability of cells to regulate their contractility becomes corrupted. Consistently, disease states, such as cardiovascular disease, fibrosis and cancer, are characterized by dramatic changes in cell and tissue mechanics, and dysregulation of forces at the cell and tissue level can activate mechanosignaling to compromise tissue integrity and function, and promote disease progression. In this Commentary, we discuss the impact of cell and tissue mechanics on tissue homeostasis and disease, focusing on their role in brain development, homeostasis and neural degeneration, as well as in brain cancer.

Shear-mediated platelet activation in the free flow: Perspectives on the emerging spectrum of cell mechanobiological mechanisms mediating cardiovascular implant thrombosis

Shear-mediated platelet activation (SMPA) is central in thrombosis of implantable cardiovascular therapeutic devices. Despite the morbidity and mortality associated with thrombosis of these devices, our understanding of mechanisms operative in SMPA, particularly in free flowing blood, remains limited. Herein we present and discuss a range of emerging mechanisms for consideration for "free flow" activation under supraphysiologic shear. Further definition and manipulation of these mechanisms will afford opportunities for novel pharmacologic and mechanical strategies to limit SMPA and enhance overall implant device safety.

Nano- and microstructured materials for in vitro studies of the physiology of vascular cells

The extracellular environment of vascular cells in vivo is complex in its chemical composition, physical properties, and architecture. Consequently, it has been a great challenge to study vascular cell responses in vitro, either to understand their interaction with their native environment or to investigate their interaction with artificial structures such as implant surfaces. New procedures and techniques from materials science to fabricate bio-scaffolds and surfaces have enabled novel studies of vascular cell responses under well-defined, controllable culture conditions. These advancements are paving the way for a deeper understanding of vascular cell biology and materials-cell interaction. Here, we review previous work focusing on the interaction of vascular smooth muscle cells (SMCs) and endothelial cells (ECs) with materials having micro- and nanostructured surfaces. We summarize fabrication techniques for surface topographies, materials, geometries, biochemical functionalization, and mechanical properties of such materials. Furthermore, various studies on vascular cell behavior and their biological responses to micro- and nanostructured surfaces are reviewed. Emphasis is given to studies of cell morphology and motility, cell proliferation, the cytoskeleton and cell-matrix adhesions, and signal transduction pathways of vascular cells. We finalize with a short outlook on potential interesting future studies.

The prospective opportunities offered by magnetic scaffolds for bone tissue engineering: a review

Magnetic scaffolds are becoming increasingly attractive in tissue engineering, due to their ability to enhance bone tissue formation by attracting soluble factors, such as growth factors, hormones and polypeptides, directly to the implantation site, as well as their potential to improve the fixation and stability of the implant. Moreover, there is increasing evidence that the synergistic effects of magnetic scaffolds and magnetic fields can promote bone repair and regeneration. In this manuscript we review the recent innovations in bone tissue engineering that exploit magnetic biomaterials combined with static magnetic fields to enhance bone cell adhesion and proliferation, and thus bone tissue growth.