Application Of Mechanical Strain Research Articles

Ab initio prediction of a two-dimensional MgO2C6 monolayer with intrinsic semiconducting characteristics: Tunable electronic and optical characteristics through the application of mechanical strain

Ab initio prediction of a two-dimensional MgO2C6 monolayer with intrinsic semiconducting characteristics: Tunable electronic and optical characteristics through the application of mechanical strain

Tensile force impairs lip muscle regeneration under the regulation of interleukin-10.

Orbicularis oris muscle, the crucial muscle in speaking, facial expression and aesthetics, is considered the driving force for optimal lip repair. Impaired muscle regeneration remains the main culprit for unsatisfactory surgical outcomes. However, there is a lack of study on how different surgical manipulations affect lip muscle regeneration, limiting efforts to seek effective interventions. In this study, we established a rat lip surgery model where the orbicularis oris muscle was injured by manipulations including dissection, transection and stretch. The effect of each technique on muscle regeneration was examined by histological analysis of myogenesis and fibrogenesis. The impact of tensile force was further investigated by the in vitro application of mechanical strain on cultured myoblasts. Transcriptome profiling of muscle satellite cells from different surgical groups was performed to figure out the key factors mediating muscle fibrosis, followed by therapeutic intervention to improve muscle regeneration after lip surgeries. Evaluation of lip muscle regeneration till 56days after injury revealed that the stretch group resulted in the most severe muscle fibrosis (n=6, fibrotic area 48.9% in the stretch group, P<0.001, and 25.1% in the dissection group, P<0.001). There was the lowest number of Pax7-positive nuclei at Days 3 and 7 in the stretch group (n=6, P<0.001, P<0.001), indicating impaired satellite cell expansion. Myogenesis was impaired in both the transection and stretch groups, as evidenced by the delayed peak of centrally nucleated myofibers and embryonic MyHC. Meanwhile, the stretch group had the highest percentage of Pdgfra+ fibro-adipogenic progenitors infiltrated area at Days 3, 7 and 14 (n=6, P=0.003, P=0.006, P=0.037). Cultured rat lip muscle myoblasts exhibited impaired myotube formation and fusion capacity when exposed to a high magnitude (ε=2688μ strain) of mechanical strain (n=3, P=0.014, P=0.023). RNA-seq analysis of satellite cells isolated from different surgical groups demonstrated that interleukin-10 was the key regulator in muscle fibrosis. Administration of recombinant human Wnt7a, which can inhibit the expression of interleukin-10 in cultured satellite cells (n=3, P=0.041), exerted an ameliorating effect on orbicularis oris muscle fibrosis after stretching injury in surgical lip repair. Tensile force proved to be the most detrimental manoeuvre for post-operative lip muscle regeneration, despite its critical role in correcting lip and nose deformities. Adjunctive biotherapies to regulate the interleukin-10-mediated inflammatory process could facilitate lip muscle regeneration under conditions of high surgical tensile force.

3D Graphene Straintronics for Broadband Terahertz Modulation

AbstractThe increasing utilization of terahertz (THz) bandwidth in both industrial and private sectors highlights the significance of efficient terahertz shielding and absorption devices. These devices play a crucial role in safeguarding electronic components from disruptive effects and rendering objects less detectable by radar systems. However, the limited availability of materials and devices hinders progress in this field. In this study, a strain engineering route is presented for the active control of terahertz shielding and absorption properties in 3D graphene through the application of mechanical strain. A straintronic modulator based on 3D graphene is demonstrated, capable of modulating absorption and reflection of THz radiation in real‐time over a wide range of 0.1–3 THz. The modulator can be tuned to exhibit either shielding capability with a specific shielding effectiveness of 0.3 × 105 dB cm2 g−1 or stealth characteristics with an average reflection loss of 25 dB and 99.4% absorption. These findings open new avenues for leveraging 2D materials in their 3D porous form, where strain‐induced changes in interlayer interactions enable control over the properties of these materials. This discovery unveils vast unexplored physical phenomena with immense potential for advanced THz imaging, radar, and electromagnetic applications.

Physiological stress improves stem cell modeling of dystrophic cardiomyopathy.

Heart failure contributes to Duchenne muscular dystrophy (DMD), which arises from mutations that ablate dystrophin, rendering the plasma membrane prone to disruption. Cardiomyocyte membrane breakdown in patients with DMD yields a serum injury profile similar to other types of myocardial injury with the release of creatine kinase and troponin isoforms. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are highly useful but can be improved. We generated hiPSC-CMs from a patient with DMD and subjected these cells to equibiaxial mechanical strain to mimic in vivo stress. Compared to healthy cells, DMD hiPSC-CMs demonstrated greater susceptibility to equibiaxial strain after 2 h at 10% strain. We generated an aptamer-based profile of proteins released from hiPSC-CMs both at rest and subjected to strain and identified a strong correlation in the mechanical stress-induced proteome from hiPSC-CMs and serum from patients with DMD. We exposed hiPSC-CMs to recombinant annexin A6, a protein resealing agent, and found reduced biomarker release in DMD and control hiPSC-CMs subjected to strain. Thus, the application of mechanical strain to hiPSC-CMs produces a model that reflects an in vivo injury profile, providing a platform to assess pharmacologic intervention.

Strain-induced catalytic enhancement in Co-BTA and Rh-BTA for efficient 2e- oxygen reduction: a DFT study.

Here we design TM-BTA catalysts for the electrochemical synthesis of hydrogen peroxide (H2O2), focusing on the efficient two-electron (2e-) oxygen reduction pathway. Employing density functional theory (DFT), we screened 17 transition metals, identifying Co-BTA and Rh-BTA as outstanding candidates based on their low overpotentials and superior catalytic activity. A key innovation is the application of mechanical strain to these catalysts, significantly optimizing their performance by modulating the d-band center. This approach enhances the adsorption of oxygen-containing intermediates, crucial for the 2e- ORR process. Our findings demonstrate that a tensile strain of 1.95% optimally enhances catalytic efficiency in both Co-BTA and Rh-BTA, substantially reducing overpotential. This research not only highlights the potential of TM-BTA catalysts in H2O2 production but also underscores the importance of strain modulation as a cost-effective and efficient method to improve the selectivity and activity of electrocatalysts, offering a novel perspective in the field of sustainable chemical synthesis.

Enhanced spin–orbit torques in strained NiFe/Pt bi-layers on flexible substrate

Magnetization manipulation caused by spin–orbit torque is one of the central themes investigated in spintronics domain. The spin–orbit torque efficiencies can be manoeuvred by application of mechanical strain. In this direction, this study furthers the effort in understanding the evolution of spin–orbit torque efficiencies in mechanically strained ferromagnet (FM)/heavy metal(HM) (Ni81Fe19/Pt) bi-layer films on flexible kapton substrate, by the use of spin torque ferromagnetic resonance (ST-FMR) measurement technique. We report a tensile strain induced enhancement in damping-like and field-like spin–orbit torque efficiencies. The effective damping-like spin torque conductivity increased by 42% on the application of 0.312% tensile strain, which is encouraging from the magnetization switching application point of view. In order to investigate the driving factors behind the enhanced damping-like spin torque conductivity, ab-initio calculations were also carried out. Our findings provide insights into the workings of strain in FM/HM bi-layer stack and is a step forward in the implementation of flexible spintronics devices.

GaN-WSSe'nin Dikey Gerinim Altında Fotokatalitik Performansının İncelenmesi

The application of mechanical strain is a crucial technique to adjust and optimize the physical properties of materials, making them potentially useful for various applications, including renewable energy resources and nanoelectronics. Hydrogen production through water splitting has been proposed as a promising solution to the energy crisis. Therefore, there is a great demand for exploring low-cost and efficient photocatalysts for this process. We investigated the electronic properties, structural properties and band alignment of WSSe/graphene-like GaN (g-GaN) heterostructure. Our results reveal that the band alignment of the AA-stacked WSSe/g-GaN heterostructure satisfies the water redox potentials at a pH of 7. In order to investigate the effect of regulation on these two heterostructures, out of plane strain ranging from -2% to 2% is applied. Results show that applying strain to the heterostructure will enhace the photocatalytic properties which was evaluated based on the valence and conduction band edge potentials.

Strain-induced structural phase transition in GeN monolayer

The recent synthesis of SiP, SiAs, GeP, and GeAs monolayers has brought two-dimensional (2D) group IV–V systems into the limelight. To date, all the fabricated structures of this class belong to the C2/m space group which has a low structural symmetry, while the class could exist in more symmetric phases (i.e., P3¯m1 and P6¯m2). The realization of more symmetric phases can enhance the intrinsic properties of these materials and increase their potential field of usage. In this study, the possibility of a structural phase transition in GeN monolayer by application of mechanical strain is investigated. Based on ab initio simulations, we first confirm the stability of the GeN monolayer in all phases, then demonstrate how a large enough compressive strain (∼12%) can transform C2/m into P3¯m1 phase. The results are interpreted by analyzing the geometry, bond order, electron localization functions, and net atomic charges of the structures. Upon transition into the P3¯m1 phase, tensile strength and in-plane stiffness double, while the compressive strength quadruples. On the other hand, the effect of the phase transition on the electronic properties is not substantial and similar band structure profiles with narrowed band gap are obtained. Our study provides insight on how to experimentally achieve the P3¯m1 phase of the GeN monolayer, which is in principle applicable to other group IV–V monolayers under suitable conditions involving the optimization of pressure, temperature, and impurity concentration. These unique features of the GeN monolayer render them ideal candidates for a variety of high technological nanoscale applications.

Biomechanical Strain Promotes the Differentiation of Murine Oogonial Stem Cells.

Cells within tissues are routinely subjected to physiological stress and strain, arising from direct interactions with neighboring cells as well as with extracellular matrix components. Accordingly, there is tremendous interest in deciphering how cells sense, and respond to, changes in biomechanical forces. In this study, we explored the effects of mechanostimulation on the differentiation of mouse female germline or oogonial stem cells (OSCs) as a model for adult stem cell function. We report that increasing levels, or repeated application of a subthreshold fixed level, of radial strain to OSCs in culture significantly increased rates of in vitro oocyte formation as a measure of stem cell differentiation. These responses involved changes in F-actin-mediated cytoskeletal tension as well as in activation of intracellular signaling by Rho-associated protein kinase (ROCK) and Yes-associated protein (YAP) phosphorylation. In addition, application of mechanical strain to OSCs enhanced association of YAP with muscle-specific cytidine-adenosine-thymidine (MCAT) response elements in the promoter stimulated by retinoic acid gene 8 (Stra8), the transcriptional activation of which is required for germline meiotic commitment. These data indicate that biomechanical strain directly promotes the differentiation of adult female germline stem cells through a signaling pathway involving F-actin, ROCK, YAP, and Stra8.

Dynamic Manipulation of DNA-Programmed Crystals Embedded in a Polyelectrolyte Hydrogel.

DNA is a powerful tool for programming the three-dimensional organization of nanomaterials, where the specificity of nucleotide base-pairing can enable precise, complex, and dynamically addressable structures like colloidal crystals. However, because these DNA-programmed materials are often only stable in solution, their organization can be easily disrupted by changes to its local environment. Methods to stabilize these materials have been developed, but often come at the expense of altering or permanently fixing the materials' structures, removing many of the benefits of using DNA interactions to program assembly. Thus, these methods limit the application of DNA-assembled structures as dynamic and programmable material components. Here, a method is presented to resolve these drawbacks for DNA-grafted nanoparticles, also known as Programmable Atom Equivalents (PAEs), by embedding assembled lattices within a hydrogel matrix. The preformed lattices are exposed to polymerizable residues that electrostatically bind to the charged backbone of the DNA ligands and form a continuous, permeating gel network that stabilizes the colloidal crystals upon introduction of a radical initiator. After embedding PAEs in a hydrogel, deformation of the macroscopic matrix results in concomitant deformation of the PAE lattices, allowing superlattice structural changes to be induced by chemical methods (such as changing solute concentration to alter swelling pressure) or by application of mechanical strain. Changes to the structure of the PAE lattices are reversible and repeatable over multiple cycles and can be either isotropic (such as by swelling) or anisotropic (such as by mechanical deformation). This method of embedding nanoparticle crystals inside of a flexible and environmentally responsive hydrogel is therefore a useful tool in extending the utility of PAEs and other micro- and nanostructures assembled with DNA.

New stable two dimensional silicon carbide nanosheets

Abstract We predict the existence of new two dimensional (2D) silicon carbide nanostructures employing ab initio density-functional theory calculations. These structures are composed of tetragonal and hexagonal rings with C─C and Si─C bonds arranged in a buckling plane. They are proven to be thermodynamically and mechanically stable with relatively low formation energy, implying potential fabrication in labs. They exhibit strong ductility and anisotropicity from their strain-stress relations and directional dependence of mechanical moduli. The materials maintain phonon stability upon the application of mechanical strain up to 27% with fantastic ductile property. The proposed 2D SiC2 structure possesses a tiny direct band gap of 0.02 eV predicted using HSE06 functional and the band gap can be opened up through multiple approaches such as hydrogenation and strain application. The gap values can be strategically tuned in the range of 0.02–1.72 eV and the direct/indirect gap nature can be further manipulated. In contrast, a closely related isostructural 2D SiC shows an indirect HSE band gap of 1.80 eV and strain engineering its value between 0.0–1.95 eV. The unique properties in these newly proposed structures might have potential applications in future nanomechanics and electronics.

The autophagic protein LC3 translocates to the nucleus and localizes in the nucleolus associated to NUFIP1 in response to cyclic mechanical stress

ABSTRACT The trabecular meshwork (TM) is a key regulatory tissue of intraocular pressure (IOP) in the anterior chamber of eye. Dysfunction of the TM causes resistance to outflow of aqueous humor, which in turn leads to elevated IOP, a main risk factor of glaucomatous neurodegeneration. Due to variations in IOP, TM cells are continuously exposed to mechanical deformations. We previously reported activation of macroautophagy/autophagy, as one of the physiological responses elicited in TM cells following mechanical strain application. By using biochemical fractionation analysis and imaging techniques, we demonstrate here for the first time the nuclear accumulation of the autophagic marker MAP1LC3/LC3 (microtubule associated protein1 light chain 3)-II, endogenous and exogenously added (AdGFP-LC3, AdtfLC3), in response to cyclic mechanical stress (CMS). Wheat germ agglutinin (WGA) and leptomycin B treatment suggest LC3 to enter the nucleus by passive diffusion, but to exit in an XPO1/CRM1 (exportin 1)-dependent manner in human TM (hTM) cells. While blockage of nuclear export leads to accumulation of LC3 with promyelocytic leukemia (PML) bodies, nuclear LC3 localizes in the nucleolus in cells under CMS. Moreover, nuclear LC3 co-immunoprecipitated with NUFIP1, a ribosome receptor for starvation-induced ribophagy. More interestingly, we further demonstrate that NUFIP1 translocates from the nucleus to LAMP2 (lysosomal associated membrane protein 2)-positive organelles in the stretched cells without triggering ribophagy, suggesting a more general role of NUFIP1 as a selective autophagy receptor for another yet-to-be-identified target in CMS and a surveillance role of nuclear LC3 against stretch-induced damage. Abbreviation AdGFP: adenovirus encoding GFP; ATG: autophagy-related; BSA: bovine serum albumin; CMS: cyclic mechanical stretch; Co-IP: coimmunoprecipitation; DAPI: 4′,6-diamidino-2-phenylindole; DFCs: dense fibrillar components; EM: electron microscopy; FCs: fibrillar centers; GCs: granular components; GFP: green fluorescent protein; hTM: human trabecular meshwork; HBSS: Hanks balanced salt solution; IOP: intraocular pressure; LAMP1/2: lysosomal associated membrane protein 1/2; LepB: leptomycin B; MTOR: mechanistic target of rapamacyin kinase; NES: nuclear export signals; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; NLS: nuclear localization signal; NPCs: nuclear pore complexes; NUFIP1: nuclear FMR1 interacting protein 1; NS: non-stretched; PBS: phosphate-buffered saline; PE: phosphatidylethanolamine; pfu: plaque-forming units; PML: promyelocytic leukemia; RFP: red fluorescent protein; RPS15A: ribosomal protein S15a; RPL26: ribosomal protein L26; rRNA: ribosomal RNA; SIRT1: sirtuin 1; SQSTM1/p62: sequestosome 1; tfLC3: mRFP-GFP tandem fluorescent-tagged LC3; TM: trabecular meshwork; WB: western blot; WDR36: WD repeat domain 36; WGA: wheat germ agglutinin; XPO1/CRM1: exportin 1.

Myoblast maturity on aligned microfiber bundles at the onset of strain application impacts myogenic outcomes

Engineered skeletal muscle grafts may be employed in various applications including the treatment of volumetric muscle loss (VML) and pharmacological drug screening. To recapitulate the well-defined structure of native muscle, tensile strains have been applied to the grafts. In this study, we cultured C2C12 murine myoblasts on electrospun fibrin microfiber bundles for 7 days in custom-built bioreactor units and investigated the impact of strain regimen and delayed onset of tensile straining on myogenic outcomes. The substrate topography induced uniaxial alignment of cells in all (strained and unstrained) groups. The engineered grafts in strained groups were subjected to 10% strain amplitude for 6 h per day. We found that both static and cyclic uniaxial strains resulted in similar morphological and gene expression outcomes. However, relative to 0% strain groups, there were stark increases in myotube diameter, myosin heavy chain (MHC) coverage, and expression of key myogenic genes (Pax 7, Troponin, MHC I, MHC IIb, MHC IIx) only if strain was applied at Days 5–7 rather than Days 3–7. This finding suggests that a critical indicator of myogenic improvement under strain in our system is the phenotype of the cells at the onset of strain and suggests that this is a key parameter that should be considered in studies where myoblasts are subjected to biophysical stimulation to promote tissue formation. Statement of SignificanceThis is the first report on the impact of the timing of the initial application of mechanical strain for improving the myogenic outcomes of 3D engineered skeletal muscle grafts. In this work, immature skeletal myoblasts were grown on topographically aligned, electrospun fibrin microfiber bundles and we applied 10% uniaxial static or cyclic strain. We concluded that the maturity of myoblasts prior to strain application, rather than strain waveform, was the primary predictor of improved myogenic outcomes, including myogenic gene expression and myotube morphology. Elucidating the optimal conditions for strain application is a vital step in recapitulating physiological myogenic properties in tissue engineered skeletal muscle constructs, with applications for treating volumetric muscle loss, disease modeling, and drug testing.

Strain Engineering Electrocatalysts for Selective CO2 Reduction

Lattice strain can enhance the activity and selectivity of electrochemical reactions by breaking the linear scaling relationship. Notwithstanding, the explicit use of strain to affect the CO2 reduction reaction (CO2RR) is rarely reported. In this Perspective, we highlight the opportunity to use strain to affect the activity and selectivity of CO2RR electrocatalysts. We summarize the existing challenges in isolating the influence of strain from convoluting factors (e.g., size, shape, electronic, and surfactant effects) that result from typical methods of inducing strain. We also propose ways to isolate strain effects using the application of mechanical strain to thin-film CO2RR catalysts. We designed this Perspective to motivate the use of joint empirical and computational studies to investigate CO2RR strain–activity–selectivity relationships.

Strain Engineering of 2D Materials: Issues and Opportunities at the Interface.

Triggered by the growing needs of developing semiconductor devices at ever-decreasing scales, strain engineering of 2D materials has recently seen a surge of interest. The goal of this principle is to exploit mechanical strain to tune the electronic and photonic performance of 2D materials and to ultimately achieve high-performance 2D-material-based devices. Although strain engineering has been well studied for traditional semiconductor materials and is now routinely used in their manufacturing, recent experiments on strain engineering of 2D materials have shown new opportunities for fundamental physics and exciting applications, along with new challenges, due to the atomic nature of 2D materials. Here, recent advances in the application of mechanical strain into 2D materials are reviewed. These developments are categorized by the deformation modes of the 2D material-substrate system: in-plane mode and out-of-plane mode. Recent state-of-the-art characterization of the interface mechanics for these 2D material-substrate systems is also summarized. These advances highlight how the strain or strain-coupled applications of 2D materials rely on the interfacial properties, essentially shear and adhesion, and finally offer direct guidelines for deterministic design of mechanical strains into 2D materials for ultrathin semiconductor applications.

The Interplay of Strain and Defect Association on the Conductivity Rare Earth Substituted CeO2

In solid state oxygen ion conductors such as CeO2 and ZrO2, aliovalent cations are used to introduce oxygen vacancies which allow ionic conduction, but which also limit the maximum achievable conductivity due to defect-defect interactions. Materials are optimised based on the size and concentration of the substituted cations, in order to minimise defect association and maximise ionic transport. To push the performance of such materials beyond their compositional limit, significant attention has turned to the application of mechanical strain. Computational studies have shown that the energy barrier for migration in CeO2 and ZrO2 can be manipulated using lattice strain. A number of studies are in broad agreement, showing that significant enhancements in the conductivity under tensile strain can be achieved.[1],[2] However, experimentally, the results on strained thin films and multilayers have been both controversial and inconstant, with vastly different findings in nominally similar systems.[3] Typically strained layers due to interfacial mismatch are grown and the thickness varied to control the volume fraction of the strained material. However this leads to difficulties controlling the density of grain boundaries, and isolating changes in the conductivity in the layers.[4] These complications mean that comparisons between experimental and computational work are challenging. Furthermore, much of the work so far on the effects of strain on the transport properties have focused on the so-called ‘optimised’ ionic conductors, such as commercial electrolytes Y-stabilised ZrO2 or Gd- or Sm-doped CeO2. Very little attention has been payed to the ‘non-optimised’ electrolytes where the defect-defect interactions are much more significant. However, as the defect association limits the conductivity for these materials a much larger enhancement in the transport properties (or a less significant reduction) due to strain may be possible. We have fabricated both ‘optimised’ and ‘non-optimised’ doped-CeO2 films by pulsed laser deposition on MgO substrates. The dopants used were La, Gd, and Yb, which represent an ionic radii mismatch with the host Ce lattice of 19.6%, 8.6%, and 1.5% respectively. Epitaxy was maintained using a double BaZrO3 and SrTiO3 buffer layer resulting in films free from grain boundaries. The thickness of the films was kept constant and the strain varied by thermal annealing (from 600°C to 1000°C) to relax the intrinsic strain occurring during growth. Crucially, this means that the strain in these materials can be tailored and the conductivity measured without complications due to grain boundary effects or changes in the volume fraction of the interface and surface. The out-of-plane and in-plane strain in the films was characterised in detail using X-ray diffraction and Raman spectroscopy, and the microstructure evaluated by high-resolution transmission electron microscopy. Impedance spectroscopy measurements showed that the conductivity of the relaxed films was in excellent agreement with bulk rare earth substituted CeO2. With increasing in-plane compressive strain, the conductivity of the films was reduced and the activation energy increased. The observed change in the activation energy with strain is in excellent agreement with computational work, and consistent with other experimental findings. In addition we show that the effect is more pronounced for Yb-substituted CeO2 than La- or Gd-substituted CeO2, suggesting that larger changes in the conductivity with strain can be obtained with ‘non-optimised’ dopant cations. [1] A. Kushima and B. Yildiz, “Oxygen ion diffusivity in strained yttria stabilized zirconia: where is the fastest strain?,” J. Mater. Chem., vol. 20, no. 23, p. 4809, 2010. [2] R. A. De Souza, A. Ramadan, and S. Hörner, “Modifying the barriers for oxygen-vacancy migration in fluorite-structured CeO2 electrolytes through strain: a computer simulation study,” Energy Environ. Sci., vol. 5, no. 1, p. 5445, 2012. [3] K. Wen, W. Lv, and W. He, “Interfacial lattice-strain effects on improving the overall performance of micro-solid oxide fuel cells,” J. Mater. Chem. A, vol. 3, no. 40, pp. 20031–20050, 2015. [4] G. F. Harrington, A. Cavallaro, D. W. McComb, S. J. Skinner, and J. A. Kilner, “The effects of lattice strain, dislocations, and microstructure on the transport properties of YSZ films,” Phys. Chem. Chem. Phys., vol. 19, pp. 14319–14336, 2017.

Experimental Investigation of Piezoresistive Effect in p-Type 4H–SiC

This letter presents for the first time the piezoresistive effect in p-type 4H–SiC. Longitudinal and transverse p-type 4H–SiC piezoresistors with a doping concentration of $10^{18}$ cm $^{-3}$ were fabricated along [ $1\overline {1}00$ ] directions. Ni/Al electrodes annealed at 1000 °C showed a good ohmic contact, and then, the longitudinal and transverse gauge factors were found to be as high as 31.5 and −27.3, respectively. The large gauge factors, attributed to the change of valance energy bands upon application of mechanical strain, and the linear relationship between the resistance change versus induced strain demonstrate the potential of p-type 4H–SiC for mechanical sensing applications.

In-situ observation of the particle microstructure of magnetorheological elastomers in presence of mechanical strain and magnetic fields

Magnetorheological elastomers are a type of smart hybrid material which combines elastic properties of a soft elastomer matrix with magnetic properties of magnetic micro particles. This composition creates a complex interplay of magnetic and elastic phenomena. The best known is the magnetorheological effect which describes the alteration of the Young’s modulus with external magnetic fields. The particle properties and their arrangement in the material play a major role in determining the resulting effects. In this paper X-ray microtomography has been utilized to analyze the particle microstructure. Besides a characterization of the particle microstructure in presence of magnetic fields, here the in-situ observation was combined with an application of mechanical strain. Thus, the situation of the sample during mechanical testing was recreated during tomography to observe the particle microstructure under the exact circumstances of occurring magnetorheological effects. A significant impact of the magnetic field and the strain on the rotation of the particles and their radial distribution was verified.

The P2X7 receptor links mechanical strain to cytokine IL-6 up-regulation and release in neurons and astrocytes.

Mechanical strain in neural tissues can lead to the up-regulation and release of multiple cytokines including interleukin 6 (IL-6). In the retina, the mechanosensitive release of ATP can autostimulate P2X7 receptors on both retinal ganglion cell neurons and optic nerve head astrocytes. Here, we asked whether the purinergic signaling contributed to the IL-6 response to increased intraocular pressure (IOP) invivo, and stretch or swelling invitro. Rat and mouse eyes were exposed to non-ischemic elevations in IOP to 50-60mmHg for 4h. A PCR array was used to screen cytokine changes, with quantitative (q)PCR used to confirm mRNA elevations and immunoblots used for protein levels. P2X7 antagonist Brilliant Blue G (BBG) and agonist (4-benzoyl-benzoyl)-ATP (BzATP) were injected intravitreally. ELISA was used to quantify IL-6 release from optic nerve head astrocytes or retinal ganglion cells. Receptor identity was confirmed pharmacologically and in P2X7-/- mice, acute elevation of IOP altered retinal expression of multiple cytokine genes. Elevation of IL-6 was greatest, with expression of IL1rn, IL24, Tnf, Csf1, and Lif also increased more than twofold, while expression of Tnfsf11, Gdf9, and Tnfsf4 were reduced. qPCR confirmed the rise in IL-6 and extracellular ATP marker ENTPD1, but not pro-apoptotic genes. Intravitreal injection of P2X7 receptor antagonist BBG prevented the pressure-dependent rise in IL-6 mRNA and protein in the rat retina, while injection of P2X7 receptor agonist BzATP was sufficient to elevate IL-6 expression. IOP elevation increased IL-6 in wild-type but not P2X7R knockout mice. Application of mechanical strain to isolated optic nerve head astrocytes increased IL-6 levels. This response was mimicked by agonist BzATP, but blocked by antagonists BBG and A839977. Stretch or BzATP led to IL-6 release from both astrocytes and isolated retinal ganglion cells. The mechanosensitive up-regulation and release of cytokine IL-6 from the retina involves the P2X7 receptor, with both astrocytes and neurons contributing to the response.

The "Mechanostat" Principle and the Osteoprotegerin-OPG/RANKL/RANK System PART II. The Role of the Hypothalamic-Pituitary Axis.

Recent literature provides us with the indication that the ratio of OPG/RANKL concentrations fluctuate in a non-linear (bell-shaped) mode, according to Frost's "mechanostat" theory, during the application of mechanical strain. A similar cellular signal transduction mechanism to mechanical loading, that may also regulate bone resorptive activities, has nowdays been proposed. Since the skeleton is considered to be an endocrine organ, as such, it may likewise be subject to hypothalamic control. This central regulatory system may continually modulate the adaptation of the bone homeostatic system to external challenges. The hypothalamic-pituitary-gonadal axis may play a role in the regulation of OPG/RANKL secretion. The "mechanostat" principle may well characterize the oscillatory properties of the signal transduction mechanism that controls hard tissue metabolism and includes biochemical apart from mechanical stimuli. J. Cell. Biochem. 118: 962-966, 2017. © 2016 Wiley Periodicals, Inc.