Types Of Mechanical Loading Research Articles

The history and the current state of the art related to structures under stress and corrosion

The paper deals with the current state of the art arising in the design of the structures, operating under traditional mechanical loading in the aggressive environment causing their corrosion. The express goal in this case is establishing the corrosion rate dependence on the stress state of the structure and considering its durability. Thus, the use of basic mathematical models that describe the effect of corrosion rate depending on the stress state of the structure is considered. The main objective of this paper is to provide a review of useful approximations that have been suggested to deal with interaction of stress and corrosion fields. The first model that considers such a relationship is the Dolinsky model, which uses a linear dependence of the stress effect on the corrosion rate. Additionally, the Gutman model, in which the dependence of the corrosion rate on stress is expressed by an exponential law, is considered. When constructing mathematical models of structures’ corrosion wear, it is also necessary to take into account the protective coatings operation and determine the incubation period duration, which is the durability of the applied protective coatings. In this regard, the use of one of these models, which takes into account the decrease in the polymer coatings’ protective properties and a combined approach to accounting for corrosion and the anti-corrosion coatings’ protective properties are presented. Determining their reliability is an equally important aspect in the design of structures subject to corrosion. Therefore, the main theories of reliability and their practical application were considered on specific examples. A characteristic feature of the work is the coverage of issues related to the optimal design of structures operating in corrosion conditions. Two classes of problems were studied. First, determining the optimal form of structures under various types of mechanical loading and the use of the above corrosion models is considered. In the second class, the use of promising optimization models related to the solution of multi-criteria problems (using the fuzzy sets theory), as well as models with a pronounced economic bias, which allow making a cost estimate of structures failure-free operation during their lifetime, is considered. This article's novelty consists of preparing a comprehensive review of the interaction of stress and corrosion conditions. Researchers are deemed to greatly benefit from knowing the existing literature along with their strengths and weaknesses.

Abstract Tu097: Titin cleavage induces loss of myocardial tensional homeostasis driving a rapid TGF-beta-independent fibrotic response

Background: Cardiomyocytes (CMs) are subjected to different types of mechanical loads in the myocardium. Depending on its origin these loads can be classified as extracellular (extracellular matrix-ECM towards CMs), intracellular (exerted by the CM contraction machinery, i.e. the sarcomeres) or intercellular (exerted between CMs). In the myocardium, all these loads are actively maintained in tensional homeostasis (TH). In this context, the study of the sarcomere protein titin is essential, because its I-band region is considered as a hub for mechanotransduction, mostly of intracellular mechanical cues. Research Questions: It has been shown that mechanical disruption of the ECM affects the myocardial TH, leading to morphological changes inside CMs. However, potential alteration of TH resulting from defective mechanics of CM proteins remains unknown due to the lack of specific tools for in vivo studies. Aims: Here we explore the in vivo effects on myocardial TH of an abrupt tensional unloading of titin. Methods: We have experimentally challenged CMs to a tensional unloading by means of titin cleavage in vivo using TEVs-TTN mice. In this model, a cassette with a Tobacco Etch Virus protease (TEVp) recognition sequence has been included in the I-band of titin. Transducing TEVp with adeno-associated virus (AAV), we were able to cleave titin in vivo , ceasing only the mechanical properties of the protein. Samples were analyzed using an array of techniques including histology, immunofluorescence, and bulk and single nuclei RNA sequencing. Results: Our results show that a mosaic expression of TEVp, which does not affect cell viability, cleaving no more than 30% of total titin. However, this leads to a fast fibrotic response (less than six days), characterized by an increase in interstitial collagen and a response from cardiac fibroblasts population. Transcriptional and phospo-SMAD2/3 analysis results suggest that this ECM response occurs without noticeable activation of the TGFβ canonical pathway. Conclusion: Taken together, our results show experimentally for the first time that titin is not only a mechanotransducer of intracellular cues. In fact, mechanical abrogation of the I-band leads to a fast ECM response mediated by cardiac fibroblasts.

Electro-Mechanical Buckling of Shallow Segments of Functionally Graded Porous Toroidal Shell Covered by Piezoelectric Actuators

The current work deals with the mechanical buckling behavior of saturated porous toroidal shell segments sandwiched by piezoelectric actuator layers. Material properties of the porous shells with nonuniform distributed porosities are assumed to vary as a specific function of the thickness and porosity parameters. The nonlinear equations of the sandwich toroidal shell having either positive or negative Gaussian curvature are obtained on the basis of Biot’s poroelasticity theory. The energy method as the minimum potential energy principle is applied to derive the governing equations of the sandwich shells. The buckling equations of the piezo-porous sandwich shells under various types of mechanical loading are established by employing the adjacent equilibrium criterion. The governing equations as a set of the coupled partial differential equations are solved using an analytical method including the Airy stress function. Closed-form solutions are derived for shallow segments of the sandwich toroidal shell with positive/negative Gaussian curvature under lateral pressure, axial compression, and hydrostatic pressure loadings. Novel numerical results are presented in this work to show the effects of important factors such as the piezoelectric layer thickness, applied voltage, shell geometrical ratio, and variation of the porosity coefficient on the buckling behavior of these structures.

Second-grade elasticity of three-dimensional pantographic lattices: theory and numerical experiments

A continuum theory of pantographic lattices, based on second-grade elasticity, is presented. The proposed model is able to describe the mechanical behavior of a type of material structure made up of multiple layers of pantographic sheets connected with a third family of fibers. Thus, these materials are characterized by an orthogonal pattern of fibers that can bend, stretch and twist. Numerical experiments illustrate the predictive potential of the model when the material is subjected to different types of mechanical loads, including compression, torsion and two kinds of bending. Analyzing the material responses for these various tests makes it possible to reveal unusual deformation patterns characteristic of such “pantographic blocks.” Numerical simulations using the finite element method are intended to assist in designing an experimental program using 3D-printed specimens made of different materials.

Vibration Analysis of Laminated Composite Plate under Thermo- Mechanical Loading

The present study focused mainly on the vibration analysis of composite laminated plates subjected tothermal and mechanical loads or without any load (free vibration). Natural frequency and dynamicresponse are analyzed by analytical, numerical and experimental analysis (by using impact hammer) fordifferent cases. The experimental investigation is to manufacture the laminates and to find mechanicaland thermal properties of glass-polyester such as longitudinal, transverse young modulus, shear modulus,longitudinal and transverse thermal expansion and thermal conductivity. The vibration test carried tofind the three natural frequencies of plate. The design parameters of the laminates such as aspect ratio,thickness ratio, boundary conditions and lamination angle were investigated using classical laminatedplate theory (CLPT) and Finite element coded by ANSYS, in addition to the design parameters ofdynamic response such as load type with respect to time, x and y dimension and temperature value forsimply supported symmetric cross ply. The main conclusion was the natural frequency could increaseand decrease depending on the boundary conditions, thickness ratio, and lamination angle, the aspectratio of the plate. Present of temperature could increase dynamic response of plate also depending onlamination angle, type of mechanical load and the value of temperature.

Physical, Rheological and Mechanical Properties of Alkali Activated Hydrogels Based on Nanofibrillated Cellulose

ABSTRACT Hydrogels are classified as a three-dimensional network system, capable of retaining large amounts of water while preserving their shape and dimensional stability. Due to their natural origin and biocompatibility with human tissue, cellulose nanofibrils are often considered to be promising candidates for bioactive hydrogels preparation. For such applications, their responsiveness under different types of mechanical load, including multiple cyclic compressions, is of crucial importance. In the present study, cellulose nanofibril-based hydrogels were initiated though a simple alkali neutralization treatment. Structural, rheological and compressive features were investigated as a function of elevated NaOH concentration and physical gelling conditions. It was found that a sufficiently concentrated alkaline solution allows the formation of mechanically robust cellulose nanofibril hydrogels, which can be dried to the state of ultralight material, aerogel, of low density (0.057 g cm −3), superior porosity (96.2%), super water absorbant capacity (1200%), and exceptional shear and compressive load resilience with elasticity modulus of 9.3 kPa. These outstanding characteristics can be predominantly attributed to the polymorphic conversion of cellulose I to cellulose II, which results from the mercerization of cellulose nanofibrils and creates a stable and firm hydrogels texture.

Features of Strain Hardening of Heterogeneous Aluminium Alloys to Enhance the Fatigue Durability

Heterogeneous aluminium alloys are in demand in the aviation industry, where the ability of the material to withstand fatigue loads is important. The topic of the article is the search for the most experimentally available methods of deformation effect on such materials in order to increase fatigue life. Unfortunately, previous studies were ambiguous due to the large number of factors influencing the fatigue of metal materials under the same type of mechanical load; so, we chose a dynamic load with pulse loading. It turned out that for heterogeneous 2024-T351 and D16CzATW alloys, shock–vibration loading (SVL) applied during static straining prolongs their further fatigue life at a certain magnitude of the deformation during the action of the pulse. For example, for the 2024-T351 alloy at the maximum stress of alternating load σmax = 400 MPa, the longest fatigue life should be expected at deformations εimp = 2–4%; and at the maximum stress of alternating (fatigue) loading of 440 MPa, it is at εimp = 3–5%. In comparison with the average values of fatigue life of the D16CzAT alloy in the initial state, fatigue life after processing increases at σmax = 340 MPa alloy by 11.6%, at a stress of σmax = 370 MPa, by 18.4%, at a stress of σmax = 400 MPa, by 21.2%. The positive effect of long-term exposure after treatment on fatigue life was also noted. The influence of the strengthening phases, such as the nanosize Θ-Al2Cu and S-CuAl2Mg particles, on the separate stages of pre-treatment of alloys and the effects of their quantities on total fatigue durability is investigated by statistical methods of transmission electron microscopy. The great attention is paid to the mechanism of formation of fatigue fracture embryos in the near-surface areas of the samples, for which analytical calculations and the experimental method of ultrasonic impact treatment (UIT) are used. It is shown that the use of UIT after SVL does not affect the fatigue life of the 2024-T351 alloy at a fatigue load frequency of 15 Hz, while the single UIT increases fatigue life of the alloy. It is concluded that the use of complex deformation loads accelerates the relaxation processes, which shorten fatigue life.

A new approach to three-phase asynchronous motor model for electric power system analysis

In this paper, a new steady-state model of a three-phase asynchronous motor is proposed to be used in the studies of electrical power systems. The model allows for obtaining the response of the demand for active and reactive power as a function of voltage and frequency. The contribution of the model is the integration of the characteristics of the mechanical load that can drive motors, either constant or variable load. The model was evaluated on a 2500 kW and 6000 V motor, for the two types of mechanical load, in a wide range of voltage and frequency, as well as four load factors. As a result of the evaluation, it was possible to verify that, for the nominal frequency and voltage variation, the type of load does not influence the behavior of the powers and that the reactive power is very sensitive to the voltage variation. In the nominal voltage and frequency deviation scenario, it was found that the type of load influences the behavior of the active and reactive power, especially in the variable load. The results demonstrate the importance of considering the model proposed in the simulation software of electrical power systems.

Effects of Different Types of Mechanical Loading on Trabecular Bone Microarchitecture in Rats.

Mechanical loading is generally considered to have a positive impact on the skeleton; however, not all types of mechanical loading have the same beneficial effect. Many researchers have investigated which types of mechanical loading are more effective for improving bone mass and strength. Among the various mechanical loads, high-impact loading, such as jumping, appears to be more beneficial for bones than low-impact loadings such as walking, running, or swimming. Therefore, the different forms of mechanical loading exerted by running, swimming, and jumping exercises may have different effects on bone adaptations. However, little is known about the relationships between the types of mechanical loading and their effects on trabecular bone structure. The purpose of this article is to review the recent reports on the effects of treadmill running, jumping, and swimming on the trabecular bone microarchitecture in small animals. The effects of loading on trabecular bone architecture appear to differ among these different exercises, as several reports have shown that jumping increases the trabecular bone mass by thickening the trabeculae, whereas treadmill running and swimming add to the trabecular bone mass by increasing the trabecular number, rather than the thickness. This suggests that different types of exercise promote gains in trabecular bone mass through different architectural patterns in small animals.

Interlaminar shear strength (ILSS) characterization of fiber metal laminates (FMLs) manufactured through VARTM process

The aircraft industry is always seeking materials with excellent mechanical properties and good strength to weight ratio. Fiber metal laminates (FMLs) are the emerging class of hybrid composite materials consisting of fiber-reinforced polymers (FRP) plies and metal sheets. Aircraft parts are subjected to different types of mechanical loading during operation. Combining the properties of FRPs and metals provides excellent resistance to impact as well as improves the fatigue performance of the aircraft. In this study, aluminum 7075-T6 sheets were used to fabricate FMLs with varying fiber reinforcements. These sheets were treated with different surface and chemical treatment processes. The short beam shear test is utilized in this work that gives practical information on interlaminar shear strength (ILSS) and it can also be employed in real design applications. The results indicated that the ILSS of carbon fiber reinforced aluminum laminates (CARALL) was higher than glass-reinforced aluminum laminates (GLARE) and aramid-reinforced aluminum laminates (ARALL) at all displacement rates. The reason for the higher ILSS of CARALL is due to the stifness of carbon fiber and the strong adhesion of carbon with aluminum metal. However, ILSS for all three types of FMLs did not change significantly which shows that it is independent of displacement rates.

Mathematical model for a magneto-thermoelastic micropolar medium with temperature-dependent material moduli under the effect of mechanical strip load

A new model of equations of generalized thermoelasticity for an isotropic medium with mechanical properties that are dependent on temperature is established. The present problem is a generalization of the three-phase-lag model, Lord and Shulman's coupled theory. The elasticity modulus is a reference temperature function which is linear. Analytical expressions of the considered variables are obtained by using the Laplace–Fourier transforms technique. The results are analysed in a deeper manner by comparing them with unique cases of absence of the magnetic field, temperature-dependent properties of the body, and two types of mechanical loads. The most significant points are highlighted.

A computational investigation on flexural response of laminated composite plates using a simple quasi-3D HSDT

In this work, a simple quasi 3-D parabolic shear deformation theory is developed to examine the bending response of antisymmetric cross-ply laminated composite plates under different types of mechanical loading. The main feature of this theory is that, in addition to including the transverse shear deformation and thickness stretching effects, it has only five-unknown variables in the displacement field modeling like Mindlin's theory (FSDT), yet satisfies the zero shear stress conditions on the top and bottom surfaces of the plate without requiring a shear correction factor. The static version of principle of virtual work was employed to derive the governing equations, while the bending problem for simply supported antisymmetric cross-ply laminated plates was solved by a Navier-type closed-form solution procedure. The adequacy of the proposed model is handled by considering the impact of side-to-thickness ratio on bending response of plate through several illustrative examples. Comparison of the obtained numerical results with the other shear deformation theories leads to the conclusion that the present model is more accurate and efficient in predicting the displacements and stresses of laminated composite plates.

Structural Analysis of 2G HTS Tapes under Different Loading Conditions for HTS Power Cable using Finite Element Modeling

In High Temperature Superconducting (HTS) power cable, HTS tapes are wound helically around a circular former and are subjected to different types of mechanical loads during manufacturing, transportation and installation of cable. The strain developed within the HTS tape during these processes may affect the superconducting properties of the tape. In the present work, 3D structural finite element (FE) models using ANSYS® are developed to obtain the strain behaviour of the tape under different loading conditions, considering the layered sandwich composite structure of 2G HTS tapes. The analysis is carried out with axial tensile and twisting loads on the tape, during helical winding of tape around the former and a combined effect of helical winding with external tensile and bending loads. The result obtained from FE simulation due to applied tensile load is compared with the established experimental result, which shows a good agreement. Further, the strain developed within the tape affects the critical current. Therefore, the strain is coupled with an empirical relation to obtain the critical current degradation of the tape. The FE analysis is carried out for five different winding pitches and four different bending radii with YBCO layer in the downward position and the corresponding critical currents are estimated. Further, a minimum winding pitch is obtained, below which the rapid degradation of critical current is initiated. The results show that the HTS tape with YBCO in downward position can withstand more amount of external load without affecting the critical axial strain of the tape.

EVALUATION OF THE RELIABILITY OF MILITARY EQUIPMENT WITH A LIMITED NUMBER OF SAMPLES

An important task of research of military equipment is the collection, processing and analysis of information about the technical condition and reliability. The performance of a combat mission and the lives of people directly depend on these technical characteristics.
 In the available regulatory and technical documentation, reliability is defined as the property of the object to maintain over time within the established limits the values of indicators that characterize the ability to perform the required functions in the specified conditions of use, maintenance, repair, storage and transportation.
 Reliability, according to the requirements of DSTU, is a complex property that includes the properties of faultlessness, maintainability, durability and preservation. NATO members already use seven reliability parameters.
 The issue of ensuring the required level of reliability is constantly addressed by a number of authors, which is presented in a wide range of scientific papers. Thus, to maintain the high technical condition of aviation equipment, the assessment of its real level is considered as a set of a large number of individual systems and subsystems with the allocation of their indicators with subsequent careful examination of the weakest ones. The division into separate systems of complex objects allows increasing the overall level of reliability. An object is understood both as an element and an arbitrary non-redundant system, which is represented by single implementations of parameters that determine its weakest components.
 For degradation processes that are caused by aging, wear, cyclic and other types of mechanical loads, two parametric Markov models of random processes are better suited: diffusion monotonic and nonmonotonic laws. The parameters of scale and form of their distributions are determined.
 The proposed technique can be widely used to calculate the reliability parameters of other technical systems. It is important to make a reasonable choice of failure criteria, which must be clearly defined for critical systems of military vehicles. Previous experience should be taken into account and databases on the reliability of analogues of the relevant samples should be compiled. The program of reliability parameters calculation of technical systems with the use of statistical functions of electronic spreadsheets is elaborated.

Shear deformation theories for elastic buckling of fluid-infiltrated porous plates: An analytical approach

In this paper, Reddy’s higher-order and Mindlin’s first-order plate theories are used for buckling analysis of porous rectangular plates subjected to various types of mechanical loading. The condition of the internal pores is considered to be either free of or saturated by fluid. Biot’s theory of poroelasticity is thereby employed to model the behaviour of fluid. Distribution of pores is assumed to vary through the thickness according to an asymmetric distribution. For each displacement field considered, five highly coupled partial differential equations are derived by means of variational principle. These systems of equations are first decoupled through an efficient method, and then solved analytically for Levy-type boundary conditions. Accuracy of the approach is examined by comparing the obtained results with those available in literature. Eventually, comprehensive parametric studies are provided to investigate the effects of geometrical parameters, boundary conditions, loading conditions, porosity coefficient and pore fluid compressibility on the buckling response of the system. The results suggest that a structure with higher equivalent rigidity is met, when its corresponding internal pores are saturated by fluid. The results of the current work can be considered as a benchmark for future studies.

Mechanical Aspects of Intervertebral Disc Injury and Implications on Biomechanics.

This article comprises a review of the literature. The purpose of this study was to elucidate the different types of structural failures exhibited in intervertebral discs (IVDs), summarize their potential causes with respect to mechanical loading conditions and the consequences on cell homeostasis and biomechanics. Many studies have been performed to gain insight into how discogenic back pain progresses in humans both in vitro and in vivo as well as in animal disc models. However, there is a major need to summarize the common factors which initiate the structural failures observed in IVDs and the typical biomechanical changes. This work could help in developing mechanisms aiming to restore the biochemical and biomechanical balance of IVDs. The different types of structural failures encountered in IVDs were reviewed from published literature. The types of mechanical loading causing these injuries and their physiological and biomechanical consequences were then summarized and linked to ongoing research in this area. The most prominent structural failures associated with IVDs are annulus tears, disc prolapse, endplate damage, disc narrowing, radial bulging, and osteophyte formation in the vertebrae. IVDs were found to be vulnerable to compression, flexion, axial rotation, and complex loading mechanisms through single impact, cyclical, and continuous loading. However, chronic loadings had a more damaging impact on the spine. Significant consequences include imbalance of metabolic enzymes and growth factors, alteration in stress profiles of IVDs and a decrease in mechanical stiffness resulting in impaired biomechanics of the spine. The mode of loading has an important impact on the severity and nature of failures seen in IVDs and the resulting consequences to biomechanics. However, further research is necessary to better understand to the mechanisms that link injury to degeneration and regeneration of IVD tissues. 3.

Self-Doping Effect in FeSe Superconductor by Pressure-Induced Charge Transfer

Several unambiguous experimental observations clearly showed that the critical temperature of FeSe superconductor depends significantly on the microstructure. Experiments also showed that the critical temperature can be greatly enhanced by the application of external pressure. The present paper deals with the effect of pressure on charge transfer and self-doping properties of the superconducting compound FeSe, based on the investigation of the pressure dependence of the Fermi surface by means of first-principles methods. From the numerically evaluated electronic and crystalline properties, the pressure-induced modifications of the FeSe Fermi surface’s topology are determined. The Luttinger theorem was also used to evaluate the carrier concentration on the Fe atomic sites from the evolution of the Fermi surface. We have found that the electronic density at the Fe sites increases with the increase in external pressure, following the distortion of Fermi surface. Our simulations reveal that the pressure-induced charge transfer from Se atoms to Fe atoms in the FeSe superconductor can be interpreted as a direct correlation between the electron carrier concentration and the applied pressure. The pressure dependence of superconducting properties of FeSe can be reasonably ascribed to a self-doping effect. The predictions about the electronic density on the Fe sites (reaching a value of 0.1, where the corresponding pressure is about 8.6 GPa) are in good agreement with experimental data available in literature. The interpretation of the pressure-induced Tc enhancement in FeSe caused by the electron transfer and self-doping effect is carried out, which can be the correct approach to explain the Tc behavior under a wide type of mechanical loading.

Increased Female Athlete Triad Knowledge Following a Brief Video Educational Intervention

To assess female high school athletes’ changes in Female Athlete Triad (Triad) knowledge following a brief educational intervention.Triad knowledge questionnaires were completed by female high school athletes before and after either an educational video intervention or control group activities.Four high schools in the Pacific Northwest.Ninety-three female high school athletes (15.9±1.2 years) participating in basketball, cheerleading, track & field, softball, soccer, golf, tennis, and volleyball.The 10-minute Social Cognitive Theory-based educational video highlighted Triad etiology, progression, impact on sports performance, and fueling strategies to decrease Triad risk.Triad knowledge score out of 7; proportion of participants who correctly answered each question.Mann-Whitney U tests assessed differences in pre and post intervention Triad knowledge scores between the control and intervention group. The McNemar test compared the proportion of participants (intervention group) who correctly answered individual Triad knowledge questions pre vs. post-intervention.Participants in the intervention group achieved greater increases in Triad knowledge following the intervention, than did control participants (P<0.001). For each Triad question, improvements in the proportion of participants (intervention group) who answered correctly was observed (P<0.05).The Triad educational video was an effective and timeefficient method for increasing Triad knowledge among female high school athletes.

Murine chondrocytes within intact medial femoral condyles have dysregulated calcium responses to mechanical loading after dmm surgery

Purpose: Intracellular calcium mobilization is known to be a downstream signaling response to different types of mechanical loading in a variety of cells, including chondrocytes. Osteoarthritis involves aberrant loading, however, the calcium responses of chondrocytes to the mechanical loading changes induced by osteoarthritis have not been examined. Therefore, the purpose of this study was to generate novel methods to begin to address this question using the destabilization of the medial meniscus (DMM) mouse model of osteoarthritis. By better understanding how chondrocyte response to loading is altered in osteoarthritis, novel targets for therapies may be uncovered. Methods: We created a novel line of mice by crossing Collagen II cre mice with GCaMP6s loxp mice. GCaMP6s is an ultra-sensitive fluorescent calcium reporter that can be genetically expressed in specific cell types using cre-loxp recombination (in this case, chondrocytes). In these Collagen II-GCaMP6s mice, when intracellular calcium increases in chondrocytes, an increase in green fluorescence can be measured. DMM surgery in these mice causes joint damage similar to wild-type mice. To apply mechanical loading to mouse femoral condyle cartilage while performing calcium imaging, we built a system using a Zeiss Axio Observer inverted fluorescent microscope and an Aurora Scientific dual-mode lever system (300C) in order to apply compressive strain with 1 μm resolution (Fig 1). This setup enables us to compress murine medial femoral cartilage against a glass coverslip while imaging from below. We verified that our applied displacement resulted in accurate movement of our sample by an Eddy sensor (Micro-Epsilon ES04) with a resolution of 0.04 μm. DMM (n=4) or sham (n=3) surgery was performed in the right knee of 10-week old male Collagen II-GCaMP6 mice. Sixteen weeks after surgery, each femur was freshly dissected and prepared for calcium imaging. Calcium Imaging and Data Analysis: A defined sodium-calcium buffer, commonly used for calcium imaging, was used for all imaging and was slowly perfused through the chamber during each experiment. Images were taken at a frequency of 1 Hz, with an exposure time of 20 ms, using a GFP filter set. For each femur, baseline images were acquired without loading for 5 min, loading using a square waveform with amplitude 7 μm and frequency 0.05 Hz was applied for 5 min, 5 min of imaging was acquired post loading with the femur out of contact, and 8 min of imaging was performed while a 50% hypo-osmotic buffer was perfused past the femur. Images were processed using custom macros in Fiji to correct for minor movement as well as to calculate (F-Fo)/Fo, where Fo = the first 2-20 frames imaged. Responses in individual chondrocytes during the different imaging phases were compared between sham and DMM using unpaired, two-tailed t-tests (GraphPad Prism 6), where p<0.05 was considered statistically significant. Results: Seven microns of compression (∼18% strain; our sham mouse medial condyle cartilage was on average 39 μm thick) in medial femoral condyles resulted in greater numbers of chondrocytes generating intracellular calcium responses in sham mice compared to DMM mice 16 weeks after surgery (3.8-fold higher; p=0.03) (Fig 2). However, on average, DMM chondrocyte calcium responses were greater in amplitude and duration than sham chondrocyte responses (2.5-fold higher; p=0.03) (Fig 2). The average peak forces observed during compression were similar for sham (13.4±2.6 mN) and DMM mice (16.3±1.6 mN) (p = 0.35). Exposure to hypo-osmotic salt solution has been used previously as a positive control for inducing intracellular calcium responses in chondrocytes as it causes cells to stretch. Here, we found that 50% hypo-osmotic solution induced similar numbers of chondrocyte responses in both sham (54±10) and DMM (42±11; p=0.46) mice 16 weeks after surgery, and similar amplitude and duration of responses (sham: 6.9±0.2 ΔF/Fo x seconds; DMM: 9.7±2.6 ΔF/Fo x seconds; p=0.36). Conclusions: Here, we have generated a novel strain of mice and a novel mechanical stimulation and imaging system in order to image real-time responses of chondrocytes to mechanical loading within intact mouse femoral condyles after DMM surgery. Our results suggest that after DMM surgery, femoral condyle chondrocytes are still able to generate intracellular calcium responses to changes in osmolarity, but they have become dysregulated in response to mild levels of cartilage compression. Future work will seek to understand which calcium signaling pathways may be mediating these changes and how these changes may contribute to other pathological cartilage changes in osteoarthritis.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Screening of key candidate genes and pathways for osteocytes involved in the differential response to different types of mechanical stimulation using a bioinformatics analysis.

This study aimed to predict the key genes and pathways that are activated when different types of mechanical loading are applied to osteocytes. mRNA expression datasets (series number of GSE62128 and GSE42874) were obtained from Gene Expression Omnibus database (GEO). High gravity-treated osteocytic MLO-Y4 cell-line samples from GSE62128 (Set1), and fluid flow-treated MLO-Y4 samples from GSE42874 (Set2) were employed. After identifying the differentially expressed genes (DEGs), functional enrichment was performed. The common DEGs between Set1 and Set2 were considered as key DEGs, then a protein-protein interaction (PPI) network was constructed using the minimal nodes from all of the DEGs in Set1 and Set2, which linked most of the key DEGs. Several open source software programs were employed to process and analyze the original data. The bioinformatic results and the biological meaning were validated by in vitro experiments. High gravity and fluid flow induced opposite expression trends in the key DEGs. The hypoxia-related biological process and signaling pathway were the common functional enrichment terms among the DEGs from Set1, Set2 and the PPI network. The expression of almost all the key DEGs (Pdk1, Ccng2, Eno2, Egln1, Higd1a, Slc5a3 and Mxi1) were mechano-sensitive. Eno2 was identified as the hub gene in the PPI network. Eno2 knockdown results in expression changes of some other key DEGs (Pdk1, Mxi1 and Higd1a). Our findings indicated that the hypoxia response might have an important role in the differential responses of osteocytes to the different types of mechanical force.