Effect Of Mechanical Loading Research Articles

How do bones grow? A mathematical description of the mechanobiological behavior of the epiphyseal plate.

Growth modulation is an emerging method for the treatment of skeletal deformities originating in the long bones or the vertebral bodies. It requires the controlled application of mechanical loads to the affected bone, causing an alteration of the growth and ossification process occurring in a cartilaginous region called epiphyseal growth plate or physis. In order to avoid the possibility of under- or over-correction, quantification of the applied forces is necessary. Pursuing this goal, here we propose a phenomenological model of mechanobiological effects on the epiphyseal growth plate, based on the observed similarity between the mechanobiologically induced growth and viscoelastic material behavior. The model incorporates mechanical loading effects on growth direction, growth rate and ossification speed; it also allows to evaluate the occurrence of transient effects. Model consistency was tested against a rather large set of experiments existing in the literature. A generic simplified geometrical model of bones was established for this. Analytical solutions for growth and ossification evolution were obtained for different loading conditions, allowing to test the ability of the model to describe bone growth under various kinds of mechanical loading conditions. Model-predicted changes regarding epiphyseal growth plate thickness as well as longitudinal growth speed are consistent with experiments in which static tension or compression were applied to long bones. Results suggest that when the mechanical load is sinusoidally variable, conflicting data existing in the literature could be explained by a previously unconsidered effect of the the applied load initial phase. The model can accurately fit data regarding torsional loads effects on growth. Mechanobiological data for humans is very scarce. For this reason, when possible, the model parameters values were estimated, for the proposed generic geometry, after growth measurements in animal models available in the literature. Although it is not possible to assert their validity for humans, the proposed model along with the obtained parameters values give a rational foundation to be used in more advanced computational studies.

Effects of bending on the electro-optical properties of a wide-band silicon-carbon nanotube-based metamaterial absorber

Metamaterials possess superior material properties that make them popular in various applications. They are commonly used in energy, medical, and military fields. Metamaterial absorbers are introduced in order to utilize them in harvesting solar energy. In this article, a novel wide-band Silicon-Carbon Nanotube (Si-CNT) based metamaterial absorber is proposed, and the effects of mechanical loading on electro-optical properties are investigated. The study is conducted within the visible and ultraviolet frequency ranges (400–1200 THz). Concave and convex bending deformations are applied to the absorber within the mentioned frequency range. The results reveal that wide-band absorption rates are achieved for the proposed absorber with a minimum rate of 91.17 % at 400.3 THz. The proposed absorber is found to be polarization-independent and showed high absorption rates up to 45° incident angle within the mentioned frequency range. The absorption rates are observed to increase and shift due to bending deformations. The mechanical stresses formed are also predicted to be below the estimated yield strength, ensuring the structural integrity of the absorber.

Модель роста черепа и формирование швов черепа в рамках теории функциональных матриц при наличии травмирующего/изменяющего биомеханику мышцы фактора. Пилотное исследование

The article presents the results of a study of the effect of mechanical loading of masticatory muscles with a continuous stretch stimulus in the direction of increasing the width / stretching / sagittal suture of an experimental animal in vivo. The technique is described, and the data of objective instrumental control, as well as the results generated by statistical processing, are presented.

Stability of hydrogel adhesion enabled by siloxane bonds

Forming anchoring sites by siloxane bonds at the hydrogel-substrate bonding interface is one of prevailing ways to achieve strong hydrogel adhesion. Considering the hydrolysis of siloxane bonds at the existence of water, we investigate the stability of siloxane bonds enabled hydrogel adhesion in various aqueous environments experimentally and theoretically. Samples of polyacrylamide (PAAm) hydrogel bonded glass substrate by siloxane bonds are prepared and immersed in various aqueous environments, including purified water, acid solution, alkaline solution, and phosphate buffered solution (PBS). We find that the PAAm hydrogel spontaneously detaches from the glass substrate in the alkaline solution for around 1 h and in the PBS for 36 days, but still firmly adheres to the glass substrate in the purified water and acid solution for 36 days. To explain the experimental findings, we incorporate the kinetic theory of bond dissociation with the Lake-Thomas model and get the evolution of hydrogel adhesion with time. By changing the activation energy of siloxane bond hydrolysis, the time required for the catastrophic decrease of hydrogel adhesion can be predicted. This work reveals the failure mechanism of siloxane bonds enabled strong hydrogel adhesion, and might inspire studies on the stability of hydrogel adhesion of other types under the combined effects of mechanical and chemical loads.

Poster 203: Mechanical Loading Effects on OA Progression Following ACL Injury and Reconstruction in a Murine Model: Radiographic Assessment of Synovial Fibroblast Activity

Poster 203: Mechanical Loading Effects on OA Progression Following ACL Injury and Reconstruction in a Murine Model: Radiographic Assessment of Synovial Fibroblast Activity

Torsion of a piezoelectric semiconductor rod of cubic crystals with consideration of warping and in-plane shear of its rectangular cross section

We study the torsion of a piezoelectric semiconductor rod of cubic crystals with a rectangular cross section. The warping and shear deformation of the cross section are also considered. The macroscopic theory of piezoelectric semiconductors is used. A one-dimensional theory is derived. A few dynamic and static problems are analyzed using the one-dimensional equations. Results show interactions between mechanical loads and redistribution of charge carriers. When the rod is under an applied voltage, the current-voltage relation is obtained. The effects of mechanical loads on the current-voltage relation is examined. These are useful to piezotronic devices based on interactions between mechanical fields and mobile charges.

Phase transition by nanoindentation in a relaxor ferroelectric single crystal PMN-0.3PT: A phase-field investigation

Nanoindentaiton testing has revealed pop-in events in load–displacement curves of relaxor single crystal PMN-0.3PT ferroelectric materials that occur when the indentation depth is small (e.g., dozens of nanometers). Although there has been speculation of an occurrence of phase transition, there is a relative lack of investigation on the domain evolution associated with the phase transition when the pop-in events appear. In the present study, nanoindentation of this material was systematically modeled using phase-field simulations, which capture the domain and phase evolution of a PMN-0.3PT ferroelectric single crystal. The results, qualitatively similar to the experimental results, revealed details of the contribution of phase transformations to pop-in events. The influence of indenter shape, size, and external electric field on the pop-in event was also examined. This work provides a computational evaluation of the effects of the phase transition mechanism in ferroelectric materials under nanoindentation and gives insight into local mechanical loading effects on these electromechanically coupled crystals.

Investigation of Electrical Transitions in the First Steps of Spark Plasma Sintering: Effects of Pre-Oxidation and Mechanical Loading within Copper Granular Media.

Spark Plasma Sintering (SPS) has become a conventional and promising sintering method for powder consolidation. This study aims to well understand the mechanisms of densification encountered during SPS treatments, especially in the early stages of sintering. The direct current (DC) electrical behavior of copper granular medium is characterized. Their properties are correlated with their microstructural evolutions through post-mortem scanning electron microscope (SEM) observations to allow a thorough understanding of the involved Branly effect that is suspected to occur in SPS. The electrical response is studied by modifying the initial thickness of the oxide layer on particles surfaces and applying various mechanical loads on the granular medium. Without load and at low current, the measured quasi-reversible behavior is connected to the formation of spots at the microcontacts between the particles. By increasing the current, the Branly transition from an insulating to a conductive state suddenly occurs. The insulating oxide layer is destroyed, and micro-bridges are created. The application of a mechanical pressure strongly modifies the DC Branly effect. Increasing low stress leads to a strong decrease in the breakdown field. For high-applied pressure, successive drops in the electric field are detected during the electrical transition. These successive drops are induced by microcracking of the insulating oxide layer.

Using a meshless method to assess the effect of mechanical loading in angiogenesis

Although it is known that blood vessels can be found in mechanically active environments, less is known about the effect of mechanical stimulus in angiogenesis. Therefore, understanding how endothelial cells respond to a mechanical stimulus is essential to improve tissue vascularization and to promote wound healing and tissue engineering development. In this work, a meshless method is used to combine an elasticity formulation with a capillary growth algorithm. The final numerical model is capable to simulate the effect of compressive loading in angiogenesis, using three strain magnitudes (5, 10 and 30% strain). In this proposed model, the vascular endothelial growth factor gradient regulates the endothelial cell migration and the compressive loading affects the branching process. The numerical results showed that all the compressive loadings tested increased the vascular network length and the number of branches, being 5% strain magnitude the most effective one. The capillary network obtained resembles the one presented in experimental assays and the obtained numerical results coincided to the experimental ones. Nevertheless, this study possesses some limitations since the viscoelastic properties of the tissue, the dynamic loading effect and the effect of the time variable were not considered. In the future, the combination of computational and experimental studies will be very useful to understand and to define which are the mechanical cues that promote angiogenesis, allowing to improve tissue vascularization and, consequently, the wound healing process.

XFEM based thermo-elastic numerical analysis of FGMs with various discontinuities

In this study, mixed-mode stress intensity factor (MMSIF) and crack growth analysis in functionally graded materials (FGMs) with discontinuities (crack, inclusion and void) are presented. The extended finite element method (XFEM) based study with the partition of unity method is utilized under thermo-mechanical loadings. The effect of mechanical and thermal loadings acting individually and combined on cracked FGM plate with other discontinuities is carried out. In mechanical loading, uniform tensile, shear, combination (tensile and shear), point, uniformly varying, and exponential loading are considered, whereas in thermal loadings, isothermal and adiabatic loadings are utilized. The objective of this present study is to find the MMSIF and crack growth analysis of FGM plate with discontinuities under different thermo-mechanical loadings, where the interaction study of discontinuities and different thermo-mechanical loadings are investigated. The present problem is modeled in MATLAB (R 2015a) environment and the results of the present model are compared with the results from the literature.

Early life vitamin D depletion and mechanical loading determine methylation changes in the RUNX2, RXRA, and osterix promoters in mice

BackgroundEarly life vitamin D exposure is linked to later skeletal health with maternal vitamin D status in pregnancy associated with neonatal bone mass. The MAVIDOS study has demonstrated that vitamin D supplementation leads to reduced RXRA DNA methylation. Mice exposed to early life vitamin D deficiency have reduced bone mass and bone accrual in response to mechanical loading. Using the tibiae of these mice, we have examined the effect of diet and mechanical loading on the DNA methylation of promoters of genetic loci important for bone growth and development and their association with bone strength.ResultsMechanical loading of mouse tibiae leads to a reduction of RXRA DNA methylation. Early life vitamin D deficiency is associated with altered methylation of osterix and Runx2 in these bones. Tibia strength was also demonstrated to be associated with a change in DNA methylation status in CpGs of the vitamin D receptor (VDR), ostrix, and RXRA genes.ConclusionsWe have shown for the first time that mechanical loading of bone and early life vitamin D deficiency leads to changes in the epigenome of this tissue in key genes in the vitamin D and osteoblast differentiation pathway.

Influence of Long-Lasting Static Stretching on Maximal Strength, Muscle Thickness and Flexibility.

Background: In animal studies long-term stretching interventions up to several hours per day have shown large increases in muscle mass as well as maximal strength. The aim of this study was to investigate the effects of a long-term stretching on maximal strength, muscle cross sectional area (MCSA) and range of motion (ROM) in humans. Methods: 52 subjects were divided into an Intervention group (IG, n = 27) and a control group (CG, n = 25). IG stretched the plantar flexors for one hour per day for six weeks using an orthosis. Stretching was performed on one leg only to investigate the contralateral force transfer. Maximal isometric strength (MIS) and 1RM were both measured in extended knee joint. Furthermore, we investigated the MCSA of IG in the lateral head of the gastrocnemius (LG) using sonography. Additionally, ROM in the upper ankle was investigated via the functional “knee to wall stretch” test (KtW) and a goniometer device on the orthosis. A two-way ANOVA was performed in data analysis, using the Scheffé Test as post-hoc test. Results: There were high time-effects (p = 0.003, ƞ² = 0.090) and high interaction-effect (p < 0.001, ƞ²=0.387) for MIS and also high time-effects (p < 0.001, ƞ²=0.193) and interaction-effects (p < 0.001, ƞ²=0,362) for 1RM testing. Furthermore, we measured a significant increase of 15.2% in MCSA of LG with high time-effect (p < 0.001, ƞ²=0.545) and high interaction-effect (p=0.015, ƞ²=0.406). In ROM we found in both tests significant increases up to 27.3% with moderate time-effect (p < 0.001, ƞ²=0.129) and high interaction-effect (p < 0.001, ƞ²=0.199). Additionally, we measured significant contralateral force transfers in maximal strength tests of 11.4% (p < 0.001) in 1RM test and 1.4% (p=0.462) in MIS test. Overall, there we no significant effects in control situations for any parameter (CG and non-intervened leg of IG). Discussion: We hypothesize stretching-induced muscle damage comparable to effects of mechanical load of strength training, that led to hypertrophy and thus to an increase in maximal strength. Increases in ROM could be attributed to longitudinal hypertrophy effects, e.g., increase in serial sarcomeres. Measured cross-education effects could be explained by central neural adaptations due to stimulation of the stretched muscles.

Thermo-mechanical analysis of strength degradation of 30SiMn2MoVA gun barrel material during continuous shooting

The internal bore of a machine gun barrel is subjected to the complex effects of cyclic high-temperature and mechanical loadings during the continuous shooting process, resulting in the accumulation of bore damages and eventually the end of the lifespan. The correlation between the ballistic performances and the material properties is a critical issue for the development of gun barrels with a long lifespan. However, it is still not fully understood yet. In this study, the thermo-mechanical analysis of the strength degradation of 30SiMn2MoVA gun barrel steel during continuous shooting is investigated. Irregular rifling deformation of the failed machine gun barrel with a 12.7 mm caliber was observed. Mechanical tensile tests revealed that severe softening occurs in the 30SiMn2MoVA steel when the temperature exceeded 600 °C, where the yield strength decreased significantly from 862 MPa at room temperature to 114 MPa at 700 °C. Transmission electron microscope observations further revealed that the recrystallization of martensitic lath and the growth of cementite softened the gun barrel steel. Moreover, the finite element models are established using the Abaqus software for the evolution of the temperature and stress of the internal wall within 180 cycles. This shows that the peak temperature increases to 730–740 °C and the peak total stress exceeds 246 MPa during 170–180 cycles, which is much higher than the yield strength of 30SiMn2MoVA gun barrel steel. Therefore, the strength of gun barrel steel at 700 °C can be suggested as the key parameter for the development of long-life gun barrels for continuous shooting.

Residual Stresses Induced while Machining Inconel-718 in Cryogenic Environment: Numerical Estimation

Nickel alloys are recognized to offer great strength, good corrosion resistance, and outstanding thermal stability when compared to typical materials, these features can be utilized in aerospace and turbine sectors. Nickel alloy is one of the most difficult to cut materials since it is having a high strain hardening propensity and low thermal conductivity. But due to the outstanding qualities of Inconel-718, these types of material cannot be ruled out, and hence they are being machined in a cryogenic environment. Many studies have been conducted in recent years to quantify and predict machining-induced residual stress. It has been concluded that the residual stress can be viewed as a function of machining parameters. However, during the cutting process, the combined effect of thermal and mechanical loads has a direct impact on the stress field. Despite conducting experimental studies, there is a significant requirement to build numerical models to simulate residual stress distribution on machined surfaces in order to identify appropriate machining settings. The effect of cryogenic cooling on residual stress has yet to be modeled. In a cryogenic environment, finite element modeling has been successfully used to forecast residual stresses caused by machining. Tungsten Carbide was used as a single-point cutting tool for 2D orthogonal cutting in a cryogenic environment using Abaqus CAE/6.14. In this research work, it has been observed that the geometrical characteristics of the tool and the cutting parameters affect the residual stress. The results provide the correlation between residual stress and the above parameters.

Effects of mechanical loadings on the performance of a piezoelectric hetero-junction

Effects of mechanical loadings on the performance of a piezoelectric hetero-junction

Bone mass and adaptation to mechanical loading are sexually dimorphic in adult osteoblast-specific ERα knockout mice.

Estrogen receptor-alpha (ERα) regulates bone mass and is implicated in bone tissue's response to mechanical loading. The effects of ERα deletion in mice depend on sex, anatomical location, and the cellular stage at which ERα is removed. Few studies have investigated the effect of age on the role of ERα in skeletal maintenance and functional adaptation. We previously demonstrated that bone mass and adaptation to loading were altered in growing 10-week-old female and male mice lacking ERα in mature osteoblasts and osteocytes (pOC-ERαKO). Here our goal was to determine the effects of ERα and mechanical loading in skeletally-mature adult mice. We subjected 26-week-old skeletally-mature adult pOC-ERαKO and littermate control (LC) mice of both sexes to two weeks of in vivo cyclic tibial loading. ERα deletion in male mice did not alter bone mass or the response to loading. Adult female pOC-ERαKO mice had reduced cancellous and cortical bone mass and increased adaptation to high-magnitude mechanical loading compared to LC mice. Thus, ERα deletion from mature osteoblasts reduced the bone mass and increased the mechanoadaptation of adult female but not male mice. Additionally, compared to our previous work in young mice, adult female mice had greatly reduced mechanoadaptation and adult male mice retained most of their mechanoadaptation with age.

Depletion of TRAP/Acp5 abolishes the bone forming effects of mechanical loading in male mice

Depletion of TRAP/Acp5 abolishes the bone forming effects of mechanical loading in male mice

Gene Expression in Response to High Frequency, Low Magnitude Loading on the Anterior Cruciate Ligament

IntroductionPrevention of Anterior Cruciate Ligament (ACL) injuries is important, as ACL injuries are associated with the development of knee osteoarthritis, increased pain, functional limitations, and decreased quality of living. Despite the focus on numerous ACL injury prevention mechanisms, ACL injury rates are still on the rise. Investigating a way to strengthen the ACL may be an alternative method to prevent ACL tears. Traditionally, tissue strengthening would occur through a high magnitude load, applied a limited number of times. However, as ligaments are designed to restrict unhealthy joint movement, high magnitude loading of ligaments is likely non‐desirable, making high frequency, low magnitude loading an intriguing possibility. Previous studies have shown bone’s ability to adapt and strengthen in response to high frequency, low magnitude loading. Therefore, we hypothesized ligaments, the connective tissue connecting bones together, would also exhibit similar adaptive properties. However, there is limited research on a typical in vivo ligament response to mechanical loading.ObjectiveThe purpose of this study was to identify what genes were altered in expression in response to high frequency, low magnitude loading.MethodsSeven New Zealand white rabbits were loaded utilizing a custom device built to apply a high frequency, low magnitude load to the rabbit’s shank. While anesthetized, rabbits were placed into the loading device with the left leg secured in a cast and attached to the load cell with a non‐strain cord (Figure 1). To ensure the loading occurred along the longitudinal axis of the ACL, the hip was extended, knee positioned at 30° knee flexion, with the device pulling on the tibia at 35‐40° to apply tibial anterior translation. Loads were applied oscillating between 2‐12 N, at 15 Hz for 20 minutes. Four hours post loading, both of the rabbit’s ACLs were harvested (loaded ACL &amp; internal control). Three rabbits served as external controls and received no loading. Total RNA was extracted from the ACLs using a Qiagen RNAeasy kit following manufacturer’s instructions. Next Generation Sequencing RNAseq detected gene expression differences between the loaded ACL and internal control ACL, and the loaded ACL and the external control ACL using a Sleuth Wald test during data analysis.ResultsIn response to mechanical loading, there were three genes differentially expressed between the loaded and the internal control ACL, none of which were annotated within the rabbit genome. Between the loaded and external control ACL, there were 121 genes differentially expressed. Grouping these genes by function, there were 15 related to mechanotransduction, five to metabolic pathways, four to interleukin response and tissue repair, three to actin cytoskeleton regulation, two relating to protein transport, and one to collagen synthesis.ConclusionsThis is the first data demonstrating a ligament adaptive response to in vivohigh frequency, low magnitude loading. Additionally, these results shed light on the possible mechanotransductive response pathway in ligament. Future studies should characterize optimal loading parameters (i.e., loading frequency, magnitude, and duration), and investigate the long‐term effects of mechanical loading on a ligament.

Effect of Mechanical Loadings on Two Unequal Slanted Cracks Length in Bi-Materials Plate

Although a lot of crack problems in bi-materials plate were previously treated, few solutions are available under mechanical loadings, arbitrary crack lengths and material combinations. In this paper the dimensionless stress intensity factors (SIFs) of two slanted cracks in the upper plate of bi-materials are considered under mechanical loadings with varying the crack length and material combinations systematically. In order to calculate the dimensionless SIFs accurately, the hypersingular integral equations (HSIEs) was formulated by using the modified complex potentials (MCP) function. The details numerical results of the dimensionless SIFs are given in tabular form and graphical presentations. Comparisons with the existing exact solutions show that the numerical results in this paper have high accuracy. Our results are described with clarifying the effect of the mechanical loadings, bi-elastic constant ratio and element size of cracks on the dimensionless SIFs.

Sliding Corrosion Fatigue of Metallic Joint Implants: A Comparative Study of CoCrMo and Ti6Al4V in Simulated Synovial Environments

Mechanical contact in a corrosive synovial environment leads to progressive surface damage at the modular interface of the joint implants. The wear debris and corrosion products degrade the synovial fluids and change the lubrication mechanisms at the joints. Consequently, the unstable joint lubrication and corrosion products will further induce the undesirable performance of the joint implants. In this study, the two major joint materials, CoCrMo and Ti6Al4V, were tested during the course of reciprocal sliding contact in simulated synovial liquids. Open circuit potential and coefficient of friction were monitored to describe electrochemical and mechanical responses. Potentiostatic test results illustrated electrochemical damage on both surfaces that modified oxidation chemistry on both surfaces. However, more significant modification of the CoCrMo surface was detected during wear in the simulated joint liquid. Even with a reduced coefficient of friction on the CoCrMo surface in sodium lactate environments, fretting current density drastically increased in corrosive sodium lactate with pH 2. However, the test results from the Ti6Al4V surface presented less coefficient of friction values, and moderate change in fretting current. Therefore, the experimental study concluded that the biocompatibility of Ti6Al4V is superior to that of CoCrMo in the combined effect of mechanical loadings and an electrochemical environment.