Dental pulp stem cells express tendon markers under mechanical loading and are a potential cell source for tissue engineering of tendon-like tissue

Postnatal mesenchymal stem cells have the capacity to differentiate into multiple cell lineages. This study explored the possibility of dental pulp stem cells （DPSCs） for potential application in tendon tissue engineering. The expression of tendon- related markers such as scleraxis, tenascin-C, tenomodulin, eye absent homologue 2, collagens I and VI was detected in dental pulp tissue. Interestingly, under mechanical stimulation, these tendon-related markers were significantly enhanced when DPSCs were seeded in aligned polyglycolic acid （PGA） fibre scaffolds. Furthermore, mature tendon-like tissue was formed after transplantation of DPSC-PGA constructs under mechanical loading conditions in a mouse model. This study demonstrates that DPSCs could be a ootential stem cell source for tissue enEineerin~ of tendon-like tissue.

Experimental Measurements of the Sensitivity of Fiber-optic Bragg Grating Sensors with a Soft Polymeric Coating under Mechanical Loading,Thermal and Magnetic under Cryogenic Conditions

The strain and temperature sensing performance of fiber-optic Bragg gratings （FBGs） with soft polymeric coating, which can be used to sense internal strain in superconducting coils, are evaluated under variable cryogenic field and magnetic field. The response to a temperature and strain change of coated-soft polymeric FBGs is tested by comparing with those of coated-metal FBGs. The results indicate that the coated-soft polymeric FBGs can freely detect temperature and thermal strain, their At variable magnetic field, the tested results indicate accuracy and repeatability are also discussed in detail. that the cross-coupling effects of FBGs with different matrixes are not negligible to measure electromagnetic strain during fast excitation. The present results are expected to be able to provide basis measurements on the strain of pulsed superconducting magnet/cable （cable- around-conduit conductors, cable-in-conduit conductors）, independently or utilized together with other strain measurement methods.

Electric potential and energy band in ZnO nanofiber tuned by local mechanical loading

Recent success in strain engineering has triggered tremendous interest in its study and potential applications in nanodevice design. In this paper, we establish a coupled piezoelectric/semiconducting model for a wurtzite structure ZnO nanofiber under the local mechanical loading. The energy band structure tuned by the local mechanical loading and local length is calculated via an eight-band k·p method, which includes the coupling of valance and conduction bands. Poisson's effect on the distribution of electric potential inversely depends on the local mechanical loading. Numerical results reveal that both the applied local mechanical loading and the local length exhibit obvious tuning effects on the electric potential and energy band. The band gap at band edges varies linearly with the applied loading. Changing the local length shifts the energy band which is far away from the band edges. This study will be useful in the electronic and optical enhancement of semiconductor devices.

Generalized modeling and experimental research on the transient response of supercapacitors under compressive mechanical loads

Supercapacitors(SCs)have been successfully used in electric vehicles or military equipment systems for their high power density.However,the mechanical impacts from vehicle crashes and missile penetration probably cause performance fluctuations or failure of SCs,which may threaten the safety of systems using SCs.In this paper,a generalized circuit model to analyze the transient process of SCs under mechanical loads is proposed.The circuit model simultaneously takes capacitance change,internal short-circuit and resistance change into account,an extra resistor-capacitor circuit(RCC)is added to simulate the nonlinear behavior during charging and discharging.Subsequently,the relationships between pressure and fundamental circuit parameters are determined by static methods.By taking the static test data into the circuit model,the transient response of different types of SCs under particular mechanical loading conditions is predicted.Finally,the influences of some crucial parameters on the voltage responses of SCs are revealed based on the simulations,which provide references for designing and optimizing mechanical load-resistant or self-sensing SCs in specific application scenarios.

Statistical analysis of mechanical properties of biological soft tissue under quasi-static mechanical loading

The mechanical properties of biological soft tissues are inextricably linked to the field of health care,and their mechanical properties can be important indicators for diagnosing and detecting diseases;they can also be used to analyze the causes of organ diseases from a pathological point of view and thus guide the deployment of medical solutions.As an effective method to characterize the mechanical properties of materials,mechanical loading experiments have been successfully applied to the mechanical properties of materials,including tension,compression,pure shear,and so on.Under quasi-static loading,when the material is a biological soft tissue material between a solid and an ideal fluid,its viscoelastic properties strongly respond to the force stimulus,and the stress-strain-time in the elastic phase will have obvious disturbance characteristics.Therefore,the existing statistical methods are often difficult to quantitatively describe the mechanical properties of materials.Therefore,this study proposes an Interval Capture Point based on the principle of integration.The experimental data based on this method can characterize its nonlinear mechanical properties well,especially when the loading speed is extremely low and the soft materials show strong disturbance characteristics.The proposed method can still accurately characterize the hyperelastic and viscoelastic properties of the mechanical properties of biological soft tissues under quasi-static loading.

Analytical analysis of hollow CORC cable under thermo-mechanical loads

According to engineering experience,the axial shrinkage caused by the refrigerant seriously endangers the performance of long‐distance conductor on round core(CORC)cables.Since outage maintenance of high‐temperature superconducting(HTS)cables is inevitable,providing appropriate compensation for cyclic temperature is one of the key technologies in the actual application of power cables.Therefore,this paper presents an analytical solution for hollow CORC cables under thermo‐mechanical loads.First,regarded as an axisymmetric composite structure,the radial temperature distribution of CORC cable under Dirichlet boundary or mixed boundary conditions was calculated.Then,assuming cable ends were axially fixed,a recursive method without variables is used to evaluate its displacement,strains,and stresses.Then,an algebraic method with axial strain as a variable is developed to analyze the mechanical behavior of the CORC cable more directly.Finally,concluded from the above derivation,a matrix equation is constructed based on continuity equations and boundary conditions,which applies to isotropic and orthotropic materials with orientations.Calculation results show that the analytical solution agrees with finite element method(FEM)results.Compared to the trial results of a 360 m CORC cable,the calculation error of axial shrinkage is within 1.63 cm,and the relative error is within 6.1%.In addition,the recursive method is the fastest to calculate axial strain,while the matrix method has a significant efficiency advantage in calculating the stresses and strains of each layer.

Dynamic mechanical loading facilitated chondrogenic differentiation of rabbit BMSCs in collagen scaffolds

Mechanical signals have been played close attention to regulate chondrogenic differentiation of bone marrow mesenchymal stem cells(BMSCs).In this study,dynamic mechanical loading simulation with natural frequencies and intensities were applied to the 3D cultured BMSCs–collagen scaffold constructs.We investigated the effects of dynamic mechanical loading on cell adhesion,uniform distribution,proliferation,secretion of extracellular matrix(ECM)and chondrogenic differentiation of BMSCs–collagen scaffold constructs.The results indicated that dynamic mechanical loading facilitated the BMSCs adhesion,uniform distribution,proliferation and secretion of ECM with a slight contraction,which significantly improved the mechanical strength of the BMSCs–collagen scaffold constructs for better mimicking the structure and function of a native cartilage.Gene expression results indicated that dynamic mechanical loading contributed to the chondrogenic differentiation of BMSCs with higher levels of AGG,COL2A1 and SOX9 genes,and prevented of hypertrophic process with lower levels of COL10A1,and reduced the possibility of fibrocartilage formation due to down-regulated COL1A2.In conclusion,this study emphasized the important role of dynamic mechanical loading on promoting BMSCs chondrogenic differentiation and maintaining the cartilage phenotype for in vitro reconstruction of tissue-engineered cartilage,which provided an attractive prospect and a feasibility strategy for cartilage repair.

The effect of mechanical loads on the degradation of aliphatic biodegradable polyesters

Aliphatic biodegradable polyesters have been the most widely used synthetic polymers for developing biodegradable devices as alternatives for the currently used permanent medical devices.The performances during biodegradation process play crucial roles for final realization of their functions.Because physiological and biochemical environment in vivo significantly affects biodegradation process,large numbers of studies on effects of mechanical loads on the degradation of aliphatic biodegradable polyesters have been launched during last decades.In this review article,we discussed the mechanism of biodegradation and several different mechanical loads that have been reported to affect the biodegradation process.Other physiological and biochemical factors related to mechanical loads were also discussed.The mechanical load could change the conformational strain energy and morphology to weaken the stability of the polymer.Besides,the load and pattern could accelerate the loss of intrinsic mechanical properties of polymers.This indicated that investigations into effects of mechanical loads on the degradation should be indispensable.More combination condition of mechanical loads and multiple factors should be considered in order to keep the degradation rate controllable and evaluate the degradation process in vivo accurately.Only then can the degradable devise achieve the desired effects and further expand the special applications of aliphatic biodegradable polyesters.

Comparison of Acoustic Emission Characteristics for C/SiC Composite Component Under Combination of Heating and Mechanical Loading

The acoustic emission（AE） characteristics of C/SiC composite component under various conditions were compared, with the purpose of identifying the possible damage and failure mechanism. During the process of the single mechanical loading, the highest amplitude of the AE signal was less than 85 dB and the main damage forms of matrix cracking and interface debonding were involved. For the heating process, high-energy AE signals with an amplitude more than 85 dB were detected and fiber fracture mechanism was determined as well due to the thermal stress caused by the mismatch of the thermal expansion coefficient between the reinforced fiber and matrix. During the combination process of the heating and mechanical loading, it was concluded that the degree of damage was much severer than the simple superposition of damage produced by the individual mechanical loading and the individual heating process.

A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone

The transport of fluid, nutrients, and signaling molecules in the bone lacunar-canalicular system （LCS） is critical for osteocyte survival and function. We have applied the fluorescence recovery after photobleaching （FRAP） approach to quantify load-induced fluid and solute transport in the LCS in situ, but the measurements were limited to cortical regions 30-50 μm underneath the periosteum due to the constrains of laser penetration. With this work, we aimed to expand our understanding of load-induced fluid and solute transport in both trabecular and cortical bone using a multiscaled image-based finite element analysis （FEA） approach. An intact murine tibia was first re-constructed from microCT images into a three-dimensional （3D） linear elastic FEA model, and the matrix deformations at various locations were calculated under axial loading. A segment of the above 3D model was then imported to the biphasic poroelasticity analysis platform （FEBio） to predict load-induced fluid pressure fields, and interstitial solute/fluid flows through LCS in both cortical and trabecular regions. Further, secondary flow effects such as the shear stress and/or drag force acting on osteocytes, the presumed mechano-sensors in bone, were derived using the previously developed ultrastructural model of Brinkman flow in the canaliculi. The material properties assumed in the FEA models were validated against previously obtained strain and FRAP transport data measured on the cortical cortex. Our results demonstrated the feasibility of this computational approach in estimating the fluid flux in the LCS and the cellular stimulation forces （shear and drag forces） for osteocytes in any cortical and trabecular bone locations, allowing further studies of how the activation of osteocytes correlates with in vivo functional bone formation. The study provides a promising platform to reveal potential cellular mechanisms underlying the anabolic power of exercises and physical activities in treating patients with skeletal deficiencies.

Bone Density and Mechanical Properties in Femoral Bone of Swim Loaded Aged Mice

Effects of swirnming on bone density and mechanical properties of femur were investigated in aged male and female mice. R/1 strain of senescence accelerated mouse (SAM) at eleven months old was used. Two groups of males and two groups of females each consisting of 7 mice were used. One male and one female groups were loaded with a swim regiment of 40 min a day, 5 days a week for 6 consecutive weeks. The remaining groups were used as the controls. All mice were fed with the standard diet and water ad libitum during the experiments.The results of this study indicated that (i) the hady weight was significantly (P<0.05) lower in the swimming groups than in the control groups in boh sexes. (ii) The bone density was significantly higher (P <0.05) in the swimming groups than in the control groups in boh sexes. However, there was no sighficant difference in cortical thickness index. (iii) In the mechanical properties of bone, there were no significant differences in the level of the maximum breaking force, the ultimate stress and the deformation between the swimndng and the contro groups in beth sexes. However, the elasticity of the bone of the female hoce in the swimming group was significantly higher (P<0.05) than that of the control group.These results suggest that regimented swimming for the aged mice might suppress age-associated bone loss, and the effect of exercise in the females is greater that in the males.

Wireless Network Security Using Load Balanced Mobile Sink Technique

Real-time applications based on Wireless Sensor Network(WSN)tech-nologies are quickly increasing due to intelligent surroundings.Among the most significant resources in the WSN are battery power and security.Clustering stra-tegies improve the power factor and secure the WSN environment.It takes more electricity to forward data in a WSN.Though numerous clustering methods have been developed to provide energy consumption,there is indeed a risk of unequal load balancing,resulting in a decrease in the network’s lifetime due to network inequalities and less security.These possibilities arise due to the cluster head’s limited life span.These cluster heads(CH)are in charge of all activities and con-trol intra-cluster and inter-cluster interactions.The proposed method uses Lifetime centric load balancing mechanisms(LCLBM)and Cluster-based energy optimiza-tion using a mobile sink algorithm(CEOMS).LCLBM emphasizes the selection of CH,system architectures,and optimal distribution of CH.In addition,the LCLBM was added with an assistant cluster head(ACH)for load balancing.Power consumption,communications latency,the frequency of failing nodes,high security,and one-way delay are essential variables to consider while evaluating LCLBM.CEOMS will choose a cluster leader based on the influence of the fol-lowing parameters on the energy balance of WSNs.According to simulatedfind-ings,the suggested LCLBM-CEOMS method increases cluster head selection self-adaptability,improves the network’s lifetime,decreases data latency,and bal-ances network capacity.

Failure transition of shear-to-dilation band of rock salt under triaxial stresses

Great potential of underground gas/energy storage in salt caverns seems to be a promising solution to support renewable energy.In the underground storage method,the operating cycle unfortunately may reach up to daily or even hourly,which generates complicated pressures on the salt cavern.Furthermore,the mechanical behavior of rock salt may change and present distinct failure characteristics under different stress states,which affects the performance of salt cavern during the time period of full service.To reproduce a similar loading condition on the cavern surrounding rock mass,the cyclic triaxial loading/unloading tests are performed on the rock salt to explore the mechanical transition behavior and failure characteristics under different confinement.Experimental results show that the rock salt samples pre-sent a diffused shear failure band with significant bulges at certain locations in low confining pressure conditions(e.g.5 MPa,10 MPa and 15 MPa),which is closely related to crystal misorientation and grain boundary sliding.Under the elevated confinement(e.g.20 MPa,30 MPa and 40 MPa),the dilation band dominates the failure mechanism,where the large-size halite crystals are crushed to be smaller size and new pores are developing.The failure transition mechanism revealed in the paper provides additional insight into the mechanical performance of salt caverns influenced by complicated stress states.

Expression analysis of a-smooth muscle actin and tenascin-C in the periodontal ligament under orthodontic loading or in vitro culture

α-smooth muscle actin （α-SMA） and tenascin-C are stress-induced phenotypic features of myofibroblasts. The expression levels of these two proteins closely correlate with the extracellular mechanical microenvironment. We investigated how the expression of α-SMA and tenascin-C was altered in the periodontal ligament （PDL） under orthodontic loading to indirectly reveal the intrinsic mechanical microenvironment in the PDL. In this study, we demonstrated the synergistic effects of transforming growth factor-β1 （TGF-β1） and mechanical tensile or compressive stress on myofibroblast differentiation from human periodontal ligament cells （hPDLCs）. The hPDLCs under higher tensile or compressive stress significantly increased their levels of α-SMA and tenascin-C compared with those under lower tensile or compressive stress. A similar trend was observed in the tension and compression areas of the PDL under continuous light or heavy orthodontic load in rats. During the time-course analysis of expression, we observed that an increase in α-SMA levels was matched by an increase in tenascin-C levels in the PDL under orthodontic load in vivo. The time-dependent variation of α-SMA and tenascin-C expression in the PDL may indicate the time-dependent variation of intrinsic stress under constant extrinsic loading.

Dynamic Fluid Flow Mechanical Stimulation Modulates Bone Marrow Mesenchymal Stem Cells

Osteoblasts are derived from mesenchymal stem cells （MSCs）, which initiate and regulate bone formation. New strategies for osteoporosis treatments have aimed to control the fate of MSCs. While functional disuse decreases MSC growth and osteogenic potentials, mechanical signals enhance MSC quantity and bias their differentiation toward osteoblastogenesis. Through a non-invasive dynamic hydraulic stimulation （DHS）, we have found that DHS can mitigate trabecular bone loss in a functional disuse model via rat hindlimb suspension （HLS）. To further elucidate the downstream cellular effect of DHS and its potential mechanism underlying the bone quality enhancement, a longitudinal in vivo study was designed to evaluate the MSC populations in response to DHS over 3, 7, 14, and 21 days. Five-month old female Sprague Dawley rats were divided into three groups for each time point： age-matched control, HLS, and HLS＋DHS. DHS was delivered to the right mid-tibiae with a daily ＂10 min on-5 min off-10 min on＂ loading regime for five days/week. At each sacrifice time point, bone marrow MSCs of the stimulated and control tibiae were isolated through specific cell surface markers and quantified by flow cytometry analysis. A strong time-dependent manner of bone marrow MSC induction was observed in response to DHS, which peaked on day 14. After 21 days, this effect of DHS was diminished. This study indicates that the MSC pool is positively influenced by the mechanical signals driven by DHS. Coinciding with our previous findings of mitigation of disuse bone loss, DHS induced changes in MSC number may bias the differentiation of the MSC population towards osteoblastogenesis, thereby promoting bone formation under disuse conditions. This study provides insights into the mechanism of time-sensitive MSC induction in response to mechanical loading, and for the optimal design of osteovorosis treatments.

Mechanical Buckling Analysis of Composite Panels with/without Cutouts

A simplified analytical solution suitable for simple stacking sequences was developed using the Euler buck- ling theory, the structure＇s equations of equilibrium and laminate panel mathematical formulation. Comparing these results with numerical results reveals the accuracy of the method and even more, allows us to validate the nu- merical analysis. Therefore, two important results are obtained： a simplified analytical solution for the buckling problem and validation of the numerical results. Another important and novel finding is related to the influence of the angle ply orientation and of the cutouts, on the buckling load. Under symmetrical boundary conditions and loading case, rectangular panels with elliptical cutouts, give better results for 90~ oriented plies than for 0 oriented ones. With a compression load applied in the X direction, and with material properties 10 times better in X direction than in Y direction, the best results are obtained when the load is aligned with the Y direction associated to the ma- terial reference frame. Moreover, panels with cutouts seem to behave better than panels without cutouts under cer- tainply orientation angles.

Peripheral nerve lengthening as a regenerative strategy

Peripheral nerve injury impairs motor, sensory, and autonomic function, incurring substantial financial costs and diminished quality of life. For large nerve gaps, proximal lesions, or chronic nerve injury, the prognosis for recovery is particularly poor, even with autografts, the current gold standard for treating small to moderate nerve gaps. In vivo elongation of intact proximal stumps towards the injured distal stumps of severed peripheral nerves may offer a promising new strategy to treat nerve injury. This review describes several nerve lengthening strategies, including a novel internal fixator device that enables rapid and distal reconnection of proximal and distal nerve stumps.

Evaluation of the weakening behavior of gas on the coal strength and its quantitative influence on the coal deformation

The coal strength and deformation properties are key factors affecting safe coal mining and highefficiency coalbed methane(CBM)development.In this paper,reconstituted coal samples are chosen to investigate the weakening behavior of gas on coal strength,meanwhile,its effects on coal deformation are quantitatively evaluated.The results indicate that the weakening degree of gas on coal strength is closely related to the confining stress and gas pressure.Compared with non-gas-saturated coals,the maximum weakening ratios of adsorbed gas to coal strength are 10.58%,18.12%,8.55%and 14.65%under the conditions of confining stress CS=3 MPa and gas pressure GP=1 MPa,CS=3 MPa and GP=2 MPa,CS=4 MPa and GP=1 MPa,and CS=4 MPa and GP=2 MPa,respectively.Furthermore,the maximum weakening ratios of free gas to coal strength are 18.27%,36.54%,14.79%and 29.58%,respectively,under above four conditions.The maximum coal bulk strain decreases as particle sizes of coal powders increase,and it has a maximum value of 0.0227 and a minimum value of 0.0191 in particle size ranges of 0.01–0.041 and 0.5–1 mm.Under the same conditions,the coal bulk strain increases with increasing gas pressure,revealing that coal deformation properties can be enhanced by gas.

Mechanotransduction of stem cells for tendon repair

Tendon is a mechanosensitive tissue that transmits force from muscle to bone.Physiological loading contributes to maintaining the homeostasis and adaptation of tendon,but aberrant loading may lead to injury or failed repair.It is shown that stem cells respond to mechanical loading and play an essential role in both acute and chronic injuries,as well as in tendon repair.In the process of mechanotransduction,mechanical loading is detected by mechanosensors that regulate cell differentiation and proliferation via several signaling pathways.In order to better understand the stem-cell response to mechanical stimulation and the potential mechanism of the tendon repair process,in this review,we summarize the source and role of endogenous and exogenous stem cells active in tendon repair,describe the mechanical response of stem cells,and finally,highlight the mechanotransduction process and underlying signaling pathways.

THERMODYNAMIC MODELING OF NANOSCALE FERROELECTRIC SYSTEMS

Thermodynamic models formulated based on the Landau free-energy expansion are popular and well suited to studies involving properties of the ferro/para-electric transition, or near it. Indeed, the general nature of thermodynamics, from which the strength of the model is derived, allows a valid model to be constructed based on simple functional forms with parameters fitted to experiments, by passing the mechanistic complexity. Despite inaccuracy due to the neglect of fluctuations, this approach has been proven effective and powerful for recent research development of ferroelectrics in nanoscale. Efforts in some important works have recently faced much challenge, when free-energy contributions have to be incorporated to account for the presence of depolarization fields, surfaces and other defects. To minimize the problems with mechanistic obscurity, it is of paramount importance that the electromagnetics, mechanics and thermodynamics involved are accounted for explicitly and with full self-consistency. It is important that the free-energy functional of nanoscale ferroelectric systems, such as ferroelectric thin films （FTF）, bilayers （FB）, superlattices （FS）, nanowires （FNW）, nanotubes （FNT） and tunneling junctions （FTJ） etc., must be derived thermodynamically from first principles.