Cyclic Tensile Stress Research Articles

Regulation of the integrin \u03b1V\u03b23- actin filaments axis in early osteogenesis of human fibroblasts under cyclic tensile stress

BackgroundIntegrins play a prominent role in osteogenic differentiation by transmitting both mechanical and chemical signals. Integrin expression is closely associated with tensile stress, which has a positive effect on osteogenic differentiation. We investigated the relationship between integrin αVβ3 and tensile stress.MethodsHuman fibroblasts were treated with c (RGDyk) and lentivirus transduction to inhibit function of integrin αVβ3. Y-15, cytochalasin D and verteporfin were used to inhibit phosphorylation of FAK, polymerization of microfilament and function of nuclear YAP, respectively. Fibroblasts were exposed to a cyclic tensile stress of 10% at 0.5 Hz, once a day for 2 h each application. Fibroblasts were harvested on day 4 and 7 post-treatment. The expression of ALP, RUNX2, integrin αVβ3, β-actin, talin-1, FAK, vinculin, and nuclear YAP was detected by Western blot or qRT-PCR. The expression and distribution of integrin αVβ3, vinculin, microfilament and nuclear YAP.ResultsCyclic tensile stress was found to promote expression of ALP and RUNX2. Inhibition of integrin αVβ3 activation downregulated the rearrangement of microfilament and the expression of ALP, RUNX2 and nuclear YAP. When the polymerization of microfilament was inhibited the expression of ALP, RUNX2 and nuclear YAP were decreased. The phosphorylation of FAK induced by cyclic tensile stress reduced by the inhibition of integrin αVβ3. The expression of ALP and RUNX2 was decreased by inhibition of phosphorylation of FAK and inhibition of nuclear YAP.ConclusionsCyclic tensile stress promotes osteogenesis of human fibroblasts via integrin αVβ3-microfilament axis. Phosphorylation of FAK and nuclear YAP participates in this process.

Different Passive Viscoelastic Properties Between the Left and Right Ventricles in Healthy Adult Ovine.

Ventricle dysfunction is the most common cause of heart failure, which leads to high mortality and morbidity. The mechanical behavior of the ventricle is critical to its physiological function. It is known that the ventricle is anisotropic and viscoelastic. However, the understanding of ventricular viscoelasticity is much less than that of its elasticity. Moreover, the left and right ventricles (LV&RV) are different in embryologic origin, anatomy, and function, but whether they distinguish in viscoelastic properties is unclear. We hypothesized that passive viscoelasticity is different between healthy LVs and RVs. Ex vivo cyclic biaxial tensile mechanical tests (1, 0.1, 0.01 Hz) and stress relaxation (strain of 3, 6, 9, 12, 15%) were performed for ventricles from healthy adult sheep. Outflow track direction was defined as the longitudinal direction. Hysteresis stress-strain loops and stress relaxation curves were obtained to quantify the viscoelastic properties. We found that the RV had more pronounced frequency-dependent viscoelastic changes than the LV. Under the physiological frequency (1 Hz), the LV was more anisotropic in the elasticity and stiffer than the RV in both directions, whereas the RV was more anisotropic in the viscosity and more viscous than the LV in the longitudinal direction. The LV was quasi-linear viscoelastic in the longitudinal but not circumferential direction, and the RV was nonlinear viscoelastic in both directions. This study is the first to investigate passive viscoelastic differences in healthy LVs and RVs, and the findings will deepen the understanding of biomechanical mechanisms of ventricular function.

Failure analysis of cracking in S30408 weld joint between cylinder and flange of pure steam sterilization pot

The sterilization pot is widely used in the production and processing of food. The cracking failure of S30408 cylinder-flange weld joint of sterilization pot was analyzed by through the analysis of the composition, macroscopic fracture morphology, metallographic morphology, residual stress, microhardness and finite element modelling. The reasons for cracking and corresponding preventive methods were put forward. The cracking in inner surface of flange is induced by the stress corrosion cracking and accelerated by fatigue. The corrosion resistance deterioration of materials and the existence of dissolved oxygen and chloride ions are the main reasons to induce cracking. The cyclic tensile stress in weld joint accelerated crack propagation in inner surface. In order to avoid crack of sterilization pot, the reduction method on welding residual stresses should be performed and the contents of chloride ion and dissolved oxygen in the medium should be strictly monitored.

Experimental investigation and viscoelastic-plastic model for sandstone under cyclic tensile stress

Experimental investigation and viscoelastic-plastic model for sandstone under cyclic tensile stress

Robust and flexible photodetector from a solution derived nanowire networks of organometallic charge transfer complex

An organometallic charge transfer (CT) complex, viz, silver- tetracyanoquinodimethane (Ag-TCNQ) has been synthesized through solution self assembly. The as synthesized product characterized through scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy indicated that highly crystalline, unidirectional, nanostructure network of Ag-TCNQ has been grown. The thin film of Ag-TCNQ based CT complex on flexible substrate exhibited excellent photoresponse characteristics under white light illumination, which is 5-fold higher than the pristine Ag nanoparticle based photodetector (PD). The modulation in photocurrent and responsivity of Ag-TCNQ PD was controlled with variation in input optical power, electrode bias and illumination wavelength. The PD displayed highest responsitivity, ca. 13.8 mA/W and photo to dark current ratio, ca. 9.2 at an optical power of 10.2 mW/cm2. The photocurrent of the device showed insignificant degradation (2.1%) when the substrate was subjected to cyclic tensile stress with bending endurance upto 500 cycles. The device also displayed outstanding opto-mechanical and optoelectronics properties by exhibiting stable, fast and reversible photo switching behavior under various tensile stress on the flexible substrate with outward bending along the conduction channel.

High cyclic tensile stress disrupts the extracellular matrix in human chondrocyte by F-actin cytoskeletal polymerization and reactive oxygen species production.

This study aims to explore the mechanism of cyclic tensile stress (CTS) on human chondrocytes (CHs) relating to the reactive oxygen species (ROS) generation and extracellular matrix (ECM) stability in vitro. A well-established CTS model with 5%, 10%, or 20% elongation was performed for CHs stretching. After CTS, the cell viability, total ROS level, main ECM components, matrix metalloproteinase (MMP), tissue inhibitor of metalloproteinase (TIMP), F-actin density, and some anti-oxidative enzymes were analyzed. Additionally, the antioxidant N-acetylcysteine (NAC) and cytochalasin D were used to suppress the ROS production and F-actin polymerization when the CHs underwent CTS, respectively. The treatment of 20% elongation-CST significantly decreased the CH viability and the expressions of collagen II, aggrecan, anti-oxidative enzymes and TIMP3/4, however, it increased the ROS accumulation, F-actin polymerization, and the expression of collagen I and MMP3/13. In contrast, the application of NAC and cytochalasin D could partly rescue the CHs from the injury caused by the high CTS. Therefore, high CTS disrupts the ECM by remodeling the F-actin cytoskeleton and promoting ROS production. Cytochalasin D and NAC are effective in rejecting F-actin cytoskeleton polymerization, and ROS accumulation through a potential synergetic process, which alleviates the ECM injury caused by High CTS.

Cyclic Tensile Stress to Rat Thoracolumbar Ligamentum Flavum Inducing the Ossification of Ligamentum Flavum

Study Design.Western blot, reverse transcription-polymerase chain reaction (RT-PCR), radiological, and histological analyses of the rat ossification of ligamentum flavum (OLF) induced by cyclic tensile stress.Objective.The aim of this study was to induce the OLF using cyclic tensile stress to rat thoracolumbar ligamentum flavum, and to investigate the possible molecular mechanism of tension-induced OLF.Summary of Background Data.Tensile stress has been considered as an important factor leading to the OLF. So far, however, no OLF induced by tension has been reported.Methods.Forty rats were randomly divided into five equal groups. For control groups, the blank and anesthesia groups were not subjected to tension. For experimental groups, the 4-, 8-, and 12-week groups were subjected to cyclic tensile stress of ligamentum flavum after abdominal anesthesia for 4 weeks, 8 weeks, and 12 weeks, respectively, using an original stress apparatus for rats. The radiological and morphological changes of rat spine, as well as the protein and mRNA expressions of CD44, bone morphogenetic protein-2 (BMP-2), integrin β3, collagen protein type I (COL1), osteopontin (OPN), runt-related transcription factor 2 (RUNX-2), and vascular endothelial growth factor (VEGF), were concerned.Results.The micro-CT showed OLF in the 4-, 8-, and 12-week group. The axial maximum occupied area of ossifications was 1.42 mm2, 3.35 mm2, and 7.28 mm2, respectively. In histopathology, chondrocytes proliferated in the experimental model; woven bone arose in the 8- and 12-week groups, and was more noticeable in the 12-week group. According to western blot and RT-PCR, the expressions of seven osteogenesis-related molecules were all increased in three experimental groups.Conclusion.Cyclic tensile stress to the ligamentum flavum in rats can induce the OLF, and the longer the duration, the more visible the osteogenesis. The upregulation and synergism of osteogenesis-related molecules may contribute to the OLF induced by tensile stress.Level of Evidence:N/A

Elastic, Conductive, and Mechanically Strong Hydrogels from Dual-Cross-Linked Aramid Nanofiber Composites.

Recent research on conductive hydrogels has revealed their potential for building advanced soft bioelectronic devices. Their mechanical flexibility, water content, and porosity approach those of biological tissues, providing a compliant interface between the human body and electronic hardware. Conductive hydrogels could be utilized in many soft tools such as neural electrodes, tactile interfaces, soft actuators, and other electroactive devices. However, most of the available conductive hydrogels exhibit weak mechanical properties, which hinders their application in durable biointegrated systems. Here, we report aramid nanofiber-based hydrogels providing a combination of high elasticity, strength, and electrical conductivity. Highly branched aramid nanofibers (ANFs) provide a robust three-dimensional (3D) framework resembling those in load-bearing soft tissues. When interlaced with poly(vinyl alcohol) (PVA) and cross-linked with both noncovalent and covalent interactions, the nanofiber composites exhibit a high water content of ∼76.4 wt %, strength of ∼7.5 MPa, ductility of ∼407%, and shape recovery of ∼99.5% under cyclic tensile stress of 0.3 MPa. Mobile ions impart a conductivity of ∼2 S/m to the hydrogels, enabling large-strain sensors with stable operation. In addition, the embedded silver nanoparticles afford broad-spectrum antimicrobial activities, which is favorable for medical devices. The versatility of aramid nanofiber-based composites suggests their further possibilities for functionalization and scalable fabrication toward sophisticated bioelectronic systems.

Mechanism of Cyclic Tensile Stress in Osteogenic Differentiation of Human Periodontal Ligament Stem Cells.

Human periodontal ligament stem cells (hPDLSCs) can undergo osteogenic differentiation under induction conditions. Cyclic tensile stress (CTS) can stimulate stem cell osteogenic differentiation. The present study explored the mechanism of CTS in hPDLSC osteogenic differentiation. The hPDLSCs of the 4th passage were selected. hPDLSCs were subjected to CTS with deformation of 10% elongation at 0.5Hz for 1, 4, 8, 12 and 24h. ALP activity and staining, ARS staining and detection of expressions of osteogenesis-related genes (RUNX2, OPN, Sp7 and OCN) were used to assess hPDLSC osteogenic differentiation ability. microRNA (miR)-129-5p and BMP2 expression and p-Smad1/5 level were detected under CTS stimulation. The binding relationship between miR-129-5p and BMP2 was predicted and verified. The osteogenic differentiation ability of CTS-treated hPDLSCs was evaluated after intervention of miR-129-5p and BMP2. CTS induced hPDLSC osteogenic differentiation, as manifested by increased ALP activities, osteogenesis-related gene expressions and mineralized nodules, together with positive ALP staining. CTS inhibited miR-129-5p expression, and promoted BMP2 expression and p-Smad1/5 level in hPDLSCs. miR-129-5p targeted BMP2. Overexpressed miR-129-5p or silenced BMP2 prevented hPDLSC osteogenic differentiation ability. We demonstrated that CTS inhibited miR-129-5p expression, and then activated the BMP2/Smad pathway, thereby showing stimulative effects on hPDLSC osteogenic differentiation.

Passive piezomagnetic monitoring of structures subjected to in-service cyclic loading: Application to the detection of fatigue crack initiation and propagation

In this research, the evolution of the piezomagnetic field of a low carbon steel under cyclic tensile stress was investigated. The objective was to explore the correlations between piezomagnetic signal measured by a fluxgate magnetometer with progressive changes that take place during the fatigue tests. Experiments show first that the piezomagnetic hysteresis loop changes drastically with the propagation of fatigue crack. A multiscale magneto-elastic model of the piezomagnetic behavior allows secondly the experimental cycles evolution to be explained.

Cyclic Mechanical Stretch Ameliorates the Degeneration of Nucleus Pulposus Cells through Promoting the ITGA2/PI3K/AKT Signaling Pathway.

Background Intervertebral disc degeneration (IVDD) is one of the major causes of low back pain and motor deficiency. Nucleus pulposus (NP) degeneration plays a key role in the process of IVDD. The mechanical and biological interactions involved in NP degeneration have not been elucidated. The present study is aimed at investigating the effect and mechanism of cyclic mechanical stretch in regulating the function and degeneration of NP cells. Methods NP cells were subjected to cyclic tensile stress (10% deformation) of 0.1 Hz for 8640 cycles. Cell proliferation was conducted through the MTT assay. The cell cycle and apoptosis were detected by flow cytometry. A gene expression profile chip was used to analyze the differentially expressed genes between the tensile stress group and the control group. Enrichment analysis of Gene Ontology (GO) annotation and signaling pathways were analyzed. Western blot and RNA interference were carried out to investigate the role of the ITGA2/PI3K/AKT pathway in the effect of cyclic mechanical stretch on NP cells. Results NP cells exhibited a greater (P < 0.05) growth rate in the tensile stress group compared to the control group. Cyclic mechanical stress significantly promoted the cell cycle transition of NP cells from the S phase to the G2/M phase. A fewer proportion of apoptotic cells were found in the tensile stress group (P < 0.05), indicating that cyclic mechanical stretch inhibits NP cell apoptosis. Microarray analysis revealed 689 significant differentially expressed genes between the two groups (P < 0.05), of which 333 genes were upregulated and another 356 genes were downregulated. Cyclic mechanical stretch altered the expression of 31 genes involved in the ITGA2/PI3K/AKT pathway and remarkably promoted this pathway in NP cells. Downregulation of ITGA2 and AKT further demonstrated that the PI3K/AKT pathway was responsible for the proliferation and COL2A1 expression of NP cells upon cyclic mechanical stretch. Conclusions Cyclic mechanical stretch promoted the proliferation and cell cycle and reversely inhibited the apoptosis of NP cells. Cyclic mechanical stretch promoted COL2A1 expression and ameliorated the degeneration of NP cells via regulation of the ITGA2/PI3K/AKT signaling pathway. Our results may provide a potential target and a possibility of IVDD disease treatment by ameliorating the degenerative changes.

Tool path selection for high-speed ball-end milling process of hardened AISI D2 steel based on fatigue resistance

This paper aims at revealing how tool paths influence the fatigue resistance of high-speed ball-end hard milled surfaces and proposing corresponding tool path selection methods. Three kinds of tool paths (tool paths A, B, and C with angles relative to the length direction of cuboid workpiece 0°, 90°, and 45°, respectively) were utilized during high-speed milling process of hardened AISI D2 steel. The fatigue resistance of samples for different tool paths was evaluated through three-point bending fatigue tests. Results shows that tool paths have significant effect on fatigue resistance, and the maximum discrepancy in fatigue life can reach about 37.6% for different tool paths. Samples for tool path C shows the longest fatigue life when radial depth of cut ae = 0.1 mm. However, with the further increase of ae, samples for tool path A have the best fatigue resistance, followed by tool path C and B. Microscopic stress concentration and effective residual stress are the main ways by which tool paths influence the fatigue resistance. Changing tool paths leads to the difference in surface topography orientation and then in degree of microscopic stress concentration. Moreover, the effective residual stress (residual stress component in direction parallel to cyclic tensile stress) is also directly determined by tool paths. Tool path selection methods are put forward based on the aforementioned influence mechanisms. This study indicates that improving the fatigue resistance of high-speed ball-end hard milled surfaces suffering given cyclic tensile stress is feasible by choosing appropriate tool paths.

Fatigue behavior and relation between fatigue resistance and tensile properties of poly(para‐phenylene‐co‐3,4'‐oxydiphenylene terephthalamide) fiber

AbstractThe poly(para‐phenylene‐co‐3,4′‐oxydiphenylene terephthalamide) (PPODTA) fiber is one of the high strength organic fibers, and it has been reported that the PPODTA fiber has superior fatigue resistance. The high strength fibers are used in the applications to utilize their high mechanical properties in general. Therefore, the long‐term durability of these fibers is also required. In this study, the fatigue tests were conducted for the PPODTA fibers. As a result, it was found that the PPODTA fibers were able to be fractured by the cyclic tensile stress, and the fatigue behavior was influenced by the stress conditions. In addition, the single fiber tensile tests were also conducted for the PPODTA fibers, and the relation between the tensile properties and the fatigue resistance of the PPODTA fiber was investigated. The fatigue resistance of the PPODTA fiber was increased with the decrease of the fiber diameter and the increase of the tensile modulus.

ShRNA knockdown of integrin‐linked kinase on hPDLCs migration, proliferation, and apoptosis under cyclic tensile stress

To investigate the roles of integrin-linked kinase (ILK) in mediating the cell migration, proliferation, and apoptosis of human periodontal ligament cells (hPDLCs) in response to cyclic tensile stress. Primary hPDLCs were obtained through the enzyme digestion and tissue culture method. Short hairpin ILK-expressing hPDLCs were constructed using a recombinant lentiviral vector that specifically targeted ILK gene expression. The silencing of the ILK gene was identified by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. The hPDLCs were seeded on a flexible substrate and loaded with cyclic tensile stress at 0.5Hz for 0, 2, 4, and 8hr, consecutively, with the Flexcell Tension System. The response of cell migration was tested by the scratch assay. Cell proliferation was characterized by optical density (OD) value of cell counting kit-8 (CCK-8) test and Ki67 mRNA expression of qRT-PCR. Cell apoptosis was determined by flow cytometry and Caspase-3 mRNA expression of qRT-PCR. Knocking down ILK substantially reduces migration and proliferation as well as regulates the sensitivity of hPDLCs to apoptosis under cyclic tensile stress. ILK can promote the proliferation and migration as well as inhibit apoptosis of hPDLCs under cyclic tensile stress.

Evolution of nonlinear elasticity and crack damage of rock joint under cyclic tension

Similar to the damage zone in the vicinity of faults, rock joints are composed of single or multiple fracture process zones, highlighting a high crack density and a decrease of Young’s modulus. Here specimens of limestone joint and granite joint were subjected to cyclic tensile stress of increasing amplitudes, up to failure. The cyclic tension tests were to study the elasticity and crack density adjacent to rock joints. Results show that the vast majority of tensile strain accommodates in the vicinity of rock joint, and rock joints have a nonlinear mechanical behavior during loading while a nearly linear behavior during unloading in the tensile stress-strain curves. A gradual reduction in Young’s modulus is seen with the increase of tensile strain. The cumulative crack damage after each stress cycle also induces a decrease in Young’s modulus. A stiffer response is found when switching from loading to unloading. During the unloading, a recovery in tensile strain and crack damage is observed, but some unrecoverable damage remains in the rock joint sample after each loading-unloading cycle. Based on the differential scheme, a constitutive model using two crack-related parameters, i.e., initial crack density and crack density increment, is developed. The model can give a micromechanical explanation and well reproduce the nonlinearity and hysteresis of tensile stress-strain curves.

High-cycle fatigue and fracture behavior of double-side friction stir welded 6082Al ultra-thick plates

For welded structures of precipitation-strengthened aluminum alloys, achieving sound joint with good fatigue property is not an easy task, especially for thick plates. In the present work, ultra-thick 6082Al-T4 alloy plates with 80 mm in thickness were double-side friction stir welded and heat-treated. The high cycle fatigue (HCF) property and fracture behavior of the joint were investigated using trisection specimens in thickness, and the key factors that affect the fracture behavior were addressed. High quality joint was achieved with the three-layered specimens fractured along the lowest hardness zone (LHZ) in the static tensile testing. Further, the fatigue life curves exhibited almost the same distribution tendency, and the same fatigue limit (110 MPa) and fatigue ratio (0.49) were achieved in the three-layered specimens. During fatigue testing, the middle and lower layers fractured along the LHZ, which was similar to those during the static tensile tests, while abnormal fracture occurred in the nugget zone (NZ) of the upper specimen. Further examination revealed that the residual stress in the NZ of the upper layer was tensile stress (+9 MPa) whereas it was compressive stress in the lower layer (–31 MPa). The tensile residual stress together with the external loaded cyclic tensile stress resulted in more serious fatigue damage in the upper layer and led to the abnormal fracture in the NZ.

Hyaluronan suppresses enhanced cathepsin K expression via activation of NF-\u03baB with mechanical stress loading in a human chondrocytic HCS-2/8 cells

Cathepsin K is a protease known to be involved in not only bone remodeling and resorption, but also articular cartilage degradation that leads to osteoarthritis (OA). Hyaluronan (HA) plays a pivotal role in maintaining homeostasis within articular chondrocytes. Intra-articular supplementation of high molecular weight hyaluronan (HMW-HA) has been widely used in OA treatment. However, its prospective mechanism of action is still unclear. In this study, we examined the suppressive effect of HA on enhanced cathepsin K expression induced by mechanical stress loading. A human chondrocytic HCS-2/8 cells were cultured in silicon chambers and subjected to cyclic tensile stress (CTS) loading. CTS loading significantly increased messenger ribonucleic acid and protein expression of cathepsin K, which appeared to be suppressed by pre-treatment with HMW-HA. Activation of nuclear factor-kappa B (NF-κB) was induced by CTS loading, and suppressed by pre-treatment with HMW-HA. Helenalin, a chemical inhibitor of NF-κB, clearly suppressed the enhanced expression of cathepsin K, as well as NF-κB activation induced by CTS loading. The suppressive effect of HMW-HA on enhanced cathepsin K expression via NF-κB inhibition impacts the effectiveness of HMW-HA in OA treatment. Our findings provide new evidence supporting the biological effectiveness of intra-articular HMW-HA injections for treatment of OA.

Expression of HIF‑1α in cycling stretch‑induced osteogenic differentiation of bone mesenchymal stem cells.

During orthodontic treatment, mechanical force is applied to the teeth, and following a series of complex metabolism changes, the position of the teeth in the alveolar bone change. This process is closely associated with primitive bone mesenchymal stem cells (BMSCs), which may differentiate into osteoblasts precursor cell. A hypoxic microenvironment may be caused by orthodontic mechanical forces between the alveolar bone and the root. Hypoxia-inducible factor 1α (HIF-1α) is a specific receptor that adapts to a hypoxic environment. The present study was designed to investigate whether HIF-1α was involved in the osteoblastic differentiation of BMSCs induced by cyclic tensile stress. During this process, HIF-1α mRNA and protein expression were detected using a reverse transcription-quantitative polymerase chain reaction and western blotting. It was revealed that alkaline phosphatase activity increased in a time-dependent manner in three different stretching strength groups, which indicates that cyclic stretch promotes the osteogenic differentiation of BMSCs. The optimal force stage of osteogenesis was an unexpected discovery, which will provide theoretical guidance for selecting the most suitable orthodontic force for tooth movement in clinical orthodontic treatment. Most importantly, all experiments revealed that HIF-1α mRNA and protein were significantly increased following stretching treatment in BMSCs. It was therefore concluded that HIF-1α may be involved in BMSCs modulating osteogenic metabolism during exposure to cyclic stretch and a hypoxic microenvironment, which may prove useful for the reconstruction of a jaw during orthodontic treatment.

TAZ contributes to osteogenic differentiation of periodontal ligament cells under tensile stress.

Bone remodeling during orthodontic treatment is achieved by the osteogenesis of human periodontal ligament cells (PDLCs) subjected to mechanical loadings. Transcriptional co-activator with PDZ-binding motif (TAZ) mediates bone remodeling in response to extracellular mechanical signals. This study aims to investigate the role of TAZ in osteogenesis of PDLCs under tensile strain. A uniaxial cyclic tensile stress (CTS) at 12% elongation and 6 cycles/min (5s on and 5s off) was applied to PDLCs. The osteogenic differentiation was determined by the protein and gene expressions of osteogenic markers using qRT-PCR and Western blot, respectively, and further by alkaline phosphatase (ALP) activity and Alizarin Red S staining. The interaction of TAZ with core-binding factor α1 (Cbfα1) was examined by co-immunoprecipitation. The immunofluorescence histochemistry was used to examine the nucleus aggregation of TAZ and the reorganization of actin filaments. Moreover, small interfering RNA-targeting TAZ (TAZsiRNA) was used for TAZ inhibition and Y-27632 was employed for Ras homologue-associated coiled-coil protein kinase (ROCK) signaling blockage. CTS clearly stimulated the nucleus accumulation of TAZ and its interaction with Cbfα1. CTS-induced osteogenesis in PDLCs was significantly abrogated by the infection with TAZsiRNA, as shown by the decreased stained nodules and protein expressions of Cbfα1, collagen type I, osterix, and osteocalcin, along with the inhibition of β-catenin signaling. Moreover, ROCK inhibition by Y-27632 hindered TAZ nucleus aggregation and its binding with Cbfα1, which subsequently lead to the decreased osteoblastic differentiation of PDLCs. Taken together, we propose that TAZ nucleus localization and its interaction with Cbfα1 are essential for the CTS-induced osteogenic differentiation in PDLCs. And such TAZ activation by CTS could be mediated by ROCK signaling, indicating the pivot role of ROCK-TAZ pathway for PDLCs differentiation.

Discontinuous slow crack growth modeling of semi-elliptical surface crack in high density polyethylene using crack layer theory

Surface flaws in structural materials are most likely to be generated during service time. One of the most general shapes of surface flaws is the semi-elliptical surface crack. Frequently, the slow crack growth (SCG) of a crack has been fitted based on the conventional Paris–Erdogan relationship. However, in the case of engineering plastics, which generally reveal a severe unrecoverable damage zone at the crack tip, the conventional Paris–Erdogan relationship is not appropriate to describe the SCG of a crack. Especially, SCG kinetics of some engineering polymers such as high-density polyethylene (HDPE) affect the SCG characteristics, i.e. non-conventional discontinuous SCG behavior, which cannot be simulated by conventional Paris–Erdogan relationship. It is known that the crack layer (CL) theory, which deals with driving forces of crack and process zone (PZ) together, can be a good mathematical model to simulate such SCG behavior. In this study, the discontinuous SCG of a semi-elliptical surface flaw in HDPE plate under cyclic tensile stress was simulated using the CL theory. Although the CL theory has the advantage of simulating the discontinuous SCG of HDPE accurately, until now the applications have been concentrated on one-dimensional slow crack growth. In this paper, the CL model for two-dimensional surface crack growth for axial and bending loading conditions was developed for the first time. The proposed model is validated with actual test results, and the role of some key CL parameters on discontinuous SCG behavior of a semi-elliptical surface flaw is investigated by intensive parametric studies.