Summary Objective To determine whether autophagy contributes to the pathogenesis of degenerative disc disease (DDD) or retards the intervertebral disc (IVD) degeneration, and investigate the possible ...relationship between compression-induced autophagy and intracellular reactive oxygen species (ROS) in nucleus pulposus (NP) cells in vitro. Methods The autophagosome and autophagy-related markers were used to explore the role of autophagy in rat NP cells under compressive stress, which were measured directly by electronic microscopy, monodansylcadaverine (MDC) staining, immunofluorescence, western blot, and indirectly by analyzing the impact of pharmacological inhibitors of autophagy such as 3-methyladenine (3-MA) and chloroquine (CQ). And the relationship between autophagy and apoptosis was investigated by Annexin-V/propidium iodide (PI)-fluorescein staining. In addition, ROS were measured to determine whether these factors are responsible for the development of compression-induced autophagy. Results Our results indicated that rat NP cells activated autophagy in response to the same strong apoptotic stimuli that triggered apoptosis by compression. Autophagy and apoptosis were interconnected and coordinated in rat NP cells exposed to compression stimuli. Compression-induced autophagy was closely related to intracellular ROS production. Conclusions Enhanced degradation of damaged components of NP cells by autophagy may be a crucial survival response against mechanical overload, and extensive autophagy may trigger autophagic cell death. Regulating autophagy and reducing the generation of intracellular ROS may retard IVD degeneration.
Summary Objective The purposes of this study were to assess whether local anesthetics (LAs), such as ropivacaine and bupivacaine, could induce apoptosis of rabbit annulus fibrosus (AF) cells in vitro ...and further to explore the possible underlying mechanism. Methods Rabbit AF cells at second passage were treated with saline solution and various concentrations of LAs. Apoptosis of AF cells were examined by cell counting kit-8 (CCK-8), Annexin V assays, Hoechst 33342 staining, and Caspase-3, -9 activity assays. The expression of apoptosis-related markers was detected by real-time PCR (RT-PCR) and Western Blot. The JC-1 staining was used to evaluate the change of mitochondrial membrane potential (MMP). Moreover, the levels of reactive oxygen species (ROS) were determined with fluorescent probe DCFH-DA. Results The results of flow cytometry indicated that LAs could induce apoptosis of rabbit AF cells in a dose-dependent manner. Apoptosis was confirmed by cell morphology, condensed nuclei and activation of Caspase-3 and -9. In addition, the molecular data showed that LAs could significantly up-regulate the expression of Bax, accompanied by a significant down-regulation of Bcl-2 expression. Furthermore, we also observed that LAs resulted in alteration of MMP and accumulation of intracellular ROS in AF cells. Blockade of ROS production by N-acetyl- l -cysteine (NAC) inhibited LAs-induced apoptosis. Conclusions These findings suggest that LAs in clinically relevant concentrations could induce apoptosis of rabbit AF cells in vitro , and the mitochondrial pathway was, at least in part, involved in the LAs-mediated apoptosis. Further investigations focusing on the potential cytotoxicity of LAs on IVD cells are needed.
Hot deformation behavior of delta-processed superalloy 718 Wang, Y.; Shao, W.Z.; Zhen, L. ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
03/2011, Volume:
528, Issue:
7
Journal Article
Peer reviewed
▶ The peak stress for hot deformation can be described by the
Z parameter. ▶ The grain size of DRX was inversely proportional to the
Z parameter. ▶ The dissolution of δ phases was greatly accelerated ...under hot deformation. ▶The δ phase stimulated nucleation can serve as the main DRX mechanism.
Flow stress behavior and microstructures during hot compression of delta-processed superalloy 718 at temperatures from 950 to 1100
°C with strain rates of 10
−3 to 1
s
−1 were investigated by optical microscopy (OM), electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM). The relationship between the peak stress and the deformation conditions can be expressed by a hyperbolic-sine type equation. The activation energy for the delta-processed superalloy 718 is determined to be 467
kJ/mol. The change of the dominant deformation mechanisms leads to the decrease of stress exponent and the increase of activation energy with increasing temperature. The dynamically recrystallized grain size is inversely proportional to the Zener–Hollomon (
Z) parameter. It is found that the dissolution rate of δ phases under hot deformation conditions is much faster than that under static conditions. Dislocation, vacancy and curvature play important roles in the dissolution of δ phases. The main nucleation mechanisms of dynamic recrystallization (DRX) for the delta-processed superalloy 718 include the bulging of original grain boundaries and the δ phase stimulated DRX nucleation, which is closely related to the dissolution behavior of δ phases under certain deformation conditions.
Flow behavior and microstructures of superalloy 718 were investigated by hot compression tests performed at temperatures ranging from 950 to 1100
°C with strain rates of 10
−3 to 1
s
−1. The ...dependence of the peak stress on deformation temperature and strain rate can be expressed by a hyperbolic-sine type equation. The activation energy for superalloy 718 is determined to be 443.2
kJ
mol
−1. A power exponent relationship between the peak strain and the
Z parameter is obtained. Microstructure analysis shows that the dynamically recrystallized grain size is inversely proportional to the
Z parameter. The nucleation mechanisms of DRX are closely related to the value of
Z parameter. Under low
Z conditions, DRX nucleation and development are mainly assisted by the formation of twins near the original grain boundaries.
Microstructure evolution during dynamic recrystallization (DRX) of superalloy 718 was studied by optical microscope and electron backscatter diffraction (EBSD) technique. Compression tests were ...performed at different strains at temperatures from 950
°C to 1120
°C with a strain rate of 10
−1
s
−1. Microstructure observations show that the recrystallized grain size as well as the fraction of new grains increases with the increasing temperature. A power exponent relationship is obtained between the dynamically recrystallized grain size and the peak stress. It is found that different nucleation mechanisms for DRX are operated in hot deformed superalloy 718, which is closely related to deformation temperatures. DRX nucleation and development are discussed in consideration of subgrain rotation or twinning taking place near the original grain boundaries. Particular attention is also paid to the role of continuous dynamic recrystallization (CDRX) at both higher and lower temperatures.
A non-isothermal ageing (NIA) process was proposed for an Al–Zn–Mg–Cu alloy aiming to accommodate heating and/or cooling procedures in large components. The precipitation was investigated ...systematically via TEM observation and DSC analysis. The age-hardening and the conductivity variation were examined to evaluate the potential in the strength and the corrosion resistance, respectively. Double cantilever beams (DCB) experiments were carried out to evaluate the stress corrosion cracking (SCC) resistance. A secondary precipitation occurs during the cooling procedure of the NIA process, which leads to an increase in the precipitates number density and thus induces an extra hardening. The secondary precipitation also contributes to the increase of conductivity of the alloy in the most part of the cooling procedure, but leads to a slight decrease at the terminal stage. The alloy׳s resistance to SCC improves persistently as the NIA proceeds. The evolution in microchemistry in grain boundary and adjacent regions is supposed to contribute to the improvement of corrosion resistance. The current study suggests that the NIA process (40°C→190°C→100°C, 20°C/h) is capable of enduing higher mechanical performances and comparable corrosion resistance to Al–Zn–Mg–Cu alloys, as compared with that of the T74 condition, which can be technically significant for ageing treatment of large components.
Deformation behavior and microstructure evolution of 7050 aluminum alloy were investigated by tensile tests conducted at different temperatures (340, 380, 420, and 460
°C) with different strain rates ...of 1.0
×
10
−4, 1.0
×
10
−3, 1.0
×
10
−2 and 0.1
s
−1. The results show that the stress level of the alloy can be presented by a Zener–Holloman parameter in a hyperbolic sine-type equation with the hot activation energy of 256.6
kJ/mol. Ductile transgranular fracture transforms progressively into ductile intergranular (or inter-subgranular) fracture with the decrease of
Z value. At the same time, the soften mechanism of the alloy during high temperature deformation transforms from dynamic recovery to continuous dynamic recrystallization with decreasing
Z value. The main deformation mechanism is usual slipping when the alloy was deformed at high
Z value. Grain boundaries sliding takes part in deformation with low
Z value. Grain boundaries migration plays the role with medium
Z value.
Hot working characteristics and microstructural mechanisms of delta-processed superalloy 718 at various temperatures and strain rates were studied using the processing maps. The results show that ...there are two domains of dynamic recrystallization (DRX) exhibited in the map: one occurring around 1050
°C and 0.001
s
−1 with a peak efficiency of 54%, and the other at 1000
°C and 0.01
s
−1 with a peak efficiency of 46%. The behavior of the pre-precipitated δ phases during hot working has a great effect on the DRX of delta-processed superalloy 718. The flow instability at the strain rates higher than 0.4
s
−1 is suggested to be associated with the inconsistent deformation due to the existence of the undissolved short needle-shaped δ phases.
•Stress relaxation behavior in the simulated age-forming process of the Al–Zn–Mg–Cu alloy can be divided into three stages.•Activation energies are 132kJ/mol, 119kJ/mol and 91kJ/mol, respectively, in ...different stages of the simulated aging-forming process.•Stress relaxation behavior in the simulated age-forming process is controlled by dislocation creep and Coble creep.•A threshold stress presents in the stress relaxation process of the Al–Zn–Mg–Cu alloy.
The stress relaxation behavior of age-forming for an Al–Zn–Mg–Cu alloy was studied using a designed device that can simulate the age forming process. The mechanism of stress relaxation was also revealed through calculating thermal activation parameters and analyzing the microstructures. The results suggested that the stress relaxation behavior of the Al–Zn–Mg–Cu alloy in the simulated age-forming process can be divided into three stages according to the stress level. The three stages of stress relaxation are: (i) the initial high stress stage, (ii) the subsequent middle stress transition stage and (iii) the last low stress equilibrium stage, respectively. The deformation activation energies are 132kJ/mol in the initial high stress stage, 119kJ/mol in the subsequent middle stress transition stage and 91kJ/mol in the last low stress equilibrium stage, respectively. The analysis of the thermal activation parameters and microstructures revealed that dislocation creep was the dominant deformation mechanism in the initial and subsequent stages of the stress relaxation; whereas diffusion creep is the mechanism in the last stage of the stress relaxation. Additionally, a special threshold stress phenomena was present in the stress relaxation of the age-forming process, which was scribed to the interaction between precipitation and dislocation in the Al–Zn–Mg–Cu alloy
The effect of finishing rolling reduction on microstructures and textures of grain oriented silicon steel was researched by optical microscopy, zeiss ultra 55 Scanning Electron Microscope (SEM) and ...Electron Backscatter Diffraction (EBSD) technique severally. The results show that the grain size of hot rolled sheets and decarburized strips decreases, while the center grain size of the normalized sheet increases with the increase of the finishing rolling reduction. The pearlite content increases with the increase of the finishing rolling reduction after normalization. Compare with the previous research, the effect of finishing rolling reduction on the grain size of primary recrystallization is greater than that of roughing rolling reduction, and large rolling reduction is beneficial to the formation of {110} texture.
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