Stress Relaxation Research Articles

Collagen-rich liver-derived extracellular matrix hydrogels augment survival and function of primary rat liver sinusoidal endothelial cells and hepatocytes

Liver sinusoidal endothelial cells (LSECs) are key targets for addressing metabolic dysfunction-associated steatotic liver disease (MASLD). However, isolating and culturing primary LSECs is challenging due to rapid dedifferentiation, resulting in loss of function. The extracellular matrix (ECM) likely plays a crucial role in maintaining the fate and function of LSECs. In this study, we explored the influence of liver-ECM (L-ECM) on liver cells and developed culture conditions that maintain the differentiated function of liver cells in vitro for prolonged periods. Porcine liver-derived L-ECM, containing 34.9 % protein, 0.045 % glycosaminoglycans, and negligible residual DNA (41.2 ng/mg), was utilized to culture primary rat liver cells in generated hydrogels. Proteomic analyses and molecular weight distribution of proteins of solubilized L-ECM revealed the typical diverse ECM core matrisome, with abundant collagens. L-ECM hydrogels showed suitable stiffness and stress relaxation properties. Furthermore, we demonstrated that collagen-rich L-ECM hydrogels enhanced LSECs' and hepatocytes' viability, and reduced the dedifferentiation rate of LSECs. In addition, hepatocyte function was maintained longer by culture on L-ECM hydrogels compared to traditional culturing. These beneficial effects are likely attributed to the bioactive macromolecules including collagens, and mechanical and microarchitectural properties of the L-ECM hydrogels.

Структурные особенности, электронный и спиновый транспорт в эпитаксиальных тонких пленках иридатов

A technique for obtaining high-quality epitaxial films of iridate (SrIrO3) by high-frequency cathode sputtering on strontium titanate (SrTiO3) and neodymium gallate (NdGaO3) substrates has been developed. The structural features and the influence of mechanical stress relaxation in thin films caused by the difference in the lattice sizes of the film and the substrate have been studied using X-ray diffraction. From the analysis of diffraction data, it was found that lattice parameter deformation is observed in the film. This indicates the emergence of stresses due to the mismatch of the lattice parameters of the film and the substrate, which leads to non-uniform stress relaxation in the film. The electronic transport parameters of thin films and the excitation of spin current in SrIrO3/La0.7Sr0.3MnO3 heterostructures have been investigated.

Simulation and Experimental Study on Stress Relaxation Response of Polycrystalline γ-TiAl Alloy under Nanoindentation Based on Molecular Dynamics.

This study employed nano-indentation technology, molecular dynamics simulation, and experimental investigation to examine the stress relaxation behaviour of a polycrystalline γ-TiAl alloy. The simulation enabled the generation of a load-time curve, the visualisation of internal defect evolution, and the mapping of stress distribution across each grain during the stress relaxation stage. The findings indicate that the load remains stable following an initial decline, thereby elucidating the underlying mechanism of load change during stress relaxation. Furthermore, a nano-indentation test was conducted on the alloy, providing insight into the load variation and stress relaxation behaviour under different loading conditions. By comparing the simulation and experimental results, this study aims to guide the theoretical research and practical application of γ-TiAl alloys.

Spring failure analysis of fire-fighting robots under high-temperature action

In order to improve the performance and reliability of fire-fighting robots in high-temperature environments, this paper analyses the spring failure of fire-fighting robots under the action of high temperatures. A hyperbolic sinusoidal rate model is used, combined with finite element analysis and experimental data, to study the creep behavior of the material. Through stress relaxation experiments and theoretical derivation, the creep intrinsic model of the material is established to investigate the failure of the spring under stress relaxation conditions. The results show that under high temperatures, the experimental results are well-fitted.

Stress-Relieving Carboxylated Polythiophene/Single-Walled Carbon Nanotube Conductive Layer for Stable Silicon Microparticle Lithium-Ion Battery Anodes

Silicon is one of the most promising anode materials for next generation Lithium ion batteries (LIBs) on account of its ultrahigh specific capacity (4200 mAh g-1) and relatively low working potential of 0.3 V (vs. Li+/Li). However, practical commercial implementation of silicon poses a great challenge due to technical difficulties such as low conductivity (10-5-10-3 S cm-1), low initial Coulombic efficiency (50-80%) and stress-induced fracture, along with SEI accumulation due to severe volume changes (~400%) inherent in silicon-based anodes.To address these challenges and advance the next generation of LIBs, we present poly[3-(potassium-4-butanoate)thiophene] (PPBT) and single-walled carbon nanotube (SWNT) coated silicon microparticles (Si MPs) (PPBT/SWNT@Si MPs) as active materials for highly stable Si-based anodes for LIB systems. The water-soluble conjugated polymer, PPBT, was selected for its ability to serve as an ion and electron conducting physical/chemical linker (10-5 S cm-1 vs. PVDF; ~ 10-8 S cm-1) to the surface of various high capacity anode active materials systems. In consideration of current practical requirements for Si-based anode materials, Si MPs were selected as starting materials due to their lower surface area than the nanoscale analogs, a characteristic that can further improve LIB bulk capacity. In addition, Si MPs are known to have high initial Coulombic efficiency and industrial compatibility. With the help of PPBT, which facilitates unraveling of entangled single-walled carbon nanotubes, SWNTs were successfully attached to the surface of the active materials. PPBT carboxylate substituents were found to be chemically bound to the Si MP surface, providing an electrochemically conductive environment in intimate contact with the 1D SWNTs and Si MPs.Due to facilitated ion/electron transport kinetics, PPBT/SWNT@SiMP anodes exhibited superior capacity retention and higher reversible capacities, even at a high current density of 8 A g-1, compared to bare Si MP anodes. Improved initial Coulombic efficiency and stable cycling performance over 300 cycles were achieved. In situ Raman spectroscopy was employed to investigate the evolution of stress on the SWNTs during lithiation/delithiation, which elucidated the mechanism underlying the enhancement in PPBT/SWNT@Si MP anode cycling performance. The single-walled carbon nanotubes within the PPBT/SWNT@Si MP anodes consistently exhibited reversible stress recovery and 45 % less tensile stress variation after the 10th cycle than SWNT@Si MP control anodes fabricated by direct mixing of the microparticles with SWNTs to create SWNT@Si MPs.Combined, the results suggest that a well-developed conductive interface can enhance the rate performance, and improve electrode stability and Coulombic efficiency. Furthermore, the PPBT/SWNT coating directly bound to the Si MP surface provides for efficient stress relaxation of Si-based electrodes, resulting in reversible lithiation/delithiation, low electrode resistance, and reduced SEI layer formation.

Enhanced stress relaxation behavior via basal 〈a〉 dislocation activity in Zircaloy-4 cladding

This work evaluates the stress relaxation behavior of textured Zircaloy-4 cladding to understand how mechanical anisotropy influences pellet-cladding interactions. Uniaxial and biaxial stress relaxation tests are performed using full-tube axial tension and internal pressurization, respectively, aiming to achieve 0.25 %, 1 %, and 2 % equivalent strains in the cladding samples at a temperature of 300 °C. Internal pressure relaxation test results display enhanced stress relaxation compared to axial testing results, particularly for samples loaded beyond yield. Results of electron backscatter diffraction indicate increased deformation microstructure during loading and increased strain homogenization and recovery during relaxation for samples loaded via internal pressurization. Analysis indicates that the increased production and activity of basal 〈a〉 dislocations play a significant role in the enhanced relaxation measured in samples subjected to internal pressurization.

Numerical modelling of multiple sclerosis: A tissue-scale model of brain lesions

Multiple Sclerosis (MS) is an autoimmune condition leading to the degeneration of brain tissue, occurring when the immune system attacks the myelin sheath surrounding axons of white brain matter thereby disrupting brain signals. This study aimed to evaluate how MS lesions alter stress distribution through grey and white brain matter with lesions (active, chronic, and inactive). A linear viscoelastic model represents the tissue-scale dynamic deformation and time dependency of brain tissue. A Prony series expansion was used to model viscous effects including stress relaxation. An elastic modulus, within the viscoelastic model, was either reduced by 11 % for active lesions, or increased by 35 % increase for inactive lesions. These material properties were then implemented to model healthy tissue, active, chronically inflamed, and inactive lesions. Finite element analysis enabled stress evaluation in response to a peak cyclic displacement of 0.5 mm (1 % strain) with the healthy model acting as a control model. Chronic lesions had the largest effect on stress induced, in terms of high (171 Pa) and low stress (108 Pa). Inactive lesions induced an increase in stress of 11 Pa with areas of low stress (105 Pa). Active lesions caused the least deviation in peak induced stress (7 Pa). In conclusion, a hierarchy in stress induced across the lesion types has been found, from highest to lowest: chronic, inactive and active, with potential implications for lesion progression. In conclusion, MS lesions within brain tissue should model lesions, avoid assuming homogeneity during degeneration, and should distinguish between active and passive lesions.

Covalent adaptable polymer networks with CO2-facilitated recyclability

Cross-linked polymers with covalent adaptable networks (CANs) can be reprocessed under external stimuli owing to the exchangeability of dynamic covalent bonds. Optimization of reprocessing conditions is critical since increasing the reprocessing temperature costs more energy and even deteriorates the materials, while reducing the reprocessing temperature via molecular design usually narrows the service temperature range. Exploiting CO2 gas as an external trigger for lowering the reprocessing barrier shows great promise in low sample contamination and environmental friendliness. Herein, we develop a type of CANs incorporated with ionic clusters that achieve CO2-facilitated recyclability without sacrificing performance. The presence of CO2 can facilitate the rearrangement of ionic clusters, thus promoting the exchange of dynamic bonds. The effective stress relaxation and network rearrangement enable the system with rapid recycling under CO2 while retaining excellent mechanical performance in working conditions. This work opens avenues to design recyclable polymer materials with tunable dynamics and responsive recyclability.

Spectrin mediates 3D-specific matrix stress-relaxation response in neural stem cell lineage commitment.

While extracellular matrix (ECM) stress relaxation is increasingly appreciated to regulate stem cell fate commitment and other behaviors, much remains unknown about how cells process stress-relaxation cues in tissue-like three-dimensional (3D) geometries versus traditional 2D cell culture. Here, we develop an oligonucleotide-crosslinked hyaluronic acid-based ECM platform with tunable stress relaxation properties capable of use in either 2D or 3D. Strikingly, stress relaxation favors neural stem cell (NSC) neurogenesis in 3D but suppresses it in 2D. RNA sequencing and functional studies implicate the membrane-associated protein spectrin as a key 3D-specific transducer of stress-relaxation cues. Confining stress drives spectrin's recruitment to the F-actin cytoskeleton, where it mechanically reinforces the cortex and potentiates mechanotransductive signaling. Increased spectrin expression is also accompanied by increased expression of the transcription factor EGR1, which we previously showed mediates NSC stiffness-dependent lineage commitment in 3D. Our work highlights spectrin as an important molecular sensor and transducer of 3D stress-relaxation cues.

Abstract Tu048: Viscoelastic remodeling of the left ventricular myocardium in myocardial infarction

Introduction. Myocardial infarction (MI) leads to cardiac myocyte death and the formation of a fibrotic scar in the left ventricular myocardium (LV). LV free wall (LVFW) remodeling in MI is known to significantly alter the biomechanical response of the LV and, in turn, LV function. While changes in the elastic behavior of the LVFW in MI have been reported, changes in the viscoelastic behavior of the LVFW remain understudied. Our objective in this study was to determine the changes in the stress relaxation behavior of the LVFW in MI. Methods. MI was induced in rats via the ligation of the LAD artery, and hearts were harvested for three groups: sham, 2-week (2wk), and 4wk post-MI (n=3 for each group). Prior to sacrifice, echocardiography was performed to estimate ejection fraction (EF). LVFW specimens were harvested and subjected to viscoelastic stress relaxation tests. The specimens were stretched to 15% along the circumferential and longitudinal directions and allowed to relax. The stress was normalized against the peak (initial) stress for each specimen for proper comparison across the groups. Results. The EF at 2wk and 4wk specimens was reduced compared to the sham specimens (Fig. 1A). The 4wk post-MI specimens showed slower stress relaxation compared to that in the sham and 2wk specimens in both directions (Figs. 1B, C). Considering a 2-minute stress relaxation span, the normalized stress in the 4wk specimens was significantly higher than the sham specimens in both directions (Fig. 1D). Conclusions. Our results suggest that the viscoelastic relaxation rate of the LVFW diminishes at late MI timepoints. A larger and more mature scar in the LVFW is expected to contribute to slower relaxation at late MI. Future studies can determine the effect of LVFW viscoelastic remodeling on LV diastolic dysfunction and impaired relaxation in MI.

Significant reduction of anisotropy in stress relaxation aging and mechanical properties improvement for 2195 Al-Cu-Li alloy subjected to plastic loading

Although the plastic loading can enhance creep deformation and yield strength, the anisotropic Stress Relaxation Aging (SRA) behavior and mechanism under plastic loading remain unclear, which presents a significant challenge in accurately shaping aluminum alloy panels. In this study, the SRA behavior of 2195-T4 Al-Cu-Li alloys were thoroughly studied under initial loading stresses within the elastic (210/250 MPa) and plastic (380/420 MPa) ranges at 180 ℃ by stress relaxation and tensile tests as well as microstructure characterization. The findings reveal that compared with those under elastic loadings, in-plane anisotropy (IPA) values of the stress relaxation amount, yield strength and fracture elongation under plastic loadings are reduced by 60%-80%, 70%-90% and 72%-89%, respectively. Similarly, IPA values of precipitate size in grains and Precipitation-Free Zones (PFZ) width at grain boundaries under plastic loading decrease by 31.4% and 94.4% respectively. These results indicate plastic loading significantly weakens the anisotropic SRA behavior, owing to numerous uniformly distributed fine T1 phases and small IPA values of both T1 precipitates size and PFZ width in various loading directions. Compared with those of elastic loading-aged alloys, yield strength of plastic loading-aged alloys shows high strength-ductility because of the combined effect of closely dispersed fine T1 precipitates, narrowed PFZ and numerous sheared and rotated T1 phases at different locations during tensile process. The uniformly distributed larger Kernel Average Misorientation (KAM) and Schmidt factor values of the plastic loading-aged alloy, as well as the cross-slip generated, also help to enhance the strength and ductility of the alloy.

Relaxation of residual stress in welded plates during long life fatigue loading

The presence of residual stress in welded components can have a significant impact on fatigue response. Residual stresses were assessed in thick welded A36 cantilever specimens (T-specimens) at the fatigue critical area. Testing involved subjecting the T-specimens to varying bending stresses and load cycles, leading to different levels of local plasticity at the weldtoe. Extensive X-ray diffraction (XRD) measurements were conducted to analyze the residual stress distribution near the weldtoe. Residual stress states were evaluated in both as-welded specimens and those subjected to fatigue loading with strain amplitudes up to 0.001 at the weldtoe stress concentration zone. The findings suggest that fatigue loading can induce changes in the welding-induced residual stress field, ranging from moderate to significant alterations. Therefore, fatigue life predictions should consider the potential evolution of residual stresses due to cyclic loading, including the effects of cyclic stress relaxation in fatigue life calculations.

Multisensory Environment Program Improving Relaxation and Reducing Stress and Anxiety for Community Health

Abstract Date Presented 03/21/24 Research exploring the impact of a customized multisensory environment experience on self-reported stress, anxiety, and relaxation with adult community participants of varying abilities. Qualitative and quantitative analysis indicate positive impact. Primary Author and Speaker: Nicole Halliwell Additional Authors and Speakers: John R. Patro, Francesca Storino, Tori Aguilar

Cause analysis of the compression spring stress relaxation of circuit breaker operating mechanism in a 220 kV Substation

Cause analysis of the compression spring stress relaxation of circuit breaker operating mechanism in a 220 kV Substation

Symmetrical vortices and laminar dust flow induced by an intense electron beam interacting with a strongly coupled dusty plasma

A strongly coupled quasi-two-dimensional dusty plasma confined electrostatically in the plasma sheath of a radio frequency (RF) plasma is irradiated by a collimated and mono-energetic pulsed electron beam (e-beam) with an energy of 13 keV and a high peak current per pulse of 30 mA. A stream of rapidly moving charged dust particles is created inside the dust crystal due to the drag force of the electrons in the e-beam. The dust flow is split into two symmetrical branches when it reaches the boundary of the round dust crystal, each following the limit of the circular confining region. This results in the formation of a double vortex flow pattern with the dust particles being transported along the irradiation direction and then aside, eventually back to the entrance position of the e-beam. The observed flow regime is laminar at all times, with the speed in the central region increasing up to 12 mm s−1 in the first 200 ms and then diminishing gradually to a steady value of about 5–6 mm s−1 during a stress relaxation time period of 360 ms. The vorticity follows a similar trend with peak values −3.8 and 3.8 s−1 and steady state values between −2.5 and 2.5 s−1 in the two symmetrical vortices. Time-resolved particle-image-velocimetry and particle-tracking-velocimetry are used to characterize the flow. Molecular dynamics simulations confirm qualitatively the experimental observations showing dust stream and double vortex formation.

Sustained Strain Applied at High Rates Drives Dynamic Tensioning in Epithelial Cells.

Epithelial cells experience long lasting loads of different magnitudes and rates. How they adapt to these loads strongly impacts tissue health. Yet, much remains unknown about their stress evolution under sustained strain. Here, by subjecting cell pairs to sustained strain, we report a bimodal stress response, where in addition to the typically observed stress relaxation, a subset of cells exhibits a dynamic tensioning process with significant elevation in stress within 100s, resembling active pulling-back in muscle fibers. Strikingly, the fraction of cells exhibiting tensioning increases with increasing strain rate. The tensioning response is accompanied by actin remodeling, and perturbation to actin abrogates it, supporting cell contractility's role in the response. Collectively, our data show that epithelial cells adjust their tensional states over short timescales in a strain-rate dependent manner to adapt to sustained strains, demonstrating that the active pulling-back behavior could be a common protective mechanism against environmental stress.

Cross-section distortion and springback characteristics of double-cavity aluminum profile in force controlled stretch-bending

A 3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method. Considering the computational accuracy and efficiency, the optimal choices of numerical parameters and algorithms in FE modelling were determined. The formation mechanisms of cross-section distortion and springback were revealed. The effects of pre-stretching, post-stretching, friction, and the addition of internal fillers on forming quality were investigated. The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress. The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile. As aluminum profile is gradually attached to bending die, the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape. After unloading the forming tools, cross-section distortion decreases obviously due to the stress relaxation, with a maximum distortion difference of 13% before and after unloading. As pre-stretching and post-stretching forces increase, cross-section distortion increases gradually, while springback first decreases and then remains unchanged. With increasing friction between bending die and profile, cross-section distortion slightly decreases, while springback increases. Cross-section distortion decreases by 83% with adding PVC fillers into the cavities of profile, while springback increases by 192.2%.

Influence of monomer structure and catalyst concentration on topological transition and dynamic properties of dicarboxylic acid‐epoxy vitrimers

AbstractThis study delineates the dependence of thermophysical behavior of acid‐epoxy vitrimers on their formulation. The stress relaxation due to the bond exchange reaction and the glass transition temperature of acid epoxy vitrimers are investigated, with respect to the influence of catalyst content and acid chain length. This is carried out for a range of dicarboxylic acids and catalyst concentrations formulated and characterized using calorimetry and dynamic mechanical analysis. The influence of acid chain length on the bond exchange rate, topological transition, and glass transition temperatures of the vitrimers is found to be significant. The activation energy of the exchange reaction varies over a wide range from 73 to 104 kJ/mol and the topology freezing temperature from 66 to 136°C with the behavior governed by the interplay between crosslinking density, network flexibility and density and distance of functional groups, with an increase of catalyst concentration leading to lower topological transition temperature and the dependence on chain length showing non‐monotonic behavior. The glass transition decreases by about 30°C as the carbon chain length increases from 6 to 14 carbons due to enhanced monomer flexibility and is not affected by the concentration of catalyst.

Strengthening Ti3SiC2/Cu brazed joint assisted with cold spray additive manufacturing: Lower brazing temperature through interdiffusion and graded reinforcement for stress relaxation

Graded composite fillers exhibit unique advantages in alleviating residual stress in ceramic/metal brazed joints. However, traditional methods for preparing graded composite fillers are often complex and may deplete their strengthening phases. In this study, cold spray additive manufacturing was employed to fabricate yttria-stabilized zirconia (YSZ)-Ti25Zr25Ni25Cu25-Ag graded composite coatings on Cu substrates to serve as fillers. The graded composite coatings and the resultant Ti3SiC2/Cu brazed joints were systematically characterized to elucidate the deposition mechanism of the coatings and its residual stress-relaxed mechanism. The bondings between particles in the coatings, based on their plastic deformation ability, were classified into noncrystalline weak bonds and homogeneous strong bonds. Both bondings facilitated the elemental interdiffusion between filler and Cu substrate during the heating process, which contributed to the formation of Ag-Cu eutectic. This significantly reduced the required brazing temperature and its induced residual stress. Furthermore, the solid phase transformation of graded-distributed YSZ within the brazing seam from tetragonal to monoclinic achieved a smooth thermal transition and releasing residual stress at the same time. Consequently, the shear strength of the brazed joint reached to the highest value of 110.23 ± 3.45 MPa, which was Much higher than the previously reported values. This study introduces a novel method for residual stress relaxation assisted with cold spray technology and broadens its application in the brazing field.

Degradability tunes ECM stress relaxation and cellular mechanics.

In native extracellular matrices (ECM), cells can use matrix metalloproteinases (MMPs) to degrade and remodel their surroundings. Likewise, synthetic matrices have been engineered to facilitate MMP-mediated cleavage that enables cell spreading, migration, and interactions. However, the intersection of matrix degradability and mechanical properties has not been fully considered. We hypothesized that immediate mechanical changes result from the action of MMPs on the ECM and that these changes are sensed by cells. Using atomic force microscopy (AFM) to measure cell-scale mechanical properties, we find that both fibrillar collagen and synthetic degradable matrices exhibit enhanced stress relaxation after MMP exposure. Cells respond to these relaxation differences by altering their spreading and focal adhesions. We demonstrate that stress relaxation can be tuned through the rational design of matrix degradability. These findings establish a fundamental link between matrix degradability and stress relaxation, which may impact a range of biological applications.