Application Of Mechanical Stress Research Articles

Heterogeneity of Endothelial Cells Impacts the Functionality of Human Pancreatic In Vitro Models.

Endothelial cells (ECs) play a crucial role in maintaining tissue homeostasis and functionality. Depending on their tissue of origin, ECs can be highly heterogeneous regarding their morphology, gene and protein expression, functionality, and signaling pathways. Understanding the interaction between organ-specific ECs and their surrounding tissue is therefore critical when investigating tissue homeostasis, disease development, and progression. In vitro models often lack organ-specific ECs, potentially limiting the translatability and validity of the obtained results. The goal of this study was to assess the differences between commonly used EC sources in tissue engineering applications, including human umbilical vein ECs (HUVECs), human dermal microvascular ECs (hdmvECs), and human foreskin microvascular ECs (hfmvECs), and organ-specific human pancreatic microvascular ECs (hpmvECs), and test their impact on functionality within an in vitro pancreas test system used for diabetes research. Utilizing high-resolution Raman microspectroscopy and Raman imaging in combination with established protein and gene expression analyses and exposure to defined physical signals within microfluidic cultures, we identified that ECs exhibit significant differences in their biochemical composition, relevant protein expression, angiogenic potential, and response to the application of mechanical shear stress. Proof-of-concept results showed that the coculture of isolated human islets of Langerhans with hpmvECs significantly increased the functionality when compared with control islets and islets cocultured with HUVECs. Our study demonstrates that the choice of EC type significantly impacts the experimental results, which needs to be considered when implementing ECs into in vitro models.

Mechanically Enhanced Detoxification of Chemical Warfare Agent Simulants by a Two-Dimensional Piezoresponsive Metal-Organic Framework.

Chemical warfare agents (CWAs) refer to toxic chemical substances used in warfare. Recently, CWAs have been a critical threat for public safety due to their high toxicity. Metal-organic frameworks have exhibited great potential in protecting against CWAs due to their high crystallinity, stable structure, large specific surface area, high porosity, and adjustable structure. However, the metal clusters of most reported MOFs might be highly consumed when applied in CWA hydrolysis. Herein, we fabricated a two-dimensional piezoresponsive UiO-66-F4 and subjected it to CWA simulant dimethyl-4-nitrophenyl phosphate (DMNP) detoxification under sonic conditions. The results show that sonication can effectively enhance the removal performance under optimal conditions; the reaction rate constant k was upgraded 45% by sonication. Moreover, the first-principle calculation revealed that the band gap could be further widened with the application of mechanical stress, which was beneficial for the generation of 1O2, thus further upgrading the detoxification performance toward DMNP. This work demonstrated that mechanical vibration could be introduced to CWA protection, but promising applications are rarely reported.

Research progress on the regulatory mechanism of integrin-mediated mechanical stress in cells involved in bone metabolism.

Mechanical stress is an internal force between various parts of an object that resists external factors and effects that cause an object to deform, and mechanical stress is essential for various tissues that are constantly subjected to mechanical loads to function normally. Integrins are a class of transmembrane heterodimeric glycoprotein receptors that are important target proteins for the action of mechanical stress stimuli on cells and can convert extracellular physical and mechanical signals into intracellular bioelectrical signals, thereby regulating osteogenesis and osteolysis. Integrins play a bidirectional regulatory role in bone metabolism. In this paper, relevant literature published in recent years is reviewed and summarized. The characteristics of integrins and mechanical stress are introduced, as well as the mechanisms underlying responses of integrin to mechanical stress stimulation. The paper focuses on integrin-mediated mechanical stress in different cells involved in bone metabolism and its associated signalling mechanisms. The purpose of this review is to provide a theoretical basis for the application of integrin-mediated mechanical stress to the field of bone tissue repair and regeneration.

Characterizing piezoelectric materials under mechanical stress in liquid media: An electrokinetic approach

Piezoelectric materials are an integral part of the modern world, as they find wide-ranging applications in various advanced domains such as telecommunications, automotive, electronics, and aerospace. Recently, these materials gained interest also for applications in liquid environments across diverse fields, including biomedical engineering, purification systems, electrocatalysis, fluid characterizations and micro/nano electromechanical systems (MEMS/NEMS). Despite their growing importance, many questions remain unanswered regarding their characterization and the evaluation of their performance in liquid media. It is critical to understand how these materials interact with surrounding ionic species under mechanical stress application. To address these questions, a novel experimental setup has been designed to characterize piezoelectric materials through electrokinetic measurements in a liquid environment. A polarized piezoelectric sample (lead zirconate titanate) is subjected to a mechanical stress, which is known to influence the piezoelectric surface charge state. This change in surface charge state can be monitored through measurement of the streaming potential. The results indicate that there is a strong correlation between the applied mechanical stress and the electrokinetic response of the piezoelectric sample. When the sample is subjected to a dynamic stress variation, its electrokinetic response closely follows the profile of the applied stress. In addition, the stress applied to the piezoelectric sample directly impacts the flow cell’s resistance. A non-piezoelectric material (alumina) is also subjected to similar stress conditions. Both electrokinetics and resistance of the flow cell remain almost unchanged for the non-piezoelectric alumina sample during the stress application. Finite element modeling is employed to model variation of surface charge on the piezoelectric sample due to stress application. The piezoelectric model is then coupled with electrokinetic and resistance models to explore the effect of stress on the electrical responses of the system. The modeling results exhibit high degree of consistency with the experimental observations.

Stress‐Assisted Erosion of Poly(Glycerol‐Co‐Sebacate) Acrylate Elastomer

AbstractIn this work, a systematic investigation is conducted on stress‐assisted erosion of the photocurable and degradable elastomer poly(glycerol sebacate) acrylate (PGSA). Without external stress, it is confirmed that the elastomer undergoes surface erosion in an aqueous environment. Upon the application of mechanical stress, the results revealed that the surface erosion rate is dramatically accelerated. By studying the stress corrosion cracking (SCC) phenomena, it is demonstrated that the crack growth speed depends on the applied load and is significantly faster than the surface erosion rate of the elastomer. It is further shown that with decreasing the cross‐link density of the elastomer, the crack growth speed during SCC can be slowed down due to the increased viscoelasticity of the material.

Effect of Pre-Rolling on Microstructure and Fatigue Crack Propagation Resistance of a Third-Generation Al-Li Alloy.

The effect of pre-rolling on the microstructure and fatigue crack (FC) propagation resistance of the Al-Cu-Li alloy was studied using tensile testing, fatigue testing, transmission electron microscopy (TEM), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The results revealed that reducing the alloy thickness through pre-rolling by up to 12% enhanced both tensile strength and yield strength, albeit at the expense of reduced elongation. In addition, the FC growth rate decreased by up to 9% pre-rolling, reaching the minimum, while the application of additional mechanical stress during the pre-rolling increases this parameter. Deformations in the Al-Cu-Li alloy with less than a 9% thickness reduction were confined to the surface layer and did not extend to the central layer. This non-uniform deformation induced a compressive stress gradient in the thickness direction and led to an inhomogeneous distribution of T1 phase, resembling the structure generated by shot peening. The superior FC propagation resistance in the 9% pre-rolled alloy could be primarily attributed to the optimum balance of compressive residual stress and work hardening.

On-Demand Control of Short-Wave Infrared Light Transparency Based on Stimuli-Responsive Association of Tetrathiafulvalene Radical Cation.

The light-transmissive properties of a solid-state tetrathiafulvalene radical cation-bis(trifluoromethanesulfonyl)imide, 1-C5•+•NTf2-, underwent instantaneous changes in the short-wave infrared (SWIR) region (1000-2500 nm) due to upon exposure to solvent vapor or the application of mechanostress at room temperature. The initial solid state of 1-C5•+•NTf2- exhibited strong absorption in the near-infrared (NIR; 700-1000 nm) and SWIR regions, whereas the absorption in the SWIR region was significantly diminished in the stimulated state induced by dichloromethane vapor. Upon cessation of vapor stimulation, the solid state spontaneously and promptly reverted to its original state, characterized by absorption bands in the NIR/SWIR region. Moreover, the SWIR absorption was absent upon the application of mechanical stress using a steel spatula. The reversal was fast and occurred within 10 s. These changes were visualized using a SWIR imaging camera under 1450-nm light irradiation. Experimental investigations demonstrated that the transparency to the SWIR light in the solid states was modulated through significant structural transformations of the associated radical cations, with transitions between columnar and isolated π-dimer structures under ambient and stimulated conditions, respectively.

On‐Demand Control of Short‐Wave Infrared Light Transparency Based on Stimuli‐Responsive Association of Tetrathiafulvalene Radical Cations

AbstractThe light‐transmissive properties of a solid‐state tetrathiafulvalene radical cation‐bis(trifluoromethanesulfonyl)imide, 1‐C5⋅+ ⋅ NTf2−, underwent instantaneous changes in the short‐wave infrared (SWIR) region (1000–2500 nm) upon exposure to solvent vapor or the application of mechanostress at room temperature. The initial solid state of 1‐C5⋅+ ⋅ NTf2− exhibited strong absorption in the near‐infrared (NIR; 700–1000 nm) and SWIR regions, whereas the absorption in the SWIR region was significantly diminished in the stimulated state induced by dichloromethane vapor. Upon cessation of vapor stimulation, the solid state spontaneously and promptly reverted to its original state, characterized by absorption bands in the NIR/SWIR region. Moreover, the SWIR absorption was absent upon the application of mechanical stress using a steel spatula. The reversal was fast and occurred within 10 s. These changes were visualized using a SWIR imaging camera under 1450‐nm light irradiation. Experimental investigations demonstrated that the transparency to the SWIR light in the solid states was modulated through significant structural transformations of the associated radical cations, with transitions between columnar and isolated π‐dimer structures under ambient and stimulated conditions, respectively.

Design and fabrication of nanometer measurement platform for better understanding of silicon mechanical properties

Semiconductor industry is experiencing unprecedented growth, still driven by Moore's law, which is continually delivering devices with improved performance at lower costs. The continuation of this development places the industry in a divergent trade-off between economic attractiveness, technological feasibility, and the need for further performance improvement. Since the mainstream semiconductor technologies are silicon-based, new disruptive innovations are needed to gain additional performance margins. The use of nanowires is the preferred approach for preserving electrostatic control in the MOS transistor channel, and the application of mechanical stress is a booster of carrier mobility. It is in this context that this paper presents the design, fabrication, theoretical modeling, and characterization of a measurement platform to characterize the mechanical tensile stress of extremely narrow Si nanowires as small as 14.2 ± 1.12 nm in width. The proposed measurement platform enables a precise control of uniaxial strain, in terms of both amplitude and location, through the implementation of a stoichiometric Si3N4 pulling strand exerting a high tensile force on silicon nanowires. Reported devices are fabricated using a silicon-on-insulator wafer with fully complementary metal–oxide–semiconductor-compatible processing and top-down approach. It is observed that the mechanical strength of nanostructured Si is size-dependent and increases with miniaturization. Characterization revealed a record tensile strength value of 7.53 ± 0.8% (12.73 ± 1.35 GPa) for the narrowest nanowires fabricated using a top-down approach.

Emission or scattering? Discriminating the origin of responsiveness in AIEgen‐doped smart polymers using the TPE dye

AbstractAggregation‐induced emission (AIE) luminogens are attractive dyes to probe polymer properties that depend on changes in chain mobility and free volume. When embedded in polymers the restriction of intramolecular motion (RIM) can lead to their photoluminescence quantum yield (PLQY) strong enhancement if local microviscosity increases (lowering of chain mobility and free volume). Nonetheless, measuring PLQY during stimuli, i.e. heat or mechanical stress, is technically challenging; thus, emission intensity is commonly used instead, assuming its direct correlation with the PLQY. Here, by using fluorescence lifetime as an absolute fluorescence parameter, it is demonstrated that this assumption can be invalid in many commonly encountered conditions. To this aim, different polymers are loaded with tetraphenylenethylene (TPE) and characterized during the application of thermal and mechanical stress and physical aging. Under these conditions, polymer matrix transparency variation is observed, possibly due to local changes in refractive index and to the formation of microfractures. By combining different characterization techniques, it is proved that scattering can affect the apparent emission intensity, while lifetime measurements can be used to ascertain whether the observed phenomenon is due to modifications of the photophysical properties of AIE dyes (RIM effect) or to alterations in the matrix optical properties.

Vertical Piezo-Optoelectronic Coupling in a 3C-SiC/Si Heterostructure for Self-Powered and Highly Sensitive Mechanical Sensing.

This paper presents a novel self-powered mechanical sensing based on the vertical piezo-optoelectronic coupling in a 3C-SiC/Si heterojunction. The vertical piezo-optoelectronic coupling refers to the change of photogenerated voltage across the 3C-SiC/Si heterojunction upon application of mechanical stress or strain. The effect is elucidated under different photoexcitation conditions and under varying tensile and compressive strains. Experimental results show that the relationship between the vertical photovoltage and applied strain is highly linear, increasing under the tensile strain while decreasing under the compressive strain. The highest sensitivities to tensile and compressive strains are 0.146 and 0.058 μV/ppm/μW, respectively, which are about 220 and 360 times larger than those of the lateral piezo-optoelectronic coupling reported in literatures. These extremely large changes in vertical photovoltages are explained by the alteration in effective mass, energy band shift, and repopulation of photogenerated holes in out-of-plane, in-plane longitudinal, and in-plane transverse directions when strains are exerted on the heterojunction. The significant enhancement of strain sensitivity will pave the way for development of ultrasensitive and self-powered mechanical sensors based on the proposed vertical piezo-optoelectronic coupling.

Effect of stress on the dissolution/crystallization of apatite in aqueous solution: a thermochemical equilibrium study.

Bone mineralization is critical to maintaining tissue mechanical function. The application of mechanical stress via exercise promotes bone mineralization via cellular mechanotransduction and increased fluid transport through the collagen matrix. However, due to its complex composition and ability to exchange ions with the surrounding body fluids, bone mineral composition and crystallization is also expected to respond to stress. Here, a combination of data from materials simulations, namely density functional theory and molecular dynamics, and experimental studies were input into an equilibrium thermodynamic model of bone apatite under stress in an aqueous solution based on the theory of thermochemical equilibrium of stressed solids. The model indicated that increasing uniaxial stress induced mineral crystallization. This was accompanied by a decrease in calcium and carbonate integration into the apatite solid. These results suggest that weight-bearing exercises can increase tissue mineralization via interactions between bone mineral and body fluid independent of cell and matrix behaviours, thus providing another mechanism by which exercise can improve bone health. This article is part of a discussion meeting issue 'Supercomputing simulations of advanced materials'.

A facile photoinitiated polymerisation route for the preparation of photonic elastomers with chiral nematic order

ABSTRACTPhotonic crystal elastomers that can change colour upon stretching or compression have potential applications in mechanical sensors and optical coatings. However, facile synthetic strategies are required for these materials to be made on a commercially viable scale. To address this issue, we report a photoinitiated polymerisation method to prepare stretchable chiral nematic cellulose nanocrystal (CNC) elastomer composites that exhibit reversible visible colour upon the application of mechanical stress. The initial CNC-elastomer composite is colourless, but when it is stretched (or compressed), the helical pitch of the chiral nematic structure is reduced to lengths corresponding to the wavelengths of the visible region, resulting in colouration. By increasing the percentage elongation of the material (ca. 50–300%), the structural colour can be tuned from red to blue. The colour of the material was characterised by reflectance optical spectroscopy and reflectance circular dichroism to confirm the wavelength and polarisation of the reflected light.

Physical, Mechanical and Transfer Properties at the Steel-Concrete Interface: A Review

The steel-concrete interface (SCI) is extensively acknowledged to affect the durability of reinforced concrete. The main objective of this paper is to conduct a state-of-the-art review that contributes to sufficient knowledge on the determination of the SCI properties and its effect on the overall performance of reinforced concrete elements. The physical characteristics at the SCI are influenced by segregation, flow, hydration, and drying shrinkage of concrete, hence affecting the presence of voids and cracks within this interface. The bond strength is one of the measures of the SCI and this is conducted through pull-out, push-in, and tie-beam testing. It was shown that the rebar shape and diameter, the anchorage length, the concrete grade strength, binder type (geopolymer concrete), and the distribution of aggregates have a significant effect on the interface properties and behavior, where geopolymer concrete offered improved bond behavior over conventional concrete. Various studies have demonstrated that the presence of the steel-concrete interface and the application of mechanical stresses contribute to the flow transfer (inflow/outflow) through the reinforced concrete structure. Some of these studies focused on the initial state of the SCI within the structure, and some conducted tests with shear loading on the SCI. Regarding the transfer properties at the SCI, it was shown that the presence of steel rebar, crack dimensions, degree of saturation of concrete, and the concrete mix design, influence the permeability of the concrete, specifically at the vicinity of the SCI, because of the development of micro-cracks at the interface. In other studies, the shear stresses were also found to affect the transfer properties through the SCI. Researchers have implemented several software solutions such as finite element models on ABAQUS and mesoscale numerical simulations and have used machine learning models that predict and verify the effects of bond failure behavior at the SCI. Good agreement was established between the numerical and actual experimental results. The influence of different exposure conditions on the steel-concrete interface that change throughout time needs to be dealt with, which includes moisture-related environmental conditions, variation in temperature, and chemical exposure. Furthermore, the influence of structural loading, such as “creep effect”, deterioration (ageing) of material must be studied at the interface. The studies were limited to short-term behavior.

Electrical Reliability of Flexible Low-Temperature Polycrystalline Oxide Thin-Film Transistors Under Mechanical Stress

Electronic devices based on flexible displays have been developed for use in various applications. Upon bending such devices, the applied mechanical force deteriorates the reliability of the devices. Therefore, a high bending reliability that is influenced by tensile and compressive forces that vary depending on the bending radius of curvature must be secured to ensure a reliable device operation. In this study, we investigated the electrical characteristics of flexible low-temperature polycrystalline silicon (LTPS) and amorphous indium–gallium–zinc–oxide (a-IGZO) thin-film transistors (TFTs) on polyimide (PI) substrate and subsequently conducted reliability evaluation of the devices under mechanical stress by applying negative bias temperature illumination stress (NBTIS). The degradations in the electrical properties, such as threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> ) shift, OFF-state current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {off}}$ </tex-math></inline-formula> ), and subthreshold slope (SS), and reliability, increased, and the reliability worsened, as the tensile force increased under decreasing radius of curvature, whereas relatively low degradation occurred under compressive force. A tensile stress-induced increase in grain boundary state density in polycrystalline silicon (poly-Si) and oxygen vacancy in a-IGZO were verified by density of state (DOS) extraction; the cracks occurring due to tensile stress were optically analyzed; the external moisture penetration along the cracks further degrades the device characteristics. This study provides an analysis of device design for ensuring reliability under the application of mechanical stress, thereby contributing to the development of reliable flexible technology.

Effect of uniaxial strain on the excitonic properties of monolayer C3N : A symmetry-based analysis

In recent years, the application of mechanical stress has become a widespread experimental method to tune the electronic and optical properties of two-dimensional (2D) materials. In this work, we investigate the impact of uniaxial tensile strain along zigzag and armchair directions on the excitonic properties of graphene-like ${\mathrm{C}}_{3}\mathrm{N}$, a single-layer indirect-gap material with relevant mechanical and optical properties. To do that, we develop a tight-binding Bethe-Salpeter equation framework based on a Wannier-function description of the frontier bands of the system, and use it to compute both dark and bright excitons of ${\mathrm{C}}_{3}\mathrm{N}$ for different applied strain configurations. Then, we use this model approach to classify excitons of pristine and strained ${\mathrm{C}}_{3}\mathrm{N}$ according to the crystal symmetry and to explain the appearance of bright excitons with intense optical anisotropy in strained ${\mathrm{C}}_{3}\mathrm{N}$, even at small strains. Finally, the effect of strain on the exciton dispersion at small center-of-mass momenta is discussed, with special focus on the implications for 2D linear-nonanalytic dispersions.

Doping dependent dual-response mechanoluminescence in ZnGa2O4

Dual-response mechanoluminescence (ML) enables light emission upon both the application and withdrawal of mechanical stress, which can provide novel opportunities for stress-sensing.

Massive production of fibroin nano-fibrous biomaterial by turbulent co-flow

Among the different polymers (proteins, polysaccharides, etc.) that make up natural fibers, fibroin is a protein produced by silk spinning animals, which have developed an optimized system for the conversion of a highly concentrated solution of this protein into high-performance solid fibers. This protein undergoes a self-assembly process in the silk glands that result from chemical gradients and by the application of mechanical stresses during the last step of the process. In the quest for a process that could mimic natural spinning at massive scales, we have discovered that turbulence offers a novel and promising solution: a turbulent liquid jet can be formed by a chemically green and simple coagulating liquid (a diluted solution of acetic acid in etanol) co-flowing with a concentrated solution of fibroin in water by the use of a Flow Blurring nebulizer. In this system, (a) the co-flowing coagulant liquid extracts water from the original protein solution and, simultaneously, (b) the self-assembled proteins are subjected to mechanical actions, including splitting and stretching. Given the non-negligible produced content with the size and appearance of natural silk, the stochastic distribution of those effects in our process should contain the range of natural ones found in animals. The resulting easily functionalizable and tunable one-step material is 100% biocompatible, and our method a perfect candidate to large-scale, low-cost, green and sustainable processing of fibroin for fibres and textiles.

Assessment of laser cutting parameters and heat-affected zone on microstructure and fatigue behaviour of carbon fibre-reinforced epoxy

In this study, the effects of laser cutting on the fatigue properties of carbon fibre-reinforced polymers are investigated. For this purpose, unidirectional carbon fibre-reinforced epoxy laminate is cut by laser. The material to be cut evaporates directly in the laser beam and the laser beam can produce thermally induced damage, which is referred to as heat-affected zones. Specimens are cut with two different parameters (varying cutting velocity and break time between passes) to widths up to 15 mm for investigation of the heat-affected zones effects on fatigue behaviour. Prior to fatigue tests microstructure is evaluated using light and scanning electron microscopy with regard to cutting geometry and heat-affected zones. Fatigue tests are performed using multiple amplitude tests with a stress ratio of 0.1, instrumented with a video extensometer system and thermocouples for strain and temperature measurements to determine the influence on mechanical properties and evaluate the sensitivity of the used testing method and measurement instrumentation for this use case. Lower cutting velocities and break time passes lead to a larger edge angle and thus in different specimen widths on front (laser inlet) and bottom (laser outlet) of the carbon fibre-reinforced epoxy laminate. Therefore, the resulting true geometry was considered using statistical approaches to eliminate possible cross-sectional errors regarding mechanical stress application. The results show that the specimen widths and process parameters impact the fatigue properties, highlighting the importance of knowledge about heat induction and the detection of inflicted laminate damage.

Mechano-regulation of Wnt/β-Catenin signaling to control paraxial versus lateral mesoderm lineage bifurcation.

Mechanical cues are involved in many biological processes, including embryonic development and patterning. For example, external mechanical forces (shear stress), lateral cell-cell interactions, and mechanical properties (stiffness and composition) of the extracellular matrix are thought to modulate Wnt signaling, which is a highly conserved pathway involved in regulating stem cell renewal, proliferation, and differentiation. In this work, we employed a customized higher-throughput shear stress induction device for the controlled application of mechanical stress to study the effects of shear stress on the differentiation of human induced pluripotent stem cells (hiPSCs) toward the three germ layers. We found that mechanical stress alters lineage commitment during ectoderm and mesoderm differentiation. We show that this effect correlates with reduced Wnt signaling, evaluated in terms of the promoter activity of an established TCF3-responsive promoter. Whole transcriptome sequencing and pathway enrichment analysis of the differentially expressed genes between hiPSC-derived mesoderm cells differentiated in the presence or absence of piston-induced shear stress confirmed that Wnt/β-catenin signaling is among the most affected developmental pathways. Furthermore, our results suggest that suitably programmed shear stress application could be used to selectively promote differentiation of hiPSCs to either lateral or paraxial mesoderm in commercially available media.