Elastic Modulus Gradient Research Articles

Associations of circulating T-cell subsets in carotid artery stiffness: the Multi-Ethnic Study of Atherosclerosis.

Arterial stiffness measured by total pulse wave velocity (T-PWV) is associated with increased risk of multiple age-related diseases. T-PWV can be described by structural (S-PWV) and load-dependent (LD-PWV) arterial stiffening. T-cells have been associated with arterial remodeling, blood pressure, and arterial stiffness in humans and animals; however, it is unknown whether T-cells are related to S-PWV or LD-PWV. Therefore, we evaluated the cross-sectional associations of peripheral T-cell subpopulations with T-PWV, S-PWV, and LD-PWV stiffness. Peripheral blood T-cells were characterized using flow cytometry and the carotid artery was measured using B-mode ultrasound to calculate T-PWV at the baseline examination in a subset of the Multi-Ethnic Study of Atherosclerosis (MESA, n=1,984). A participant-specific exponential model was used to calculate S-PWV and LD-PWV based on elastic modulus and blood pressure gradients. The associations between five primary (p-significance<0.01) and twenty-five exploratory (p-significance<0.05) immune cell subpopulations, per 1-SD increment, and arterial stiffness measures were assessed using adjusted, linear regressions. For the primary analysis, higher CD4+CD28-CD57+ T-cells were associated with higher LD-PWV (β=0.04 m/s, p<0.01) after adjusting for co-variates. For the exploratory analysis, T-cell subpopulations that commonly shift with aging towards memory and differentiated/immunosenescent phenotypes were associated with greater T-PWV, S-PWV, and LD-PWV after adjusting for co-variates. In this cross-sectional study, several T-cell subpopulations commonly associated with aging were related with measures of arterial stiffness. Longitudinal studies that examine changes in T-cell subpopulations and measures of arterial stiffness are warranted.

A stretchable and self-powered strain sensor with elastomeric electret

Stretchable deformation sensors play an important role in the perception and autonomy of soft robots. While various sensors have been reported, the mechanical sensor with self-powered capability and stretchability to suit extreme environment is urgently required. In this study, a stretchable, self-powered, sensitivity adjustable, and long-term stability strain sensor based on the stretchable electret is researched for deformation monitoring. This stretchable and self-powered sensor is composed of the dielectric elastomer with designed elastic modulus gradient and the stretchable electret with elastomeric and Nano-particles. The electro-mechanical capability of this designed sensor is researched and optimized by multi-objective optimization approach. The sensor exhibits self-powered capability, stretchability (tensile strain from 0% to 20%), tunable sensitivity (optimized from 5.7 to 5.9 pC mm−1), and stability, where electromechanical performance remains stable after 8000 stretching cycles. The feasibility of its autonomous sensing which promotes a wide range of potential application in soft robotics is demonstrated. This elastic modulus gradient-induced and net charge design significantly broadened the potential applications with large deformation and low-attached stiffness.

Design of a gradient elastic modulus transition layer based on film-substrate adhesion

The codeformation process of Ti6Al4V (TC4) substrate and chromium nitride (CrN) films with dense/loose CrN and gradient elastic modulus CrN/CrNx/Cr(N) (G-CrN) structures under normal impact load were simulated by changing the thicknesses of the films or the loose CrN and G layers. The dispersed distribution of interfacial tensile stresses and strains of G-CrN films improved the layers’ codeformation, compared with the firm large layer of the dense/loose CrN films. The stress reduced as the loose/G layer thicknesses increased. The 4.7 μm CrN films with various thicknesses of the G-layers, 0.2 µm, 0.6 µm, 0.75 µm and 0.9 µm, were prepared on TC4 to evaluate the film-substrate adhesions and verify the simulated deformation procedure. A G-layer between a ceramic film and its alloy substrate is needed, and the 0.83–1.08 µm thicknesses of the G-layers were suggested for the CrN/TC4 system varied with the films’ thicknesses. The dispersed distribution of the tensile stress and strain within the G-CrN film was the mechanism of the film-substrate adhesion improvement.

&lt;i&gt;Hofmeister&lt;/i&gt; effect regulated gel iontronic sensors for wide-range pressure perception

&lt;p&gt;Flexible pressure sensors, vital for medical, human-machine interaction, and intelligent recognition applications due to their high-sensitivity, excellent-linearity, and broad-pressure response, face challenges in achieving a harmonious balance among these attributes. Inspired by the gradient modulus in human skin layers, we proposed a pioneering method to adjust the gradient elastic modulus of amino trimethylene phosphonic acid (ATMP)-assisted polyvinyl alcohol (PVA) hydrogel through the &lt;i&gt;Hofmeister&lt;/i&gt; effect, introducing micro-pyramid electrodes. This innovative approach successfully constructs a bio-gradient gel iontronic sensor (BGGITS) with an ultra-wide-range perception. The BGGITS exhibits a linear high-sensitivity of 700 kPa&lt;sup&gt;-1&lt;/sup&gt; within a broad-pressure detection range of up to 800 kPa. The composite design, integrating gradient gel and microstructure electrodes, demonstrates exceptional pressure resolution and mechanical stability. This biomimetic skin pressure sensor holds promise for achieving linear high-sensitivity across a broader pressure range simultaneously and may find applications in electronic skin for health monitoring and tactile perception in the future.&lt;/p&gt;

Dynamic behavior of axially functionally graded pipe conveying gas–liquid two-phase flow

The dynamic behavior of an axially functionally graded pipeline conveying gas–liquid two-phase flow is studied using the Euler–Bernoulli beam model and the generalized integral transform method (GITT). The influence of changes in functionally graded material parameters, boundary conditions, and gas volumetric fraction of two-phase flow on the linear stability of functionally graded pipes is investigated. The results indicate that the gradient of elastic modulus has a significant influence on the complex frequency, critical velocity for instability, and coupling flutter of the functionally graded pipeline. Additionally, the gradient of density has a significant effect on the complex frequency of the functionally graded pipe. The boundary conditions of the pipe have a significant influence on its dynamic response. The pipe exhibits higher stability when both ends are fixed, followed by the combination of fixed support and simple support. Conversely, the condition of simply supported at both ends is the most susceptible to instability. The gas volumetric fraction also plays a significant role in the dynamic behavior of functionally graded pipes conveying gas–liquid two-phase fluids.

Functionally Graded Steels Obtained via Electron Beam Powder Bed Fusion

Electron-Beam Powder Bed Fusion (EB-PBF) is one of the most important metal additive manufacturing (AM) technologies. In EB-PBF, a focused electron beam is used to melt metal powders in a layer by layer approach. In this investigation two pre-alloyed steel-based powders, stainless steel 316L and V4E, a tool steel developed by Uddeholm, were used to manufacture functionally graded materials. In the proposed approach two powders are loaded into the feeding container, V4E powder on top of 316L one, preventing their mixing. Such type of feeding yields components with two distinct materials separated by a zone with gradual transition from 316L to V4E. Microstructure and local mechanical properties were evaluated in the manufactured samples. Optical Microscopy, Scanning Electron Microscopy and EDX on the polished cross-sections show a gradual microstructural and compositional transition from characteristic 316L at the bottom of the specimens to the tool steel towards the top. Nanoindentation experiments confirmed a consequent gradient in hardness and elastic modulus, which gradually increase towards the top surface of the samples. The achieved results provide great possibilities to tailor the composition, microstructure, mechanical properties, and wear resistance by combining different powders in the powder bed AM technology. Potential applications include the tooling industry, where hard and wear-resistant materials are demanded on the surface with tougher and more ductile materials in the core of the tool.

An Asymmetric Interlocked Structure with Modulus Gradient for Ultrawide Piezocapacitive Pressure Sensing Applications

AbstractHighly sensitive electronic skin (e‐skin) sensors with considerable operating range offer great possibilities for health care, human–‐machine interfaces, and intelligent robotics. Although subtle microstructures have been used in recent years to improve the sensitivity and sensing range of e‐skin sensors, the trade‐off between these features remains a big challenge to overcome. Here, an asymmetric interlocked gradient elastic modulus (AIGM) structure is designed for the first time to provide sufficient deformation space to the traditional interlocked structure while ensuring high sensitivity, and the gradient elastic modulus further extends the sensing range of the AIGM structure‐based sensors, which exhibit a maximum sensitivity of as high as 9.89 kPa−1 with an ultrawide working range that extends to above 530 kPa at the same time. As a demo, this sensor is integrated into an intelligent adjustable mouse platform for physiological signal monitoring, pressure feedback, and modulus adjustment, providing a viable alternative for hand disease prevention.

Variation in enamel mechanical properties throughout the crown in catarrhine primates

Enamel mechanical properties vary across molar crowns, but the relationship among mechanical properties, tooth function, and phylogeny are not well understood. Fifteen primate lower molars representing fourteen taxa (catarrhine, n = 13; platyrrhine, n = 1) were sectioned in the lingual–buccal plane through the mesial cusps. Gradients of enamel mechanical properties, specifically hardness and elastic modulus, were quantified using nanoindentation from inner (near the enamel-dentine junction), through middle, to outer enamel (near the outer enamel surface) at five positions (buccal lateral, buccal cuspal, occlusal middle, lingual cuspal, lingual lateral). Cuspal positions had higher mechanical property values than lateral positions. Middle enamel had higher mean hardness and elastic modulus values than inner and outer locations in all five crown positions. Functionally, the thicker-enameled buccal cusps of lower molars did not show evidence of increased resistance to failure; instead, lingual cusps—which show higher rates of fracture—had higher average mechanical property values, with no significant differences observed between sides. Preliminary phylogenetic results suggest there is relatively little phylogenetic signal in gradients of mechanical properties through the enamel or across the crown. There appears to be common mechanical property patterns across molar crowns in Catarrhini and potentially among primates more broadly. These results may allow more precise interpretations of dental biomechanics and processes resulting in mechanical failure of enamel in primates, such as wear and fracture.

Adhesion of a cylindrical punch with elastic properties that vary radially

The adhesion of a rigid substrate and an adhered straight cylindrical punch with a non-homogeneous elastic modulus is analyzed. The stress distributions are obtained along the interface for various elastic modulus gradients. The calculations are performed in the commercial finite element software Abaqus using a user material (UMAT) subroutine to control the dependence of Young’s modulus on the radial position. The UMAT code is shared in the paper. The results reveal that the decreasing elastic modulus toward the perimeter of the punch can be used to significantly reduce the normal stress magnitudes in the singularity domain, which leads to stronger adhesion. The increase in the adhesion strength is characterized numerically. The effect of Poisson’s ratio is also analyzed.

Role of galectin-3 in the elastic response of radial growth phase melanoma cancer cells.

Melanoma is originated from the malignant transformation of the melanocytes and is characterized by a high rate of invasion, the more serious stage compromising deeper layers of the skin and eventually leading to the metastasis. A high mortality due to melanoma lesion persists because most of melanoma lesions are detected in advanced stages, which decreases the chances of survival. The identification of the principal mechanics implicated in the development and progression of melanoma is essential to devise new early diagnosis strategies. Cell mechanics is related with a lot of cellular functions and processes, for instance motility, differentiation, migration and invasion. In particular, the elastic modulus (Young's modulus) is a very explored parameter to describe the cell mechanical properties; most cancer cells reported in the literature smaller elasticity modulus. In this work, we show that the elastic modulus of melanoma cells lacking galectin-3 is significantly lower than those of melanoma cells expressing galectin-3. More interestingly, the gradient of elastic modulus in cells from the nuclear region towards the cell periphery is more pronounced in shGal3 cells. RESEARCH HIGHLIGHTS: AFM imaging and force spectroscopy were used to investigate the morphology and elasticity properties of healthy HaCaT cells and melanoma cells WM1366, with (shSCR) and without (shGal3) expression of galectin-3. It is shown the effect of galectin-3 protein on the elastic properties of cells: the cells without expression of galectin-3 presents lower elastic modulus. By the results, we suggest here that galectin-3 could be used as an effective biomarker of malignancy in both melanoma diagnostic and prognosis.

Interphase elastic modulus characterization in glass/epoxy composite using combined peridynamics and experimental method

This paper introduces a novel combined technique to characterize the elastic modulus gradient for glass/epoxy interphase. The developed procedure is applicable to all fiber-reinforced polymer (FRP) composites. Interphase in FRP composites plays a vital role in the mechanical performance of the material. Scientists almost characterized this region using nanoscale test methods such as atomic force microscopy (AFM) and scratch tests. These local methods characterize the elastic properties at a specific region near the fiber and, usually, are utilized for all regions around the fiber. This paper proposes a combined peridynamic and single-fiber micro tensile test method to characterize the overall elastic modulus gradient at the interphase region. The advantages of peridynamic as a non-local method are used to model the multiscale regions of interphase, fiber, and matrix. Single-fiber micro tensile tests are performed by the authors, and variations of displacements and strains are measured by the digital image correlation method. The obtained displacements are used as target values in the developed peridynamic code, and by performing peridynamic analyses, the elastic modulus variation along the interphase is automatically extracted. Furthermore, the variations of stresses and strains are investigated at the specimens’ cross-section using different hypotheses for the interphase region.

Stability of axially functionally graded pipe conveying fluid: Generalized integral transform solution

The stability of axially functionally graded pipe conveying fluid is analyzed based on the Euler–Bernoulli beam theory. The governing equation for transverse vibration is transformed into an infinite system of second-order ordinary differential equations by the generalized integral transform technique, which is truncated at finite terms to find the complex frequency as a function of flow and structural parameters. The effects of the elastic modulus and density distributions on the linear stability of axially functionally graded pipe are investigated by parametric studies. It is shown that the complex frequency, critical velocity of buckling instability and coupled flutter of the axially functionally graded pipe were significantly influenced by the elastic modulus gradient. The density gradient distribution significantly affects the complex frequency of the axially functionally graded pipe.

Parametric Design of Hip Implant With Gradient Porous Structure.

Patients who has been implanted with hip implant usually undergo revision surgery. The reason is that high stiff implants would cause non-physiological distribution loadings, which is also known as stress shielding, and finally lead to bone loss and aseptic loosening. Titanium implants are widely used in human bone tissues; however, the subsequent elastic modulus mismatch problem has become increasingly serious, and can lead to stress-shielding effects. This study aimed to develop a parametric design methodology of porous titanium alloy hip implant with gradient elastic modulus, and mitigate the stress-shielding effect. Four independent adjustable dimensions of the porous structure were parametrically designed, and the Kriging algorithm was used to establish the mapping relationship between the four adjustable dimensions and the porosity, surface-to-volume ratio, and elastic modulus. Moreover, the equivalent stress on the surface of the femur was optimized by response surface methodology, and the optimal gradient elastic modulus of the implant was obtained. Finally, through the Kriging approximation model and optimization results of the finite element method, the dimensions of each segment of the porous structure that could effectively mitigate the stress-shielding effect were determined. Experimental results demonstrated that the parameterized design method of the porous implant with gradient elastic modulus proposed in this study increased the strain value on the femoral surface by 17.1% on average. Consequently, the stress-shielding effect of the femoral tissue induced by the titanium alloy implant was effectively mitigated.

Skin-inspired tactile sensor based on gradient pore structure enable broad range response and ultrahigh pressure resolution

Tactile sensing is highly essential for the dexterous manipulation of robots. Nevertheless, the existed tactile sensors fail to realize high sensitivity and pressure resolution in a large pressure range, simultaneously. To concern this issue, we present a skin-structure inspired strategy to prepare gradient pore microstructure (GPS) films which thus have gradient elastic modulus along film thickness direction, similar to the dermis of skin. The tactile sensors made of this GPS films show an improved sensitivity of 3.74 kPa−1, an ultrahigh pressure resolution of 0.06% and broad range response of 0–800 kPa because of high structural compressibility and stress adaptation characteristics of GPS film. Meanwhile, the sensors achieve a fast response time of 15 ms and a low detection limit of 1.65 Pa as well as good cycle stability. Further, an 8 × 8 sensors array shows a performance of accurate real-time pressure mapping. Therefore, GPS-based sensors provide a new avenue to realize high-performance tactile perception in the artificial intelligence equipment.

Effect of Elastic Modulus Gradient on Osteoclastic Metabolic Behavior on Bioabsorbable Substrates Prepared by Welding PLA and PCL

This study aimed to evaluate the effect of the elastic modulus gradient on the osteoclastic metabolic behavior on the functional gradient substrates prepared by welding PLA and PCL. First, the elastic modulus distribution of the substrates with the elastic modulus gradient in the depth-direction were directly evaluated and verified by the tensile and indentation tests. Then, the osteoclasts were cultured on the PLA-side surface of the PCL/PLA functional gradient substrates. The osteoclastic metabolic behavior was evaluated by the ATR method using a FT-IR. As a result, it was confirmed that the elastic modulus of the PCL/PLA functional gradient substrates decreased from the PLA side to the PCL side. This indicates that the functional gradient substrates have the elastic modulus gradient successfully. The FT-IR measurement revealed that the osteoclastic dissolution rate of the substrates increased with the increase of the culture period until 4 weeks, and then decreased at the 5th week. This indicates that the elastic modulus gradient in the depth direction could control the osteoclastic metabolic behavior.

Giant flexoelectric response via mechanical and material design in elastomers

Strain gradient, a source of mechanical asymmetry in dielectrics, causes electric polarization, which we call flexoelectricity. Manipulating the strain gradient is fundamental in the study of flexoelectricity and its applications. This work describes a mechanical design approach to creating an elastic modulus gradient for the generation and enhancement of flexoelectricity. Furthermore, by combining material design and non-uniform geometric shape, theories and experiments have indicated enhanced flexoelectricity by one order of magnitude. In addition, the flexoelectric response increases with respect to the elastic modulus gradient, developing a new approach to manipulating flexoelectricity by mechanical design. The flexoelectric effect of this multi-configuration design is significantly improved compared to either method individually due to the enlarged equivalent dipole moment gradient created by manipulating the magnitude and density of the dipole moments. This work provides an approach to tuning flexoelectricity through the combination of mechanical and material design, further promoting flexoelectric-based applications in sensing, actuation, and energy harvesting.

An enhanced flexoelectric dielectric elastomer actuator with stretchable electret

Actuation has been applied with dielectric elastomers (DE) in soft robotics and bio-mimic devices due to their ultra-large deformation range, easy patterning, light weight, and they are highly expected for high electro-mechanical efficiency and low stimulating power. Flexoelectricity describes the strain gradient-induced electric polarization, which is strongly related to geometry and deformation ranges. The electro-mechanical coupling effect with flexoelectricity in elastomeric materials are then highly expected. In this work, elastic modulus gradient of a DE actuator is designed for bending motion by flexoelectricity, and electric charge is inserted and immobilized inside the material to further enhance the electro-mechanical capability. Elastic modulus gradient is designed, and electric charges are immobilized to enlarge the electro-mechanical coupling efficiencies of this flexoelectric actuator. The bending angle of the actuator is inversely proportional to the cube of general thickness of actuator, and the immobilized electric charge extensively enlarged the actuation capability. With elastic modulus gradient and electret, the actuating bending angle is enlarged with low stimulating voltage. This work provides an enhanced flexoelectric actuating method with material and mechanical design, and highlights low-voltage actuating approach with piezoelectric-like effect of stretchable electrets.

“Viscotaxis”- directed migration of mesenchymal stem cells in response to loss modulus gradient

Directed cell migration plays a crucial role in physiological and pathological conditions. One important mechanical cue, known to influence cell migration, is the gradient of substrate elastic modulus (E). However, the cellular microenvironment is viscoelastic and hence the elastic property alone is not sufficient to define its material characteristics. To bridge this gap, in this study, we investigated the influence of the gradient of viscous property of the substrate, as defined by loss modulus (G″) on cell migration. We cultured human mesenchymal stem cells (hMSCs) on a collagen-coated polyacrylamide gel with constant storage modulus (G′) but with a gradient in the loss modulus (G″). We found hMSCs to migrate from high to low loss modulus. We have termed this form of directional cellular migration as “Viscotaxis”. We hypothesize that the high loss modulus regime deforms more due to creep in the long timescale when subjected to cellular traction. Such differential deformation drives the observed Viscotaxis. To verify our hypothesis, we disrupted the actomyosin contractility with myosin inhibitor blebbistatin and ROCK inhibitor Y27632, and found the directional migration to disappear. Further, such time-dependent creep of the high loss material should lead to lower traction, shorter lifetime of the focal adhesions, and dynamic cell morphology, which was indeed found to be the case. Together, findings in this paper highlight the importance of considering the viscous modulus while preparing stiffness-based substrates for the field of tissue engineering. Statement of significanceWhile the effect of substrate elastic modulus has been investigated extensively in the context of cell biology, the role of substrate viscoelasticity is poorly understood. This omission is surprising as our body is not elastic, but viscoelastic. Hence, the role of viscoelasticity needs to be investigated at depth in various cellular contexts. One such important context is cell migration. Cell migration is important in morphogenesis, immune response, wound healing, and cancer, to name a few. While it is known that cells migrate when presented with a substrate with a rigidity gradient, cellular behavior in response to viscoelastic gradient has never been investigated. The findings of this paper not only reveal a completely novel cellular taxis or directed migration, it also improves our understanding of cell mechanics significantly.

Ti–6Al–4V microstructural functionally graded material by additive manufacturing: Experiment and computational modelling

In this study, a functionally graded material (FGM) was fabricated using a powder bed fusion additive manufacturing technique. The FGM evaluated was Ti–6Al–4V, due to its importance in the medical device and aerospace sectors. The microstructure at selected build locations was analysed using both scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques, where a gradient was observed both in terms of grain morphology and texture intensity. In addition, nanoindentation on the FGM sample shows a near quadratic shaped smooth gradient elastic modulus profile, with peak values at the midpoint of the gauge length. A tensile test to failure was conducted on the FGM sample with the aid of digital image correlation for surface strain analysis. Results show a gradient of local maximum principal strain in the highly {0001} textured section, while the reference sample in the control group shows a near-uniform strain distribution throughout the whole gauge length. A crystal plasticity finite element (CPFE) model was developed to explain the effect of texture on the mechanical properties adopting the microscopy-informed texture intensity gradient. Despite exhibiting higher elastic modulus (in the transverse direction, as measured via nanoindentation) the mid-section of the gauge length had a higher concentration of strain when loaded in the axial tensile direction, corresponding to build direction. The microscopy and computational modelling show that this apparent contradiction was explained via a high intensity of {0001} texture in the mid-section, leading to favourable conditions for axial strain accumulation.

Multilayered Composites with Modulus Gradient for Enhanced Pressure-Temperature Sensing Performance.

Highly sensitive and flexible composite sensors with pressure and temperature sensing abilities are of great importance in human motion monitoring, robotic skins, and automobile seats when checking the boarding status. Several studies have been conducted to improve the temperature-pressure sensitivity; however, they require a complex fabrication process for micro-nanostructures, which are material-dependent. Therefore, there is a need to develop the structural designs to improve the sensing abilities. Herein, we demonstrate a flexible composite with an enhanced pressure and temperature sensing performance. Its structural design consists of a multilayered composite construction with an elastic modulus gradient. Controlled stress concentration and distribution induced by a micropatterned structure between the layers improves its pressure and temperature sensing performance. The proposed composite sensor can monitor a wide range of pressure and temperature stimuli and also has potential applications as an automotive seat sensor for simultaneous human temperature detection and occupant weight sensing.