Increase In Shear Modulus Research Articles

Ammonium-Chloride-Potassium Lysing Buffer Treatment of Fully Differentiated Cells Increases Cell Purity and Resulting Neotissue Functional Properties.

Juvenile and fetal, primary, fully differentiated cells are widely considered to be ideal cell types for tissue engineering applications. However, their use in tissue engineering may be hindered through contamination by undesirable cell types. These include blood-associated cells as well as unwanted resident cell types found both in healthy and pathologic donor tissues. Ammonium-chloride-potassium (ACK) lysing buffer is used to lyse red blood cells (RBCs) during the isolation of stem cell populations, but has not been explored for the purification of fully differentiated cells. This study sought to investigate the effect of ACK buffer treatment of freshly isolated, fully differentiated cells to increase cell purity and enhance the formation of biofunctional engineered neotissues; this was tested in the well-established cartilage tissue engineering model of the self-assembling process using fetal ovine articular chondrocytes (foACs) and juvenile bovine articular chondrocytes (jbACs). ACK buffer treatment of foACs and jbACs decreased the number of contaminating RBCs by over 60% and additionally reduced the number of apoptotic chondrocytes in the cell isolates. Reducing the number of contaminating RBCs removed cellular detractors to the self-assembling process and eliminated an apoptotic stimulus, thus improving neocartilage homogeneity, chondrocyte distribution, and extracellular matrix deposition within the neotissues. For example, in foAC neocartilage, ACK buffer treatment ultimately led to a 170% increase in compressive aggregate modulus, a 130% increase in shear modulus, an 80% increase in tensile modulus, and a 130% increase in ultimate tensile strength of the neocartilage. This work represents the first time that ACK buffer has been used to purify fully differentiated cells and subsequently increase the functional properties of neotissue.

Analysis of the Maximum Dynamic Shear Modulus and Particle Arrangement Properties of Saturated Soft Clay Soils

In this paper, using the resonant column test, electron microscope observation, and microscopic structure analysis, the relationship between the maximum dynamic shear modulus and the microscopic particles arrangement of remolded clay soil was examined. Focusing on the soil microstructure, this study found that, as the effective consolidation stress increases, the soil particles are rearranged in an orientation parallel to the direction of maximum principal stress and maximum shear stress. The probabilistic entropy of the soil particle arrangement decreases, the mechanical wave velocity in the continuous medium of the soil particles increases, and the maximum dynamic shear modulus increases.

Structure and properties of Na2O-TiO2-SiO2 glasses: Role of Na and Ti on modifying the silica network

Changes in the structure and properties of xNa2O-yTiO2-(1-x-y)SiO2 glasses have been studied with regards to composition through Raman spectroscopy, Brillouin light scattering, and dilatometry. Twelve glasses with compositions x=10, 15, 20, and 25, and y=4, 7, and 10 were prepared through a traditional melt quench method. Na2O was found to increase the density, refractive index, coefficient of thermal expansion (CTE), bulk modulus, and Poisson's ratio of glasses, and to decrease Young's modulus and shear modulus. Density, refractive index, Young's modulus, shear modulus, bulk modulus and Poisson's ratio increase with the increase of TiO2 content. CTE was found to increase with the initial addition of 4mol% TiO2 and to remain constant with further additions, regardless of the Na2O content. Changes in the Raman spectra with composition have been discussed and related to the changes in resulting properties.

Influence of γ radiation on the shear modulus of magnetorheological elastomer

The influence of γ radiation on the shear modulus of magnetorheological elastomer was investigated. Experimental results show that both the initial shear modulus and the magnetic-field-induced shear modulus increase first and then decrease with increasing γ radiation dose. Two factors are considered to explain the experimental results. One is the radiation-induced crosslinking and degradation reaction which influences the shear modulus of the polymer matrix of magnetorheological elastomer. The other is change of the saturation magnetization of the carbonyl iron particle which influences the magnetic-field-induced shear modulus.

Abdominal wall muscle elasticity and abdomen local stiffness on healthy volunteers during various physiological activities

The performance of hernia treatment could benefit from more extensive knowledge of the mechanical behavior of the abdominal wall in a healthy state. To supply this knowledge, the antero-lateral abdominal wall was characterized in vivo on 11 healthy volunteers during 4 activities: rest, pullback loading, abdominal breathing and the “Valsalva maneuver”. The elasticity of the abdominal muscles (rectus abdominis, obliquus externus, obliquus internus and transversus abdominis) was assessed using ultrasound shear wave elastography. In addition, the abdomen was subjected to a low external load at three locations: on the midline (linea alba), on the rectus abdominis region and on lateral muscles region in order to evaluate the local stiffness of the abdomen, at rest and during “Valsalva maneuver”. The results showed that the “Valsalva maneuver” leads to a statistically significant increase of the muscle shear modulus compared to the other activities. This study also showed that the local stiffness of the abdomen was related to the activity. At rest, a significant difference has been observed between the anterior (0.5N/mm) and the lateral abdomen locations (1N/mm). Then, during the Valsalva maneuver, the local stiffness values were similar for all locations (ranging from 1.6 to 2.2N/mm). This work focuses on the in vivo characterization of the mechanical response of the human abdominal wall and abdomen during several activities. In the future, this protocol could be helpful for investigation on herniated patients.

Cellular Response to Reagent-Free Electron-Irradiated Gelatin Hydrogels.

As a biomaterial, it is well established that gelatin exhibits low cytotoxicity and can promote cellular growth. However, to circumvent the potential toxicity of chemical crosslinkers, reagent-free crosslinking methods such as electron irradiation are highly desirable. While high energy irradiation has been shown to exhibit precise control over the degree of crosslinking, these hydrogels have not been thoroughly investigated for biocompatibility and degradability. Here, NIH 3T3 murine fibroblasts are seeded onto irradiated gelatin hydrogels to examine the hydrogel's influence on cellular viability and morphology. The average projected area of cells seeded onto the hydrogels increases with irradiation dose, which correlates with an increase in the hydrogel's shear modulus up to 10 kPa. Cells on these hydrogels are highly viable and exhibits normal cell cycles, particularly when compared to those grown on glutaraldehyde crosslinked gelatin hydrogels. However, proliferation is reduced on both types of crosslinked samples. To mimic the response of the hydrogels in physiological conditions, degradability is monitored in simulated body fluid to reveal strongly dose-dependent degradation times. Overall, given the low cytotoxicity, influence on cellular morphology and variability in degradation times of the electron irradiated gelatin hydrogels, there is significant potential for application in areas ranging from regenerative medicine to mechanobiology.

Normal and Fibrotic Rat Livers Demonstrate Shear Strain Softening and Compression Stiffening: A Model for Soft Tissue Mechanics.

Tissues including liver stiffen and acquire more extracellular matrix with fibrosis. The relationship between matrix content and stiffness, however, is non-linear, and stiffness is only one component of tissue mechanics. The mechanical response of tissues such as liver to physiological stresses is not well described, and models of tissue mechanics are limited. To better understand the mechanics of the normal and fibrotic rat liver, we carried out a series of studies using parallel plate rheometry, measuring the response to compressive, extensional, and shear strains. We found that the shear storage and loss moduli G’ and G” and the apparent Young's moduli measured by uniaxial strain orthogonal to the shear direction increased markedly with both progressive fibrosis and increasing compression, that livers shear strain softened, and that significant increases in shear modulus with compressional stress occurred within a range consistent with increased sinusoidal pressures in liver disease. Proteoglycan content and integrin-matrix interactions were significant determinants of liver mechanics, particularly in compression. We propose a new non-linear constitutive model of the liver. A key feature of this model is that, while it assumes overall liver incompressibility, it takes into account water flow and solid phase compressibility. In sum, we report a detailed study of non-linear liver mechanics under physiological strains in the normal state, early fibrosis, and late fibrosis. We propose a constitutive model that captures compression stiffening, tension softening, and shear softening, and can be understood in terms of the cellular and matrix components of the liver.

Dual mode gelation behavior of silk fibroin microgel embedded poly(ethylene glycol) hydrogels.

Hydrogel formation by more than two cross-linking mechanisms is preferred for the sophisticated manipulation of hydrogel properties. Both chemical and physical crosslinks are often utilized for fabricating stimuli-responsive hydrogels or for compensating the drawbacks of the single crosslinking method. In this study, silk fibroin (SF) microgel embedded poly(ethylene glycol) (PEG) hydrogels were fabricated by dual mode cross-linking based on thiol-ene photo-click chemistry and β-sheet formation of SF. Norbornene-functionalized SF (SF-NB) was incorporated into PEG hydrogels by photo-cross-linking. The equilibrium shear modulus of SF-PEG hybrid hydrogels decreased with increasing SF-NB content. However, the incorporation of SF-NB caused stiffening of SF-PEG hybrid hydrogels gradually over 5 days and the gel modulus was maintained for 2 weeks. In contrast, the modulus of pure PEG hydrogels decreased continuously owing to hydrolytic degradation of ester bonds in the PEGNB macromers. Structural analysis revealed that such a post-gelation stiffening effect was caused by β-sheet transition in SF microgels embedded in the PEG hydrogel matrix. PEG hydrogels incorporated with 4 wt% SF microgels exhibited about 2-fold increase in shear modulus compared with the modulus on day 1 post-gelation. To evaluate the compatibility of these hydrogels as cell culture matrices, the cytotoxicity of the hydrogel was examined using in situ encapsulated A549 cells. SF-PEG hybrid hydrogels showed no apparent cytotoxicity and promoted the proliferation of encapsulated A549 cells even at a higher gel modulus compared with cells in pure PEG hydrogels. These results suggest that SF-PEG hybrid hydrogels fabricated by dual mode crosslinking serve as good candidates for three-dimensional cell culture requiring temporal control of hydrogel stiffness.

Elastic Properties of the Solid Electrolyte Li7La3Zr2O12(LLZO)

The oxide known as LLZO, with nominal composition Li7La3Zr2O12, is a promising solid electrolyte for Li-based batteries due to its high Li-ion conductivity and chemical stability with respect to lithium. Solid electrolytes may also enable the use of metallic Li anodes by serving as a physical barrier that suppresses dendrite initiation and propagation during cycling. Prior linear elasticity models of the Li electrode/solid electrolyte interface suggest that the stability of this interface is highly dependent on the elastic properties of the solid separator. For example, dendritic suppression is predicted to be enhanced as the electrolyte’s shear modulus increases. In the present study a combination of first-principles calculations, acoustic impulse excitation measurements, and nanoindentation experiments are used to determine the elastic constants and moduli for high-conductivity LLZO compositions based on Al and Ta doping. The calculated and measured isotropic shear moduli are in good agreement and fall ...

Ab initiostudy of anisotropic mechanical properties of LiCoO2 during lithium intercalation and deintercalation process

The mechanical properties of LixCoO2 under various Li concentrations and associated anisotropy have been systematically studied using the first principles method. During the lithium intercalation process, the Young's modulus, bulk modulus, shear modulus, and ultimate strength increase with increasing lithium concentration. Strong anisotropy of mechanical properties between a-axis and c-axis in LixCoO2 is identified at low lithium concentrations, and the anisotropy decreases with increasing lithium concentration. The observed lithium concentration dependence and anisotropy are explained by analyzing the charge transfer using Bader charge analysis, bond order analysis, and bond strength by investigating partial density of states and charge density difference. With the decrease of Li concentration, the charge depletion in the bonding regions increases, indicating a weaker Co-O bond strength. Additionally, the Young's modulus, bulk modulus, shear modulus, and toughness are obtained by simulating ab initio tensile tests. From the simulated stress-strain curves, LixCoO2 shows the highest toughness, which is in contraction with Pugh criterion prediction based on elastic properties only.

Effects of mean net stress and cyclic deviatoric stress on the cyclic behavior of normally consolidated unsaturated kaolin

Experimental study of the cyclic behavior of unsaturated materials is more complex than that of the saturated materials due to the required equipment, experience and time. Furthering investigations in the field of unsaturated materials is necessary to better understand its complexity and sensitivity of unsaturated cyclic parameters to different determinants such as suction path, stress path, loading speed, deviatoric stress amplitude, physical specifications, and etc. To this end, the main focus of this study has been to analyze the effects of factors such as mean net stress and deviatoric stress levels in fast cyclic loading on the cyclic behavior of a normally consolidated unsaturated fine-grained trade soil, namely the Zenoz kaolin. Various unsaturated tests were performed in three mean net stress levels and three amplitudes of cyclic deviatoric stress levels. Results showed that increase of suction in the same strain level leads to increase in stiffness in normally consolidated samples (i.e. increase in elastic modulus and shear modulus and decrease in damping ratio). Also, in the same suction value and strain level, increase of the mean net stress during the isotropic consolidation causes to the denser normally consolidated samples and results to increase of elastic modulus and shear modulus, and decrease of damping ratio.

Probing intermolecular interactions of ZnO-nanoparticle-reinforced molten energetic material

In this work, metal oxide nanoparticle ZnO was employed for the reinforcement of TNT. Scanning electronic microscopy (SEM) was used to study the microstructure on the fractured surface of TNT/nano-ZnO, and ultraviolet–visible (UV-Vis) spectroscopy was utilized for structure characterization. Moreover, to understand the reinforcing mechanism between ZnO and TNT, quantum chemistry and molecular dynamics simulation were undertaken to investigate the intermolecular interaction and mechanical properties. It is concluded that with 2.85 wt% ZnO nanoparticle addition, the amount of voids and defects decreases with the increase in bulk and shear modulus. The modified TNT/ZnO composite has high heat of formation, negative oxygen balance, and good detonation properties, which is expected to be a candidate for high-energy blended explosives.

Influence of aging and thermomechanical cycling on the magnetostriction and magnetic shape memory effect in martensitic alloy

An influence of internal stress created by the crystal defects on the magnetically induced reorientation (MIR) of martensite variants in the ferromagnetic shape memory alloy (FSMA) has been analyzed. Using the internal stress conception, a noticeable influence of the spatial reconfiguration of crystal defects on the ordinary magnetostriction of FSMA and magnetic shape memory (MSM) effect has been predicted. It has been shown that the defect reconfiguration, which stabilizes the martensitic phase during martensite aging, increases the shear elastic modulus. The increase of shear modulus reduces the magnetostriction value and in this way suppresses the MSM effect. The magneto-thermo-mechanical training of aged alloys destabilizes the martensitic phase, restores the initial magnetostriction value, and promotes the MSM effect.

Factors that influence muscle shear modulus during passive stretch

Although elastography has been increasingly used for evaluating muscle shear modulus associated with age, sex, musculoskeletal, and neurological conditions, its physiological meaning is largely unknown. This knowledge gap may hinder data interpretation, limiting the potential of using elastography to gain insights into muscle biomechanics in health and disease. We derived a mathematical model from a widely-accepted Hill-type passive force–length relationship to gain insight about the physiological meaning of resting shear modulus of skeletal muscles under passive stretching, and validated the model by comparing against the ex-vivo animal data reported in our recent work (Koo et al. 2013). The model suggested that resting shear modulus of a slack muscle is a function of specific tension and parameters that govern the normalized passive muscle force–length relationship as well as the degree of muscle anisotropy. The model also suggested that although the slope of the linear shear modulus–passive force relationship is primarily related to muscle anatomical cross-sectional area (i.e. the smaller the muscle cross-sectional area, the more the increase in shear modulus to result in the same passive muscle force), it is also governed by the normalized passive muscle force–length relationship and the degree of muscle anisotropy. Taken together, although muscle shear modulus under passive stretching has a strong linear relationship with passive muscle force, its actual value appears to be affected by muscle’s mechanical, material, and architectural properties. This should be taken into consideration when interpreting the muscle shear modulus values.

Changes in physical-mechanical properties and structure of ferritic-pearlitic steel 15Kh2NMFA caused by severe low-temperature deformation and exposure to alternating magnetic field

It is shown for the low-plasticity ferritic-pearlitic steel 15Kh2NMFA (2Cr, 1Ni, 0.5Mn, 0.5Mo), subjected to severe rolling deformation at 90 K, that the treatment by the alternating magnetic field results in a substantial decrease of the yield strength and an increase of fracture stress, total elongation, necking and dynamic shear modulus. This is accompanied by reduction of the internal friction background and coercive force. The changes in the physical-mechanical properties and the structure are related to magnetic- and electrical-nature processes giving rise to stress relaxation in the microvolumes with a high density of deformation defects.

Shear wave propagation and elasticity imaging of soft tissues under compression

In efforts to improve detection sensitivity of shear wave elasticity imaging of target tissue lesions with relatively small mechanical contrast to the background tissues, shear wave propagation characteristics in tissues under compression loading have been studied. A finite element hyperelastic tissue model was constructed to characterize the changes of propagating shear wave subject to different mechanical loading and to guide in vitro experiments. The shear wave speed sharply increased in an inclusion from 2.4 m/s to 6.3 m/s while it increased from 2.0 m/s to 4.0 m/s in the background tissue with overall compression loading from 0% to 30%. Increased shear wave reflection at the boundary of the inclusion due to increased mechanical contrast was lowered using a directional filter. In vitro experiments were performed using a soft phantom block (0.5% agar with 5% gelatin) that contains a hard inclusion (1.5% agar with 5% gelatin) of a long cylinder (D: 8 mm). The reconstructed shear modulus of the inclusion exhibited noticeable nonlinearity, in contrast to linear increase of shear modulus in the surrounding phantom. As a result, the elastic modulus contrast of the inclusion to the surrounding phantom was increased from 0.47 to 1.41 at compression from 0% to 30%.

Shear modulus of heavy oils: Confinement effects in rheometer measurements

Abstract Viscosity of heavy oil constitutes an important property that governs the productivity of these reservoirs. The viscosity of these crude oils is highly dependent on many variables like temperature, frequency, and strain amplitude. In this paper we show that viscosity measurements of heavy oils can also depend on a measurement variable like the gap thickness in a parallel plate rheometer. In this paper we measured how the confinement of heavy oils between parallel plates induces an increase in shear modulus. We propose that the increase in shear modulus can be linked to the surface-active nature of heavy oils that can cause re-orientation of the molecules at the surface of the plates and producing a measurable increase in the shear modulus. The findings were observed in three different samples of heavy oils. The results of this work have major implications in the measurement of viscosity of heavy oils but more importantly in the flow of heavy oils in porous media.

Impact of moisture content on dynamic mechanical properties and transition temperatures of wood

The dynamic shear modulus and the loss modulus of Betula alba, Ulmus parvifolia, Quercus robur, Acer platanoides, Tilia cordata, Fraxinus excelsior and Pinus sylvestris wood were measured using an inverted torsion pendulum within a wide temperature range. The glass transition temperature of the lignin–carbohydrate complex and the decomposition temperature of the wood cellulose were estimated. The temperature band from 170°C to 240°С shows the transition of the lignin–cellulose complex from the glassy to the rubbery state. Mechanical properties of different types of wood are affected by moisture and anatomical differences, but glass transition and decomposition temperatures are the same. More than 5% of moisture in the wood stored at normal conditions were found. After drying, the increase of dynamic shear modulus of wood over the entire region of the glassy state was observed. The intensity of maximum peak of dynamic loss modulus is also increased due to activation of the segmental motion of macromolecules of the ligno-carbon complex. The decomposition temperature of the cellulose crystallites was unchanged for specimens containing moisture and for dried specimens.

Evidence for intermuscle difference in slack angle in human triceps surae

This study examined whether the slack angle (i.e., the joint angle corresponding to the slack length) varies among the synergists of the human triceps surae in vivo. By using ultrasound shear wave elastography, shear modulus of each muscle of the triceps surae was measured during passive stretching from 50° of plantar flexion in the knee extended position at an angular velocity of 1°/s in 9 healthy adult subjects. The slack angle of each muscle was determined from the ankle joint angle–shear modulus relationship as the first increase in shear modulus. The slack angle was significantly greater in the medial gastrocnemius (20.7±6.7° plantarflexed position) than in the lateral gastrocnemius (14.9±6.7° plantarflexed position) and soleus (2.0±4.8° dorsiflexed position) and greater in the lateral gastrocnemius than in the soleus. This study provided evidence that the slack angle differs among the triceps surae; the medial gastrocnemius produced passive force at the most plantarflexed position while the slack angle of the soleus was the most dorsiflexed position.

Characterization of Carbopol® hydrogel rheology for experimental tectonics and geodynamics

One of the long-standing challenges of modern tectonics and geodynamics is to fully understand the strong strain localization and its effects observed in the lithosphere, which presents viscous, as well as elastic and brittle properties. Recently yield stress–shear thinning hydrogels, such as Carbopol®, have been employed in analog modeling because of its great potential for mimicking the non-Newtonian behavior of rocks. Conversely its use has been limited by the difficulties in assessing its rheology and in preparing uniform samples. Ergo, it is essential to ensure a standard recipe, yielding to a reproducible behavior, no matter which rheometer model is used. We carried out, at four institutions (FAST, GFZ, IPGP and LET), a benchmark for developing a standard preparation and for testing the comparability of results. Then, we conducted a systematical rheological characterization of a wide range of Carbopol® formulas as a function of concentration, composition, pH, temperature and aging. Results show that neutral pH favors higher viscosity. The shear modulus, yield stress, viscosity, and shear thinning behavior increase with concentration. The linear viscoelastic range increases with concentration contrarily to what is observed in gelatins or colloidal suspensions. A weak inverse relationship between temperature and viscosity is found. Similarly, aging reduces both the viscosity and loss modulus, with reduction more evident for low concentration samples. Scaling analysis revealed that low concentration samples, i.e. <0.1wt.%, exhibiting shear thinning behavior and low yield stress, are appropriate to model the rising of thermal instabilities. Those at 0.5–1.0wt.%, showing yield stress in the order of hundreds of Pa and n ranging between 1.6 and 3.4 are good candidates to mimic the non-linear ductile behavior of crustal rocks. We conclude that tuning the visco-elasto-plastic rheology of Carbopol® would make this material a good candidate for modeling of also other geological processes.