Agarose as a tissue mimic for porcine kidney at the micro-length scale.

The calculation model for prediction both of storage and loss moduli is suggested. Consideration is made on the basis of the atomic constants that take into account the contribution of each atom and the polar group in the van der Waals volume and shear modulus at high frequencies. The relations obtained allow us to calculate the shear modulus, storage modulus, and loss modulus as a function of frequency, temperature and molecular weight distribution.

Muscle stiffness has been reported to increase following eccentric muscle exercise, but to date only indirect methods have been used to measure it. This study aimed to use Magnetic Resonance Elastography (MRE), a noninvasive imaging technique, to assess the time-course of passive elasticity changes in the medial gastrocnemius and soleus muscles before and after a bout of eccentric exercise. Shear storage modulus (G') and loss modulus (G'') measurements were made in eight healthy subjects for both muscles in vivo before, one hour after, 48 hours after and 1 week after eccentric exercise. The results show a 21% increase in medial gastrocnemius storage modulus following eccentric exercise with a peak occurring ~48 hours after exercise (before exercise 1.15 ± 0.23 kPa, 48 hours after 1.38 ± 0.27 kPa). No significant changes in soleus muscle storage modulus were measured for the exercise protocol used in this study, and no significant changes in loss modulus were observed. This study provides the first direct measurements in skeletal muscle before and after eccentric exercise damage and suggests that MRE can be used to detect the time course of changes to muscle properties.

The in-situ monitoring and characterization of the mechanical properties of wood and timber materials is of great importance due to their broad structural applications. The purpose of this study was to propose a nondestructive method to assess the moisture-dependent viscoelastic behavior of structural wood using the guided Lamb wave propagation. Twelve green poplar wood specimens with different moisture content (MC) underwent the Lamb wave propagation tests and the wave characteristics were acquired. The viscoelastic properties of the wood specimens, including the shear storage and shear loss moduli and the loss factor, were then estimated through the solution of the corresponding inverse Lamb wave propagation problem using the experimentally measured Lamb wave characteristics. The structural stiffness and damping of wood specimens were affected by their MC, as the Lamb wave amplitude and velocity significantly decreased with MC. While the shear storage modulus decreased with MC, the shear loss modulus and loss factor increased with MC, resulting in a higher viscoelastic behavior. The loss factor of the wood specimens was estimated to be between 5.88% and 8.49% for different classes of MC, showing an increase of 44% with MC. The Lamb wave propagation method offers a strong tool for nondestructive characterization of the viscoelastic properties of wood materials and structures over a broad MC range. Wood materials show a significant viscoelastic behavior which is highly impacted by their MC. The loss factor can play an important role in the characterization and classification of structural wood and timber with different MC.

Dynamic and static elastic moduli of packable and flowable composite resins and their development after initial photo curing

Filler Effects of Oil Droplets on Physical Properties of Emulsion Gels

Crosslinked injectable hyaluronic acid (HA)-gelatin (Ge) hydrogels have remarkable viscoelastic and biological properties for vocal fold tissue engineering. Patient-specific tuning of the viscoelastic properties of this injectable biomaterial could improve tissue regeneration. The frequency-dependent viscoelasticity of crosslinked HA-Ge hydrogels was measured as a function of the concentration of HA, Ge, and crosslinker. Synthetic extracellular matrix hydrogels were fabricated using thiol-modified HA and Ge, and crosslinked by poly(ethylene glycol) diacrylate. A recently developed characterization method based on Rayleigh wave propagation was used to quantify the frequency-dependent viscoelastic properties of these hydrogels, including shear storage and loss moduli, over a broad frequency range; that is, from 40 to 4000 Hz. The viscoelastic properties of the hydrogels increased with frequency. The storage and loss moduli values and the rate of increase with frequency varied with the concentrations of the constituents. The range of the viscoelastic properties of the hydrogels was within that of human vocal fold tissue obtained from in vivo and ex vivo measurements. Frequency-dependent parametric relations were obtained using a linear least-squares regression. The results are useful to better fine-tune the storage and loss moduli of HA-Ge hydrogels by varying the concentrations of the constituents for use in patient-specific treatments.

One-step solvothermal synthesis of porous MnFe2O4 nanoflakes and their magnetorheological properties

Effect of two different Flammulina velutipes polysaccharides on the physicochemical and digestive properties of rice starch and their interaction mechanisms

Microscale assessment of corneal viscoelastic properties under physiological pressures

Green composites of polypropylene and eggshell: Effective biofiller size reduction and dispersion by single-step processing with solid-state shear pulverization

Inversion methods in shear wave elastography use simplifying assumptions to recover the mechanical properties of soft tissues. Consequently, these methods suffer from artifacts when applied to media containing strong stiffness contrasts, and do not provide a map of the viscosity. In this work, the shear wave field recorded inside and around an inclusion was used to estimate the viscoelastic properties of the inclusion and surrounding medium, based on an inverse problem approach assuming local homogeneity of both media. An efficient semi-analytical method was developed to model the scattering of an elastic wave by an irregular inclusion, based on a decomposition of the field by Bessel functions and on a decomposition of the boundaries as Fourier series. This model was validated against finite element modeling. Shear waves were experimentally induced by acoustic radiation force in soft tissue phantoms containing stiff and soft inclusions, and the displacement field was imaged at a high frame rate using plane wave imaging. A nonlinear least-squares algorithm compared the model to the experimental data and adjusted the geometrical and mechanical parameters. The estimated shear storage and loss moduli were in good agreement with reference measurements, as well as the estimated inclusion shape. This approach provides an accurate estimation of geometry and viscoelastic properties for a single inclusion in a homogeneous background in the context of radiation force elastography.

Electrorheological (ER) fluid’s storage shear modulus (G’) and loss factor (η) have been directly measured using small amplitude forced oscillating rheometer as a function of oscillating frequency, strain amplitude and applied electric field. Two types of experiment were performed; (a) frequency sweep and (b) amplitude sweep. Two kinds of sample were employed for this experiment; cornstarch in corn oil and zeolite particles in silicone oil. The storage shear modulus (G’) was a strong function of driving frequency. Generally, G’ increased with driving frequency. On the other hand, the loss factor (η) was not well behaved as storage modulus, but as the driving frequency increases η slightly decreases was the trend of the material’s characteristics. Also G’ was a strong function of strain amplitude. Generally, G’ decreased with increasing strain, but η increases slightly with increasing strain amplitude. For G’, cornstarch in corn oil ER fluid has higher values than zeolite based fluid as we increased the applied electric field. On the other hand, zeolite based fluid has higher values for η. There is a reasonable agreement between theory and experiment.

The transient response of a polymer-coated surface acoustic wave (SAW) vapour sensor depends on partitioning and diffusion of vapour species into the polymer in conjunction with its thickness and viscoelastic properties. The shapes of transient signals carry information about vapour identities due to specificity of the partition coefficient and the diffusion coefficient. The analysis of transient signals therefore offers a simpler approach for vapour identification in comparison to conventional electronic nose systems that employ a broadly selective sensor array. The transient response-based methods are however not developed to a similar level of maturity as their sensor array counterparts. The main reason for this is associated with complex signal generation kinetics and polymer viscoelasticity. The latter is independent of vapour identities (assuming low concentrations) but influences sensor response through nonlinear dependences on polymer thickness and viscoelastic coefficients. In this paper, we endeavour to find out whether viscoelasticity and its manifestation through thickness dependences could be turned into an advantage for transient-based vapour identification. Using an established SAW sensor model with additive noise we analyse sensor transients by wavelet decomposition and principal component analysis (PCA) for various combinations of polymer thickness, viscoelastic storage and loss moduli and noise level. We calculate vapour class separability measures defined on the basis of scatter matrices of principal components of wavelet coefficients to determine the discrimination ability of sensor transients for various combinations of film thickness and viscoelastic parameters. The simulation experiments are performed by considering a polyisobutylene-coated SAW oscillator sensor under exposure to seven volatile organic compounds (chloroform, chlorobenzene, o-dichlorobenzene, n-heptane, toluene, n-hexane and n-octane). The film thicknesses are varied from thin film (where mass loading dominates) to thick film through fundamental film resonance (where viscoelastic effects dominate) to very thick film regions spanning over a few higher order resonances. The storage and loss shear moduli are varied to simulate conditions of glassy, glassy-rubbery and rubbery phases of polymer. The transient response generation incorporates an additive noise source with uniform distribution over a specified range. Effect of noise variation on class separability is also studied. A comparison of the wavelet transform method is made with the phase space-based partial-least-squares regression method for feature extraction. In conclusion, it is found that (i) vapour class separability increases with polymer thickness for all viscoelastic conditions from glassy to rubbery, except near film resonances, (ii) near resonance class separability dramatically declines for films with no or low loss, (iii) by imparting finite viscoelastic losses to polymer coatings, not only are the detrimental effects of film resonance eliminated but also the sensor performance improves, and (iv) viscoelastic effects produce better noise immunity in thick film sensors. This analysis provides a new perspective for designing high-performance transient sensors through optimization of film thickness for specific polymer selections.

ABSTRACTSulfonated polyether ether ketone (SPEEK), an ionic polymer, has been shown to be a potential candidate for fuel cell electrolyte as a proton exchange membrane. Rheological behavior of SPEEK solutions is of great interest to understand the molecular associations as well as due to implications in membrane processing. In this work, SPEEK of various degrees of sulfonation (58–80) was prepared and rheology of concentrated solutions of SPEEK was studied. The rheological properties were evaluated using steady and oscillatory shear. It was found that steady shear viscosity and storage modulus at any given concentration, is the highest for the lowest degree of sulfonation SPEEK solutions in N‐methyl‐2‐pyrrolidone. The low frequency plateau in storage modulus was observed at some combinations of degrees of sulfonation and concentrations, indicating gel‐like behavior in these SPEEK solutions. No significant change in rheological behavior was observed with different polar solvents. Increase of several orders of magnitude in viscosity, storage and loss moduli were observed with increasing concentrations. The role of hydrophobic aggregation and inter‐chain associations in determining rheology of SPEEK solutions is argued based on comparisons with other material systems. The rheological behavior of SPEEK solutions with 70 as the degree of sulfonation, suggests crossover from hydrophobic‐hydrophilic balance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40044.

Dynamic mechanical analysis and rotational or compressional rheometry provide complementary techniques for determining the thermomechanical properties of a sample over a wide temperature range. From the glassy to the melt phase, the modulus of a material may decrease by a factor of 10 6 or more. Such a range is difficult to cover with reasonable accuracy with a single instrument. Those optimised for fluids tend to perform poorly with solid samples, and vice versa. Dynamic mechanical analysers are designed to operate through the glassy and rubbery regimes, in which a large load is required to deform the sample sufficiently to provide displacement signals with a reasonably high signal-to-noise ratio. In the flow regime, better resolution is provided by rheometers, which are optimised to deal with fluids, including polymer melts, and are generally more sensitive. Rotational rheometers (mostly the controlled-stress type) are now complemented by a novel rheological measuring technique, introduced here as dynamic compressional rheology. Dynamic compressional rheology is a novel technique (robust and cost-effective) for which the analytical expressions yielding the shear loss and storage moduli have only recently been developed.