Viscoelastic Shear Research Articles

Viscoelasticity and Dielectric Measurement of Small Sample Volume for Diagnostic Platform of Synovial Fluid

The synovial fluid is found in joints of vertebrates and contains a high molecular weight polysaccharide (hyaluronan) acting as a modifier to ensure proper lubrication. Both, its concentration and molecular weight are subject to pathological alterations in certain diseases. Laboratory analysis of physical properties is difficult because of the limited amount of sample volume (usually below 100 μl). We present a sensor platform which requires volumes below 10μl to measure the viscoelastic properties in the kilohertz range and the electrochemical impedance spectrum (EIS) from 102 to 106 Hz. Two electrodynamic acoustic shear wave transducers are used to measure both the single-sided viscoelastic shear impedance and the transmission of shear waves. The same elements are used as electrodes for measuring the EIS with a precision impedance analyser. The device is supposed to be used for clinical diagnosis and therapy tracking.

Nanorheology by atomic force microscopy.

We present an Atomic Force Microscopy (AFM) based method to investigate the rheological properties of liquids confined within a nanosize gap formed by an AFM tip apex and a solid substrate. In this method, a conventional AFM cantilever is sheared parallel to a substrate surface by means of a lock-in amplifier while it is approaching and retracting from the substrate in liquid. The normal solvation forces and lateral viscoelastic shear forces experienced by the AFM tip in liquid can be simultaneously measured as a function of the tip-substrate distance with sub-nanometer vertical resolution. A new calibration method is applied to compensate for the linear drift of the piezo transducer and substrate system, leading to a more precise determination of the tip-substrate distance. By monitoring the phase lag between the driving signal and the cantilever response in liquid, the frequency dependent viscoelastic properties of the confined liquid can also be derived. Finally, we discuss the results obtained with this technique from different liquid-solid interfaces. Namely, octamethylcyclotetrasiloxane and water on mica and highly oriented pyrolytic graphite.

Ultra wideband (0.5–16 kHz) MR elastography for robust shear viscoelasticity model identification

Changes in the viscoelastic parameters of soft biological tissues often correlate with progression of disease, trauma or injury, and response to treatment. Identifying the most appropriate viscoelastic model, then estimating and monitoring the corresponding parameters of that model can improve insight into the underlying tissue structural changes. MR Elastography (MRE) provides a quantitative method of measuring tissue viscoelasticity. In a previous study by the authors (Yasar et al Magn. Reson. Med. 70 479–89), a silicone-based phantom material was examined over the frequency range of 200 Hz–7.75 kHz using MRE, an unprecedented bandwidth at that time. Six viscoelastic models including four integer order models and two fractional order models, were fit to the wideband viscoelastic data (measured storage and loss moduli as a function of frequency). The ‘fractional Voigt’ model (spring and springpot in parallel) exhibited the best fit and was even able to fit the entire frequency band well when it was identified based only on a small portion of the band. This paper is an extension of that study with a wider frequency range from 500 Hz to 16 kHz. Furthermore, more fractional order viscoelastic models are added to the comparison pool. It is found that added complexity of the viscoelastic model provides only marginal improvement over the ‘fractional Voigt’ model. And, again, the fractional order models show significant improvement over integer order viscoelastic models that have as many or more fitting parameters.

Cage effect for the velocity correlation functions of a Brownian particle in viscoelastic shear flows.

The long-time limit behavior of velocity correlation functions (VCFs) for an underdamped Brownian particle in an oscillatory viscoelastic shear flow is investigated using the generalized Langevin equation with a power-law memory kernel. The influence of a fluctuating environment is modeled by an additive external fractional Gaussian noise. The exact expressions of the correlation functions of the fluctuating components of velocity for the Brownian particle in the shear plane have been calculated. Also, the particle's angular momentum is found. It is shown that in a certain region of the system parameters an interplay of the shear flow, memory effects, and external noise can induce a bounded long-time behavior of the VCFs, even in the shear flow direction, where in the case of internal noise the velocity process is subdiffusive, i.e., unbounded in time. Moreover, we find resonant behavior of the VCFs and the angular momentum versus the shear oscillation frequency, implying that they can be efficiently excited by oscillatory shear. The role of the initial positional distribution of particles is also discussed.

Effects of enzymatic treatments on the depth-dependent viscoelastic shear properties of articular cartilage.

Osteoarthritis (OA) is a disease that involves the erosion and structural weakening of articular cartilage. OA is characterized by the degradation of collagen and proteoglycans in the extracellular matrix (ECM), particularly at the articular surface by proteinases including matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs).(1) Degradation of collagen and proteoglycans is known to alter shear mechanical properties of cartilage, but study of this phenomenon has been focused on bulk tissue properties. The purpose of this study was to assess microscale cartilage damage induced by trypsin or collagenase using a technique to measure the local shear viscoelastic properties. Safranin-O histology revealed a decrease in proteoglycans near the articular surface after collagenase and trypsin digestions, with proteoglycan depletion increasing in time. Similarly, confocal reflectance micrographs showed increasing collagen degradation in collagenase treated samples, although the collagen network remained intact after trypsin treatment. Both treatments induced changes in shear modulus that were confined to a narrow range (∼400µm) near tissue surface. In addition, collagenase altered the total energy dissipation distribution by up to a factor of 100, with longer digestion times corresponding to higher energy dissipation. The ability to detect local mechanical signatures in tissue composition and mechanics is an important tool for understanding the spatially non-uniform changes that occur in articular cartilage diseases such as OA.

Characterization of novel hyaluronic acid matrix systems for vaginal administration of metronidazole

ABSTRACTPolymers such as Hyaluronic acid (HA), Polyethylene glycol‐400 (PEG‐400) and Xanthan Gum (XG) are promising in drug delivery applicationsbecause of their biomedical and pharmaceutical potential applications. In HA 2%‐PEG 400 systems, the effect of pH and PEG‐400 concentration were evaluated. The viscosity of HA‐PEG 400 formulations slightly increased with PEG‐400 concentration. Viscoelastic properties and shear thinning character was strongly dependent on pH. Structured systems were obtained at pH 3, with an increase of several orders of magnitude in zero‐shear viscosity values. When XG 1% structured system is added on HA (0, 0.5, and 2%) and PEG‐400 5%, a sharp increase of viscosity can be observed, obtaining a gel‐like behaviour for HA 0.5%‐XG 1%‐PEG 400 5% formulation. Finally, metronidazole release profiles in HA 2% formulations with different PEG‐400 concentrations at pH 4.5 were studied. At least 90% of metronidazole was releasedat 24 h. However, the addition of XG 1% to the HA (0.5 and 2%)‐PEG 400 5% systems delayed the drug release. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41313.

Morphology and elasticity of polystyrene-block-polyisoprene diblock copolymers in the melt

The influence of morphology on the viscoelastic properties of melts of microphase-separated polystyrene-block-polyisoprene (PS-b-PI) diblock copolymers was investigated in oscillatory shear and creep recovery experiments. By means of anionic polymerization, three PS-b-PI diblock copolymers with a narrow molecular weight distribution and different types of morphology (spherical, cylindrical and lamellar microstructure) were prepared. Linear viscoelastic shear oscillations and creep recovery experiments in shear were performed in order to determine the elastic and viscous properties of the diblock copolymers in the melt at small and large time scales. Our analysis reveals that melts of diblock copolymers are characterized by a pronounced elastic behavior leading to a relatively large recoverable deformation in creep recovery experiments. The elasticity of the diblock copolymers is also revealed by the appearance of the creep-ringing effect. Morphological investigations were carried out to establish relations between microstructure and melt elasticity. Since ordering phenomena take place in melts of diblock copolymers until an equilibrium morphology is achieved, the storage modulus G′ of diblock copolymer melts increases with time up to a steady-state value.

Curcumin-Encapsulated Hexagonal Liquid Crystalline Formed by Brij 97/NaDC Mixtures

The phase diagram of a five-components Brij 97-NaDC/IPM-PEG 400/H2O system was determined at 25°C. The hexagonal liquid crystalline phase (H1) was found in this system. By use of small-angle x-ray scattering (SAXS), polarization microscopy, and rheology techniques, the influence of composition, temperature, and addition of curcumin on H1 phase was studied. It is shown that: 1) the investigated hexagonal liquid crystals exhibit a strong shear thinning behavior and viscoelasticity and the strength of the network of H1 phase becomes weaker with increasing oil content; 2) the frequency-dependent moduli of H1 samples decreases as the temperature increases and the steady-state limiting viscosity of the hexagonal samples shows an Arrhenius-like dependence on temperature; and 3) samples in H1 phase containing curcumin retained their organized hexagonal structure. The SAXS results show that the curcumin molecules may be solubilized both into the apolar core of cylinders together with IPM and in the polar domain coexisting with PEG 400 between the cylinders. When curcumin is encapsulated in samples with low oil content, there is a significant decrease in the frequency-dependent moduli. The tendency of frequency behavior for samples incorporating curcumin as a function of temperature is weakened.

Comparison of Poroviscoelastic Models for Sound and Vibration in the Lungs

Noninvasive measurement of mechanical wave motion (sound and vibration) in the lungs may be of diagnostic value, as it can provide information about the mechanical properties of the lungs, which in turn are affected by disease and injury. In this study, two previously derived theoretical models of the vibroacoustic behavior of the lung parenchyma are compared: (1) a Biot theory of poroviscoelasticity and (2) an effective medium theory for compression wave behavior (also known as a "bubble swarm" model). A fractional derivative formulation of shear viscoelasticity is integrated into both models. A measurable "fast" compression wave speed predicted by the Biot theory formulation has a significant frequency dependence that is not predicted by the effective medium theory. Biot theory also predicts a slow compression wave. The experimentally measured fast compression wave speed and attenuation in a pig lung ex vivo model agreed well with the Biot theory. To obtain the parameters for the Biot theory prediction, the following experiments were undertaken: quasistatic mechanical indentation measurements were performed to estimate the lung static shear modulus; surface wave measurements were performed to estimate lung tissue shear viscoelasticity; and flow permeability was measured on dried lung specimens. This study suggests that the Biot theory may provide a more robust and accurate model than the effective medium theory for wave propagation in the lungs over a wider frequency range.

Measurement of shear viscoelasticity using dual acoustic radiation pressure induced by continuous-wave ultrasounds

It is important to evaluate the viscoelasticity of muscle for assessment of its condition. However, quantitative and noninvasive diagnostic methods have not yet been established. In our previous study, we developed a method, which used ultrasonic acoustic radiation forces irradiated from two opposite horizontal directions, for measurement of the viscoelasticity. Using two continuous wave ultrasounds, an object can be actuated with an ultrasonic intensity, which is far lower (0.9 W/cm2) than that in the case of the conventional acoustic radiation force impulse (ARFI) method. In the present study, in vitro experiments using phantoms made of polyurethane rubber and porcine muscle tissue embedded in a gelatin block were conducted. We actuated phantoms by ultrasonic radiation force and measured the propagation velocity of the generated shear wave inside the phantoms using a diagnostic ultrasound system. The viscoelasticities of phantoms were estimated by fitting a viscoelastic model, i.e., the Voigt model, to the frequency characteristic of the measured shear wave propagation speed. In the mechanical tensile test, a softer polyurethane phantom exhibited a lower elasticity and a higher viscosity than a polyurethane phantom with a higher elasticity and a lower viscosity. The viscoelasticity measured by ultrasound showed the same tendency as that in the tensile test. Furthermore, the viscoelasticity of the phantom with porcine muscular tissue was measured in vitro, and the estimated viscoelasticity agreed well with that reported in the literature. These results show the possibility of the proposed method for noninvasive and quantitative assessment of the viscoelasticity of biological soft tissue.

Longitudinal measurement of extracellular matrix rigidity in 3D tumor models using particle-tracking microrheology.

The mechanical microenvironment has been shown to act as a crucial regulator of tumor growth behavior and signaling, which is itself remodeled and modified as part of a set of complex, two-way mechanosensitive interactions. While the development of biologically-relevant 3D tumor models have facilitated mechanistic studies on the impact of matrix rheology on tumor growth, the inverse problem of mapping changes in the mechanical environment induced by tumors remains challenging. Here, we describe the implementation of particle-tracking microrheology (PTM) in conjunction with 3D models of pancreatic cancer as part of a robust and viable approach for longitudinally monitoring physical changes in the tumor microenvironment, in situ. The methodology described here integrates a system of preparing in vitro 3D models embedded in a model extracellular matrix (ECM) scaffold of Type I collagen with fluorescently labeled probes uniformly distributed for position- and time-dependent microrheology measurements throughout the specimen. In vitro tumors are plated and probed in parallel conditions using multiwell imaging plates. Drawing on established methods, videos of tracer probe movements are transformed via the Generalized Stokes Einstein Relation (GSER) to report the complex frequency-dependent viscoelastic shear modulus, G*(ω). Because this approach is imaging-based, mechanical characterization is also mapped onto large transmitted-light spatial fields to simultaneously report qualitative changes in 3D tumor size and phenotype. Representative results showing contrasting mechanical response in sub-regions associated with localized invasion-induced matrix degradation as well as system calibration, validation data are presented. Undesirable outcomes from common experimental errors and troubleshooting of these issues are also presented. The 96-well 3D culture plating format implemented in this protocol is conducive to correlation of microrheology measurements with therapeutic screening assays or molecular imaging to gain new insights into impact of treatments or biochemical stimuli on the mechanical microenvironment.

Longitudinal Measurement of Extracellular Matrix Rigidity in 3D Tumor Models Using Particle-tracking Microrheology

The mechanical microenvironment has been shown to act as a crucial regulator of tumor growth behavior and signaling, which is itself remodeled and modified as part of a set of complex, two-way mechanosensitive interactions. While the development of biologically-relevant 3D tumor models have facilitated mechanistic studies on the impact of matrix rheology on tumor growth, the inverse problem of mapping changes in the mechanical environment induced by tumors remains challenging. Here, we describe the implementation of particle-tracking microrheology (PTM) in conjunction with 3D models of pancreatic cancer as part of a robust and viable approach for longitudinally monitoring physical changes in the tumor microenvironment, in situ. The methodology described here integrates a system of preparing in vitro 3D models embedded in a model extracellular matrix (ECM) scaffold of Type I collagen with fluorescently labeled probes uniformly distributed for position- and time-dependent microrheology measurements throughout the specimen. In vitro tumors are plated and probed in parallel conditions using multiwell imaging plates. Drawing on established methods, videos of tracer probe movements are transformed via the Generalized Stokes Einstein Relation (GSER) to report the complex frequency-dependent viscoelastic shear modulus, G*(ω). Because this approach is imaging-based, mechanical characterization is also mapped onto large transmitted-light spatial fields to simultaneously report qualitative changes in 3D tumor size and phenotype. Representative results showing contrasting mechanical response in sub-regions associated with localized invasion-induced matrix degradation as well as system calibration, validation data are presented. Undesirable outcomes from common experimental errors and troubleshooting of these issues are also presented. The 96-well 3D culture plating format implemented in this protocol is conducive to correlation of microrheology measurements with therapeutic screening assays or molecular imaging to gain new insights into impact of treatments or biochemical stimuli on the mechanical microenvironment.

Analysis of glass transition and relaxation processes of low molecular weight polystyrene-b-polyisoprene diblock copolymers

The objective of this study is to analyze the glass transition temperature and relaxation processes of low molecular weight polystyrene-block-polyisoprene diblock copolymers with different compositions, synthesized via anionic polymerization. Thermal properties were investigated by differential scanning calorimetry and dynamic-mechanical thermal analysis, while the morphologies at room temperature were investigated by transmission electron microscopy and small-angle X-ray scattering. The χN values indicate that the diblock copolymers lie near the weak segregation regime. Three different experimental techniques were applied to determine the dynamic properties, i.e., linear viscoelastic shear oscillations, creep recovery experiments, and dielectric spectroscopy. The rheological experiments were performed above the order–disorder transition temperature where the diblock copolymers behave like a Maxwell fluid. Our results indicate that the presence of the polyisoprene segments strongly influences the monomeric friction coefficient and the tendency to form entanglements above the order–disorder temperature. Consequently, the zero-shear rate viscosity of a diblock copolymer is much lower than the zero-shear rate viscosity of the neat polystyrene block (the polystyrene precursor of the polymerization procedure). Dielectric spectroscopy enables the analysis of relaxation processes below the glass transition of the polystyrene microphase. Frequency sweeps indicate the dynamic glass transition of the polyisoprene blocks, which are partly mixed with the polystyrene blocks, which are always the majority component in the block copolymers of this study.

A homogenization-enriched viscodamage model for cement-based material creep

We develop in this study a viscodamage model for cementitious materials based on the concept of pseudo-strains introduced by Schapery [1] coupled with the damage model of Mazars [2]. The pseudo-strains approach allows for reformulation of the initial viscoelastic problem as an equivalent elastic one by using a simple correspondence principle. The viscoelastic model results from a homogenization procedure in which the Mori–Tanaka scheme is applied in the Laplace–Carson space for estimating the effective linear viscoelastic bulk and shear moduli of the material. A composite made of a linear viscoelastic matrix described by a generalized Maxwell model and containing distributed spherical elastic inclusions and pores is adopted as a simplified representation of the material under consideration. One interesting feature of our approach is that exact analytical expressions for both bulk and shear moduli in the time space are derived in simple cases where a limited number of Maxwell chains are involved to describe the matrix behavior. The evolutions of the damage variable are governed by an equivalent pseudo-strain calculated from the pseudo-strains. The viscodamage model is applied to the simulation of cement paste basic creep tests available in the literature. After a proper identification of the parameters, an analysis of the results obtained with moderate creep loading reveals that the total strains evolutions are due mainly to the viscous characteristics of the material and to a lesser extent to the damage growth. The effects of the pore volume fraction of the material and of high load-levels leading to the specimen rupture on the creep response are further investigated and discussed.

Measuring viscoelasticity of soft tissues using shear and guided waves

Elasticity imaging has emerged as a viable clinical tool for assisting in diagnosis of certain diseases such as liver fibrosis and cancer. Many methods have been developed for generating and measuring shear waves in soft tissues. The advantage of using shear waves is that the shear wave velocity is proportional to the mechanical material properties of the tissues under investigation. Soft tissues are inherently viscoelastic and considerable effort has been made to quantify the dispersion, or variation of frequency, of the velocity and attenuation of shear waves. This is accomplished by measuring the shear wave motion and using Fourier-based techniques to extract the shear wave velocity and attenuation. Additional considerations are made in tissues where geometric dispersion is also present such as in the heart. Viscoelastic characterization of the shear viscoelasticity of soft tissues in vivo such as human liver, human kidney, and swine heart will be shown. We will also demonstrate parameterization of the results by using a model-free approach or by fitting the shear wave velocity dispersion to rheological models. The diagnostic value of the viscoelastic parameters will be discussed for each particular application. [This work was supported in part by NIH Grant Nos. DK092255, DK082408, and EB002167.]

Analysis of nonlinear shear stress–strain response of unidirectional GF/EP composite

Reasons for nonlinear stress–strain curves in shear of unidirectional glass fibre composite are analysed. Laminate with stacking sequence [45/−45]s is used in tensile quasi-static as well as in tensile creep and strain recovery tests to study the development of viscoelastic and viscoplastic shear strains in local coordinates of the ply. It is shown that Zapa’s integral representation of viscoplasticity is applicable for this material and methodology for parameter determination is given. Schapery’s nonlinear viscoelastic material model was used for shear response characterisation and the nonlinearity parameters’ dependence on the shear stress was determined and described by fitting functions. Microdamage development is quantified by measuring axial modulus and Poisson’s ratio of the laminate. The obtained nonlinear viscoelastic, viscoplastic model with included effect of microdamage was successfully used to predict the nonlinear shear stress–strain curve in strain controlled tensile loading.

Rheological assessment of a polymeric spherical structure using a three-dimensional shear wave scattering model in dynamic spectroscopy elastography

With the purpose of assessing localized rheological behavior of pathological tissues using ultrasound dynamic elastography, an analytical shear wave scattering model was used in an inverse problem framework. The proposed method was adopted to estimate the complex shear modulus of viscoelastic spheres from 200 to 450 Hz. The inverse problem was formulated and solved in the frequency domain, allowing assessment of the complex viscoelastic shear modulus at discrete frequencies. A representative rheological model of the spherical obstacle was determined by comparing storage and loss modulus behaviors with Kelvin-Voigt, Maxwell, Zener, and Jeffrey models. The proposed inversion method was validated by using an external vibrating source and acoustic radiation force. The estimation of viscoelastic properties of three-dimensional spheres made softer or harder than surrounding tissues did not require a priori rheological assumptions. The proposed method is intended to be applied in the context of breast cancer imaging.

Optimization of Soy-Butter from Sprouted Soybean and its Quality Parameters

The time and temperature of roasting of sprouted soybean was optimized using response surface method. The effect of roasting on sprouted whole kernel of soybean indicated that roasting time and temperature individually, as well as in combination, had a significant effect on hardness of roasted kernels. Sprouted soybean kernels were roasted at optimized temperature (127C) and time (37 min) and subsequently made into soy-butter (SB) and compared with reference soy-butter (RSB) on the basis of nutrient content, particle size, color, sensory quality and rheology. SB contained 38 g/100 g protein and 34 g/100 g fat. There was significant difference (P < 0.05) between RSB and SB in L* values. Sprouting improved flavor scores and SB showed higher organoleptic acceptability compared with RSB on a 9-point hedonic scale. Rheology showed that SB behaved like viscoelastic shear thinning material; like Bingham plastic at lower shear rates and Herschel-Bulkley (HB) fluid at higher shear rates. Practical Applications Soybean is an important crop due to its high protein content but soy products are not very popular due to problems of trypsin inhibitor, off-flavors, etc. Sprouting is a process known to improve the nutritional and functional quality while reducing the content of trypsin inhibitors and off-flavors of the bean and consequently of the product. SB, a comparatively new product of soybean, offers all positive attributes of soybeans, sprouting and sensory qualities of vegetable butters. A new process for manufacture of SB has been proposed in this paper. The nutrient quality, particle size and rheology have been studied. The process is simple and does not require any expensive or specialized equipment for commercial manufacture. Quality attributes of the product have been modeled so that effect of any change in process on the quality of product can be predicted or the manufacture process can be modified to achieve certain quality attribute.

COMPUTATIONAL MODEL TO DESIGN CIRCULAR RUNNER CONDUIT FOR PLASTIC INJECTION MOULD

Analytical solution quest for viscoelastic shear th inning fluid flow through circular conduit is a mat ter of great prominence as it directly evolvesmost efficient criteria to investigate various responses of independent parameters. En visaging this facet present endeavour attempts to develop a computational model for designing runner conduit lateral dimension in a plastic injection mould through which thermoplastic melt gets injected. At outset injection phenomenon is represented by gover ning equations on the basis of mass, momentum and energy conservation principles [ 1]. Embracing Hagen Poiseuille flow problem analogo us to runner conduit injection the manuscript uniquely imposes runner co nduit inlet and outlet boundary conditions along wi th relative to appropriate assumptions; governing equations evolve a computati on model as criteria for designing. To overwhelm No n-Newtonian’s abstruse Weissenberg-Rabinowitsch correction factor has been adopted byaccommodating thermoplastic melt behavio ur towards the final stage of derivation. The resulting final computatio nal model is believed to express runner conduit dim ensions as a function of available type of injection moulding machine specif ications, characteristics of thermoplastic melt and required features of component being moulded. Later the equation so obtained has bverified by using dimensional analysis method .

The rheology and processing behavior of starch and gum-based dysphagia thickeners

The addition of a starch or gum-based thickener to patient fluids with dysphagia is commonly carried out, but the mechanism behind the efficacy of this treatment is not fully understood. This paper describes the rheological behavior of two commercially available thickening powders and an additional xanthan gum solution with a view to explaining the efficacy of thickened fluids in terms of their rheology. Both linear viscoelastic and steady shear data were obtained for the fluids together with filament extensional stretch, decay, and breakup data. In order to follow the behavior of the fluids in a processing situation, a mechanical “Cambridge Throat” was designed and tested. The action of the tongue was modeled using a constant torque cam that forced fluid contained within a flexible membrane through a model throat. Movie photography captured images of the fluid behavior and showed that for a constant tongue torque, the transit time within the model throat increased with increasing fluid viscosity, with implications for the time available for the successful function of the larynx, throat muscles, and epiglottis.