Changes In Viscoelastic Properties Research Articles

Effect of addition of selected solid cosolutes on viscoelastic properties of model processed cheese containing pectin

The aim of this study was to investigate the effect of various selected solid low-molecular cosolutes ( d-glucose, d-fructose, d-galactose, lactose, saccharose; target concentrations in samples 1% w/w) on viscoelastic properties of model processed cheese (40% w/w dry matter and 50% w/w fat in dry matter) without and with pectin addition (target concentrations in final products: 0.2% w/w and 0.4% w/w, respectively). Dynamic oscillation rheometry with parallel plate geometry was used to evaluate the changes in viscoelastic properties of samples. All applied low-molecular cosolutes (1% w/w) decreased the firmness of processed cheese. The nature of cosolute was not significant, i.e. the firmness of final products was declined by various cosolutes to the similar level regardless of their (i) reducing or non-reducing ability; (ii) structure (mono- or disaccharide, aldose or ketose); or (iii) steric arrangement (comparison of two epimers – d-glucose and d-galactose). The reduction of sample rigidity due to cosolute addition was observed in both cases, i.e. in processed cheese without and also with pectin.

In Situ Monitoring of Conformational Changes of and Peptide Bindings to Calmodulin on a 27 MHz Quartz-Crystal Microbalance

Conformational changes of calmodulin (CaM) by additions of Ca(2+) ions and bindings of CaM-binding peptides to Ca(2+)/CaM followed by conformational changes were monitored by a CaM-immobilized 27 MHz quartz-crystal microbalance (QCM) with an admittance analysis. Both the binding and the conformational change events could be detected from the time-dependence of frequency decreases (mass increases) and energy dissipation decreases (elasticity increases), respectively. When Ca(2+) ions were injected to a QCM cell on which biotinylated CaM was immobilized with avidin-biotin interactions, a frequency increase (a mass decrease) and an energy dissipation decrease (an elasticity increase) were observed because of the dehydration and the elasticity increase caused by conformational changes from the flexible CaM to the rigid Ca(2+)/CaM exposing the hydrophobic surface. In the case of the addition of CaMKII-peptide in the Ca(2+)/CaM-immobilized QCM, the immediate frequency decrease (the mass increase) due to the binding of the peptide to Ca(2+)/CaM and the following energy dissipation decrease (the elasticity increase) with a time lag were observed. This suggests that the interaction of the CaMKII-peptide to Ca(2+)/CaM follows an allosteric binding mode. Binding kinetics of the peptide to Ca(2+)/CaM (k(1) and k(-1)) and kinetics of the following conformational change of Ca(2+)/CaM (k(2) and k(-2)) could be obtained. This technique is useful to investigate biomolecular interactions involving the conformational and/or viscoelastic property changes that are biologically important.

CHARACTERIZATION OF VISCOELASTIC PROPERTIES OF INDIVIDUAL RICE GRAIN BY MEASURING MECHANICAL IMPEDANCE

ABSTRACT The viscoelastic properties of individual rice grains were measured by using a novel oscillatory squeezing instrument. Specifically, rice grains at different moisture contents and cooking durations were chosen as the model grain, and their viscoelastic characteristics, namely viscous modulus and elastic modulus, were determined. During the measurement, the grains were squeezed between a rigid bottom plate and a top round element oscillating at random frequencies in the range of 10–30,000 rad/s. The mechanical impedance of the rice samples, defined as the ratio between the force applied to the samples and the oscillation velocity, was obtained and used to calculate viscoelastic parameters. Measurements with the grains having moisture content between 12.8 and 29.1% indicated that both viscous and elastic moduli of the samples decreased significantly with increasing moisture content. The measured mechanical impedances of the samples showed that changes in viscoelastic properties for various cooking periods can be also monitored using the proposed oscillatory squeezing method. PRACTICAL APPLICATIONSIn this study, a method for measuring viscoelastic properties of individual rice grain is presented. The technique is simple and easy to use. It can generate data for both elastic and viscous modulus properties for a single grain. There may be various practical applications for this instrument, such as textural characterization of grains having various chemical compositions and effect of cooking parameters on texture. The presented method can be also used to obtain textural differences between different varieties.

Optofluidic stretching of RBCs using single optical tweezers

AbstractOur previous studies demonstrated a huge difference in rotational speed of trapped red blood cells under diseased condition, which was presumably attributed to change in viscoelastic properties. Here, we report use of single optical tweezers combined with viscous drag for stretching of the trapped cell. Significant differences were observed in the measured viscoelastic parameters of fresh and aged/malaria‐infected RBCs under hypotonic condition. The technique was also found to provide information about adhesion properties of RBCs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Identification of viscoelastic parameters of skin with a scar in vivo, influence of soft tissue technique on changes of skin parameters

The goal of the experiment was to develop an identification method capable of objective detection of changes of viscoelastic properties of skin with a scar remaining after a modified radical mastectomy. We compared the intact skin and the skin with a scar, a scar before and after physiotherapy. We used two methods. The first one is based on measurements of the local dynamic deformation response of the skin and the second one is the matrix identification of static deformation that identifies properties of the whole tested region of the explored tissues. We identified the skin stretchability, shiftability against deeper layers and deeply analysed both the methods. In some patients, we found statistically proven difference. In all these cases the measurement methods have detected changes of the observed tissue condition. We found both methods to be potentially applicable after further improvements as a diagnostic tool, which can contribute to the improvement of postoperative care of patients.

Effect of soluble dietary fibre addition on rheological and breadmaking properties of wheat doughs

The aim of this experimental work was to evaluate the effect of inulin addition on the rheological properties of common wheat doughs and bread quality. Three commercial fructan products of different number average degree of polymerisation (DPn) were used (DPn = 10 for inulin ST; DPn = 23 for inulin HP and HP-gel). Inulin contents from 2.5 to 7.5% on dry matter (wheat flour plus inulin) were used. Dough rheological properties were investigated using farinograph and dynamic rheological measurements. Upon addition of dietary fibre (DF), significant increase in mixing time and stability, and decrease in water absorption were recorded. Inulin ST exerted greater effect on water absorption than HP products. Inulin with high DP determined large changes in linear viscoelastic properties of dough. The storage modulus ( G′) gradually increased and tan δ decreased with increasing levels of inulin HP and HP-gel, which contribute to the overall dough elasticity and strength. The increase in solid-like behaviour with DF content prevented expansion of wheat dough during the fermentation stage. No significant differences were observed between sample HP and HP-gel. Enrichment with inulin ST led to lower changes in linear viscoelastic properties of dough at farinograph water absorption than inulin HP. Bread volume was significantly reduced and crumb hardness was enhanced by inulin HP level in the range 5–7.5%. When inulin ST was added to a flour suitable for breadmaking, a trend of increasing bread volume with the increase of DF content was found.

Enzyme-Catalyzed Formation and Structure Characteristics of A Protein-Based Hydrogel

A protein-based hydrogel with tunable gelation time and mechanical strength was obtained by the hydrogelation of soy protein isolate (SPI) in the presence of microbial transglutaminase (MTGase). In order to control the gelation process and understand the relationship between the property and network structure of the formed SPI hydrogel, the changes of viscoelastic properties with time during the gelation process were monitored by the use of dynamic rheometry. The measurements were carried out at different protein concentrations, enzyme amounts, and reaction temperatures to clarify their effects on the gelation kinetics. In particular, the fractal characteristics of the SPI hydrogels formed in the presence and absence of MTGase were examined by relating the rheological data to a scaling model. In addition, the resultant SPI hydrogel matrix was investigated for the controlled release of 5-aminosalicylic acid as the model drug.

Change of viscoelastic property and morphology of fibrin affected by antithrombin III and heparin: QCM-Z and AFM study

Viscoelastic property and morphology of fibrin, which is caused by the enzymatic action of thrombin on fibrinogen, was studied quantitatively as a function of antithrombin III (AT) and heparin concentration by adding fibrinogen, heparin, AT, and thrombin, sequentially. A quartz crystal microbalance with impedance analysis (QCM-Z) was used to detect the change of viscoelastic properties as well as the thickness of adsorbed layer during fibrin formation process, while AFM was used to characterize the surface morphology of fibrin layer under the influence of two known anticoagulants. By the addition of fibrinogen initially, a rigid and thin fibrinogen layer with rather smooth surface morphology was formed on the substrate. Then, the addition of thrombin in the absence of AT and heparin, resulted in viscous and thick fibrin gel with textured surface morphology. As an anticoagulant, AT was added before the injection of thrombin, but AT in the absence of heparin showed only marginal effects at higher concentration of AT than that of thrombin. On the contrary, the thick and viscous fibrin layer was altered gradually to more fibrinogen-like layer as the heparin concentration increases at low concentrations of AT, demonstrating the powerful anticoagulant effect by heparin/AT complex. Interestingly, heparin alone without AT was also effective in preventing fibrin formation, influencing the viscoelastic property and morphology of fibrin.

Rheological properties of asphalt mixtures containing various fibers

Rheological characteristics of fiber-modified asphalt mixture were investigated. Cellulous fiber, polyester fiber and mineral fiber were used as additives for asphalt mixture, and the dosages were 0.3%, 0.3%, 0.4%, respectively. Dynamic modulus test using superpave simple performance tester (SPT) was adopted to study the dynamic modulus and phase angle for the control mixture and fiber-modified ones at various temperatures and frequencies. Test results show that the rheological properties can be improved significantly by the addition of various fibers. The dynamic modulus increases with the increase of frequency, and the phase angle decreases with the increase of frequency. When various fibers are used, the dynamic modulus increases and phase angle decreases at each frequency. This indicates that the stiffness and the elastic portion of fiber-modified asphalt mixtures can be enhanced when various fibers are used, which results in the change of viscoelastic properties of mixtures. The creep test results show that the total strain and the permanent strain of asphalt mixtures during load-unload cycle can be significantly reduced, which results in the improvement of resistance to permanent deformation for asphalt mixtures containing various fiber additives. The Burgers model can be employed effectively to illustrate the rheological properties of fiber modified asphalt mixtures.

Electrochemically Active Dendritic−Linear Block Copolymers via RAFT Polymerization: Synthesis, Characterization, and Electrodeposition Properties

We describe a series of well-defined dendritic−linear block copolymer architectures via the reversible addition−fragmentation chain transfer (RAFT) polymerization technique. Using dendritic chain transfer agents (CTA)s possessing a single dithioester moiety at the focal point, RAFT polymerization was carried out to attach polystyrene (PS) and poly(methyl methacrylate) (PMMA) chains of controlled lengths by kinetic control. To provide electrochemical functionality, the dendritic CTAs were designed with carbazole moieties at the periphery of the structures. The results on the electrochemical polymerization of the carbazole moieties at the periphery of the dendritic component of the block copolymers reveal quantitative cyclic depositions with changes in viscoelastic properties of the deposited films as monitored by the electrochemical quartz crystal microbalance technique. The electroactive dendritic blocks proved to be an effective electrochemically active macromonomer for the electrodeposition of these str...

Relationship between viscoelastic properties of soft denture liners and clinical efficacy

Soft denture liners are applied for denture wearers who cannot tolerate a hard-based denture due to a thin and non-resilient oral mucosa and/or severe alveolar resorption. This material distributes and absorbs masticatory forces by means of the cushioning effect. Clinical success of the materials depends both on their viscoelastic properties and on durability. Acrylic resins and silicones are mainly available for permanent soft liners. The acrylic permanent soft liners demonstrate viscoelastic behavior while silicone permanent soft liners demonstrate elastic behavior. The improvement in masticatory function is greater in dentures lined with the acrylic materials than in those lined with silicone products. However, the acrylic materials exhibit a more marked change in viscoelastic properties and loss of cushioning effect over time than silicones. From the standpoint of durability, the silicones are preferred. It is important to understand viscoelastic properties and durability of each soft denture liner and to select the material according to the clinical situations and purposes. The ideal permanent soft liners have a relatively high value of loss tangent and storage modulus, and high durability. Further research is necessary to develop the ideal soft denture liner.

Viscoelastic Property Mapping along Encrusted Polymeric Urinary Catheters

Mapping of the material viscoelastic property variation along the length axis of polymeric stents. Five pigtail ureteral stents and five percutaneous stents placed in vivo for different periods were studied. Viscoelastic property changes along the length of polymeric stents were measured using the dynamic mechanical analysis technique. The type of encrustations was identified using FT-IR spectroscopy and their morphology by scanning electron microscopy (SEM). Variations in viscoelastic stiffness were confirmed for both types of stents. In a few cases, the variation was quite large (400%). Various encrustation types and/or organic sheathing of the salt were found to be responsible for this effect. In detail, calcium oxalate monohydrate (COM) plaques for percutaneous and COM/organic layer for pigtail stents were recognized by FT-IR spectroscopy and SEM observation to invoke reinforcing effects along the stent axes. The phenomenon of stiffness variation along the stent axes requires further study to understand the mechanism behind it and consequently to improve the biomaterial and design of specific areas of stents as well as to avoid encrustations. This further research might lead in the near future to the development of new types of polymer stents for drug-eluting specialized areas.

The rebodying of stirred yoghurt: interactions between proteins

The aim of the present study was to identify the nature of bonds established between protein particles after stirring that are responsible for the texture improvement of stirred yoghurts, called rebodying. Using a constant model yoghurt at pH 4.4, the effects of changes in the physicochemical conditions at stirring were studied on the subsequent rebodying. Short term rebodying was measured as the changes in viscoelastic properties at 4 degrees C during 20 h after stirring, while long-term rebodying was measured as the viscosity changes during 28 d storage at 4 degrees C. Moreover, stirred gels obtained from either set gels that were allowed time or not for ionic equilibration were compared. Increasing or decreasing ionic strength did not change the properties of stirred gels. Calcium chloride addition significantly decreased G'0 h, G'20 h and tan20 h but did not induce changes in the gel microstructure as observed by confocal scanning microscopy. Yoghurt rebodying could not be explained by fulfilling ionic equilibrium. Moreover, N-ethyl maleimide addition had no effect on the stirred yoghurt. Attractive electrostatic and disulphide interactions were not involved in the gel rebodying and increasing calcium concentration in the set gel limited rebodying.

Arterial structure and function in end-stage renal disease

Cardiovascular disease is a major cause of morbidity and mortality in patients with end-stage renal disease (ESRD). Macrovascular disease develops rapidly in ESRD patients and is responsible for the high incidence of left ventricular hypertrophy, ischemic heart disease, cerebrovascular accidents, and peripheral artery diseases. Occlusive lesions due to atheromatous plaques frequently cause these complications; however, atherosclerosis represents only one form of structural response to metabolic and hemodynamic alterations interfering with the "natural" process of aging. The spectrum of arterial alterations in ESRD is broader, including large artery remodeling, changes in viscoelastic properties, and stiffening of arterial walls. Nonatheromatous remodeling principally changes the dampening function of arteries, characterized by stiffening of arterial walls and with deleterious effects on the left ventricle and coronary perfusion. The origin of arterial stiffening in ESRD patients is multifactorial, with extensive arterial calcifications as an important covariate.

The Effects of Thermal Cycles on the Impact Fatigue Properties of Thermoplastic Matrix Composites

The effects of thermal cycles on the impact fatigue properties of unidirectional carbon fibre reinforced polyetherimide (PEI) matrix composites were investigated. During the thermal cycles, samples were immersed into boiling water (100 °C) and subsequently to ice water (0 °C), 50, 200 and 500 times. The changes in viscoelastic properties of the composites were investigated by means of dynamic mechanical thermal analyzer (DMTA). At the second step, thermal cycled composites were subjected to repeated impact loadings, with different impact energies. Instrumented impact test results were presented as a function of force, energy, deformation during the experiments. The scanning electron microscope (SEM) studies were done in order to understand the morphology of fractured samples after impact fatigue loading. The number of thermal cycles and applied impact energy of the hammer are found to have a great importance on the fracture morphology of repeatedly impacted material, as expected.

Viscoelastic properties of polyacrylonitrile terpolymers during thermo‐oxidative stabilization (cyclization)

AbstractA study on the thermo‐oxidative stabilization (cyclization) of polyacrylonitrile (PAN) terpolymers using dynamic mechanical thermal analysis (DMTA) is reported in this article. When the changes in viscoelastic properties were monitored in a rectangular tension mode, besides the tan δ peak characteristic of the glass transition observed below 200°C, the copolymer and the terpolymer displayed a second peak above 200°C due to the cyclization leading to the formation of ladder structures. The initiation temperature of the cyclization process as well as the peak temperature is found to depend on the acid value and the composition of the precursor polymer. The results presented show that monitoring the changes in viscoelastic properties during cyclization provides insight into the material properties as a result of the chemical changes that are taking place. These observations were confirmed by structural characterization using IR spectroscopy, and the observed chemical changes agree with the literature studies, as due to the thermal cyclization process. Copyright © 2008 John Wiley & Sons, Ltd.

Success and complication rates of endoscopic third ventriculostomy for adult hydrocephalus: a series of 108 patients

Background The clinical response to ETV of adult patients with noncommunicating hydrocephalus may differ from that of children because of such factors as chronicity of hydrocephalus, physiologic differences in CSF dynamics, and changes in brain viscoelastic properties. We sought to determine which factors might predict clinical success and failure. Methods A retrospective single-surgeon case series analysis was performed. This was a consecutive case series for which the goal of the ETV procedures was shunt independence. One hundred ten ETV procedures were performed in 108 adult patients (mean, 48 years; range, 17-88 years). There were 52 cases of idiopathic aqueductal stenosis, 47 cases of mass lesions causing noncommunicating hydrocephalus, plus 9 other miscellaneous obstructive etiologies. Results Long-term shunt independence was achieved in 77% of patients. Two additional patients, who initially failed, later achieved success after reoperation and remained shunt free for the duration of their follow-up. Therefore, after reoperation, shunt independence was achieved in 79% of patients. Of the patients who ultimately failed, 11 failed within 1 month. Therefore, 52% who ultimately failed had more than 1 month of shunt-free existence (mean, 10 months). There were 6 surgical complications, including 2 deaths related to intracranial hemorrhage from brain tumors (not directly related to ETV per se), and 10 medical complications. The median hospital length-of-stay was 3 days. The median follow-up was 8 months (range, 0-95 months). Conclusions Endoscopic third ventriculostomy is an effective treatment option for adult patients with noncommunicating hydrocephalus. Although most procedures resulted in long-term shunt independence, more than half of the eventual failures were delayed, and therefore, appropriate follow-up is required.

Polyepoxide–water interactions: Influence of the chemical structure of the network

We have investigated the influence of the chemical structure of polyepoxide networks on the sorption behaviour and water-induced changes of viscoelastic and mechanical properties. The β relaxation was found to be unaffected by the presence of adsorbed water for an anhydride and an aromatic amine based polyepoxide. The anhydride based network shows better behaviour in a water environment than the aromatic amine based network in terms of plasticisation, reversibility of the degradation and loss of mechanical properties. This has been attributed to (i) a smaller crosslinking density, leading to a smaller specific volume in the glassy state and thus a smaller water uptake and (ii) a strong interaction between water and tertiary amines in epoxide–aromatic amine networks. This interaction, probably of electrostatic nature, would result from the delocalization of the doublet of the nitrogen atom. The results are critically compared to the literature on aliphatic amine based polyepoxides, where the dependence of the β relaxation on the water content is proposed to be related to the electron-donating ability of the aliphatic chain.

Elastometric sensing using higher flexural eigenmodes of microcantilevers

We present a method to detect with high sensitivity the viscoelastic property changes of sensor coatings on microcantilever arrays due to radiation, analyte binding, or adsorption. The method uses higher order flexural eigenmodes to identify the location and magnitude of the nonuniform elasticity changes in the microcantilever coating. We demonstrate the method by monitoring the time evolution of resonance frequencies and Q factors of different flexural eigenmodes of microcantilevers functionalized with a small drop of a photosensitive polymer as it is exposed to ultraviolet radiation. The method is particularly well suited for measuring quantitatively the time varying viscoelastic properties of thin films or biological materials attached to microcantilevers.

Quartz Crystal Microbalance Studies of Multilayer Glucagon Fibrillation at the Solid-Liquid Interface

We have used a quartz crystal microbalance with dissipation (QCM-D) to monitor the changes in layer thickness and viscoelastic properties accompanying multilayer amyloid deposition in situ for the first time. By means of atomic force microscope imaging, an unequivocal correlation is established between the interfacial nucleation and growth of glucagon fibrils and the QCM-D response. The combination of the two techniques allows us to study the temporal evolution of the interfacial fibrillation process. We have modeled the QCM-D data using an extension to the Kelvin-Voigt viscoelastic model. Three phases were observed in the fibrillation process: 1), a rigid multilayer of glucagon monomers forms and slowly rearranges; 2), this multilayer subsequently evolves into a dramatically more viscoelastic layer, containing a polymorphic network of micrometer-long fibrils growing from multiple nucleation sites; and 3), the fibrillar formation effectively stops as a result of the depletion of bulk-phase monomers, although the process can be continued without a lag phase by subsequent addition of fresh monomers. The robustness of the QCM-D technique, consolidated by complementary atomic force microscope studies, should make it possible to combine different components thought to be involved in the plaque formation process and thus build up realistic models of amyloid plaque formation in vitro.