Cone-plate Rheometer Research Articles

Estimation of Cellular Forces during Migration through Non-Linear and Non-Affine Collagen Networks

Reconstituted collagen gels are a widely used environment to study cell migration in three dimensions. Collagen gels show strain stiffening and a strong lateral contraction during extension (Poisson ratio > 0.5). This behavior is not explained by linear elastic theory. To make quantitative estimates about the cellular forces and local mechanical properties of the matrix that the migrating cell encounters, a constitutive model of the gel is needed. On a microscopic scale, collagen gels consist of a network of mechanically coupled collagen fibrils that show buckling under compression and tautening and alignment under extension. These effects give rise to non-affine behavior of the network, which is virtually impossible to model or simulate numerically on a larger scale. Instead, we take advantage of the fact that the effects of a non-affine deformation is well captured by an affine network with non-linear elements. We extract the nonlinear force-length relationship of the network elements from two types of rheological measurements. First, we stretch and compress a collagen gel in the horizontal direction and measure its vertical contraction and dilation. From this we extract the asymmetry of the force-length relationship between extension and compression. Second, we shear a collagen gel in a cone plate rheometer. From this we extract the force-length relationship under extension. Finally, with a finite element analysis we compute the deformation field of a collagen gel around a contracting ellipsoid. We find that our model recapitulates the complex gel deformations typically measured around invasive tumor cells, such as a very large contraction of the gel surface above the cell.

Effect of Ultra High Molecular Weight Polyacrylonitrile (UHMW-PAN) on the Rheological Behavior of PAN/DMSO Solution

The effects of ultra high molecular weight Polyacrylonitrile (UHMW-PAN) on the rheological behavior of PAN/DMSO solution have been investigated using a cone-plate rheometer in this work. The rheological behavior was characterized by steady shear and oscillation test It is observed from the measurements that, the rheological behavior of the polymer mixture of UHMW-PAN and AMW-PAN makes a difference to the AMW-PAN solution due to macromolecular entanglements, the viscosities of the solutions decreased with the rising of shear rate, shear viscosity rise with the increase of the molecular weight of the UHMW-PAN. For dynamic experiments, a steady increase of both and with the increase of oscillation frequency and molecular weight of UHMW-PAN was seen for all samples. The and increase with the decrease of the temperature or with the increase of the contents of the UHMW-PAN.

Rheological non-Newtonian behaviour of ethylene glycol-based Fe2O3 nanofluids

The rheological behaviour of ethylene glycol-based nanofluids containing hexagonal scalenohedral-shaped α-Fe2O3 (hematite) nanoparticles at 303.15 K and particle weight concentrations up to 25% has been carried out using a cone-plate Physica MCR rheometer. The tests performed show that the studied nanofluids present non-Newtonian shear-thinning behaviour. In addition, the viscosity at a given shear rate is time dependent, i.e. the fluid is thixotropic. Finally, using strain sweep and frequency sweep tests, the storage modulus G', loss modulus G″ and damping factor were determined as a function of the frequency showing viscoelastic behaviour for all samples.

Synthesis and Properties of Alkylbenzene Sulfonate Gemini Surfactants with High Viscosity in Dilute Solution without Additives

Several new dialkyldibenzene disulfonate Gemini surfactants with high viscosity have been synthesized by a new method and analysed by 1H NMR, ESI-MS, and IR. The influence of spacer and alkyl chain length on their melting temperatures and Krafft temperatures were researched. These surfactants exhibit special viscoelastic properties even in dilute solutions without addictives, which can be observed visually and also researched by cone-plate rheometer at different concentrations.

Comparison of Two Platelet Activation Markers Using Flow Cytometry After In Vitro Shear Stress Exposure of Whole Human Blood

Platelet activation is the initiating step to thromboembolic complications in blood-contacting medical devices. Currently, there are no widely accepted testing protocols or relevant metrics to assess platelet activation during the in vitro evaluation of new medical devices. In this article, two commonly used platelet activation marker antibodies, CD62P (platelet surface P-selectin) and PAC1 (activated GP IIb/IIIa), were evaluated using flow cytometry. Anticoagulant citrate dextrose solution A (ACDA) and heparin anticoagulated human blood from healthy donors were separately exposed to shear stresses of 0, 10, 15, and 20 Pa for 120 s using a cone-plate rheometer model, and immediately mixed with the platelet marker antibodies for analysis. To monitor for changes in platelet reactivity between donors and over time, blood samples were also evaluated after exposure to 0, 2, and 20 µM of adenosine diphosphate (ADP). Following ADP stimulation, the percentage of both CD62P and PAC1 positive platelets increased in a dose dependent fashion, even 8 h after the blood was collected. After shear stress stimulation, both CD62P and PAC1 positive platelets increased significantly at shear stress levels of 15 and 20 Pa when ACDA was used as the anticoagulant. However, for heparinized blood, the PAC1 positive platelets decreased with increasing shear stress, while the CD62P positive platelets increased. Besides the anticoagulant effect, the platelet staining buffer also impacted PAC1 response, but had little effect on CD62P positive platelets. These data suggest that CD62P is a more reliable marker compared with PAC1 for measuring shear-dependent platelet activation and it has the potential for use during in vitro medical device testing.

Influence of Oleic Acid on the Rheology and in Vitro Release of Lumiracoxib from Poloxamer Gels

Transdermal delivery of anti-inflammatory lumiracoxib (LM) could be an interesting strategy to avoid the side effects associated with systemic delivery, but it is ineffective due to the drug poor skin penetration. We have investigated the effects of oleic acid (OA), a lipid penetration enhancer, on the in vitro release of LM from poloxamer-based delivery systems (PBDS). The rheological behavior (shear rate dependent viscosity) and gelation temperature through measurements of optimal sol-gel transition temperatures (Tsol-gel) were also carried out in these systems. In vitro release studies of LM from PBDS were performed using cellulose acetate as artificial membrane mounted in a diffusion system. The amount of LM released was divided by exposition area (microg/cm2) and these values were plotted as function of the time (h). The flux of the drug across the membrane (J) was calculated from the slope of the linear portion of the plot and expressed as microg/cm2. h -1. The determination of viscosity was carried out at different shear rates (gamma) between 0.1- 1000 S-1 using a parallel plate rheometer. Oscillatory measurements using a cone-plate geometry rheometer surrounded by a double jacket with temperature varying 4-40 degrees C, was used in order to determine Tsol-gel. Increase of both polymer and OA concentrations increases the viscosity of the gels and consequently reduces the in vitro LM release from the PBDS, mainly for gels containing OA at 10.0% compared to other concentrations of the penetration enhancer. Tsol-gel transition temperature was decreased by increasing viscosity; in some cases the formulation was already a gel at room temperature. Rheological studies showed a pseudoplastic behavior, which facilitates the flow and improves the spreading characteristics of the formulations. Taken together, the results showed that poloxamer gels are good potential delivery systems for LM, leading to a sustained release, and also have appropriate rheological characteristics. Novelty of the work: A transdermal delivery of non-steroidal antinflammatory drugs like lumiracoxib (LM) can be an interesting alternative to the oral route of this drug, since it was recently withdraw of the market due to the liver damage when systemically administered in tablets as dosage form. There are no transdermal formulations of LM and it could be an alternative to treat inflammation caused by arthritis or arthrosis. Then, an adequate delivery system to LM is necessary in order to release the drug properly from the PBDS as well as have good characteristics related to semi-solid preparations for transdermal application, which were evaluated through in vitro release studies and rheological behavior in this paper, respectively.

Analysis of the structure and mass transport properties of clay nanocomposites based on amorphous PET

AbstractThe aim of this work is to characterize the rheological and permeability behavior of nanocomposites based on amorphous poly(ethylene terephthalate) (PETg) and organically modified montmorillonites (omMMT), obtained by melt intercalation. The use of PETg instead of semicrystalline PET is believed to reduce the risks associated to organic modifier degradation during processing at high temperatures. X‐ray and transmission electron microscopy analysis performed on the PETg nanocomposites showed that processing for long time at temperatures lower than melting of semicrystalline PET allowed to obtain a partially intercalated structure with some degree of exfoliation. The rheological behavior of PETg nanocomposites was studied as a function of shear rate in a cone–plate rheometer in order to correlate the viscosity with the aggregation state of omMMT. A simple model accounting for an apparent increase of rheological units size, associated with the intercalation of PETg macromolecules into omMMT galleries, is proposed. The glass transition temperature, Tg, as a function of the volume fraction of omMMT content of the nanocomposite, was measured using differential scanning calorimetry. Finally, the water vapour permeability of PETg nanocomposites was correlated to the volume fraction of the impermeable inorganic part of the omMMT. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Poro-Viscoelastic Behavior of Gelatin Hydrogels Under Compression-Implications for Bioelasticity Imaging

Ultrasonic elasticity imaging enables visualization of soft tissue deformation for medical diagnosis. Our aim is to understand the role of flow-dependent and flow-independent viscoelastic mechanisms in the response of biphasic polymeric media, including biological tissues and hydrogels, to low-frequency forces. Combining the results of confined and unconfined compression experiments on gelatin hydrogels with finite element analysis (FEA) simulations of the experiments, we explore the role of polymer structure, loading, and boundary conditions in generating contrast for viscoelastic features. Feature estimation is based on comparisons between the biphasic poro-elastic and biphasic poro-viscoelastic (BPVE) material models, where the latter adds the viscoelastic response of the solid polymer matrix. The approach is to develop a consistent FEA material model (BPVE) from confined compression-stress relaxation measurements to extract the strain dependent hydraulic permeability variation and cone-plate rheometer measurements to obtain the flow-independent viscoelastic constants for the solid-matrix phase. The model is then applied to simulate the unconfined compression experiment to explore the mechanics of hydropolymers under conditions of quasi-static elasticity imaging. The spatiotemporal distributions of fluid and solid-matrix behavior within the hydrogel are studied to propose explanations for strain patterns that arise during the elasticity imaging of heterogeneous media.

Non-linear Rheology Of Collagen Type I Gels Probed On The Length Scale Of A Migrating Cell

Recent investigations showed that the dimensionality of the environment in which living cells are cultured - flat 2D culture wells versus 3D biopolymer networks - has a strong effect on cell morphology, metabolism and migration. The reason for these differences are unclear. What is lacking is a fundamental understanding of the mechanical and morphological properties of 3D matrices at varying length scales.We probe the local microrheology of a series of reconstituted collagen gels with different concentrations (1.2 - 2.4 mg/ml) by applying a calibrated force on embedded magnetic particles (O4.5μm) using magnetic tweezers. The resulting strain field within the matrix is visualized by tracking the positions of polystyrene spheres (O1μm) embedded in the collagen gels. This strain field is compared to expectations from continuum theory. In addition, the local microrheology is compared to bulk rheological properties measured in a cone-plate rheometer. At low forces and strains below 3%, local and bulk rheological properties agree closely, and the strain field follows that of a continuum linear elastic material. At higher strains, marked non-linear strain stiffening occurs, showing an increase in modulus of nearly 20-fold until the material eventually yields. Because of the non-uniform shear conditions around magnetic beads in the local microrheology experiments, the non-linear stiffening appeared to be less pronounced, but the strain field spread much farther out than expected from continuum theory. These data suggest that the strain stiffening behavior of collagen gels, together with the well-documented ability of cells to sense the stiffness of their surroundings, could account for the differences in cell behavior seen in 2D versus 3D culture conditions.

Rheological behavior of fibre-filled polymer melts at low shear rate. Part II. Experimental investigation

In this study, rheological properties of carbon fibre-filled polypropylene and polyethylene melts at low shear rate were measured using a cone-plate rheometer. The melts with high fibre loading show complex shear flow depending on the fibre concentration, its length and length distribution, as well as on shear rate and matrix characteristics. The existence of yield stress and time-dependent or shear-strain-dependent properties are also discussed and compared with previous results. The shear flow in the narrow gap of cone-plate rheometer influences the fibre assembly. However, the effect of low shear rate on the structure of fibre assembly is negligible.

Phase behavior and its viscoelastic response of polylactide/poly(ε-caprolactone) blend

Polylactide (PLA)/polycaprolactone (PCL) blends with various blend ratios were prepared via melt mixing. The morphology, linear and non-linear viscoelastic properties of the blend were studied using scanning electron microscope (SEM) and cone-plate rheometer. Three typical immiscible morphologies, i.e., spherical droplet, fibrous and co-continuous structure can be observed at various compositions. The elasticity ratio was proposed to play an important role together with the viscosity on the phase inversion because PLA/PCL blend presents a high viscosity ratio between two components. Two emulsion models were used to predict the linear viscoelastic properties of the blend with various morphologies. The Palierne model gives better fit compared with the G–M model, but both fail to predict the viscoelastic properties of the co-continuous blend. The viscoelastic behavior of those blends shows different temperature dependence due to their different morphologies. The principle of time–temperature superposition (TTS) is only valid for the co-continuous blend while fails with the rheological data of those blends with discrete spherical and fibrous domain structure. Moreover, although the discrete phase is difficult to be broken up due to the high viscosity ratio of the systems, the change of viscoelastic responses of those blends before and after preshear shows large difference, indicating that different morphologies have different sensitivity to the steady shear flow.

Influence of Multiwalled Carbon Nanotube on Rheological Behavior of Mesophase Pitches

The rheological behaviors of mesophase pitch containing different contents (0, 1.0, 2.0 wt%) of multi-wall carbon nanotubes (MWNTs) were studied by using ARES cone-plate rheometer. The dynamic response of mesophase pitch containing MWNTs was different from that of pure mesophase pitch due to the MWNTs as a suspension in viscous pitch. The dynamic viscosity increased with increasing the amount of MWNTs, which is a clear evidence of the interruption of MWNTs in mesophase pitch. Also, the phase angle result indicates that mesophase pitch containing MWNT had less elastic nature than pure mesophase pitch.

532 コーンプレート型せん断応力負荷装置による細胞ソーティング(T10-3 マイクロ・ナノバイオテクノロジー(3):デバイス開発・医療応用を目指して,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

532 コーンプレート型せん断応力負荷装置による細胞ソーティング(T10-3 マイクロ・ナノバイオテクノロジー(3):デバイス開発・医療応用を目指して,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

11603 コーンプレート型せん断応力負荷装置を用いた細胞ソーティングモデルの構築(バイオエンジニアリング,一般講演,学術講演)

Hematopoietic stem cells (HSCs) have the ability to renew themselves and the ability to differentiate all blood cell types. They play an important role in the treatment of leukemia. They are extracted from peripheral blood or bone marrow, however, the rate of HSCs is rare. So a system which extracts HSCs from peripheral blood or bone marrow efficiently and gently is required. We developed a cell sorting system using a cone-plate rheometer for extraction of rare cells from cell mixture. The separation principle of this system is based on specific adhesion by the antigen-antibody reaction between cells and antibody-coated plate. In this paper, we evaluated the performance of this cell sorting system.

Effect of natural additives on the rheological properties of cellulose fiber disperse systems

Some polysaccharides were added to cellulose fiber disperse systems to improve their rheological properties. The viscoelastic properties of the systems were measured with a parallel-plates or a cone-plate type rheometer. For the thin systems, their flocculation behaviors were also observed with a high-speed camera as well as the flow properties. Although Tororoaoi mucilage, which is used as a dispersant in the Japanese traditional papermaking, had no effect on the systems, guar gum and xylan had preferable effects on reducing the dynamic moduli. For all the systems, a power law relation was found between the dynamic moduli and the fiber concentrations; however, the exponent value was varied with the addition amount and kind of the polymers. These additives had no significant effect on reducing flocculation of the systems but preferable effect on reducing the stress leaps of the systems. The sedimentation volume measurements well represent the effect of the added polysaccharides. These results indicate that the addition of guar gum or xylan reduces the friction at the fiber contact points; and moreover, it makes the fibers lie in the better order and laminate more regularly.

Synthesis and characterization of clay-nanocomposite solvent-based polyurethane adhesives

In this work nanocomposite adhesives obtained using an organically modified montmorillonite (OMM) in a polyurethane matrix were studied. An amount of organoclay ranging from 3% up to 18% by weight was added to the polyol resin before mixing with isocyanate. In particular, a typical adhesive formulation used in laminated films for food packaging was studied. The effect of different preparation procedures was compared in order to correlate exfoliation with rheological and mechanical properties. The basal distance of OMM before and after mixing with the polyol and after curing was characterized by X-ray diffraction. Composites with low content of OMM show an intercalated structure. A mix of exfoliated and intercalated layers was observed in the composites with the highest OMM content, before and after curing. The basal distance of OMM decreases after solvent mixing and curing, suggesting that exfoliation and intercalation are improved with respect to the uncured system. The viscosity of polyols-OMM systems was studied as function of shear rate in a cone-plate rheometer in order either to check the possible degradation of the polyol oligomer on to correlate the viscosity with the aggregation state of OMM. Viscoelastic properties of polyol oligomer were obtained by shear dynamic mechanical tests in the frequency range 0.1–16 rad/s. Finally the tensile properties of polyurethane clay-nanocomposites were measured.

합성조건에 따른 Polyacrylamide 수화 겔의 흐름변성 성질

of synthetic conditions and water content on rheological properties of polyacrylamide hydrogels were studied. The non-Newtonian flow curves of polyacrylamide hydrogels were obtained by using a cone-plate rheometer. The rheological parameters were obtained by applying non-Newtonian equation to the flow curves for polyacrylamide hydrogels. The polyacrylamide hydrogels are shear thinning under increasing shear rate modes which result in thixotropic behavior. These flow properties are controlled by the characteristics of flow units and the interaction among the flow segments.

Reversible Self-Association Increases the Viscosity of a Concentrated Monoclonal Antibody in Aqueous Solution

This study was conducted to investigate the effect of reversible protein self-association on the viscosity of concentrated monoclonal antibody solutions. The viscosities of the monoclonal antibody solutions were measured by either a capillary viscometer or a cone-plate rheometer at different protein concentrations, pH, and ionic strength. Soluble aggregates were determined by size exclusion chromatography, light scattering, and analytical ultracentrifugation. Self-association of protein at high protein concentration was monitored by sedimentation equilibrium analysis using a preparative ultracentrifuge and a microfractionator. The viscosity of one of the monoclonal antibodies investigated is highly dependent on protein concentration, pH, and ionic strength of buffer and charged excipients. This antibody shows the highest viscosity near its pI at low ionic strength conditions. Sedimentation equilibrium analysis suggests that this antibody tends to reversibly self-associate at high protein concentration. The self-association appears to be quite weak and is not detectable by sedimentation velocity and size exclusion chromatography at low protein concentration. There are no significant differences in the amounts of non-dissociable soluble aggregates formed between low viscosity and high viscosity samples. These results suggest that the reversible multivalent self-association of this protein appears to be mediated mainly by electrostatic interactions of charged residues and results in unusually high viscosity of this monoclonal antibody in solution at low ionic strength conditions.

Effect of University of Wisconsin organ-preservation solution on haemorheology

Abstract In conventional cold-storage organ preservation, the donor organ is flushed with University of Wisconsin (UW) solution at 0–4°C. The initial flush is used to wash out blood from the microcirculation to allow optimal preservation with the UW solution. The component hydroxyethyl starch (HES) of UW is known to cause relatively high viscosity and a possible interaction with blood, i.e. increased red blood cell (RBC) aggregation. The aim of this study was to investigate the influence of the HES component on the viscosity of UW and the aggregation behaviour of blood during washout. Viscosity aspects were measured with a cone-plate rheometer. HES-induced RBC aggregation was studied by means of an optical aggregation measuring device. The experiments were carried out with rat whole blood and mixtures of rat whole blood with UW-solution and UW without HES (UWmod), at 4°C. The viscosity of blood at 4°C is two-times higher than at 37°C; the UW/blood mixture at 4°C is 1.3-times more viscous than blood at 37°C; the 4°C UWmod/blood mixture equals the viscosity of blood at 37°C. The UW/blood mixture shows a ninefold increased aggregation compared with whole blood. These aggregates are larger than the diameter of the sinusoids in the rat liver. A mixture of whole blood and UWmod shows a lower aggregation than blood. Apart from an increased viscosity, HES in UW causes increased RBC aggregation. The aggregates are larger than the diameter of the sinusoids. Initial washout could be optimised by preflushing to improve the viability of the liver and to decrease delayed graft function.

Effect of University of Wisconsin organ-preservation solution on haemorheology.

In conventional cold-storage organ preservation, the donor organ is flushed with University of Wisconsin (UW) solution at 0-4 degrees C. The initial flush is used to wash out blood from the microcirculation to allow optimal preservation with the UW solution. The component hydroxyethyl starch (HES) of UW is known to cause relatively high viscosity and a possible interaction with blood, i.e. increased red blood cell (RBC) aggregation. The aim of this study was to investigate the influence of the HES component on the viscosity of UW and the aggregation behaviour of blood during washout. Viscosity aspects were measured with a cone-plate rheometer. HES-induced RBC aggregation was studied by means of an optical aggregation measuring device. The experiments were carried out with rat whole blood and mixtures of rat whole blood with UW-solution and UW without HES (UWmod), at 4 degrees C. The viscosity of blood at 4 degrees C is two-times higher than at 37 degrees C; the UW/blood mixture at 4 degrees C is 1.3-times more viscous than blood at 37 degrees C; the 4 degrees C UWmod/blood mixture equals the viscosity of blood at 37 degrees C. The UW/blood mixture shows a ninefold increased aggregation compared with whole blood. These aggregates are larger than the diameter of the sinusoids in the rat liver. A mixture of whole blood and UWmod shows a lower aggregation than blood. Apart from an increased viscosity, HES in UW causes increased RBC aggregation. The aggregates are larger than the diameter of the sinusoids. Initial washout could be optimised by pre-flushing to improve the viability of the liver and to decrease delayed graft function.