Biorheology - Volume 42, issue 3

Authors: van Turnhout, Mark | Peters, Gerrit | Stekelenburg, Anke | Oomens, Cees

Article Type: Research Article

Abstract: The objective of the current study was to determine the in vitro passive transverse mechanical properties of skeletal muscle with Dynamic Mechanical Thermal Analysis (DMTA) tests. The starting hypotheses was that the time–temperature‐superposition principle could be used to expand the DMTA results to a 1 kHz frequency range. Experiments were performed with rat hind leg skeletal muscle tissue samples on a rotational rheometer using a parallel plate geometry. Because of the small size and low modulus of the samples, the standard test geometry was altered and the samples were shifted from the center to the edge of the plates. From …strain sweep tests it became clear that for strains smaller than 0.003 the muscle tissue behaves linearly. In the linear region storage moduli ranged between 24 kPa (ω=1 rad/s) and 42 kPa (ω=100 rad/s) at T=4°C and 22 kPa and 33 kPa at 29°C within the experimental frequency range. The loss modulus decreased with increasing frequency and ranged between 7 and 4 kPa at 4°C and 4.5 and 3.5 kPa at 29°C. Although the properties are clearly temperature dependent, a temperature shift in phase angle δ could not be detected, thus Time Temperature Superposition is not allowed for skeletal muscle in vitro. Show more

Keywords: Viscoelastic, time–temperature‐superposition, impact frequencies, oscillatory shear, soft tissue, alternative geometry

Citation: Biorheology, vol. 42, no. 3, pp. 193-207, 2005

Authors: Nicolle, S. | Lounis, M. | Willinger, R. | Palierne, J.‐F.

Article Type: Research Article

Abstract: The literature review about the shear linear properties of brain tissue reveals both a large discrepancy in the existing data and a crucial lack of information at high frequencies associated with traffic road and non‐penetrating ballistic impacts. The purpose of this study is to clarify and to complement the linear material characterisation of brain tissue. New data at small strains and high frequencies were obtained from oscillatory experiments. The tests were performed on thin porcine white matter samples (corona radiata) using an original custom‐designed oscillatory shear testing device. At 37°C, the results showed that the mean storage modulus (G′) and …the mean loss modulus (G″) increased with the frequency (0.1 to 6310 Hz) from 2.1±0.9 kPa to 16.8±2.0 kPa and from 0.4±0.2 kPa to 18.7±2.3 kPa respectively. The reliability of these new dynamic data was checked over a partially common frequency range by conducting similar experiments using a standard rheometer (Bohlin C‐VOR 150). Data were also compared in the time field. From these experiments, the relaxation modulus (G(t)) was found to decrease from 24.4±2.1 kPa to 1.0±0.3 kPa between 10−5 s and 270 s. Show more

Keywords: Impact biomechanics, brain injury, tissue mechanics, linear viscoelasticity

Citation: Biorheology, vol. 42, no. 3, pp. 209-223, 2005

Authors: Yang, Qing‐wu | Mou, Lin | Lv, Feng‐lin | Wang, Jing‐zhou | Wang, Lin | Zhou, Hong‐jie | Gao, Dong

Article Type: Research Article

Abstract: TLR4 plays an important role in atherosclerosis, but little is known about the precise mechanism. Herein, we investigated the role of TLR4/NF‐κB signaling pathway in monocyte–endothelial adhesion induced by low shear stress and Ox‐LDL. We found that low shear stress up‐regulated TLR4 expression in endothelial cells, and that ox‐LDL exerted an obvious synergistic action as revealed by RT‐PCR and Western blotting analysis. Low shear stress also significantly up‐regulated IL‐8 expression in endothelial cells. Meanwhile, NF‐κB activity and the adhesion force of monocytes were increased, and there was a synergetic action of ox‐LDL. However, following transfection with a functional mutant of …TLR4 (C3H/HeJ, TLR4 Dicd) or addition of anti‐human TLR4 mAb, IL‐8 expression was obviously decreased, NF‐κB activity in cells remarkably inhibited, and the adhesion force of monocyte significantly reduced. Nevertheless, anti‐human TLR2 mAb had no similar effects. These findings suggest that TLR4 may be involved in the early stages of atherosclerosis, associating ox‐LDL, inflammation/infection, and low shear stress. Therefore, TLR4 is expected to be a new target for preventing and treating atherosclerosis. Show more

Keywords: Cell adhesion, signaling transduction, IL‐8, inflammation, atherosclerosis, monocyte

Citation: Biorheology, vol. 42, no. 3, pp. 225-236, 2005

Authors: Alexy, T. | Wenby, R.B. | Pais, E. | Goldstein, L.J. | Hogenauer, W. | Meiselman, H.J.

Article Type: Research Article

Abstract: The technical complexity of previous rheometers has tended to limit the availability of blood viscosity data obtained over a wide range of shear rates. However, an automated tube‐type viscometer, the Rheolog™, has been developed; it employs a disposable flow assembly and less than five minutes are required to obtain blood viscosity results over a shear rate range of 1–1500 s−1 . We have carried out validation studies of the Rheolog™ using normal human blood and have compared these results with those obtained by cone‐plate and Couette viscometers; storage time and temperature effects were also evaluated. Replicate measurements indicated mean CV …levels less than 5%, and were independent of hematocrit and shear rate. Rheolog™ blood viscosity data agreed closely with those from other viscometers: average Rheolog™ differences from mean cone‐plate and Couette values were −0.3% at 28% hematocrit, −1.4% at 41% hematocrit (i.e., native), and 1.0% at 56% hematocrit. Storage at room temperature up to 8 hours and at 4°C up to 4 days had minimal effects whereas notable changes were observed when stored for 3 hours at 37°C. Our results indicate that, within the hematocrit and shear rate limits employed herein, the Rheolog™ provides rapid, accurate and reproducible blood viscosity data, and suggest its usefulness for both basic science and clinical studies. Show more

Keywords: Blood, Rheolog, shear rate, viscometer, viscosity

Citation: Biorheology, vol. 42, no. 3, pp. 237-247, 2005