Biorheology - Volume 39, issue 6

Authors: Baum, C. | Fleischer, L.‐G. | Roessner, D. | Meyer, W. | Siebers, D.

Article Type: Research Article

Abstract: The rheological properties of the stratum corneum of the pilot whale (Globicephala melas) were investigated with emphasis on their significance to the self‐cleaning abilities of the skin surface smoothed by a jelly material enriched with various hydrolytic enzymes. The gel formation of the collected fluid was monitored by applying periodic‐harmonic oscillating loads using a stress‐controlled rheometer. In the mechanical spectrum of the gel, the plateau region of the storage modulus G′ (<1200 Pa) and the loss modulus G″ (>120 Pa) were independent of frequency (ω=43.98 to 0.13 rad·s−1 ,τ=15 Pa, T=20°C), indicating high elastic performance of a covalently cross‐linked viscoelastic …solid. In addition, multi‐angle laser light scattering experiments (MALLS) were performed to analyse the potential time‐dependent changes in the weight‐average molar mass of the samples. The observed increase showed that the gel formation is based on the assembly of covalently cross‐linked aggregates. The viscoelastic properties and the shear resistence of the gel assure that the enzyme‐containing jelly material smoothing the skin surface is not removed from the stratum corneum by shear regimes during dolphin jumping. The even skin surface is considered to be most important for the self‐cleaning abilities of the dolphin skin against biofouling. Show more

Keywords: Skin, rheology, gel formation, whales, Globicephala melas, self‐cleaning abilities, multi‐angle laser light scattering (MALLS)

Citation: Biorheology, vol. 39, no. 6, pp. 703-717, 2002

Authors: Zhao, Jingbo | Yang, Jian | Vinter‐Jensen, Lars | Zhuang, Fengyuan | Gregersen, Hans

Article Type: Research Article

Abstract: Morphometric and passive biomechanical properties were studied in isolated segments of the duodenum, jejunum and ileum in 22 EGF‐treated rats and 12 control rats. The rats were allocated to groups with EGF treatment for 2, 4, 7, and 14 days (n=6 for each EGF treatment group except n=4 for the 14 days group) or saline treatment (n=3 for each group). The intestinal segments were pressurized with Krebs solution from 0 to 8 cmH2 O for duodenum and 0 to 6 cmH2 O for jejunum and ileum using a ramp distension protocol. The diameter and length were recorded at different pressure …levels. Circumferential and longitudinal stresses (force per area) and strains (deformation) were computed from the length, diameter, pressure and the zero‐stress state data. EGF treatment was associated with pronounced morphometric changes, e.g., the wall thickness, wall area, and the circumferential lengths significantly increased during EGF treatment in all intestinal segments (P<0.05). Histological analysis showed that the thickness and area of the layers increased after EGF treatment. With respect to the biomechanical data, the opening angle increased in all segments during EGF treatment with the highest value in the 14 days EGF treatment group (P<0.05). The same result was found for residual strain and the residual strain gradient through the intestinal wall. Linear regression analysis demonstrated that the opening angle mainly depended on the mucosa thickness and area. Furthermore, the circumferential stiffness increased in the duodenum and decreased in the jejunum and ileum during EGF treatment. A plateau was reached after 7 days where after it started to normalize (P<0.01). In the longitudinal direction, all intestinal segments became stiffer after EGF treatment for 7 days. After 14 days the curve started to normalize in duodenum and jejunum but not in the ileum. Show more

Keywords: Biomechanics, epidermal growth factor (EGF), intestine, stress–strain distribution, zero‐stress state

Citation: Biorheology, vol. 39, no. 6, pp. 719-733, 2002

Authors: Liu, Zizhen | Bilston, Lynne E.

Article Type: Research Article

Abstract: Characterization of the mechanical properties of soft biological tissues is important for establishing the mechanical tolerances of the tissues, and for input to computational models. In this work, the viscoelastic properties of bovine liver tissue in shear loading have been measured using relaxation and constant shear rate loading. The tissue is nonlinearly viscoelastic for strains greater than 0.2%, has a yield strain of approximately 10, and shows moderate strain‐rate sensitivity. The response can be modelled using a nonlinear viscoelastic differential model previously developed for brain tissue.

Keywords: Viscoelasticity, biomechanics, mechanical properties, hepatic tissue

Citation: Biorheology, vol. 39, no. 6, pp. 735-742, 2002

Authors: Provenzano, Paolo P. | Rutland, Christopher J.

Article Type: Research Article

Abstract: This paper proposes a model for wall shear stress in arterial stenosis based on boundary layer theory. Wall shear stress estimates are obtained by solving the momentum integral equation using the method proposed by Walz and applying this method to various stenosis geometries for Reynolds numbers (Re) of Re=59–1000. Elevated wall shear stress may be of importance when considering thrombosis and vascular erosion in stenosis, as well as the potential for debris from the stenotic area to ‘break away’ and cause further pathology. The values of shear stress obtained using the model in this study agree well with published values …of wall shear stress. When compared to a previously published boundary layer model utilizing the Thwaites method (Reese and Thompson, 1998), the model proposed herein performs better at higher Re while the model utilizing the Thwaites method performs better at lower Re. Wall shear stresses are shown to increase with increasing stenosis (increased area reduction) for a given stenosis length, increase with increasing Re for a given stenosis geometry, and increase for steeper stenosis of the same constriction. The boundary layer model proposed can be easily implemented by clinical researchers to provide in vivo estimates of wall shear stress through arterial stenoses. Show more

Keywords: Wall shear stress, boundary layer theory, arterial stenosis

Citation: Biorheology, vol. 39, no. 6, pp. 743-754, 2002

Authors: Mekheimer, Kh.S.

Article Type: Research Article

Abstract: The problem of peristaltic transport of a couple stress fluid in uniform and non‐uniform two‐dimensional channels has been investigated under zero Reynolds number with long wavelength approximation. Blood is represented by a couple stress fluid (a fluid which its particles size are taken into account, a special case of a non‐Newtonian fluid). It is found that the pressure rise decreases as the couple stress fluid parameter γ increases (i.e., small size fluid particle). So the pressure rise for a couple stress fluid (as a blood model) is greater than that for a Newtonian fluid. Also the pressure rise increases as …the amplitude ratio ϕ increases for different values of γ. Further, the pressure rise in the case of non‐uniform geometry is found to be much smaller than the corresponding value in the case of uniform geometry. Finally, the maximum pressure rise when the mean flow rate over one period of the wave, $\bar{Q}$ =0, increases as ϕ increases and γ decreases. Show more

Keywords: Peristaltic transport, couple stress fluid, non‐uniform channel

Citation: Biorheology, vol. 39, no. 6, pp. 755-765, 2002

Article Type: Abstract

Citation: Biorheology, vol. 39, no. 6, pp. 767-786, 2002

Article Type: Other

Citation: Biorheology, vol. 39, no. 6, pp. 787-794, 2002