Biorheology - Volume 51, issue 6

Authors: Balasso, Andrea | Bauer, Jan S. | Liebig, Thomas | Dorn, Franziska | Zimmer, Claus | Liepsch, Dieter | Prothmann, Sascha

Article Type: Research Article

Abstract: BACKGROUND: The growth and rupture of cerebral aneurysms is intrinsically related to the hemodynamics prevailing in the diseased area. Therefore, a better understanding of intra-aneurysmal hemodynamics is essential for developing effective treatment methods. OBJECTIVE: The intention of this study was to evaluate the intra-aneurysmal flow and flow reduction induced by flow diverters in a true-to-scale elastic aneurysm model, obtained from real patient data. METHODS: Based on the computed tomography angiography (CTA) data of a fusiform aneurysm of a 34 year old patient, an elastic silicon rubber model of the aneurysm was produced. A physiologic pulsatile …flow was created with a circulatory experimental set-up, and a non-Newtonian perfusion fluid was used as a substitute for human blood. Hemodynamics were measured by LDA before and after flow diverter implantation. RESULTS: Implantation of a flow diverter device resulted in a reduction of intra-aneurysmal maximum flow velocities of 97.8% at the inflow zone, 89.1% in the dome and 89.3% at the outflow zone, when compared to the native model. A significant reduction of 94% in the mean intra-aneurysmal velocity was found. CONCLUSIONS: This promising methodology can optimize patient treatment and will correlate with computational simulations to evaluate their reliability. Show more

Keywords: Stent, flow diversion, endovascular, non-Newtonian fluid, laser Doppler anemometry

DOI: 10.3233/BIR-14019

Citation: Biorheology, vol. 51, no. 6, pp. 341-354, 2014

Authors: Kilic-Erkek, Ozgen | Kilic-Toprak, Emine | Kucukatay, Vural | Bor-Kucukatay, Melek

Article Type: Research Article

Abstract: BACKGROUND: Hemorheological responses to swimming exercise have never been investigated in spontaneously hypertensive rats (SHR). OBJECTIVE: We aimed to investigate the effects of moderate intensity swimming exercise followed by detraining on erythrocyte deformability and aggregation in SHR. METHODS: SHR and WKY rats were randomized into sedentary, exercised, detrained (5 weeks) and late detrained (10 weeks) groups. Swimming exercise of 60 min, 5 days/week, 10 weeks was applied. Systolic blood pressure (SBP), heart rate, body weights were measured every 2 weeks. Erythrocyte deformability and aggregation were determined by ektacytometry. RESULTS: Exercise training reduced SBP …in both WKY and SHR rats and decreased erythrocyte aggregation in SHR group. SBP lowering effect of exercise was maintained until a detraining period equal to the duration of the exercise protocol, while 5 weeks of detraining reverted the improvements observed in erythrocyte aggregation of hypertensive rats. Although exercise training did not affect erythrocyte deformability, detraining for 10 weeks decreased RBC deformability in normotensive, but not in hypertensive rats. CONCLUSIONS: It can be suggested that, the exercise training applied herein has favorable effects on circulation not only by lowering blood pressure, but also by decreasing erythrocyte aggregation which are reversed after 5 weeks of detraining in SHR. Show more

Keywords: Swimming, physical inactivity, hypertension, erythrocyte deformability, red blood cell aggregation

DOI: 10.3233/BIR-14030

Citation: Biorheology, vol. 51, no. 6, pp. 355-367, 2014

Authors: Li, Haiyue | Zhang, Yanhang

Article Type: Research Article

Abstract: BACKGROUND: Viscoelastic materials contain a continuous spectrum of relaxation time constants that cannot be measured directly from experiments. To model the viscoelastic behavior, discrete Generalized Maxwell model is usually chosen phenomenologically from direct fitting. OBJECTIVE: In the present study, a theoretical framework was developed to determine the continuous spectrum of relaxation time constants, and then applied to study the dynamic rheological behavior of collagen gel using a parallel plate rheometer. METHODS: Frequency sweep tests were performed to determine the storage and loss modulus of collagen gel. To obtain the continuous relaxation spectrum, Tikhonov regularization method …was employed to solve the Fredholm integral equations. A Finite Element Model (FEM) was created to simulate the rheological measurement with viscous material parameters obtained from both direct fitting and continuous spectrum. RESULTS: Discrete spectrum obtained by direct fitting method is not unique and highly depends on the specified fitting criteria. Continuous spectrum obtained by Tikhonov regularization effectively eliminates the possibility of getting nonunique solutions. The storage and loss modulus calculated from FEM compared well with the experimental results. CONCLUSIONS: Continuous relaxation spectrum can be determined based on dynamic rheological shear measurements, and incorporated into FEM to study the behavior of viscoelastic materials. Show more

Keywords: Relaxation time constants, continuous spectrum, viscoelastic behavior, oscillatory shear measurements, Tikhonov regularization, Prony series, finite element modeling

DOI: 10.3233/BIR-14032

Citation: Biorheology, vol. 51, no. 6, pp. 369-380, 2014

Authors: Tada, Shigeru | Natsuya, Tomoyuki | Tsukamoto, Akira

Article Type: Research Article

Abstract: BACKGROUND: Cell manipulation and separation technologies have potential biological and medical applications, including advanced clinical protocols such as tissue engineering. OBJECTIVE: An aggregation model was developed for a human carcinoma (HeLa) cell suspension exposed to a uniform AC electric field, in order to explore the field-induced structure formation and kinetics of cell aggregates. METHODS: The momentum equations of cells under the action of the dipole–dipole interaction were solved theoretically and the total time required to form linear string-like cluster was derived. The results were compared with those of a numerical simulation. Experiments using HeLa cells …were also performed for comparison. RESULTS: The total time required to form linear string-like clusters was derived from a simple theoretical model of the cell cluster kinetics. The growth rates of the average string length of cell aggregates showed good agreement with those of the numerical simulation. In the experiment, cells were found to form massive clusters on the bottom of a chamber. The results imply that the string-like cluster grows rapidly by longitudinal attraction when the electric field is first applied and that this process slows at later times and is replaced by lateral coagulation of short strings. CONCLUSIONS: The findings presented here are expected to enable design of methods for the organization of three-dimensional (3D) cellular structures without the use of micro-fabricated substrates, such as 3D biopolymer scaffolds, to manipulate cells into spatial arrangement. Show more

Keywords: Dipole–dipole interaction, cell assembly analysis, cell cluster formation, power law scaling

DOI: 10.3233/BIR-14034

Citation: Biorheology, vol. 51, no. 6, pp. 381-397, 2014

Authors: Summers, Michael P. | Parmigiani, John P.

Article Type: Research Article

Abstract: BACKGROUND: Blubber is a thick adipose tissue located beneath the dermas. Its viscoelastic properties affect whale tracking tag design, hydrodynamics, and acoustical properties that can be used to study animal behavior and avoid ship strikes. OBJECTIVE: Measure the dynamic shear storage and loss moduli for whale blubber at distances below the dermas for several species. Also, measure the non-collagen and collagen protein content to explore a correlation to viscoelastic properties. METHODS: Blubber samples were obtained from whale strandings (humpback, sperm, and two gray) in the Pacific Northwest. Shear moduli were measured at oscillation frequencies of …0.31 Hz to 25 Hz using a rotational rheometer. Protein content was measured using a staining protocol. RESULTS: Storage modulus and loss modulus variation with frequency was very consistent across all samples tested. Log-linear and extended polynomials respectively had R-squared values of at least 0.96. Variation of both moduli with depth was fit reasonably well by fourth-order polynomials. Protein content trends varied with species. CONCLUSIONS: The samples used in this study were necrotic tissue, however the variation with frequency and to a lesser extent depth was very consistent and may have a broader applicability. Protein content was not found to correlate to moduli values. Show more

Keywords: Soft tissue, viscoelastic, protein, collagen, histology

DOI: 10.3233/BIR-14036

Citation: Biorheology, vol. 51, no. 6, pp. 399-408, 2014

Authors: Ludwig, Taryn E. | Cowman, Mary K. | Jay, Gregory D. | Schmidt, Tannin A.

Article Type: Research Article

Abstract: BACKGROUND: The contribution of proteoglycan 4 (PRG4) to synovial fluid and hyaluronan (HA) solution rheology are poorly understood. The effects of PRG4 disulfide-bonded structure on viscosity and viscosity of newly available full-length recombinant human PRG4 (rhPRG4) have not previously been reported. OBJECTIVE: This study determined the viscosity of PRG4 and rhPRG4, R/A (reduced and alkylated) PRG4 and rhPRG4, and PRG4 and rhPRG4 + HA solutions. METHODS: Steady shear viscosities of 1.5 MDa HA, PRG4 from bovine cartilage explant culture, rhPRG4 and (rh)PRG4 + HA solutions were measured with 40 mm parallel plate fixtures. RESULTS: PRG4 demonstrated shear-dependent …viscosity at high concentrations, but Newtonian behaviour at low concentrations and when disulfide-bonded/multimeric structure was disrupted by R/A. rhPRG4 demonstrated Newtonian behaviour over all concentrations tested and upon R/A. At high HA concentrations, rhPRG4 reduced solution viscosity, suggesting a binding interaction. At low HA concentrations, solution viscosity was increased relative to HA alone, possibly due to self-association of rhPRG4. Effects of PRG4 on HA solution viscosity were dependent on PRG4’s disulfide-bonded structure. CONCLUSIONS: The finding that rhPRG4 can increase the viscosity of low concentration HA solutions suggests that supplementation with rhPRG4 may help mitigate the loss in synovial fluid viscosity experienced with decreased HA concentration in osteoarthritis. Show more

Keywords: Synovial fluid biomacromolecule interactions, alterations in synovial fluid viscosity with disease, steady shear viscosity experiments, osteoarthritis biotherapeutics development

DOI: 10.3233/BIR-14037

Citation: Biorheology, vol. 51, no. 6, pp. 409-422, 2014

Article Type: Other

Citation: Biorheology, vol. 51, no. 6, pp. 423-426, 2014