Home About us Contact
|
Home About us Contact | ||
|
|
||
Oscillatory Shear Tests (oscillatory + shear_test)
Selected AbstractsEffect of cell seeding concentration on the quality of tissue engineered constructs loaded with adult human articular chondrocytesJOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, Issue 1 2008Sebastian Concaro Abstract Many aspects of the process of in vitro differentiation of chondrocytes in three-dimensional (3D) scaffolds need to be further investigated. Chitosan scaffolds were produced by freeze-drying 3% w/v 90% DDA chitosan gels. The effect of the cell seeding concentration was evaluated by culturing human adult chondrocytes in chitosan scaffolds After the first passage, cells were seeded into chitosan scaffolds with a diameter of 8 mm. The final cell seeding concentration per cm3 of chitosan scaffold was: Group A, 3 × 106; Group B, 6 × 106; Group C, 12 × 106; and Group D, 25 × 106 cells. After 14 and 28 days in 3D culture, the constructs were assesed for collagen, glucosaminoglycans and DNA content. The mechanical properties of the constructs were determined using a dynamic oscillatory shear test. The histological aspect of the constructs was evaluated using the Bern score. The collagen and GAG concentration increased, varying the cell seeding concentration. There was a significant increase in proteoglycan and hydroxyproline production between groups C and D. The sulphated GAG content increased significantly in the group D as compared to the other groups. The mechanical properties of the different constructs increased over time, from 9.6 G,/kPa at 14 days of 3D culture to 14.6 G,/kPa at 28 days under the same culture conditions. In this study we were able to determine that concentrations of 12,25 million cells/cm2 are needed to increase the matrix production and mechanical properties of human adult chondrocytes under static conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Rheological study of ternary mixtures and pectic gels of red fruit pulpsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2007Charles Windson Isidoro Haminiuk Summary In this work, the rheological behaviour of ternary mixtures of strawberry, blackberry and raspberry pulps in steady shear was studied using the response surface methodology. In addition, the rheology of pectic gels extracted from these pulps was investigated by means of oscillatory shear tests. The flow curves were adequately described by the rheological model of Herschel,Bulkley. All the formulations analysed exhibited shear-thinning behaviour. The rheological responses were influenced by the difference in pulp proportions and also by the temperatures (20 and 60 °C). The quadratic and cubic models used to fit the response were considered suitable owing to the higher values of determination coefficient (R2). The pectic gels from strawberry, blackberry and raspberry showed a strong gel character, with strawberry presenting the stronger gel, which was confirmed by the Cox,Merz experiment, degree of esterification and average molecular weight data. [source] Influence of water content, time, and temperature on the rheological behavior of polyethylene terephtalateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010A. M. C. Souza Abstract In this work, the main factors affecting the rheological behavior of polyethylene terephtalate (PET) in the linear viscoelastic regime (water content, time delay before test, duration of experiment, and temperature) were accessed. Small amplitude oscillatory shear tests were performed after different time delays ranging from 300 to 5000 s for samples with water contents ranging from 0.02 to 0.45 wt %. Time sweep tests were carried out for different durations to explain the changes undergone by PET before and during small amplitude oscillatory shear measurements. Immediately after the time sweep tests, the PET samples were removed from the rheometer, analyzed by differential scanning calorimetry and their molar mass was obtained by viscometry analysis. It was shown that for all the samples, the delay before test and residence time within the rheometer (i.e. duration of experiment) result in structural changes of the PET samples, such as increase or decrease of molar mass, broadening of molar mass distribution, and branching phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Engineering investigations on the potentiality of the thermoformability of HDPE charged by wood flours in the thermoforming partPOLYMER ENGINEERING & SCIENCE, Issue 8 2009F. Erchiqui A dynamic finite element method is used to analyze the thermoformability of composites containing wood and a thermoplastic matrix for five different proportions of wood flour. Linear viscoelastic properties can be obtained by small amplitude oscillatory shear tests and the viscoelastic behavior is characterized using the Lodge model. To account for enclosed gas volume, which inflates the thermoplastic composite membrane, a thermodynamic approach is used to express the external work in terms of a closed volume. Pressure load is deduced by thermodynamic law using the Redlich,Kwong gas equation. The Lagrangian method together with the assumption of membrane theory is used in the finite element implementation. In addition, the influence of air flow on thickness and stress and the energy required to form a thin polymeric part in the thermoforming process are analyzed for five different proportions of wood flour in the HDPE material. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] | ||||||||||