The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Timothy M Wick - One of the best experts on this subject based on the ideXlab platform.
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effect of low oxygen tension on tissue engineered cartilage construct development in the Concentric Cylinder bioreactor
Tissue Engineering, 2004Co-Authors: Sunil Saini, Timothy M WickAbstract:Cartilage is exposed to low oxygen tension in vivo, suggesting culture in a low-oxygen environment as a strategy to enhance matrix deposition in tissue-engineered cartilage in vitro. To assess the effects of oxygen tension on cartilage matrix accumulation, porous polylactic acid constructs were dynamically seeded in a Concentric Cylinder bioreactor with bovine chondrocytes and cultured for 3 weeks at either 20 or 5% oxygen tension. Robust chondrocyte proliferation and matrix deposition were achieved. After 22 days in culture, constructs from bioreactors operated at either 20 or 5% oxygen saturation had similar chondrocyte densities and collagen content. During the first 12 days of culture, the matrix glycosaminoglycan (GAG) deposition rate was 19.5 × 10-9 mg/cell per day at 5% oxygen tension and 65% greater than the matrix GAG deposition rate at 20% oxygen tension. After 22 days of bioreactor culture, constructs at 5% oxygen contained 4.5 ± 0.3 mg of GAG per construct, nearly double the 2.5 ± 0.2 mg of GA...
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Concentric Cylinder bioreactor for production of tissue engineered cartilage effect of seeding density and hydrodynamic loading on construct development
Biotechnology Progress, 2003Co-Authors: Sunil Saini, Timothy M WickAbstract:A Concentric Cylinder bioreactor has been developed to culture tissue engineered cartilage constructs under hydrodynamic loading. This bioreactor operates in a low shear stress environment, has a large growth area for construct production, allows for dynamic seeding of constructs, and provides for a uniform loading environment. Porous poly-lactic acid constructs, seeded dynamically in the bioreactor using isolated bovine chondrocytes, were cultured for 4 weeks at three seeding densities (60, 80, 100 x 10 6 cells per bioreactor) and three different shear stresses (imposed at 19, 38, and 76 rpm) to characterize the effect of chondrocyte density and hydrodynamic loading on construct growth. Construct seeding efficiency with chondrocytes is greater than 95% within 24 h. Extensive chondrocyte proliferation and matrix deposition are achieved so that after 28 days in culture, constructs from bioreactors seeded at the highest cell densities contain up to 15 x 10 6 cells, 2 mg GAG, and 3.5 mg collagen per construct and exhibit morphology similar to that of native cartilage. Bioreactors seeded with 60 million chondrocytes do not exhibit robust proliferation or matrix deposition and do not achieve morphology similar to that of native cartilage. In cultures under different steady hydrodynamic loading, the data demonstrate that higher shear stress suppresses matrix GAG deposition and encourages collagen incorporation. In contrast, under dynamic hydrodynamic loading conditions, cartilage constructs exhibit robust matrix collagen and GAG deposition. The data demonstrate that the Concentric Cylinder bioreactor provides a favorable hydrodynamic environment for cartilage construct growth and differentiation. Notably, construct matrix accumulation can be manipulated by hydrodynamic loading. This bioreactor is useful for fundamental studies of construct growth and to assess the significance of cell density, nutrients, and hydrodynamic loading on cartilage development. In addition, studies of cartilage tissue engineering in the well-characterized, uniform environment of the Concentric Cylinder bioreactor will develop important knowledge of bioprocessing parameters critical for large-scale production of engineered tissues.
Yuwen Zhang - One of the best experts on this subject based on the ideXlab platform.
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two and three dimensional numerical simulations of natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots
International Journal of Heat and Mass Transfer, 2014Co-Authors: Kun Zhang, Mo Yang, Yuwen ZhangAbstract:Two-dimensional and three-dimensional numerical simulations were carried out to simulate the natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots. For the case of steady flow, the numerical solutions in 2D and 3D simulations are in good agreement with the experimental results. When the convection in experiment becomes unsteady convection at the larger slot degree, the oscillated solutions in 3D simulation differ essentially from steady solutions in 2D simulation. The critical Rayleigh numbers from steady to unsteady flow in the 3D simulations are lower than those in the 2D simulations.
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experimental study on natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots
International Journal of Thermal Sciences, 2014Co-Authors: Kun Zhang, Mo Yang, Jin Wang, Yuwen ZhangAbstract:Abstract Detailed experimental analysis is presented for natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots. For the case of φ = 90°, where φ is the angle of slot opening from the vertical axis, and two types of temperature fields were obtained at the same Rayleigh number of 5.49 × 104. It is demonstrated that the steady state solution was not unique and was dependent on the initial conditions, which is related to static bifurcation. For the two cases of φ = 0° and φ = 45°, the natural convection turned to unsteady, although the boundary conditions were not time-dependent. The most obvious oscillation regions were above the inner Cylinder, and the amplitude increased with increasing Rayleigh numbers. The nonlinear characteristic of these problems led to the multiplicity of convections and self-sustained oscillation.
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numerical analysis of natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots
Numerical Heat Transfer Part A-applications, 2011Co-Authors: Kun Zhang, Mo Yang, Yuwen ZhangAbstract:Detailed numerical analysis is presented for natural convection heat transfer in a cylindrical envelope with an internal Concentric Cylinder with slots. Governing equations are discretized using the finite volume method, and solved using SIMPLE algorithm with QUICK scheme. The results show that the system can reach steady state and be symmetric when the Rayleigh number is below 4 × 105. When the Rayleigh number is greater than 6 × 105, an asymmetric periodical solution is obtained although the initial field and boundary conditions were symmetric. As the Rayleigh numbers increase further, a quasi-periodic solution of the system is achieved at Ra = 2 × 106, and the periodicity is lost at Ra = 6 × 106. It is ascertained that the oscillatory flow undergoes several bifurcations and ultimately evolves to a chaotic flow.
Sunil Saini - One of the best experts on this subject based on the ideXlab platform.
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effect of low oxygen tension on tissue engineered cartilage construct development in the Concentric Cylinder bioreactor
Tissue Engineering, 2004Co-Authors: Sunil Saini, Timothy M WickAbstract:Cartilage is exposed to low oxygen tension in vivo, suggesting culture in a low-oxygen environment as a strategy to enhance matrix deposition in tissue-engineered cartilage in vitro. To assess the effects of oxygen tension on cartilage matrix accumulation, porous polylactic acid constructs were dynamically seeded in a Concentric Cylinder bioreactor with bovine chondrocytes and cultured for 3 weeks at either 20 or 5% oxygen tension. Robust chondrocyte proliferation and matrix deposition were achieved. After 22 days in culture, constructs from bioreactors operated at either 20 or 5% oxygen saturation had similar chondrocyte densities and collagen content. During the first 12 days of culture, the matrix glycosaminoglycan (GAG) deposition rate was 19.5 × 10-9 mg/cell per day at 5% oxygen tension and 65% greater than the matrix GAG deposition rate at 20% oxygen tension. After 22 days of bioreactor culture, constructs at 5% oxygen contained 4.5 ± 0.3 mg of GAG per construct, nearly double the 2.5 ± 0.2 mg of GA...
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Concentric Cylinder bioreactor for production of tissue engineered cartilage effect of seeding density and hydrodynamic loading on construct development
Biotechnology Progress, 2003Co-Authors: Sunil Saini, Timothy M WickAbstract:A Concentric Cylinder bioreactor has been developed to culture tissue engineered cartilage constructs under hydrodynamic loading. This bioreactor operates in a low shear stress environment, has a large growth area for construct production, allows for dynamic seeding of constructs, and provides for a uniform loading environment. Porous poly-lactic acid constructs, seeded dynamically in the bioreactor using isolated bovine chondrocytes, were cultured for 4 weeks at three seeding densities (60, 80, 100 x 10 6 cells per bioreactor) and three different shear stresses (imposed at 19, 38, and 76 rpm) to characterize the effect of chondrocyte density and hydrodynamic loading on construct growth. Construct seeding efficiency with chondrocytes is greater than 95% within 24 h. Extensive chondrocyte proliferation and matrix deposition are achieved so that after 28 days in culture, constructs from bioreactors seeded at the highest cell densities contain up to 15 x 10 6 cells, 2 mg GAG, and 3.5 mg collagen per construct and exhibit morphology similar to that of native cartilage. Bioreactors seeded with 60 million chondrocytes do not exhibit robust proliferation or matrix deposition and do not achieve morphology similar to that of native cartilage. In cultures under different steady hydrodynamic loading, the data demonstrate that higher shear stress suppresses matrix GAG deposition and encourages collagen incorporation. In contrast, under dynamic hydrodynamic loading conditions, cartilage constructs exhibit robust matrix collagen and GAG deposition. The data demonstrate that the Concentric Cylinder bioreactor provides a favorable hydrodynamic environment for cartilage construct growth and differentiation. Notably, construct matrix accumulation can be manipulated by hydrodynamic loading. This bioreactor is useful for fundamental studies of construct growth and to assess the significance of cell density, nutrients, and hydrodynamic loading on cartilage development. In addition, studies of cartilage tissue engineering in the well-characterized, uniform environment of the Concentric Cylinder bioreactor will develop important knowledge of bioprocessing parameters critical for large-scale production of engineered tissues.
Kun Zhang - One of the best experts on this subject based on the ideXlab platform.
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two and three dimensional numerical simulations of natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots
International Journal of Heat and Mass Transfer, 2014Co-Authors: Kun Zhang, Mo Yang, Yuwen ZhangAbstract:Two-dimensional and three-dimensional numerical simulations were carried out to simulate the natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots. For the case of steady flow, the numerical solutions in 2D and 3D simulations are in good agreement with the experimental results. When the convection in experiment becomes unsteady convection at the larger slot degree, the oscillated solutions in 3D simulation differ essentially from steady solutions in 2D simulation. The critical Rayleigh numbers from steady to unsteady flow in the 3D simulations are lower than those in the 2D simulations.
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experimental study on natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots
International Journal of Thermal Sciences, 2014Co-Authors: Kun Zhang, Mo Yang, Jin Wang, Yuwen ZhangAbstract:Abstract Detailed experimental analysis is presented for natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots. For the case of φ = 90°, where φ is the angle of slot opening from the vertical axis, and two types of temperature fields were obtained at the same Rayleigh number of 5.49 × 104. It is demonstrated that the steady state solution was not unique and was dependent on the initial conditions, which is related to static bifurcation. For the two cases of φ = 0° and φ = 45°, the natural convection turned to unsteady, although the boundary conditions were not time-dependent. The most obvious oscillation regions were above the inner Cylinder, and the amplitude increased with increasing Rayleigh numbers. The nonlinear characteristic of these problems led to the multiplicity of convections and self-sustained oscillation.
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numerical analysis of natural convection in a cylindrical envelope with an internal Concentric Cylinder with slots
Numerical Heat Transfer Part A-applications, 2011Co-Authors: Kun Zhang, Mo Yang, Yuwen ZhangAbstract:Detailed numerical analysis is presented for natural convection heat transfer in a cylindrical envelope with an internal Concentric Cylinder with slots. Governing equations are discretized using the finite volume method, and solved using SIMPLE algorithm with QUICK scheme. The results show that the system can reach steady state and be symmetric when the Rayleigh number is below 4 × 105. When the Rayleigh number is greater than 6 × 105, an asymmetric periodical solution is obtained although the initial field and boundary conditions were symmetric. As the Rayleigh numbers increase further, a quasi-periodic solution of the system is achieved at Ra = 2 × 106, and the periodicity is lost at Ra = 6 × 106. It is ascertained that the oscillatory flow undergoes several bifurcations and ultimately evolves to a chaotic flow.
Ding Jing - One of the best experts on this subject based on the ideXlab platform.
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the simulation of the steady state Concentric Cylinder method for determining thermal conductivity of sodium nitrate
Energy Procedia, 2014Co-Authors: Pan Gechuanqi, Lu Jianfeng, Wei Xiaolan, Ding JingAbstract:Abstract As molten salts are becoming more and more popular with electricity generation and other industries which need molten salts as thermal energy storages, our attentions on molten salts’ thermophysics properties are increasing every year. Thermal conductivity is a key parameter when designing apparatus applied in related industries. Although there are some researchers studying the thermal conductivity of molten salts for years, few can measure it accurately. Most of them measure the thermal conductivity of molten salts by steady-state Concentric Cylinder method because the method is simpler and easier to design and carry out. In this paper, the steady-state Concentric Cylinder method for determining thermal conductivity of sodium nitrate is simulated with pure conduction condition and natural convection is considered later. The influence of natural convection on molten salt heat transfer is discussed at last.