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    Effect of scaffold architecture on cell seeding efficiency: A discrete phase model CFD analysis
    (Pergamon-Elsevier Science Ltd, 2019) Ali, Davar
    Within perfusion cell culture systems, scaffold architecture is able to control important biological parameters such as permeability and fluid flow-induced shear stress. As well, one of the main factors affecting the final fate of this process as well as optimal cell differentiation and proliferation in these systems is initial adhesion of cells to scaffolds. In this study, the effect of scaffold architecture on the adhesion of the cells was computationally investigated. For this purpose, four scaffold models including double-diamond, gyroid, FR-D, and Schwarz-primitive were designed using triply periodic minimal surface (TPMS) geometry with a constant porosity of 80%. As well, the inlet velocity of zero to simulate static cell culture and three different inlet velocities for modeling the dynamic cell culture conditions were also selected. The results showed that cell culture efficiency of scaffolds could be changed up to seven times from architecture to architecture under the same conditions. The efficiency of cell culture in scaffolds with tortuous architecture was also reported higher than those with relatively straight microchannels. In terms of culture methods, unlike dynamic cell culture model in which almost a homogeneous cell distribution was observed in static cell culture simulation, more cells adhered, but they had agglomerated in the scaffold entrance regions and had failed to reach all regions. The results of this study shed more light on the selection and design of scaffold architecture for optimal cell culture in tissue engineering.
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    Permeability and fluid flow-induced wall shear stress in bone scaffolds with TPMS and lattice architectures: A CFD analysis
    (Elsevier, 2020) Ali, Davar; Ozalp, Mehmet; Blanquer, Sebastien B. G.; Onel, Selis
    Fluid flow dynamics within porous scaffolds for tissue engineering play a critical role in the transport of fundamental materials to the cells and in controlling the biocompatibility of the scaffold. Properties such as permeability and fluid flow-induced wall shear stress characterize the biological behavior of the scaffolds. Bioactivity depends on the diffusion of oxygen and other nutritious elements through the porous medium and fluid flow-induced shear stress is known as the dominant mechanical stimulant of cell differentiation and proliferation within the scaffolds. In this study, eight different bone scaffold models with a constant porosity of 80% were designed computationally using the TPMS and lattice-based structures. We investigated the fluid flow within the scaffolds using CFD analysis. The results of the work showed that scaffold architecture has a significant impact on the permeability and that scaffold permeability can vary up to three times depending on the architecture. The scaffolds with the minimal variation in their channel size exhibited the highest permeability. We investigated the distribution statistics of wall shear stress on the walls of the scaffolds and showed that a correlation between the architecture of the scaffolds and the distribution statistics of wall shear stress did not exist. The outcomings of this work can be promising in designing better scaffolds in tissue engineering from a biological point of view. (C) 2019 Elsevier Masson SAS. All rights reserved.
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    Permeability and fluid flow-induced wall shear stress of bone tissue scaffolds: Computational fluid dynamic analysis using Newtonian and non-Newtonian blood flow models
    (Pergamon-Elsevier Science Ltd, 2018) Ali, Davar; Sen, Sadri
    Among the factors that are important in successful bone tissue regeneration through scaffolds are permeability and fluid flow-induced wall shear stress (WSS) because of the direct contribution of these factors to cell bioactivities. The permeability of scaffolds is usually measured using fluids such as water, which are characterized as Newtonian materials with constant viscosity. However, using the fluid properties of blood as bases in measuring permeability can lead to more realistic results given that scaffolds are implanted in the body, where the only flowing fluid (i.e., blood) is a non-Newtonian fluid. Moreover, the linear relationship of WSS with fluid viscosity challenges the use of Newtonian fluids in determining WSS magnitude. With consideration for these issues, we investigated permeability and WSS through computational fluid dynamics (CFD) analyses of lattice based and gyroid scaffold architectures with Newtonian and non-Newtonian blood flow properties. With reference to geometrical parameters and the pressure drops derived from the CFD analyses, the permeability levels of the Newtonian and non-Newtonian models were calculated by exploiting the classic and modified Darcy's equations, respectively. Results showed that both scaffold architectures were several times more permeable in the Newtonian blood flow models than in their non-Newtonian counterparts. Within the scaffolds, the non Newtonian flow of blood caused almost twice the magnitude of WSS originating from Newtonian blood flow. These striking discrepancies in permeability and WSS between the two blood models were due to differences in their viscosity behaviors.