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    The Behaviour of Scaffolds for Bone under Torsional Loading with Different Architectures; a Numerical Analysis
    (Ieee, 2020) Ali, Daver
    Given that human hones are subjected to various loads during movement. Therefore, the scaffolds that they are designed for hone defects replacement should also he tested under the same loading conditions. In this study, the torsional behaviour of the scaffolds was investigated using four different lattice-based architectures. The scaffolds were designed in three porosity levels of 60%, 75% and 90%. Therefore, twelve models of the scaffolds were obtained. To determine their performance under torsional loading, the shear modulus of each model was calculated using finite element analysis. The results showed that in the scaffolds with lower porosity the scaffold's architecture does not play a main role in the shear modulus. However, in scaffolds with a porosity of 90%, the shear modulus was affected by the architecture of the scaffold. For example, a scaffold with an octet structure showed three times higher shear modulus in compare to a scaffold with a truncated -octahedron architecture. As a conclusion in the design of scaffolds with high porosity, scaffold architecture plays an important role in its torsional behaviour and should be considered as a design parameter. The results of this study showed that the torsional behaviour of scaffolds depends on both porosity and architecture.
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    Effect of Blood Viscosity on Pressure and Shear Stress on the Walls of an Artery with Stenosis
    (Ieee, 2018) Ali, Daver; Onel, Selis
    Blood flow dynamics in arteries with stenosis is a critical issue. In this study, the effect of blood viscosity on the pressure and wall shear stress that form on the walls of an artery with a 70% reduced cross-sectional area was investigated using computational fluid dynamics. It was observed that the increase in blood viscosity caused an increase in the pressure and shear stress on the walls of normal arteries and those with stenosis. It has been shown that these parameters increase linearly with increasing blood viscosity in a normal artery and behave nonlinearly along the different regions of an artery with stenosis.
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    Enhancing the Mechanical Properties of Auxetic Metamaterials by Incorporating Nonrectangular Cross Sections into Their Component Rods: A Finite Element Analysis
    (Wiley-V C H Verlag Gmbh, 2023) Kavakli, Humeyra Sevval; Ali, Daver
    Herein, four prevalent architectures of metamaterials, namely, the arc-star, star, reentrant, and antichiral models, are examined to study the effects of the cross-sectional shapes of component rods on the stiffness and Poisson's ratios of the materials. Four differently sized cross sections of rods are designed, and two types of cross-sectional geometries-square and I-shaped-are adopted. Aspect ratios of 0.5, 0.75, and 1 are considered for the I-shaped cross-sectional models. A total of 64 metamaterial models are analyzed. The results show that the stiffness and negative Poisson's ratios of the metamaterials depend primarily on their architectures. For example, the antichiral model exhibits approximately 13 times more stiffness than its arc-star counterpart. The cross-sectional geometries of the component rods also play an essential role in the mechanical behaviors of the metamaterials. For instance, the antichiral architecture, which consists of bars with an I-shaped section that has a width-to-height ratio of 0.5, has an elastic modulus 9 times greater than that of the model composed of bars with a square cross section. This study shows that it is possible to design metamaterials several times stronger simply by changing the shape of the cross section of their constituent elements without compromising on their lightweight property.
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    Influence of stem-cell size and culture media flowing modality on cell’s fate within a microchannel; a numerical analysis
    (2021) Ali, Daver
    The dynamic cell culture process has been widely used in tissue engineering. The success of cell culture is influenced by many factors, one of which is how the cells are transferred from the bioreactor to the scaffolds through microchannels. The risk that can reduce the success of the cell culture process is that the cells do not reach the final destination correctly. In this study, the movement of stem cells through a microchannel was theoretically analysed using discrete phase computational fluid dynamics. Three factors of cell size, fluid flow rate and fluid viscosity were investigated on their sedimentation rate before reaching the microchannel outlet. Considering four sizes of 10, 15, 20 and 30 µm for cells, four flow rates of 20, 50, 90 and 180 µl/min in addition, four viscosities of 0.001, 0.005, 0.01 and 0.025 Pa.s were selected for culture media left us a total number of 64 models. The results of the analysis showed that cells with smaller size have a better chance of reaching the microchannel outlet and larger cells are more likely to sediment. Also, higher flow velocities as well as higher fluid viscosity delivering more cells to the destination. The results of this study shed more light on the regulation and control of dynamic cell culture parameters.
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    Mimicking Bone Anisotropic Structure with Modified Gyroid Scaffolds; A Finite Element Analysis
    (Gazi Univ, 2021) Ali, Daver
    The structure of the bone is very complex and heterogeneous; this causes different mechanical and biological properties in its longitudinal and transverse directions. For example, the modulus of elasticity and the permeability of the trabecular bone in a longitudinal and radial direction can vary up to several times. Therefore, implant design that matches these differences is necessary to maximize compliance with the host bone. Given that, in this study, a gyroid structure that generally is used in bone scaffolds was modified to design anisotropic scaffolds. Therefore, the gyroid triply periodic minimal surface trigonometric function was manipulated, and five different architectures were denoted as G(-50), G(-25), G(0), G(+25), and G(+50) with a constant porosity of 80% were developed. The effective elastic moduli of the models were calculated using finite element analysis. The results showed an anisotropicity rate of 0.21, 0.62, 1.50 and 2.23 in elastic moduli for G(-50), G(-25), G(+25) and G(+50) models respectively. As well, the permeability of the models was calculated using computational fluid dynamics (CFD) analysis. Anisotropic models showed different permeability in longitudinal and transverse directions. Longitudinal permeability to lateral direction rate were 0.67, 0.80, 1.25 and 1.47 for G(-50), G(-25), G(+25) and G(+50) models respectively.