Numerical accuracy comparison of two boundary conditions commonly used to approximate shear stress distributions in tissue engineering scaffolds cultured under flow perfusion
Numerical accuracy comparison of two boundary conditions commonly used to approximate shear stress distributions in tissue engineering scaffolds cultured under flow perfusion
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DOI：
10.1002/cnm.3132
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发表时间：
2018-11-01
影响因子：
2.1
通讯作者：
Voronov, Roman S.
中科院分区：
文献类型：
--
作者：
Kadri, Olufemi E.;Williams, Cortes, III;Voronov, Roman S.
引言流动诱导的剪切应力已被发现是前成骨细胞在3D多孔支架接种和连续流灌注下培养的刺激因素。然而，由于支架的复杂内部结构，局部剪切力的整个支架计算是计算密集的。相反，通过提取支架的较小部分获得的代表性体积元素（RVE）通常用于文献中，而没有数值精度标准。目的方法因此，本研究的目标是检查如何密切整个支架模拟近似的两种类型的边界条件，用于使RVE：“壁边界条件”（WBC）和“周期性边界条件”（PBC）。为此，晶格玻尔兹曼方法流体动力学模拟被用来模拟从高分辨率微计算机断层扫描图像获得的3D支架重建中的表面剪切应力。结果发现，尽管RVE足够大于支架孔径的6倍（这是文献中发现的唯一准确性准则），但两种类型的边界条件仍然显着低估了应力：平均误差在20%和80%之间，取决于支架的孔隙率。此外，发现误差随着孔隙度的增加而增加。这可能是由于小孔主导流场，从而当支架孔隙率小时，抵消了不切实际的边界条件的影响。最后，发现PBC总是比WBC更准确和计算效率更高。因此，它是推荐的RVE类型。
Introduction Flow-induced shear stresses have been found to be a stimulatory factor in pre-osteoblastic cells seeded in 3D porous scaffolds and cultured under continuous flow perfusion. However, due to the complex internal structure of the scaffolds, whole scaffold calculations of the local shear forces are computationally intensive. Instead, representative volume elements (RVEs), which are obtained by extracting smaller portions of the scaffold, are commonly used in literature without a numerical accuracy standard. Objective Method Hence, the goal of this study is to examine how closely the whole scaffold simulations are approximated by the two types of boundary conditions used to enable the RVEs: "wall boundary condition" (WBC) and "periodic boundary condition" (PBC). To that end, lattice Boltzmann method fluid dynamics simulations were used to model the surface shear stresses in 3D scaffold reconstructions, obtained from high-resolution microcomputed tomography images. Results It was found that despite the RVEs being sufficiently larger than 6 times the scaffold pore size (which is the only accuracy guideline found in literature), the stresses were still significantly under-predicted by both types of boundary conditions: between 20% and 80% average error, depending on the scaffold's porosity. Moreover, it was found that the error grew with higher porosity. This is likely due to the small pores dominating the flow field, and thereby negating the effects of the unrealistic boundary conditions, when the scaffold porosity is small. Finally, it was found that the PBC was always more accurate and computationally efficient than the WBC. Therefore, it is the recommended type of RVE.