Computational Fluid Dynamics Study of the Effects of Surface Roughness on Permeability and Fluid Flow-Induced Wall Shear Stress in Scaffolds

In this work, we investigated surface roughness effects on bone scaffold permeability and fluid flow-induced wall shear stress (WSS) using computational fluid dynamics (CFD) analysis. Scaffolds are made of interconnected microchannels, whose fluid flow can be examined from the perspective of fluid flow dynamics. Given that the roughness of microchannel surfaces serves a non-negligible function in the fluid dynamics within the channels, it is believed that the wall roughness of scaffolds can play an important role in their permeability and WSS. Given the criticality of permeability and WSS in the effective biological functioning of scaffolds, we investigated manufacturing-induced surface roughness effects on the two aforementioned biocompatibility characteristics. To this end, three scaffolds with square pores of different sizes (300, 600, and 900 µm) and identical porosity (63%) were designed. Six roughness levels (0, 4, 8, 12, 16, and 20 µm) were established for the scaffold walls, thus enabling us to develop 18 scaffold models. The pressure drop and WSS in the scaffolds were then measured by CFD. Scaffold permeability was calculated using Darcy's law, with reference to geometrical parameters and the pressure drop derived from the CFD analysis. In all the scaffolds, high roughness decreased permeability and WSS. A significant difference in WSS reduction was found between the models with smooth scaffolds and the models with scaffolds that had a roughness of 20 µm. Except for the scaffold with a pore size of 300 µm, all the others showed no considerable change in permeability at different roughness levels.