Microfluid-dynamics in Three-dimensional Engineered Cell Systems

Bioreactors allowing direct perfusion of culture medium through tissueengineered constructs may overcome diffusion limitations associated with static culturing, and may provide flow-mediated mechanical stimuli. The hydrodynamic stress imposed on cells in these systems will depend not only on the culture medium flow rate but also on the scaffold three-dimensional (3D) micro-architecture. We performed computational fluid dynamics (CFD) simulations of the flow of culture medium through 3D porous scaffolds, cultured in a direct perfusion bioreactor, with the aim of predicting the shear stress acting on cells adhering on the scaffold walls as a function of various parameters that can be set in a tissue-engineering experiment. We developed three CFD models: Model 1 was built from histological sections of a fibre scaffold, Model 2 was built from micro-computed tomography reconstruction of a porous foam, and Model 3 was based on an idealized geometry of the actual porous foam. The simulations predicted different distributions of the shear stresses acting on the scaffold walls for each scaffold geometry modelled. In contrast, the simulations predicted the same value of median shear stress in all of the three models. Our results provide a basis for the completion of more exhaustive quantitative studies to further assess the relationship between perfusion, under known micro-fluid dynamic conditions, and tissue growth in vitro.