(Dr. Paul Neitzel, advisor)

"Numerical Simulation of the Fluid Mechanics of a Spinner Flask Bioreactor"

Abstract

During the growth of articular cartilage in bioreactors, parameters such as composition, shape, and cell function of the final construct are known to be strongly influenced by the hydrodynamic forces present in the bioreactor. Therefore, it is necessary to understand and precisely determine the characteristics of the flow field of the bioreactor to achieve more efficient and controlled methods for in vitro tissue growth. Polymer scaffolds are placed in the spinner-flask bioreactor in where the flow is driven by a rotating magnetic bar. The Reynolds number based on the angular velocity and bar length is 1750, which induces a turbulent state. The presence of turbulent flow in such a complex geometry makes the use of numerical techniques necessary to solve the governing equations.

Fluent, a commercial software package, was used to numerically simulate the flow field in the spinner flask. To model the bar rotation, the moving-rotating mesh feature was used, and to model the turbulent flow the k-e turbulence model with standard wall functions was employed. The Reynolds-averaged Navier-Stokes equations were solved and the mean values of the flow field parameters were determined. In addition, scaffolds were modeled first as solid, which simulates the final state of the tissue, and then as porous media with different permeabilities, which simulates the initial state of the fibrous felt and the variation of the porosity with the growth of tissue. The forces acting on the felt faces were determined for all these regimes and the flow rate through the porous scaffolds was found. Finally, the results for the case of the scaffold modeled as solid cylinder were compared with the values obtained by PIV measurements.