Bed expansion properties of tissue engineering particles in a fluidised bed bioreactor

Abstract

Fluidised bed bioreactors (FBBs) are a promising alternative to provide high cell densities and a more defined culture environment for 2D and 3D cell cultures. However, for their wider use in biotechnology applications, a better understanding of their hydrodynamics is required. In this work, the fluidisation properties of three common particles in tissue engineering - single cells, cells clusters, and gel microbeads - were evaluated and compared to established liquid fluidisation correlations. Only a few studies to date have attempted to characterise the hydrodynamic behaviour of gel beads, while none were found for the other two particle types studied here. All particles were in the micrometre size range and their densities were found to be near-equal to the fluid phase. The particle terminal velocities were measured and corrected for hindrance effects, but these values were poorly predicted by equations proposed for rigid smooth spheres. Bed expansion data was presented in the form of logarithmic plots of velocity against voidage and analysed in terms of Richardson & Zaki parameters (n, expansion index and k, correction factor). Linear relationships were observed in these graphs; however, the fitting parameters were incorrectly predicted by the established equations. Therefore, modified Richardson-Zaki correlations were developed by using experimental parameters for n and k, to enable other users to set up FBBs for tissue engineering applications.