Development of a Packed Bed Bioreactor for Cartilage Tissue Engineering

Efficient transport of regulatory molecules is one of the main requirements for directing the growth and differentiation of bone marrow stromal cells (BMSC). We have designed and utilized a packed bed bioreactor system for cultivation of murine BMSC immobilized in alginate microbeads produced by electrostatic droplet generation. Continuous medium perfusion at velocities that are physiological for cartilage and bone (~ 100 μm/s) provided convective mass transport through the packed bed while the small bead diameter (~ 500 μm) ensured short diffusion distances to the immobilized cells. Over 5 weeks of cultivation, the cells remained viable at a constant density whereas the alginate microbeads retained size and spherical shape. Cell density used in this study ( 5 x 10 cells/ml) was found to be too low to result in cartilage tissue formation. However, in several cases, loosely bonded groups of beads and merged beads without visible boundaries were observed, implying that higher cell densities may lead to development of a continuous extracellular matrix. This study indicates the potentials of the packed bed bioreactor system in conjunction with alginate microbeads as cell carriers, for precise regulation of the cellular microenvironment in cartilage tissue engineering.