Development of funnel-type fluidized bed reactor system using microcarriers for cultures of adherent cells

Microcarriers with a high surface-to-volume ratio within bioreactor systems have been used for several decades to develop scalable and cost-effective processes for cultivating adherent cells to produce therapeutic cells, vaccines, and proteins. However, the agitation equipment in bioreactors, which is essential for suspending microcarriers and maintaining homogeneous culture conditions, generates high shear forces that adversely affect the growth of adherent cells. Fluidized bed reactors (FBRs), which are capable of suspending particles solely with liquid flow without an impeller, could provide a solution for these issues. Typical FBRs with cylindrical columns encounter difficulties in controlling the fluidized bed, due to a narrow flow rate range for fluidization and changes in the characteristics of microcarriers as cells grow, despite the advantages of low-shear forces. This leads to the failure of microcarrier fluidization and reduced efficiency of the microcarrier-based cell culture. In this study, we demonstrate a newly developed funnel-type fluidized bed reactor (FFBR) system with enhanced culture stability and evaluated its performance by culturing mouse fibroblasts (L929) and human mesenchymal stem cells. The FFBR exhibits stable operation over the entire culture period, unlike the FBRs with cylindrical columns. The cell density per culture area achieved with the FFBR was comparable to that obtained using the two-dimensional plastic culture system for both cell types. The FFBR is a useful tool for the expansion of adherent cells due to its stability and scalability, making it suitable for research, development, and manufacturing for therapeutic applications.