Rheology of CHO Cell Suspensions and Its Effects on High-Density Cultivation Process and Bioreactor Design

With the rapidly growing demand for monoclonal antibodies (mAbs) worldwide, optimizing the high-density and ultra-high-density cultivation processes of Chinese hamster ovary (CHO) cells has become crucial for enhancing production efficiency. Shear stress and mass transfer have always been the vital operating parameters for the bioreactor in creating a suitable microenvironment for cell growth and antibody production. However, researchers have not actively focused on the rheology of CHO cell suspensions and its impact on these parameters in bioreactors. The factors influencing the rheology of suspensions were first investigated in this study. The findings demonstrated that the shear-thinning behavior of the suspension was primarily affected by the cell volume fraction (Φ). As Φ increases, the shear-thinning behavior gradually weakened, and the viscosity increased. The Sisko model was used to characterize rheology, while computational fluid dynamics simulations evaluated its impact on bioreactor performance. The simulation results revealed that the rheology of the suspensions caused a multiple increase in shear stress and a 10%-40% decrease in the volumetric mass transfer coefficient (kLa) in the bioreactor. Therefore, the effects of rheology cannot be ignored while designing operating parameters. This study established empirical correlations among Pg/V, Vg, Φ, and kLa, thus delivering guidance for selecting appropriate operating parameters in high-density and ultra-high-density cell cultivation processes. The findings provide a scientific foundation for optimizing CHO cell cultivation processes and quantifying suitable microenvironment parameters for cell growth and production. They also offer novel ideas and strategies for scaling up and optimizing the structural parameters of bioreactors.