Systematic evaluation of high-throughput scale-down models for single-use bioreactors (SUB) using volumetric gas flow rate as the criterion

Abstract

Developing representative bioreactor scale-down models is a critical part in process development and characterization. Here we present a systematic analysis of high-throughput scale-down models (ambr®250, 250 mL) developed for 500 L or 2000 L single-use bioreactors using engineering approaches. A main scaling criterion, vvm (volume of gas per volume of liquid per minute), was studied for scale-down model development after analyzing bioreactor hydrodynamic environment and gas transfer characteristics. Two different processes with distinguished peak cell densities (12–14 vs. 20–25 × 106 cells/mL) for a monoclonal antibody (mAb) were evaluated. We demonstrated that scaling-down using similar vvm as the criterion is feasible in reproducing large-scale gas transfer characteristics for both cell densities, though more challenging in high-density conditions. Furthermore, a range of pCO2 levels could be generated through vvm modulations. The same vvm approach was successfully applied to two other mAbs. Practical aspects of ambr®250 operations, especially the impact of background air sparge rate and antifoam addition on dissolved oxygen control and gas transfer, were also discussed. Understanding and managing gas transfer gaps between small- and large-scale bioreactors is expected to streamline scale-up effort, and equally importantly scale-down activities for process characterization.