Abstract Summary (Max 250 words)
The industrial-scale production of adeno-associated virus (AAV) by transient transfection of HEK293 cells remains a key challenge for gene therapy manufacturing. Scaling from shaken culture systems to stirred tank bioreactors introduces changes in hydrodynamic conditions, where biological and engineering parameters influence process robustness and productivity. Few studies investigate these engineering factors, making detailed understanding essential for successful scale-up. This work presents the characterisation of the Xcellerex™ Xplatform reactor (Cytiva) equipped with the 6B-R50 impeller. A 1 L geometrically scaled-down model of the 50 L system is evaluated across a range of working volumes, agitation speeds, vessel configurations and impeller rotation directions. Emphasis is given to the effective baffle volume immersed in the liquid, as this parameter influences vortex formation. Experiments demonstrate that the 6B-R50 impeller exhibits power numbers of 1.7 and 2.4 under anticlockwise and clockwise rotation, respectively. These values align with those reported for three-pitched blade impellers, supporting its applicability for mammalian cell culture. Reduced baffle submergence leads to earlier vortex formation and increased free-surface deformation, conditions that may negatively impact mammalian cell cultures due to hydrodynamic stress. Power consumption is determined using the air-bearing technique, while mixing and flow dynamics are assessed by the Dual Indicator System for Mixing Time and particle image velocimetry, PIV, respectively. This study presents the first detailed characterisation of the Xplatform bioreactor. The findings support rational process design and scale-up strategies, providing a solid foundation for viral vector production in stirred tank bioreactors.
