Fluid Mechanics of cell transduction at various scales of pharmaceutical bioreactors

• Validated CFD simulations of transduction processes within bioreactors can provide fluids dynamics insight into these experimentally opaque systems. • The strain rates that exist in different bioreactors are varied and the effect on transduction performance is not necessarily intuitive. • Bioreactor transduction performance correlates reasonably well with the local strain rate that cells experience. • The poorest measured transduction performance occurs when cells spend prolonged time near reactor side walls, where damaging high strain rates exist. • Dewetting of the reactor walls could also contribute to poor bioreactor performance, as well as the effects of mixing on reactant and product species. This study employs computational fluid dynamics (CFD) to analyse the scale-up of bioreactors used for lentiviral vector (LVV) transduction of hematopoietic stem cells. LVV transduction is used in the manufacture of many current and promising gene therapies. Two sizes of bioreactors are considered, containing liquid volumes of 0.5 mL and 60 mL, respectively. The smaller system consists of a well plate on a reciprocating shaker, as used in (for example) initial product development, while the larger commercial bioreactor consists of a larger cylindrical chamber that relies on intermittent vessel rotation for mixing. The simulations were validated using previously published experimental fluid dynamics data. Cell transduction efficiency was measured within the two reactors to compare against the fluid dynamics of the process obtained via CFD. Findings highlight the critical impact that local strain rates have on transduction efficiency. In the larger system, high rotational speeds push cells toward the vessel side walls, where a recirculation zone traps them in regions of elevated strain. This phenomenon correlates with lower transduction performance. Additionally, under these conditions in the larger system, the model predicts dewetting of the bottom reactor surface which reinforces outward cell movement and may directly further harm transduction efficiency. Transduction in the smaller system, and in the larger system at lower rotational speeds, is found to be superior to the larger system at higher rotational speeds, suggesting that the critical strain rate at which strain rate disrupts LVV transduction lies within the range of approximately 280 s −1 to 2070 s −1 .