(75e) Facing Heterogeneities in Bioprocesses, a Downscale Approach Tailored to Suit Large Scale Conditions

Nowadays, a majority of mammalian cell cultivations is performed in stirred bioreactors of various sizes. While heterogeneity of the hydrodynamic stress, covering several orders of magnitude, is well documented with increasing bioreactor size, additional heterogeneities such as DO and CO2 are becoming more important. Furthermore, perturbations in pH can be observed when pH is controlled via acid/base addition. Commonly in the process development stage, scale dependent parameters are usually neglected, often resulting in a different behavior of the culture when transferred to large scale production bioreactors with volumes of several thousand liters.

            The aim of this work is to incorporate the variation of scale dependent variables, e.g. shear stress, DO and pH, into a typical 3L development scale bioreactor. A trajectory analysis performed in a validated CFD model was used to evaluate the frequencies, maximum values and exposure times of hydrodynamic stress, DO and pH to which cells are exposed along their journey through a large scale bioreactor. Obtained values were used to design an external loop, driven by a centrifugal pump, attached to a 3L bioreactor, enabling us to independently vary shear frequency, shear value and shear exposure time. After proper testing and characterization, further development was done by considering the heterogeneity of DO and pH perturbations commonly seen in large scale bioreactors. Comparison of cell cultivations in such scale-down model showed better agreement with large scale data compared to those obtained from conventional 3L bioreactors.