Development of a two-compartment system to model pH-inhomogeneities occurring in large-scale bioreactors

Abstract

Mammalian cells are highly sensitive to fluid dynamic stress conditions. Therefore, agitation is even more limited than in microbial processes, resulting in long mixing times at large-scale reactors. This can cause inhomogeneities if liquids are added from the top of the reactor. Such heterogeneities might influence product quality, quantity and cell physiology. As postulated and validated in literature, pH-perturbations have an influence on cell physiology. Therefore, this thesis focuses on pH-inhomogeneities. To investigate those effects of inhomogeneities already during process development, scale-down models are necessary. For implementation of these models two-compartment systems can be applied. There are only a few existing scale-down models for pH-inhomogeneity studies in mammalian bioprocesses. In the majority of the applied systems, already the system itself causes changes in process performance. This must be avoided. Only the inhomogeneity itself may cause different process performance, to be able to perform scale-down experiments with clear results on physiological influences. The aim of this thesis was to develop and characterize a small-scale two-compartment system for pH-inhomogeneity studies of an industrial large-scale Chinese Hamster Ovary (CHO) cell bioprocess, which has a comparable process performance to a standard cultivation. After the investigation of the appropriate pump and three setups in total, a two-compartment system as stirred-tank-reactor – plug-flow-reactor approach with 2.5 L total batch volume and a centrifugal pump was constructed. This system had a comparable process performance and the goal of this thesis was achieved. The developed two-compartment scale-down system is a novelty, since there is no two-compartment scale-down system for the investigation of base-addition caused pH-inhomogeneities at CHO bioprocesses published yet, which has a comparable process performance to a standard cultivation and an inhomogeneity volume of less than 10%. With this system, clear results on physiological influences of pH inhomogeneities can now be achieved.