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Experimental and theoretical studies of protein transport in hollow-fibre bioreactors for mammalian cell culture Labecki, Marek

Abstract

Cultivation of marnrnalian cells in the extracapillary space (ECS) of hollow-fibre bioreactors (HFBRs) is increasingly used for the production of useful proteins such as monoclonal antibodies. One of the greatest challenges associated with the operation of HFBRs is the maintenance of a uniform cell growth environment. In particular, the distributions of growth-factor proteins can be highly heterogeneous, leading to poor performance or even failure of the culture. Another important aspect of HFBR operation is the harvesting of product proteins from the ECS. Considering the high costs of the product and media proteins, there is a strong motivation for carrying out studies that will provide a better understanding of protein behaviour in HFBRs. The main focus of this thesis was the development of mathematical models describing different aspects of protein transport in HFBRs. The models were validated using protein concentration data collected during cell-free HFBR experiments. A one-dimensional Krogh cylinder model was employed to analyse hindered transmembrane transport relevant to the leakage of smaller proteins from the ECS. A two-dimensional porous medium model (PMM) was used to simulate open-shell operations such as harvesting. An advanced, three-dimensional PMM formulation permitted an extensive analysis of gravity-influenced free-convective ECS protein transport at different HFBR orientations. The dynamics of protein leakage in HFBRs was found to depend on many factors, including initial protein placement, perfusion flow rate, and the addition of a nonleaking protein to the ECS. An open-shell ECS shunt was predicted to be a viable alternative to the traditional closed-shell HFBR configuration, while cocurrent harvesting was found more efficient than countercurrent harvesting. Most studies revealed that the protein transfer between the fibre bundle and the manifolds played a significant role in ECS protein redistribution. Numerous model simulations confirmed the occurrence of forced-convective downstream polarisation of ECS proteins under typical operating conditions. The heterogeneity of protein distribution was greatly reduced by directing the perfusion flow upward, in which case strong free-convective flows mixed the contents of the ECS. These effects were most pronounced in cartridges oriented vertical-up, which might be a nonstandard but nonetheless promising configuration for use in future HFBR cell culture.

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