CFD for Characterizing Standard and Single-use Stirred Cell Culture Bioreactors

Driven by global competition and rising cost pressure in the pharmaceutical industry, over the last ten years single-use bioreactors have been increasingly used for animal cell cultivations in screening experiments, seed inoculum and seed train productions as well as in small and medium scale production processes of proteins (in particular, antibodies and vaccines). In contrast to re-usable bioreactors made of glass or stainless steel, single-use bioreactors consist of a flexible or rigid cultivation vessel which has been gamma-sterilized and made ready for the purchaser to use. After harvest, the cultivation vessel is discarded, which results in a lower risk of cross-contamination, and eliminates the need for steam sterilization and cleaning [Eibl et al. (2010)]. Nowadays a multitude of single-use bioreactors are commercially available, which can be categorized according to the type of power input into static and dynamic systems. The latter can be further subdivided into hydraulically, pneumatically and mechanically driven bioreactors and their combinations, the so-called hybrid systems [Eibl et al. (2011)]. Mechanically driven single-use bioreactors represent the largest group and are mixed by either orbital-shaken, wave-induced or stirrer motion. While wave-mixed bioreactors (e.g. from GE Healthcare, Sartorius Stedim Biotech, Applikon Biotechnology) were initially dominant, nowadays stirred bag systems (such as Hyclone® Single Use Bioreactor S.U.B., BIOSTAT® CultiBag STR, XDRTM-DSTB animal) are more frequently used, mainly due to the broad experience already obtained with conventional stirred cell culture bioreactors [Eibl et al. (2011)]. The flexible cultivation bags are fixed and shaped by a temperature-controlled stainless steel container. This design is also used in the BIOSTAT® CultiBag STR from Sartorius Stedim Biotech, which is available at different scales from 50 to 1,000 L. The bag geometry, the impellers and the aeration system are designed in a similar way to Sartorius Stedim’s re-usable stirred cell culture bioreactors to ensure comparability of single-use and classical processes, and thus facilitate integration of singleuse bioreactor technologies into modern cultivation processes [De Wilde et al. (2009); Noack et al. (2011)]. Until summer 2009, stirred bag bioreactors were available only at working volumes exceeding 50 L for manufacturing and cost reasons. The introduction of the first single-use stirred bioreactors with a rigid cultivation vessel (Mobius® CellReady 3L bioreactor and CelliGen® BLU SUB) bridged the gap for stirred systems between laboratory and pilot scale