Influence of Pluronic F68 on Oxygen Mass Transfer Christian Sieblist, Marco Jenzsch, and Michael Pohlscheidt Pharmaceutical Biotech Production, Roche Diagnostics GmbH, Penzberg, Germany DOI 10.1002/btpr.1770 Published online Month 00, 2013 in Wiley Online Library (wileyonlinelibrary.com) Pluronic F68 is one of the most used shear protecting additives in cell culture cultiva- tions. It is well known from literature that such surface-active surfactants lower the surface tension at the gas-liquid interface, which influences the mass transfer. In this study, the effect of Pluronic F68 on oxygen mass transfer in aqueous solutions was examined. There- fore, the gassing in/gassing out method and bubble size measurements were used. At low concentrations of 0.02 g/L, a 50% reduction on mass transfer was observed for all tested spargers and working conditions. An explanation of the observed effects by means of Hig- bie’s penetration or Dankwerts surface renewal theory was applied. It could be demon- strated that the suppressed movement of the bubble surface layer is the main cause for the significant drop down of the k L a-values. For Pluronic F68 concentrations above 0.1 g/L, it was observed that it comes to changes in bubble appearance and bubble size strongly dependent on the sparger type. By using the bubble size measurement data, it could be shown that only small changes in mass transfer coefficient (k L ) take place above the critical micelle concentration. Further changes on overall mass transfer at higher Pluronic F68 con- centrations are mainly based on increasing of gas holdup and, more importantly, by increas- ing of the surface area available for mass transfer. V C 2013 American Institute of Chemical Engineers Biotechnol. Prog., 000:000–000, 2013 Keywords: Pluronic F68, oxygen mass transfer, cell culture, large scale bioreactors Introduction The demand of complex therapeutic proteins and antibod- ies for the detection and treatment of diseases such as cancer has increased significantly in the past few decades. Between 1950 and 2008, a total of 1,222 new molecular entities were approved by the regulatory authorities, and recombinant pro- teins, antibodies, and antibody drug conjugates will be the major source of revenues in future. 1,2 Because of their ability to properly fold and glycosylate such proteins, animal cells are often the ideal expression system, and the Chinese ham- ster ovary cells have become the working horse of the indus- try. 3–5 The cultivation of mammalian cells requires complex media design, specific bioreactor design, and robust process control systems. 6 These requirements are based on the spe- cific characteristics of mammalian cells, like, for example, a missing cell wall, which makes them sensitive to shear force and fluctuation in the cell culture environment. 7,8 Therefore, the bioreactor has to realize sufficient homogenization and mass transfer 9,10 at low shear force. 11,12 Hydrodynamic shear force is caused by several means in bioreactors. In most cases, aeration by air sparging or mechanical power input by agitation of the culture to achieve homogeneous mixing and sufficient mass transfer (O 2 and CO 2 ) is the major source of shear force. Among others, these factors are a function of geometry and design of the bioreactor including the impeller, the sparger design affecting primary bubble size, power input and tip speed of the impeller, as well as aeration or sparge rates. Since, in general, low power inputs are used in animal cell cultures, the most dominating source of shear force is associated with aeration, in particular bubble burst at the liq- uid surface. 7,13–17 Power input by impellers and rising of bubbles in the liquid is of secondary importance for shear force. 18–21 Besides these physical factors, the media composition and the use of additives have a major influence on mass transfer, shear protection, and fluid dynamic of the bioreactor. To reduce the impact of shear force to the cells, a lot of research has been conducted to protect the cells by different media additives. Experiments were performed with methyl- cellulose, 7 starch solutions, protein-containing solutions (albumin, serum, etc.), or nonionic tensides. Effective protec- tion could be demonstrated by different sera and nonionic tensides (e.g., Pluronic). 22 Serum of animal or human origin is like any other nonchemically defined media component not favorable in production processes due to contamination risks and significant batch-to-batch variability. Hence, Plur- onic and other nonionic tensides are commonly used in the base media formulation of most manufacturing processes. The concentration can vary broadly in commercially avail- able media-for example, Pluronic F68 varies in a range of 0.5–3 g/L. 23–25 The efficiency and effectiveness of Pluronic F68 in rela- tion to protection of cells against shear force has been described previously. 17,18,21,26–33 An overview to Pluronic polyols and cell protection is described in the Encyclopedia Correspondence concerning this article should be addressed to C. Sieblist at Christian.Sieblist@roche.com V C 2013 American Institute of Chemical Engineers 1