The Poloxamer family of surfactants are commonly used in the biopharmaceutical industry as cell culture media additives to protect cells from the turbulent environment of sparged bioreactors. Despite the widespread use of poloxamers in cell culture, their performance as cell protectants varies depending on their physical structure, molecular weight, and batch-to-batch composition. In this study, the interfacial properties of Poloxamer 188 (P188), Poloxamer 407 (P407), and a mixture of P188 and P407 were characterized to investigate the mechanism of surfactant-mediated shear protection of mammalian cells. The foam stability and equilibrium surface tension of these surfactant systems correlated with their ability to mitigate physical damage to cells in a turbulent environment. We demonstrate that while P188 can function as highly effective shear protectant, the presence of a surface-active contaminant can greatly hinder its protective characteristics. P407 was found to function as such an interfacially active "impurity," disrupting shear protection when mixed with P188 by preferentially adsorbing to the gas-liquid and membrane-liquid interface. Addition of surface-active impurities altered the interfacial properties of the surfactant system and could be detected using an equilibrium surface tension assay. The mechanism of disruption by P407 was determined to be independent of cell-to-bubble attachment, suggesting that poloxamer adsorption to and subsequent reinforcement of the cell membrane may play a key role in protecting cells in high shear environments. This investigation contributes to our understanding of the mechanism of surfactant-mediated shear protection of cells and demonstrates that a surface tension assay can be utilized as a screening tool to ensure that poloxamer lots are free of surface active impurities.
Keywords: Bioreactors; Foam stability; Interfacial tension; Mammalian cells; Poloxamer; Shear sensitivity.
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