Bioreactor Scale‐Up

Abstract

Large‐scale bioreactors are used for producing biological products (e.g., monoclonal antibodies, fusion proteins, enzymes) expressed in mammalian cells. Compared with small‐scale bioreactors, they are intrinsically more challenging in mixing and mass transfer and require more optimization. Proper bioreactor scale‐up is needed to ensure productivity and product quality. Here, common approaches and challenges in industrial mammalian cell culture scale‐up are covered. These are different from the scale‐up challenges and methodologies typically used in microbial bioreactors, since cell‐culture bioreactors operate in different agitation power and gas flow regimes. Engineering considerations including mass transfer, mixing, and hydrodynamic stress are presented in detail. Single‐use bioreactors are focused due to their rapid adoption by industry in clinical and commercial production. Though the main body of this article is on suspension cultures, special considerations in scaling‐up microcarrier‐based cultures are also briefly discussed. Finally, new challenges and desired improvements in scaling up high density cultures are presented.

Development of a scale‐up strategy for Chinese hamster ovary cell culture processes using the kLa ratio as a direct indicator of gas stripping conditions

“…We focused on the power input per unit volume ( P / V ) values obtained from the calculations, and the k L a ratio, which is determined by both k L a(O 2 ) and k L a(CO 2 ). Several studies have proven that CO 2 does not accumulate at the larger scale when the k L a ratio is used as the scale‐up strategy 19‐21 . The stripping of CO 2 from the culture medium is related to both k L a(CO 2 ) and the aeration rate.…”

A perspective‐driven and technical evaluation of machine learning in bioreactor scale‐up: A case‐study for potential model developments

“…Furthermore, many of these factors are not typically measured or reported in the literature or may be qualitative, such as the type of impeller/sparger. A comprehensive literature review was therefore conducted to identify factors most crucial to scale up for possible inclusion in a machine learning algorithm: Parameters including power input per volume, gas mass transfer coefficient (k L a), gas flow rates, impeller tip speed, mixing time, and Reynolds number are often analyzed to obtain insights for matching key performance indicators across bioreactor scales [63–65]. These scale‐specific parameters can represent many qualitative and quantitative variables pertaining to mixing, mass transfer, and shear damage to cells. There are many factors affecting power consumption in a stirred‐tank bioreactor including impeller design and configuration, sparger design and location, fluid properties, and vessel baffling.…”

“…A power number is then incorporated into power consumption calculations to account for these factors [66–68]. The Reynolds number characterizing the bioreactor fluid regime represents the ratio of inertial to viscous forces in the culture media, as well as the fluid properties [64, 69] and provides a good characterization of the fluid environment in the bioreactor. The scale or production rate is indicated by the bioreactor volume; however, the bioreactor volume is not the sole size‐related factor determining flow‐field‐relevant effects in a bioreactor; various aspect ratios and vessel diameters can be employed for the same vessel volume. The aspect ratio affects gas bubble formation and residence time, leading to changes in the oxygen transfer rate and CO 2 stripping rate [28].…”

“…Parameters including power input per volume, gas mass transfer coefficient (k L a), gas flow rates, impeller tip speed, mixing time, and Reynolds number are often analyzed to obtain insights for matching key performance indicators across bioreactor scales [ 63 , 64 , 65 ]. These scale‐specific parameters can represent many qualitative and quantitative variables pertaining to mixing, mass transfer, and shear damage to cells.…”

“…The Reynolds number characterizing the bioreactor fluid regime represents the ratio of inertial to viscous forces in the culture media, as well as the fluid properties [ 64 , 69 ] and provides a good characterization of the fluid environment in the bioreactor.…”