Scale-Up analysis for a CHO cell culture process in large-scale bioreactors
ABSTRACT Bioprocess scale-up is a fundamental component of process development in the biotechnology industry. When scaling up a mammalian cell culture process, it is important to consider factors such as mixing time, oxygen transfer, and carbon dioxide removal. In this study, cell-free mixing studies were performed in production scale 5,000-L bioreactors to evaluate scale-up issues. Using the current bioreactor configuration, the 5,000-L bioreactor had a lower oxygen transfer coefficient, longer mixing time, and lower carbon dioxide removal rate than that was observed in bench scale 5- and 20-L bioreactors. The oxygen transfer threshold analysis indicates that the current 5,000-L configuration can only support a maximum viable cell density of 7 x 10(6) cells mL(-1). Moreover, experiments using a dual probe technique demonstrated that pH and dissolved oxygen gradients may exist in 5,000-L bioreactors using the current configuration. Empirical equations were developed to predict mixing time, oxygen transfer coefficient, and carbon dioxide removal rate under different mixing-related engineering parameters in the 5,000-L bioreactors. These equations indicate that increasing bottom air sparging rate is more efficient than increasing power input in improving oxygen transfer and carbon dioxide removal. Furthermore, as the liquid volume increases in a production bioreactor operated in fed-batch mode, bulk mixing becomes a challenge. The mixing studies suggest that the engineering parameters related to bulk mixing and carbon dioxide removal in the 5,000-L bioreactors may need optimizing to mitigate the risk of different performance upon process scale-up.
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- "A practical explicit formula is (4) where H 2 O is the concentration of water in the liquid phase, He C Henry's constant for CO 2 , p the actual total pressure and y C the molar fraction of CO 2 in the gas phase. In literature (e.g., Xing et al. ), y C is most often assumed to be the carbon dioxide concentration in the air pressed into the sparger and that is the very problem. Due to mass transfer across the bubble interfacial area, A B , changes in the amount n C of CO 2 within a single representative gas bubble along its path in the continuous liquid phase can be described by the simple ordinary differential equation in n C (5) which can easily be derived from Eq. (1). "
ABSTRACT: Most discussions about stirred tank bioreactors for cell cultures focus on liquid-phase motions and neglect the importance of the gas phase for mixing, power input and especially CO(2) stripping. Particularly in large production reactors, CO(2) removal from the culture is known to be a major problem. Here, we show that stripping is mainly affected by the change of the gas composition during the movement of the gas phase through the bioreactor from the sparger system towards the headspace. A mathematical model for CO(2)-stripping and O(2)-mass transfer is presented taking gas-residence times into account. The gas phase is not moving through the reactor in form of a plug flow as often assumed. The model is validated by measurement data. Further measurement results are presented that show how the gas is partly recirculated by the impellers, thus increasing the gas-residence time. The gas-residence times can be measured easily with stimulus-response techniques. The results offer further insights on the gas-residence time distributions in stirred tank reactors.Biotechnology Journal 12/2011; 6(12):1547-56. DOI:10.1002/biot.201100153 · 3.71 Impact Factor
Conference Paper: Particle Swarm Optimization (PSO) for reflector antenna shaping[Show abstract] [Hide abstract]
ABSTRACT: It has been shown that reflector antenna systems can benefit substantially from careful shaping of the main or sub-reflectors, or both, in order to maximize the antenna's performance (Duan, D.-W. and Rahmat-Samii, Y., 1995). Shaped reflectors can be used to achieve high efficiencies and gains, low side-lobe levels, and arbitrarily contoured beams. As the demands placed on satellite broadcasting and communications channels and the use of space-borne radar applications increase, so too do the requirements for the antennas on which these systems rely. The paper establishes particle swarm optimization as a candidate for solving difficult reflector synthesis problems. This is done by developing the tools required to perform the reflector synthesis and solving an example to serve as proof-of-concept. The example is to shape the main reflector of a reflector antenna with F/D=1.0, such that the scanning performance of the antenna. is improved.Antennas and Propagation Society International Symposium, 2004. IEEE; 07/2004
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ABSTRACT: Semisteady state cultures are useful for studying cell physiology and facilitating media development. Two semisteady states with a viable cell density of 5.5 million cells/mL were obtained in CHO cell cultures and compared with a fed-batch mode control. In the first semisteady state, the culture was maintained at 5 mM glucose and 0.5 mM glutamine. The second condition had threefold higher concentrations of both nutrients, which led to a 10% increase in lactate production, a 78% increase in ammonia production, and a 30% reduction in cell growth rate. The differences between the two semisteady states indicate that maintaining relatively low levels of glucose and glutamine can reduce the production of lactate and ammonia. Specific amino acid production and consumption indicated further metabolic differences between the two semisteady states and fed-batch mode. The results from this experiment shed light in the feeding strategy for a fed-batch process and feed medium enhancement. The fed-batch process utilizes a feeding strategy whereby the feed added was based on glucose levels in the bioreactor. To evaluate if a fixed feed strategy would improve robustness and process consistency, two alternative feeding strategies were implemented. A constant volume feed of 30% or 40% of the initial culture volume fed over the course of cell culture was evaluated. The results indicate that a constant volumetric-based feed can be more beneficial than a glucose-based feeding strategy. This study demonstrated the applicability of analyzing CHO cultures in semisteady state for feed enhancement and continuous process improvement.Biotechnology Progress 05/2009; 26(3):797-804. DOI:10.1002/btpr.362 · 1.88 Impact Factor