A practical approach in bioreactor scale-up and process transfer using a combination of constant P/V and vvm as the criterion

An in-silico analysis of hydrodynamics and gas mass transfer characteristics in scale-down models for mammalian cell cultures

Bioprocess scale-up and technology transfer can be challenging due to multiple variables that need to be optimized during process development from laboratory scale to commercial manufacturing. Cell cultures are highly sensitive to key factors during process transfer across scales, including geometric variability in bioreactors, shear stress from impeller and sparging activity, and nutrient gradients that occur due to increasing blend times. To improve the scale-up and scale-down of these processes, it is important to fully characterize bioreactors to better understand the differences that will occur within the culture environment, especially the hydrodynamic profiles that will vary in vessel designs across scales. In this study, a comprehensive hydrodynamic characterization of the Ambr® 250 mammalian single-use bioreactor was performed using time-accurate computational fluid dynamics simulations conducted with M-Star computational fluid dynamics software, which employs lattice-Boltzmann techniques to solve the Navier-Stokes transport equations at a mesoscopic scale. The single-phase and two-phase fluid properties within this small-scale vessel were analyzed in the context of agitation hydrodynamics and mass transfer (both within the bulk fluid and the free surface) to effectively characterize and understand the differences that scale-down models possess when compared to their large-scale counterparts. The model results validate the use of computational fluid dynamics as an in-silico tool to characterize bioreactor hydrodynamics and additionally identify important free-surface transfer mechanics that need to be considered during the qualification of a scale-down model in the development of mammalian bioprocesses.

Scale-up analysis of geometrically dissimilar single-use bioreactors

Cell culture scale-up is a challenging task due to the simultaneous change of multiple hydrodynamic process characteristics and their different dependencies on the bioreactor size as well as variation in the requirements of individual cell lines. Conventionally, the volumetric power input is the most common parameter to select the impeller speed for scale-up, however, it is well reported that this approach fails when there are huge differences in bioreactor scales. In this study, different scale-up criteria are evaluated. At first, different hydrodynamic characteristics are assessed using computational fluid dynamics data for four single-use bioreactors, the Mobius® CellReady 3 L, the Xcellerex™ XDR-10, the Xcellerex™ XDR-200, and the Xcellerex™ XDR-2000. On the basis of this numerical data, several potential scale-up criteria such as volumetric power input, impeller tip speed, mixing time, maximum hydrodynamic stress, and average strain rate in the impeller zone are evaluated. Out of all these criteria, the latter is found to be most appropriate, and the successful scale-up from 3 to 10 L bioreactor and to 200 L bioreactor is confirmed with cell culture experiments using Chinese Hamster Ovary cell cultivation.

Scale-Up of Capsular Polysaccharide Production Process by Haemophilus influenzae Type b Using kLa Criterion

Polyribosyl-ribitol-phosphate (PRP) from Haemophilus influenzae type b (Hib) is an active immunizing molecule used in the production of the vaccine against H. influenzae, and industrial production could contribute to satisfying a world demand especially in developing countries. In this sense, the aim of this study was to establish a scale-up process using the constant oxygen mass transfer coefficient (k_La) such as the criterion for production of PRP in three different sizes of bioreactor systems. Three different k_La values (24, 52 and 80 h⁻¹) were evaluated in which the biological influence in a 1.5 L bioreactor and 52 h⁻¹ was selected to scale-up the production process until a 75 L pilot-scale bioreactor was achieved. Finally, the fed-batch phase was started under a dissolved oxygen concentration (pO₂) at 30% of the saturation in the 75 L bioreactor to avoid oxygen limitation; the performance of production presented high efficiency (9.0 g/L DCW-dry cell weight and 1.4 g/L PRP) in comparison with previous scale-up studies. The yields, productivity and kinetic behavior were similar in the three-size bioreactor systems in the batch mode indicating that k_La is possible to use for PRP production at large scales. This process operated under two stages and successfully produced DCW and PRP in the pilot scale and could be beneficial for future bioprocess operations that may lead to higher production and less operative cost.

Industrial Case-Study-Based Computational Fluid Dynamic (CFD) Modeling of Stirred and Aerated Bioreactors

Industrial bioreactors featuring inadequate geometry and operating conditions may depress the effectiveness and the efficiency of the hosted bioprocess. Computational fluid dynamics (CFD) can be used to find a suitable operating match between the target bioprocess and the available bioreactor. The aim of this work is to investigate the feasibility of addressing bioreactor improvement problems in the bioprocess industry with the aid of such mainstream tools as industry-standard CFD. This study illustrates how to effectively simulate both the impeller rotation and air supply and discusses the way toward model validation at the 4.1 m³ capacity scale. Referring to experimentally measured process values, the developed full-scale model successfully predicted the power draw, liquid phase level, and mixing time with errors lower than 4.6, 1.1, and 6.7%, respectively, thus suggesting the illustrated approach as a best practice design method for the bioprocess industry. The validated model was employed to improve performance by reducing the power draw in aerated conditions with a minimal operational derating.

Development of a miniature bioreactor model to study the impact of pH and DOT fluctuations on CHO cell culture performance as a tool to understanding heterogeneity effects at large-scale

Understanding the impact of spatial heterogeneities that are known to occur in large‐scale cell culture bioreactors remains a significant challenge. This work presents a novel methodology for mimicking the effects of pH and dissolved oxygen heterogeneities on Chinese hamster ovary (CHO) cell culture performance and antibody quality characteristics, using an automated miniature bioreactor system. Cultures of 4 different cell lines, expressing 3 IgG molecules and one fusion protein, were exposed to repeated pH and dissolved oxygen tension (DOT) fluctuations between pH 7.0–7.5 and DOT 10%–30%, respectively, for durations of 15, 30, and 60 min. Fluctuations in pH had a minimal impact on growth, productivity, and product quality although some changes in lactate metabolism were observed. DOT fluctuations were found to have a more significant impact; a 35% decrease in cell growth and product titre was observed in the fastest growing cell line tested, while all cell lines exhibited a significant increase in lactate accumulation. Product quality analysis yielded varied results; two cell lines showed an increase in the G0F glycan and decrease in G1F, G2F, and Man5; however, another line showed the opposite trend. The study suggests that the response of CHO cells to the effects of fluctuating culture conditions is cell line specific and that higher growing cell lines are most impacted. The miniature bioreactor system described in this work therefore provides a platform for use during early stage cell culture process development to identify cell lines that may be adversely impacted by the pH and DOT heterogeneities encountered on scale‐up. This experimental data can be combined with computational modeling approaches to predict overall cell culture performance in large‐scale bioreactors.

New Insights from Locally Resolved Hydrodynamics in Stirred Cell Culture Reactors

The link between hydrodynamics and biological process behavior of antibody-producing mammalian cell cultures is still not fully understood. Common methods to describe dependencies refer mostly to averaged hydrodynamic parameters obtained for individual cultivation systems. In this study, cellular effects and locally resolved hydrodynamics were investigated for impellers with different spatial hydrodynamics. Therefore, the hydrodynamics, mainly flow velocity, shear rate and power input, in a single- and a three-impeller bioreactor setup were analyzed by means of CFD simulations, and cultivation experiments with antibody-producing Chinese hamster ovary (CHO) cells were performed at various agitation rates in both reactor setups. Within the three-impeller bioreactor setup, cells could be cultivated successfully at much higher agitation rates as in the single-impeller bioreactor, probably due to a more uniform flow pattern. It could be shown that this different behavior cannot be linked to parameters commonly used to describe shear effects on cells such as the mean energy dissipation rate or the Kolmogorov length scale, even if this concept is extended by locally resolved hydrodynamic parameters. Alternatively, the hydrodynamic heterogeneity was statistically quantified by means of variance coefficients of the hydrodynamic parameters fluid velocity, shear rate, and energy dissipation rate. The calculated variance coefficients of all hydrodynamic parameters were higher in the setup with three impellers than in the single impeller setup, which might explain the rather stable process behavior in multiple impeller systems due to the reduced hydrodynamic heterogeneity. Such comprehensive insights lead to a deeper understanding of the bioprocess.

Benchtop Bioreactors in Mammalian Cell Culture: Overview and Guidelines

Bioreactors are manufactured apparatuses that allow the generation of a specific environment for the highly controlled cultivation of living cells. Originally used for microbial production systems, they have found widespread applications in fields as diverse as vaccine production, plant cell cultivation, and the growth of human brain organoids and exist in equally diverse designs (Chu and Robinson, Curr Opin Biotechnol 12(2):180-187, 2001; Qian et al., Nat Protoc 13:565-580, 2018). Manufacturing of biologics is currently mostly performed using a stirred tank bioreactor and CHO host cells and represents the most "classical" bioreactor production process. In this chapter, we will therefore use the cultivation of suspension Chinese hamster ovary (CHO) cells for recombinant protein production in a stirred tank bioreactor as an example. However, general guidelines provided in this chapter are transferable to different bioreactor types and host cells (Li et al., MAbs 2(5):466-479, 2010).The preparation and operation of a bioreactor (also referred to as upstream process in a biotechnological/industrial setting) is comprised of three main steps: expansion (generation of biomass), production (batch, fed-batch, or continuous process), and harvest. The expansion of cells can last from few days to weeks depending on the number of cells at the start, the cellular doubling time, and the required biomass to inoculate the production bioreactor. The production phase lasts a few weeks and is a highly sensitive phase as the concentration of different chemicals and physical parameters need to be tightly controlled. Finally, the harvest will allow the separation of the product of interest from large particles and then the desired material (cell culture supernatant or cells) is transferred to the downstream process.The raw materials used during the upstream phase (all three steps) need to be aligned with the final purpose of the manufactured product, as the presence of residual impurities may have an impact on suitability of the final product for a desired purpose.

Equal mixing time enables scale-down and optimization of a CHO cell culture process using a shaken microbioreactor system

The advancement of microbioreactor technology in recent years has transformed early- and mid-stage process development. The monitoring and control capabilities of microbioreactors not only promote the quick accumulation of process knowledge but has also led to an increased scalability when compared to traditionally used systems such as shake flasks and microtitre plates. This study seeks to establish a framework for the micro-Matrix microbioreactor (Applikon-Biotechnology BV) as process development tool. Using the Dual Indicator System for Mixing Time, the system was initially characterized for mixing properties at varying operating conditions, which was found to yield mixing times between 0.9 and 41.8 s. A matched mixing time was proposed as scale-down criterion for an IgG4 producing GS-CHO fed-batch process between a 5 L stirred tank reactor (STR) and the micro-Matrix microbioreactor. Growth trends, maximum viable cell concentrations, final titre, and glycoprofiles were nearly identical at both scales. The scale-down model was then employed to optimize a bolus feeding regime using response surface methodology, which led to a 25.4% increase of the space-time yield and a 25% increase of the final titre. The optimized feeding strategy was validated at the small-scale and successfully scaled up to the 5 L STR. This work for the first time provides a framework of how the micro-Matrix microbioreactor can be implemented in a bioprocess development workflow and demonstrates scalability of growth and production kinetics as well as IgG4 glycosylation between the micro-Matrix and a benchtop-scale STR system.

High density bioprocessing of human pluripotent stem cells by metabolic control and in silico modeling

To harness the full potential of human pluripotent stem cells (hPSCs) we combined instrumented stirred tank bioreactor (STBR) technology with the power of in silico process modeling to overcome substantial, hPSC‐specific hurdles toward their mass production. Perfused suspension culture (3D) of matrix‐free hPSC aggregates in STBRs was applied to identify and control process‐limiting parameters including pH, dissolved oxygen, glucose and lactate levels, and the obviation of osmolality peaks provoked by high density culture. Media supplements promoted single cell‐based process inoculation and hydrodynamic aggregate size control. Wet lab‐derived process characteristics enabled predictive in silico modeling as a new rational for hPSC cultivation. Consequently, hPSC line‐independent maintenance of exponential cell proliferation was achieved. The strategy yielded 70‐fold cell expansion in 7 days achieving an unmatched density of 35 × 10⁶ cells/mL equivalent to 5.25 billion hPSC in 150 mL scale while pluripotency, differentiation potential, and karyotype stability was maintained. In parallel, media requirements were reduced by 75% demonstrating the outstanding increase in efficiency. Minimal input to our in silico model accurately predicts all main process parameters; combined with calculation‐controlled hPSC aggregation kinetics, linear process upscaling is also enabled and demonstrated for up to 500 mL scale in an independent bioreactor system. Thus, by merging applied stem cell research with recent knowhow from industrial cell fermentation, a new level of hPSC bioprocessing is revealed fueling their automated production for industrial and therapeutic applications.

Measuring particle concentration of multimodal synthetic reference materials and extracellular vesicles with orthogonal techniques: Who is up to the challenge?

The measurement of physicochemical properties of polydisperse complex biological samples, for example, extracellular vesicles, is critical to assess their quality, for example, resulting from their production and isolation methods. The community is gradually becoming aware of the need to combine multiple orthogonal techniques to perform a robust characterization of complex biological samples. Three pillars of critical quality attribute characterization of EVs are sizing, concentration measurement and phenotyping. The repeatable measurement of vesicle concentration is one of the key‐challenges that requires further efforts, in order to obtain comparable results by using different techniques and assure reproducibility. In this study, the performance of measuring the concentration of particles in the size range of 50–300 nm with complementary techniques is thoroughly investigated in a step‐by step approach of incremental complexity. The six applied techniques include multi‐angle dynamic light scattering (MADLS), asymmetric flow field flow fractionation coupled with multi‐angle light scattering (AF4‐MALS), centrifugal liquid sedimentation (CLS), nanoparticle tracking analysis (NTA), tunable resistive pulse sensing (TRPS), and high‐sensitivity nano flow cytometry (nFCM). To achieve comparability, monomodal samples and complex polystyrene mixtures were used as particles of metrological interest, in order to check the suitability of each technique in the size and concentration range of interest, and to develop reliable post‐processing data protocols for the analysis. Subsequent complexity was introduced by testing liposomes as validation of the developed approaches with a known sample of physicochemical properties closer to EVs. Finally, the vesicles in EV containing plasma samples were analysed with all the tested techniques. The results presented here aim to shed some light into the requirements for the complex characterization of biological samples, as this is a critical need for quality assurance by the EV and regulatory community. Such efforts go with the view to contribute to both, set‐up reproducible and reliable characterization protocols, and comply with the Minimal Information for Studies of Extracellular Vesicles (MISEV) requirements.

Influence of Microenvironment on Mesenchymal Stem Cell Therapeutic Potency: From Planar Culture to Microcarriers

Human mesenchymal stem cells (hMSCs) are a promising candidate in cell therapy as they exhibit multilineage differentiation, homing to the site of injury, and secretion of trophic factors that facilitate tissue healing and/or modulate immune response. As a result, hMSC-derived products have attracted growing interests in preclinical and clinical studies. The development of hMSC culture platforms for large-scale biomanufacturing is necessary to meet the requirements for late-phase clinical trials and future commercialization. Microcarriers in stirred-tank bioreactors have been widely utilized in large-scale expansion of hMSCs for translational applications because of a high surface-to-volume ratio compared to conventional 2D planar culture. However, recent studies have demonstrated that microcarrier-expanded hMSCs differ from dish- or flask-expanded cells in size, morphology, proliferation, viability, surface markers, gene expression, differentiation potential, and secretome profile which may lead to altered therapeutic potency. Therefore, understanding the bioprocessing parameters that influence hMSC therapeutic efficacy is essential for the optimization of microcarrier-based bioreactor system to maximize hMSC quantity without sacrificing quality. In this review, biomanufacturing parameters encountered in planar culture and microcarrier-based bioreactor culture of hMSCs are compared and discussed with specific focus on cell-adhesion surface (e.g., discontinuous surface, underlying curvature, microcarrier stiffness, porosity, surface roughness, coating, and charge) and the dynamic microenvironment in bioreactor culture (e.g., oxygen and nutrients, shear stress, particle collision, and aggregation). The influence of dynamic culture in bioreactors on hMSC properties is also reviewed in order to establish connection between bioprocessing and stem cell function. This review addresses fundamental principles and concepts for future design of biomanufacturing systems for hMSC-based therapy.

Osmolality as a lever to modulate the N-glycolylneuraminicacid (Neu5Gc) level of a recombinant glycoprotein produced in Chinese hamster ovary cells

Glycoproteins could be highly sialylated, and controlling the sialic acid levels for some therapeutic proteins is critical to ensure product consistency and efficacy. N-acetylneuraminic acid (Neu5Ac, or NANA) and N-glycolylneuraminic acid (Neu5Gc, or NGNA) are the two most common forms of sialic acids produced in mammalian cells. As Neu5Gc is not produced in humans and can elicit immune responses, minimizing Neu5Gc formation is important in controlling this quality attribute for complex glycoproteins. In this study, a sialylated glycoprotein was used as the model molecule to study the effect of culture osmolality on Neu5Gc. A 14-day fed-batch process with osmolality maintained at physiological levels produced high levels of Neu5Gc. Increase of culture osmolality reduced the Neu5Gc level up to 70-80%, and the effect was proportional to the osmolality level. Through evaluating different osmolality conditions (300-450 mOsm/kg) under low or high pCO₂ , we demonstrated that osmolality could be an effective process lever to modulate the Neu5Gc level. Potential mechanism of osmolality impact on Neu5Gc is discussed and is hypothesized to be cytosol NADH availability related. Compared with cell line engineering efforts, this simple process lever provides the opportunity to readily modulate the Neu5Gc level in a cell culture environment.

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

Herein, we described a scale-up strategy focused on the dissolved carbon dioxide concentration (dCO₂ ) during fed-batch cultivation of Chinese hamster ovary cells. A fed-batch culture process for a 2000-L scale stainless steel (SS) bioreactor was scaled-up from similarly shaped 200-L scale bioreactors based on power input per unit volume (P/V). However, during the 2000-L fed-batch culture, the dCO₂ was higher compared with the 200-L scale bioreactor. Therefore, we developed an alternative approach by evaluating the k_L a values of O₂ (k_L a[O₂ ]) and CO₂ [k_L a(CO₂ )] in the SS bioreactors as a scale-up factor for dCO₂ reduction. The k_L a ratios [k_L a(CO₂ )/k_L a(O₂ )] were different between the 200-L and 2000-L bioreactors under the same P/V condition. When the agitation conditions were changed, the k_L a ratio of the 2000-L scale bioreactor became similar and the P/V value become smaller compared with those of the 200-L SS bioreactor. The dCO₂ trends in fed-batch cultures performed in 2000-L scale bioreactors under the modified agitation conditions were similar to the control. This k_L a ratio method was used for process development in single-use bioreactors (SUBs) with shapes different from those of the SS bioreactor. The k_L a ratios for the SUBs were evaluated and conditions that provided k_L a ratios similar to the 200-L scale SS bioreactors were determined. The cell culture performance and product quality at the end of the cultivation process were comparable for all tested SUBs. Therefore, we concluded that the k_L a ratio is a powerful scale-up factor useful to control dCO₂ during fed-batch cultures.

Scale-down simulators for mammalian cell culture as tools to access the impact of inhomogeneities occurring in large-scale bioreactors

During the scale-up of a bioprocess, not all characteristics of the process can be kept constant throughout the different scales. This typically results in increased mixing times with increasing reactor volumes. The poor mixing leads in turn to the formation of concentration gradients throughout the reactor and exposes cells to varying external conditions based on their location in the bioreactor. This can affect process performance and complicate process scale-up. Scale-down simulators, which aim at replicating the large-scale environment, expose the cells to changing environmental conditions. This has the potential to reveal adaptation mechanisms, which cells are using to adjust to rapidly fluctuating environmental conditions and can identify possible root causes for difficulties maintaining similar process performance at different scales. This understanding is of utmost importance in process validation. Additionally, these simulators also have the potential to be used for selecting cells, which are most robust when encountering changing extracellular conditions. The aim of this review is to summarize recent work in this interesting and promising area with the focus on mammalian bioprocesses, since microbial processes have been extensively reviewed.

Feeding tricarboxylic acid cycle intermediates improves lactate consumption and antibody production in Chinese hamster ovary cell cultures

Media components play an important role in modulating cell metabolism and improving product titer in mammalian cell cultures. To sustain cell productivity, highly active oxidative metabolism is desired. Here we explored the effect of tricarboxylic acid (TCA) cycle intermediates supplementation on lactate metabolism and productivity in Chinese hamster ovary fed-batch cultures. Direct addition of 5 mM alpha-ketoglutarate (α-KG), malic acid, or succinic acid in the basal medium did not have any significant impact on culture performance. On the other hand, feeding α-KG, malic acid, and succinic acid in the stationary phase, either as a single solution or as a mixture, significantly improved lactate consumption, reduced ammonium accumulation, and led to higher cell specific productivity and antibody titer (~35% increase for the best condition). Delivering those intermediates as an acidic solution for pH control eliminated CO₂ sparging and accumulation. Feeding TCA cycle intermediates was also demonstrated to be superior to feeding lactic acid or pyruvic acid in titer improvement. Taken together, feeding TCA cycle intermediates was effective in improving lactate consumption and increasing product titer, which is likely due to enhanced oxidative metabolism in an extended duration.

Enabling speed to clinic for monoclonal antibody programs using a pool of clones for IND-enabling toxicity studies

The importance of speed to clinic for medicines that may address unmet medical needs puts pressure on product development timelines. Historically, both toxicology and first-in-human clinical materials are generated using the same clonal-derived cells to ensure safety and minimize any development risks. However, cell line development with single cell cloning is time consuming, and aggravated by the time needed to screen for a lead clone based on cell line stability and manufacturability. In order to achieve faster timelines, we have used pools of up to six clones for earlier production of drug substance for regulatory filing-enabling toxicology studies, and then the final single clone was selected for production of clinical materials. This approach was enabled by using platform processes across all stages of early development, including expression vectors, host cell lines, media, and production processes. Through comprehensive cell culture and product quality analysis, we demonstrated that the toxicology material was representative of the clinical material for all six monoclonal antibody programs evaluated. Our extensive development experience further confirmed that using a pool of clones for toxicology material generation is a reliable approach to shorten the early development timeline.

Microbioreactors for Process Development and Cell-Based Screening Studies

Microbioreactors (MBRs) have emerged as potent cultivation devices enabling automated small-scale experiments in parallel while enhancing their cost efficiency. The widespread use of MBRs has contributed to recent advances in industrial and pharmaceutical biotechnology, and they have proved to be indispensable tools in the development of many modern bioprocesses. Being predominantly applied in early stage process development, they open up new fields of research and enhance the efficacy of biotechnological product development. Their reduced reaction volume is associated with numerous inherent advantages - particularly the possibility for enabling parallel screening operations that facilitate high-throughput cultivations with reduced sample consumption (or the use of rare and expensive educts). As a result, multiple variables can be examined in a shorter time and with a lower expense. This leads to a simultaneous acceleration of research and process development along with decreased costs.MBRs range from simple miniaturized cultivations vessels (i.e., in the milliliter scale with limited possibilities for process control) to highly complex and automated small-scale microreactors with integrated sensors that allow for comprehensive screenings in very short time or a precise reflection of large-scale cultivation conditions. Progressive developments and improvements in manufacturing and automation techniques are already helping researchers to make use of the advantages that MBRs offer. This overview of current MBR systems surveys the diverse application for microbial and mammalian cell cultivations that have been developed in recent years.

Recent Developments in Bioprocessing of Recombinant Proteins: Expression Hosts and Process Development

Infectious diseases, along with cancers, are among the main causes of death among humans worldwide. The production of therapeutic proteins for treating diseases at large scale for millions of individuals is one of the essential needs of mankind. Recent progress in the area of recombinant DNA technologies has paved the way to producing recombinant proteins that can be used as therapeutics, vaccines, and diagnostic reagents. Recombinant proteins for these applications are mainly produced using prokaryotic and eukaryotic expression host systems such as mammalian cells, bacteria, yeast, insect cells, and transgenic plants at laboratory scale as well as in large-scale settings. The development of efficient bioprocessing strategies is crucial for industrial production of recombinant proteins of therapeutic and prophylactic importance. Recently, advances have been made in the various areas of bioprocessing and are being utilized to develop effective processes for producing recombinant proteins. These include the use of high-throughput devices for effective bioprocess optimization and of disposable systems, continuous upstream processing, continuous chromatography, integrated continuous bioprocessing, Quality by Design, and process analytical technologies to achieve quality product with higher yield. This review summarizes recent developments in the bioprocessing of recombinant proteins, including in various expression systems, bioprocess development, and the upstream and downstream processing of recombinant proteins.

An Industrial Perspective on Scale-Down Challenges Using Miniaturized Bioreactors

Miniaturized stirred bioreactors (MSBRs) are gaining popularity as a cost-effective approach to scale-down experimentation. However, realizing conditions that reflect the large-scale process accurately can be challenging. This article highlights common challenges of using MSBRs for scale-down. The fundamental difference between oxygen mass transfer coefficient (k_La) and oxygen transfer rate scaling is addressed and the difficulty of achieving turbulent flow and industrially relevant tip speeds is described. More practical challenges of using MSBR systems for scale-down are also discussed, including the risk of vortex formation, changed volume dynamics, and wall growth. By highlighting these challenges, the article aims to create more awareness of these difficulties and to contribute to improved design of scale-down experiments.

Effective bioreactor pH control using only sparging gases

pH control is critical in bioreactor operations, typically realized through a two-sided control loop, where CO₂ sparging and base addition are used in bicarbonate-buffered media. Though a common approach, base addition could compromise culture performance due to the potential impact from pH excursions and osmolality increase in large-scale bioreactors. In this study, the feasibility of utilizing control of sparge gas composition as part of the pH control loop was assessed in Chinese hamster ovary (CHO) fed-batch cultures. Fine pH control was evaluated in multiple processes at different setpoints in small-scale ambr®250 bioreactors. Desired culture pH setpoints were successfully maintained via air sparge feedback control. As part of the pH control loop, air sparging was increased to improve CO₂ removal automatically, hence increase culture pH, and vice versa. The effectiveness of this pH control strategy was seamlessly transferred from ambr®250 to 200 L scale, demonstrating scalability of the proposed methodology. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2743, 2019.

Scale-Down Model Development in ambr systems: An Industrial Perspective

High-Throughput (HT) technologies such as miniature bioreactors (MBRs) are increasingly employed within the biopharmaceutical manufacturing industry. Traditionally, these technologies have been utilized for discrete screening approaches during pre-clinical development (e.g., cell line selection and process optimization). However, increasing interest is focused towards their use during late clinical phase process characterization studies as a scale-down model (SDM) of the cGMP manufacturing process. In this review, the authors describe a systematic approach toward SDM development in one of the most widely adopted MBRs, the ambr 15 and 250 mL (Sartorius Stedim Biotech) systems. Recent efforts have shown promise in qualifying ambr systems as SDMs to support more efficient, robust and safe biomanufacturing processes. The authors suggest that combinatorial improvements in process understanding (matching of mass transfer and cellular stress between scales through computational fluid dynamics and in vitro analysis), experimental design (advanced risk assessment and statistical design of experiments), and data analysis (combining uni- and multi-variate techniques) will ultimately yield ambr SDMs applicable for future regulatory submissions.

Characterizing the fluid dynamics of the inverted frustoconical shaking bioreactor

The authors conducted a three-dimensional computational fluid dynamics (CFD) simulation to calculate the flow field in the inverted frustoconical shaking bioreactor with 5 L working volume (IFSB-5L). The CFD models were established for the IFSB-5L at different operating conditions (different shaking speeds and filling volumes) and validated by comparison of the liquid height distribution in the agitated IFSB-5L. The "out of phase" operating conditions were characterized by analyzing the flow field in the IFSB-5L at different filling volumes and shaking speeds. The values of volumetric power consumption (P/V_L ) and volumetric mass transfer coefficient (k_L a) were determined from simulated and experimental results, respectively. Finally, the operating condition effect on P/V_L and k_L a was investigated. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:478-485, 2018.

Bench-Scale Stirred-Tank Bioreactor for Recombinant Protein Production in Chinese Hamster Ovary (CHO) Cells in Suspension

Most pharmaceutical biotechnology companies use stirred-tank bioreactors (STR) for recombinant protein manufacturing. These bioreactors are used at a variety of different scales ranging from bench to production scales, with working volumes from 10 mL to 25,000 L. Bench-scale STRs are commonly used to culture mammalian cells for process development, to troubleshoot production scale bioreactors using scale-down models (SDM), or to conduct fundamental research. In this chapter, we describe the operations of a bench-scale STR for the production of recombinant proteins with suspension-adapted Chinese hamster ovary (CHO-DG44) cells. These operations include bioreactor setup and configuration, batching media, inoculation of the seed cell culture, production phase, and harvest of cell-free fluids.

Impact of Pluronic® F68 on hollow fiber filter-based perfusion culture performance

High cell density is an important factor in achieving high bioreactor productivity. To meet the oxygen demand with density at >100 × 10⁶ cells/mL, a frit sparger is often used. In this study, the impact of Pluronic^® F68 on a perfusion process using a frit sparger was studied. The perfusion process was developed using an alternating tangential flow device with a 0.2 µm PES hollow fiber filter. Pluronic^® F68 at 2 g/L was sufficient in preventing cell damage at gas flow rate of ~0.20 vvm from a drilled hole sparger (0.5 mm) but inadequate at ~0.025 vvm from a frit sparger (20 µm). Increase of Pluronic^® F68 concentration to 5 g/L prevented cell death at up to ~0.10 vvm from the frit sparger and was able to maintain high cell density at high viability in the range of 60-80 × 10⁶ cells/mL. Such positive effect was demonstrated in both 3- and 200-L bioreactors. Supplementing additional Pluronic^® F68 was also effective in restoring cell growth/viability from low viability cultures. Increased Pluronic^® F68 concentration had no adverse impact on target antibody, HCP, and Pluronic^® F68 transmissions.