Computational investigation of fluid dynamics in a recently developed centrifugal impeller bioreactor

Analysis of hollow wall effect on the fluid dynamics in the orbitally shaken bioreactors

Orbitally shaking bioreactors (OSRs) have recently been increasingly applied in the biopharmaceutical industry because they can provide a suitable environment for mammalian cell growth and protein expression. Fluid dynamics information is crucial for analyzing or optimizing of different types of bioreactors. Considering that the structure has an important influence on the fluid dynamics in a bioreactor, it necessary to design or optimize its structure by the computational fluid dynamics (CFD) approach. The aim of this study is to optimize the wall structure of a hollow cylinder OSR proposed in our previous work. Based on previous research, the influences of the hollow wall of the OSR on fluid dynamics and the volumetric mass transfer coefficient ([Formula: see text]) were analysed by the established CFD model. The results showed that the mixing performance of OSR could be improved by decreasing the installation height of the hollow wall. An installation height of 30 mm was found to be most favourable for mixing. The reliability of the CFD model was verified by comparing the liquid wave height and liquid wave shape between the simulation and experiment. The shear stress in the hollow cylinder OSR was proven gentle for mammalian cell cultivation.

A novel scale-up strategy for cultivation of BHK-21 cells based on similar hydrodynamic environments in the bioreactors

The scale-up of animal cell cultivation is important but remains complex and challenging. In the present study, we propose a novel scale-up strategy for baby hamster Syrian kidney-21 (BHK-21) cell cultivation based on similar hydrodynamic environments. The hydrodynamic characteristics of the different scale bioreactors were determined by computational fluid dynamics (CFD) and further correlated with the agitation speed. The optimal hydrodynamic environment for cell cultivation and vaccine production was determined from the cultivation experiments of BHK-21 cells in 5-L laboratory-scale bioreactors equipped with different impellers at various agitation speeds. BHK-21 cell cultivation was scaled up from 5-L to 42-, 350-, and 1000-L bioreactors by adjusting the agitation speed to make the hydrodynamic features similar to those in the 5-L bioreactor, especially for the shear rate in the impeller zone (γimp) and energy dissipation rate in the tank bulk zone (εtan). The maximum cell density and cell aggregation rate in these scaled-up bioreactors were in the range of 4.6 × 106 ~ 4.8 × 106 cells/mL and 16 ~ 20%, which are comparable to or even better than those observed in the 5-L bioreactor (maximum cell density 4.8 × 106 cells/mL, cell aggregation rate 21%). The maximum virus titer of 108.0 LD50/mL achieved in the 1000-L bioreactor was close to 108.3 LD50/mL that obtained in the 5-L bioreactor. Hence, the scale-up strategy proposed in this study is feasible and can efficiently facilitate the scale-up processes of animal cell cultivation.

Microcarrier-based stem cell bioprocessing: GMP-grade culture challenges and future trends for regenerative medicine

Recently, stem cell-based therapies have been proposed as an alternative for the treatment of many diseases. Stem cells (SCs) are well known for their capacity to preserve themselves, proliferate, and differentiate into multiple lineages. These characteristics allow stem cells to be a viable option for the treatment of diverse diseases. Traditional methodologies based on 2-dimensional culture techniques (T-flasks and Petri dishes) are simple and well standardized; however, they present disadvantages that limit the production of the cell yield required for regenerative medicine applications. Lately, microcarrier (MC)-based culture techniques have emerged as an attractive platform for expanding stem cells in suspension systems. Although the use of stem cell expansion on MCs has recently shown significant increase, their implementation for medical purposes is been hampered by bottlenecks in upstream and downstream processing. Therefore, there is an urgent need in the development of bioprocesses that simplify stem cell cultures under xeno-free conditions and detachment from MCs without diminishing their pluripotency and viability. A critical analysis of the factors that impact the up and downstream bioprocessing on MC-based stem cell cultures is presented in this review. This analysis aims to raise the awareness of the current drawbacks that limit MC-based stem cell bioprocessing in regenerative medicine and propose alternatives to overcome them.

Numerical Simulation of Bubble-Liquid Two-Phase Turbulent Flows in Shallow Bioreactor

An improved second-order moment bubble-liquid two-phase turbulent model is developed to predict the hydrodynamic characteristics of the shallow bioreactor using two height-to-diameter ratios of H/D = 1.4 and H/D = 2.9. The two-phase hydrodynamic parameters, the bubble normal and shear stress, the bubble energy dissipation rate, the bubble turbulent kinetic energy, etc. were numerically simulated. These parameters increased along with flow direction and constituted a threat to cells living at far distance away from the gas jetting inlet regions, rather than a finding of higher cell damage at near the jetting inlet region, as reported by Babosa et al. 2003. A new correlation named the turbulent energy production of bubble-liquid two-phase flow was proposed to successfully verify this experimental observation. A smaller H/D ratio makes more contributions to the generation of lower turbulent energy productions, which are in favor of the alleviation of cell damage. The extremely long and narrow shape of the bioreactor is deteriorative for cell living.

Analyzing the suitability of a baffled orbitally shaken bioreactor for cells cultivation using the computational fluid dynamics approach

Orbitally shaken bioreactors (OSRs) is one of important bioreactors for mammalian cells cultivation in suspension, especially for the screening of valuable microorganisms and in basic bioprocess development experiments. However, the suitability of OSRs for cells culture in large scale is still under development. In this article, a new kind of OSRs with baffle structure was proposed and a three-dimensional CFD model was established to analyze the influence of baffle structure on the flow field. Lower installation height of baffles was found suitable for improving the mixing efficiency. Compared to the unbaffled OSR, the baffled OSR could enhance the level of oxygen transfer largely but the oxygen transfer rate was independent on the baffle installation height. Moreover, as the baffle installation height increased, the energy transferred for liquid motion was decreased. Finally, the shear stress of the baffled OSRs proposed was gentle for mammalian cells growth. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2746, 2019.

Characterizing the fluid dynamics in the flow fields of cylindrical orbitally shaken bioreactors with different geometry sizes

Orbitally shaken bioreactors (OSRs) are commonly used for the cultivation of mammalian cells in suspension. To aid the geometry designing and optimizing of OSRs, we conducted a three-dimensional computational fluid dynamics (CFD) simulation to characterize the flow fields in a 10 L cylindrical OSR with different vessel diameters. The liquid wave shape captured by a camera experimentally validated the CFD models established for the cylindrical OSR. The geometry size effect on volumetric mass transfer coefficient (k_La) and hydromechanical stress was analyzed by varying the ratio of vessel diameter (d) to liquid height at static (h _L), d/h _L. The highest value of k_La about 30 h^-1 was observed in the cylindrical vessel with the d/h _L of 6.35. Moreover, the magnitudes of shear stress and energy dissipation rate in all the vessels tested were below their minimum values causing cells damage separately, which indicated that the hydromechanical-stress environment in OSRs is suitable for cells cultivation in suspension. Finally, the CFD results suggested that the d/h _L higher than 8.80 should not be adopted for the 10 L cylindrical OSR at the shaking speed of 180 rpm because the "out of phase" state probably will happen there.

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.

Hydrodynamics and Mass Transfer Simulation in Airlift Bioreactor with Settler using Computational Fluid Dynamics

In this work, the effect of inlet-gas superficial velocity over the circulation liquid velocity, gas holdup and mass transfer, from an airlift bioreactor with settler were studied by Computational Fluid Dynamics (CFD) modeling and contrasted with experimental results. Multiphase mixture model and κ-ε turbulence model were used to describe the two phases gas-liquid flow pattern in airlift bioreactor. The hydrodynamic parameters such as liquid circulation velocity and gas holdup were computed by solving the governing equations of continuity, moment and turbulence transport using the finite volume method. Global mass transfer coefficient was evaluated through the Higbie’s penetration theory and the two-phase fluid dynamic theory. Comparison between our numerical data and experimental data previously reported in the literature was done. Numerical and experimental data were very close, and the differences found were discussed in terms of the limitations of this study.

Comparing the performances of circular ponds with different impellers by CFD simulation and microalgae culture experiments

In this study, a numerical simulation using computational fluid dynamics (CFD) was used to investigate the hydrodynamic characteristics of circular ponds with three different impellers (hydrofoil, four-pitched-blade turbine, and grid plate). The reliability of the CFD model was validated by particle image velocimetry (PIV). Hydrodynamic analyses were conducted to evaluate the average velocity magnitude along the light direction (Uz), turbulence properties, average shear stress, pressure loss and the volume percentage of dead zone inside circular ponds. The simulation results showed that Uz value of hydrofoil was 58.9, 40.3, and 28.8% higher than those of grid plate with single arm, grid plate with double arms and four-pitched blade turbines in small-scale circular ponds, respectively. In addition, hydrofoil impeller with down-flow operation had outstanding mixing characteristics. Lastly, the results of Chlorella pyrenoidosa cultivation experiments indicated that the biomass concentration of hydrofoil impeller with down-flow operation was 65.2 and 88.8% higher than those of grid plate with double arms and four-pitched-blade turbine, respectively. Therefore, the optimal circular pond mixing system for microalgae cultivation involved a hydrofoil impeller with down-flow operation.

Advances and Practices of Bioprocess Scale-up

: This chapter addresses the update progress in bioprocess engineering. In addition to an overview of the theory of multi-scale analysis for fermentation process, examples of scale-up practice combining microbial physiological parameters with bioreactor fluid dynamics are also described. Furthermore, the methodology for process optimization and bioreactor scale-up by integrating fluid dynamics with biokinetics is highlighted. In addition to a short review of the heterogeneous environment in large-scale bioreactor and its effect, a scale-down strategy for investigating this issue is addressed. Mathematical models and simulation methodology for integrating flow field in the reactor and microbial kinetics response are described. Finally, a comprehensive discussion on the advantages and challenges of the model-driven scale-up method is given at the end of this chapter.