Characterizing the fluid dynamics of the inverted frustoconical shaking bioreactor

Quantification and modeling of macroparticle-induced mechanical stress for varying shake flask cultivation conditions

In biotechnological processes, filamentous microorganisms are known for their broad product spectrum and complex cellular morphology. Product formation and cellular morphology are often closely linked, requiring a well-defined level of mechanical stress to achieve high product concentrations. Macroparticles were added to shake flask cultures of the filamentous actinomycete Lentzea aerocolonigenes to find these optimal cultivation conditions. However, there is currently no model concept for the dependence of the strength and frequency of the bead-induced stress on the process parameters. Therefore, shake flask simulations were performed for combinations of bead size, bead concentration, bead density and shaking frequency. Contact analysis showed that the highest shear stresses were caused by bead-bottom contacts. Based on this, a newly generated characteristic parameter, the stress area ratio (SAR), was defined, which relates the bead wall shear and normal stresses to the total shear area. Comparison of the SAR with previous cultivation results revealed an optimum pattern for product concentration and mean product-to-biomass related yield coefficient. Thus, this model is a suitable tool for future optimization, comparison and scaling up of shear-sensitive microorganism cultivation. Finally, the simulation results were validated using high-speed recordings of the bead motion on the bottom of the shake flask.

Challenges of influencing cellular morphology by morphology engineering techniques and mechanical induced stress on filamentous pellet systems-A critical review

Filamentous microorganisms are main producers of organic acids, enzymes, and pharmaceutical agents such as antibiotics and other active pharmaceutical ingredients. With their complex cell morphology, ranging from dispersed mycelia to dense pellets, the cultivation is challenging. In recent years, various techniques for tailor-made cell morphologies of filamentous microorganisms have been developed to increase product formation and have been summarised under the term morphology engineering. These techniques, namely microparticle-enhanced cultivation, macroparticle-enhanced cultivation, and alteration of the osmolality of the culture medium by addition of inorganic salts, the salt-enhanced cultivation, are presented and discussed in this review. These techniques have already proven to be useful and now await further proof-of-concept. Furthermore, the mechanical behaviour of individual pellets is of special interest for a general understanding of pellet mechanics and the productivity of biotechnological processes with filamentous microorganisms. Correlating them with substrate uptake and finally with productivity would be a breakthrough not to be underestimated for the comprehensive characterisation of filamentous systems. So far, this research field is under-represented. First results on filamentous pellet mechanics are discussed and important future aspects, which the filamentous expert community should deal with, will be presented and critically discussed.

Recommended turbulent energy dissipation rate for biomass and lipid production of Scenedesmus obliquus in an aerated photosynthetic culture system

Effects of turbulent energy dissipation rate (increased from 1.28 × 10^-6 to 1.67 × 10^-5 m² s^-3) on Scenedesmus obliquus biomass and lipid accumulation at different aeration rates (0.3, 0.6, 0.9, 1.2, and 1.5 L min^-1) were investigated. The turbulent energy dissipation rate was calculated by CFD model simulation. When the turbulent energy dissipation rate increased to 7.30 × 10^-6 m² s^-3, the biomass and lipid productivity increased gradually, and finally reached their maximum values of 1.11 × 10⁷ cells mL^-1 and 16.0 mg L^-1 day^-1, respectively. When it exceeded 7.30 × 10^-6 m² s^-3, the biomass and lipid productivity showed a decreasing trend. Therefore, the most favorable turbulent energy dissipation rate for S. obliquus growth and lipid accumulation was 7.30 × 10^-6 m² s^-3.

The cell yields and biological characteristics of stromal/stem cells from lipoaspirate with different digestion loading ratio

Effective harvesting procedure for adipose tissue is demanded by the affordable Good Manufacturing Practice-Compliant Production of clinical-grade adipose tissue-derived stem cells (hADSCs). Enzymatic digestion using collagenase is the most reliable method of adipose tissue-derived stem cells (hADSCs) isolation, while the optimized loading volume ratios of digestion to container during the shaking process of adipose tissue and collagenase mixture are still lacking. This study was conducted to determine the optimized loading volume ratio (mixture to container) for enzymatic digestion of Stromal/Stem Cells from lipoaspirate. Lipoaspirates were obtained from twelve women immediately after liposuction. Then tissue from each patient was divided into four groups according to different loading volume ratios in 50 ml centrifugal tube: 0.2 group, 0.4 group, 0.6 group, 0.8 group. Stromal vascular fractions (SVF) were obtained from each group, then total cell counts, viability and viable cell count were performed. hADSCs were harvested at passage (P) 2, whose morphologies, immunophenotypes, proliferation, and tri-differentiation abilities were compared. 0.4 loading volume ratio provided the highest cell yield, favorable viability and viable cell yield. The proliferation and triple differentiation ability of hADSCs obtained by 0.4 group was not inferior to that of other groups. Therefore, 0.4 may be the optimal loading volume ratio for hADSCs isolation from lipoaspirate by enzymatic digestion in current setting.

Numerical simulation of scaling-up an inverted frusto-conical shaking bioreactor with low shear stress for mammalian cell suspension culture

Shear stress is one of the key factors affecting the large-scale culture of mammalian cells. In this study, numerical simulation based on computational fluid dynamics was used to conduct a flow-field analysis of 7, 50, 200, and 1200 L inverted frusto-conical shaking bioreactors. The results show that the shear rate, specific mass transfer area (a), and volumetric oxygen mass transfer coefficient (kLa) gradually decreased as the scale of the bioreactor increased. Through application of BHK21 and CHO cells in 7, 200, and 1200 L bioreactors, it was found that the cell density and antibody expression level increased as the volume of the bioreactor increased. Moreover, the antibody expression level in a 1200 L bioreactor was nearly 30% and 35% higher than that of 7 and 200 L bioreactors, respectively. The results demonstrate that the environment with a larger volume is more suitable for the growth and antibody expression of CHO cells, indicating shear stress might be the most critical factor affecting the scale-up of mammalian cells.

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.