(404f) Application of Eccentricaly Agitated Stirred Tanks in Biotechnology Settings: Examples, Advantages and Challenges

In this contribution we provide examples of the use of eccentrically agitated stirred tanks in biotechnology applications and discuss their potential advantages. Both at the lab scale and in industrial practice, stirred tank bioreactors are the most common cell culture platform. However, stirred tank bioreactors are designed based on conventional stirred tanks geometries (namely tanks agitated with Rushton turbines or axial impellers concentrically located) that are not necessarily ideal for some cell culture applications.

We use stirred tanks equipped with off-centered inclined (45°) disc impellers in four different cell culture scenarios: (a) culture of a recombinant strain of the aerobic bacteria Escherichia coli (producer of a vaccine candidate); (b) culture of tobacco plant cells (Nicotiana tabacum); (c) culture of Chineese Hamster Ovarium (CHO) cells producers of a follow-on monoclonal antibody (mAb); and (d) small scale culture of human hematopoietic stem cells.

The potential use of small scale eccentric stirred tank systems (30 mL) for screening applications is discussed. In the case of recombinant E. coli cultures, the specific growth rate calculated from experiments in 30 mL eccentric bioreactors is similar than the one observed in 1L instrumented bioreactors with concentric agitation. However, the maximum cell density is significantly lower in the eccentric system. In the case of CHO cell cultures, both the specific growth rate and the maximum cell density measured in the small scale eccentric bioreactor are similar or higher than those determined in culture bottles (30 mL), Erlenmeyer flasks (100 mL), or fully instrumented bioreactors (1L). These results suggest that the proposed eccentric bioreactor system can be used for biopharmaceutical screening applications without sacrifice of accuracy on the determination of specific growth rates, even in the case of aerobic bacteria.

 Comparatively, eccentric stirred tank systems provide good mixing at low RPM values (and low shear rates). Consequently, these systems could be advantageous for the culture of presumably shear sensitive organisms such as plant or mammalian cells. Human hematopoietic stem cells were successfully expanded 10 fold in suspension conditions using an eccentric mini-bioreactor system (30 mL). CHO cells, producers a follow-on monoclonal antibody, were successfully cultured in fully instrumented eccentric bioreactors (1 L). The mAb productivity, growth rate, and maximum cell concentration observed in eccentric cultures was equivalent to that observed in conventional bioreactors. Nicotiana tabacum cells were also cultured in instrumented eccentric bioreactors. In this case, cultures were sustained in good conditions (viability above 80%) for longer times than in conventional concentric stirred tanks.

 In all these case models, the cell culture performance is similar (if not better) than that observed in conventional culture systems. Our results suggest adequate mixing performance, practicality and scalability of the studied eccentric stirred tank geometry.