For decades, stirred-tank reactors (STRs) have been the gold standard in cell cultivation, particularly in large-scale processes. However, rocking-motion (RM) technology offers an efficient alternative that can be a better choice for certain applications. In a November 2022 webinar, Tobias Schenk (product manager at Sartorius) discussed the two technologies, highlighting the strengths of each and how they can be used in tandem for optimal results.

The Presentation
RM bioreactor technology mixes nutrients into cell culture media using a wave motion that results in passive gassing. For instance, culture media can be infused into Flexsafe single-use (SU) bioprocess bags, which are designed to maintain cells in optimal culture conditions. Sartorius offers three options for Flexsafe RM bags: a basic bag for cultivation under constant conditions, an optical bag for processes in which pH and dissolved oxygen (DO) levels need monitoring, and a perfusion bag that is suitable for sensitive cell lines. All three formats are compatible with the Biostat RM line of bioreactor systems, which leverage temperature-controlled rocker platforms. The Biostat RM system’s control tower enables customization and automation of process parameters using Biobrain software for adapting to customer needs.

RM systems can be used in preclinical and clinical studies for fast protein production. In commercial manufacturing, the technology is ideal for large-scale seed expansion and for small-scale production of monoclonal antibodies (MAbs) and other recombinant proteins.

Unlike RM technology, conventional STR designs integrate active stirring, using impeller blades to support cell culture media nutrition and growth with active gassing. Biostat STR models can be equipped with Flexsafe bags that bear additional sensors such as BioPAT Viamass probes, allowing users to control feed and bleed in their cell cultures.

Flexsafe RM, STR, and 3D bag designs all consist of the same film, which supports cell growth, improves lot-to-lot consistency, and helps to ensure robustness, purity, and stability.

Schenk cited external studies that compared cultivation results for HEK 293 cell lines between RM and STR systems. Both technologies showed similar levels of viable cell density and maximum product titer. However, the technologies require different setups. RM technology can leverage SU bags (such as Flexsafe systems) that are presterilized for immediate use. By contrast, Univessel multiuse STR equipment requires downtime for cleaning and sterilization, giving RM an advantage in efficiency.

For some applications, RM and STR systems work in tandem, as seen in experiments that Schenk presented relating to high-density N – 1 perfusion culture using automated inoculation. RM bioreactors of different capacities all reached 100 million Chinese hamster ovary (CHO) cells/mL in under seven days, maintaining viability above 90%. After reaching the 100-million set point, the STR system was inoculated with cells from the RM, starting the perfusion process in a Biostat STR 200-L bioreactor.

Similarly, RM and STR technologies work well together in cultivating fed-batch seed trains. Users can begin by inoculating RM bioreactors with small amounts of cells, then scale up to a stirred tank at ≤2,000 L.

Schenk pointed out that stirred-motion technology often has cooling functionality that is unavailable in RM bioreactors, making the former systems ideal for large-scale production up to 2,000 L. RM technology is cheaper to maintain, easier to set up, and advantageous for working with shear-sensitive cell lines such as stem cells and chimeric antigen receptor (CAR) T cells. Although STRs traditionally have been used in mesenchymal stem cell (MSC) cultures, a 2016 publication showed that RM technology can provide similar results depending on the microcarriers.

Questions and Answers
Can cells be harmed by transfer from a Biostat RM reactor to a Biostat STR system? Transferring cell culture from an RM model to a Biostat STR model is no different than transferring from one stirred bioreactor to another. In cases where shear stress is a factor for sensitive cells, a lower pump speed is advisable.

How do you regulate oxygen levels while controlling pH in RM reactors? In RM reactors, pH can be monitored with optical sensors. Users can control pH by adding ingredients to cell culture media. If users see values that are below or above an optimal cell culture threshold, oxygen can be added by increasing the shake rate of the reactor and exchanging media to keep pH at the desired level.

Find the full webinar online at www.bioprocessintl.com/category/webinars.