(8f) AMBR®250 Scale-DOWN MODEL Limitations and MASS Transfer Characterization

Cell culture process development and process characterization studies leverage bench-scale bioreactor systems as scale-down models for large scale manufacturing. The ambr^®250 micro-scale bioreactor platform is a bench-scale system that offers customizable automation and individualized bioreactor control to support high-throughput workflows. While ambr^®250 bioreactors provide an excellent option to facilitate expansive studies, there are some scale-dependent limitations that must be addressed to develop an appropriate scale-down model. Power input and mass transfer are inherent scale-dependent principles which are directly impacted by the mixing and gassing strategies implemented at small scale, and small-scale operational parameters must be defined with the key study outcomes in mind.

During the development of an ambr^®250 scale-down model for process characterization studies, we observed limitations that caused sharp, transient drops in the dissolved oxygen (DO) level. This phenomenon was found to correlate with the particular set of bioreactor parameters, which led us to perform additional bioreactor characterization studies for mass transfer of dissolved gases. Our results expand upon previous works by incorporating the mass transfer contribution from the transient headspace gas composition, assess multiple bioreactor fill volumes, and leverage representative cell culture media. In our ambr^®250 kLa calculations we found that both the transient headspace gas composition and the bioreactor working volume contribute significantly to overall mass transfer. Then the magnitude and duration of impacts on ambr^®250 DO control resulting from antifoam additions, feed additions, and bioreactor uncapping at various time points during a production run were compared to theoretical modeling based on our kLa calculations. We conclude by providing alternative approaches for scaled-down process parameters to achieve consistent DO control in ambr^®250 bioreactors.