Novel Stirred High-Throughput Mini-Bioreactors for Bioprocess Development: Evaluation of Scale-Down From a Typical Bench-Scale Bioreactor

High-throughput bioreactors could offer an economical alternative to bench-scale systems for Bioprocess development. They could also bridge the gap between un-instrumented culture devices such as shake-flasks, and instrumented bench-scale systems thus lowering the development time at the bench-scale. Bench-scale bioreactors that are the mainstay in cell culture process development are widely accepted as scale-down models of large-scale impeller driven bioreactors. The novel high-throughput mini-bioreactors (HTBRs) not only have the advantage of non-invasive, disposable optical sensing and control for %DO and pH, but also have overhead stirring that sets them apart from the existing high-throughput systems that mainly rely on magnetic stirring or shaking. However, the new HTBR system needs to be validated as a scale-down model of the existing bench-scale bioreactors to be certain that HTBR data is transferable to other bioreactor scales. Generally, physical parameters such as k_La, mixing time, P/V are used for scaling.  However, it is recognized that engineering challenges exist to obtain complete comparability between the two scales, as depicted by cell growth and product quality which are the true measures of scalability. This scale-down study aims to study the effect of HTBR and conventional reactor design as well as environmental parameters on cell culture process scale-down, including a comparison at the gene level using DNA microarrays. This study is also a first demonstration of mammalian cell culture in new controlled mini-bioreactors.  To achieve a 150-fold scale-down from bench-scale to the HTBR, oxygen transfer rate (OTR) was matched.  However, complete cell growth and product comparability was not achieved. An initial growth lag as well as lower end product titer was observed. These were surmised to be attributable to oxidative stress and free-radical damage conditions in the HTBRs; and preliminary DNA microarray results corroborated this. Further scale-down evaluation was done by comparing the mixing times between the mini-bioreactor and bench-scale, using the paddle and pitched blade impeller configurations. Based on our findings, if relevant modifications can be made to the HTBRs, scalability can be achieved pending further scale-down studies.