Assessing mixing performance and power consumption in the ambr® 250 bioreactor

The ambr® 250, a miniaturized bioreactor extensively used in biopharmaceutical R&D, was characterized to evaluate power and mixing dynamics for mammalian cell culture applications. The study analyzed the effects of agitation speed, impeller configuration, internal components, working volume, and feed placement on dimensionless mixing number ( Nt m ) and power number ( N P ) . Six impeller designs, including single and dual elephant ear (EE) configurations with varied angles and diameters, were investigated. Down-pumping (DP) mode reduced Nt m by 54% and increased cumulative N P by 14–22% compared to up-pumping (UP) mode. Mixing time ( t m ) remained consistent between single and dual EE impellers, though cumulative N P was 33% higher for single EE impellers. Dual EE impellers in DP mode achieved the lowest power input per volume ( P / V ) for similar t m . Spatial mixing time distribution and probe-induced effects on mixing parameters were also assessed. An early transition to turbulence was observed at Reynolds numbers ( Re ) below 10,000 in unbaffled systems, regardless of the presence of internal components such as baffles and probes. Probes increased N P and Nt m by 49% and 26%, respectively. This characterization advances understanding of milliliter-scale bioreactor performance and provides a foundation for optimizing the design and operation of mammalian cell-based processes. • Mixing dynamics in the ambr® 250 system with single and dual EE impellers. • Early onset of turbulence observed at lower Reynolds number (typical for <1 L reactors). • Significant impact of internals (baffles, probes and lines) on mixing and power. • Strategic feed inlet positioning and working volume for enhanced mixing in ambr® 250 system.