STRs are one of the most conventional bioreactors. Due to its advantages such as easy scale-up, good fluid mixing and oxygen transfer ability, alternative impellers and easy compliance with cGMP requirements, STRs are commonly used. However, this type of bio- reactor also has several limitations, such as high power consump- tion, high shear, and the concerns about sealing and stability of shafts in tall bioreactors. Compared to microorganisms, both animal cells and plant cells are shear-sensitive, which results in remarkable efforts to modify and optimize the impeller system in order to balance mix- ing and mass transfer requirement and potential damage by hydro- dynamic force. Numerous modifications of conventional STRs have been made by developing new impeller designs such as a centrifu- gal impeller (Fig. 1) [4-8]. Several biopharmaceutical manufactur- ers have successfully implemented STRs at 10,000 to 20,000 liter

STRs are one of the most conventional bioreactors. Due to its advantages such as easy scale-up, good fluid mixing and oxygen transfer ability, alternative impellers and easy compliance with cGMP requirements, STRs are commonly used. However, this type of bio- reactor also has several limitations, such as high power consump- tion, high shear, and the concerns about sealing and stability of shafts in tall bioreactors. Compared to microorganisms, both animal cells and plant cells are shear-sensitive, which results in remarkable efforts to modify and optimize the impeller system in order to balance mix- ing and mass transfer requirement and potential damage by hydro- dynamic force. Numerous modifications of conventional STRs have been made by developing new impeller designs such as a centrifu- gal impeller (Fig. 1) [4-8]. Several biopharmaceutical manufactur- ers have successfully implemented STRs at 10,000 to 20,000 liter