Propellers Were Invented In 1830...
Not recommended for stem cells.Propellers are by their very nature, turbulent devices. They create a flow across a blade element causing fluid, particles and cells to be accelerated, compressed and passed through pressure and velocity differentials that are very turbulent. Mixing is a chaotic event with a propeller and results in an uneven distribution of cells, gas and nutrients.
Propellers create dead zones just under the hub of the propeller. Differing circulatory zones develop in the vessel; two beside the drive shaft, one on the surface and perhaps two more at the perimeter of the propeller. In small vessels, at slow speeds, this may work with some materials. However, when live cells and vaccines are the subject of the mixing effort, scale up is severely compromised by the use of a propeller. The reasons are many.
As one increases the diameter of the propeller in an effort to scale up, tip speed becomes an issue. To compensate, users typically reduce the speed of the propeller and add another propeller to the shaft in order to provide the mixing energy required for a vessel. Now with two propellers, more zones of turbulence develop and the internal dynamics of the vessel become even more chaotic.
Simply stated, stem cells will not grow in a two propeller vessel and therefore propellers are not a scale up option in this new field of regenerative medicine and are becoming increasingly problematic in many vaccine applications.
The evolution of mixing requirements for advanced materials has overtaken the utility of the propeller and its more than 150 year reign. It is now time to embrace the BACH impeller and to break the barriers holding back advanced biochemistry solutions.