Q.21 Since mammalian cells are sensitive to shear, scale-up of a mammalian cell process must consider, among other parameters, the following
(given N = rotations/time, D = diameter of impeller):
- πND
- πN2D
- πND2
- None of these
Mastering Mammalian Cell Scale-Up: Key to Shear-Sensitive Bioprocessing
Mammalian cells demand careful bioreactor scale-up due to shear sensitivity from agitation. The correct parameter focuses on impeller tip speed. This ensures cell viability during production scaling.
Correct Answer
The right choice is πND, representing impeller tip speed (v_tip = π × N × D).
This parameter directly correlates with maximum shear exposure near impeller blades.
Maintaining constant tip speed during scale-up minimizes cell damage in larger vessels.Why Tip Speed Matters
Mammalian cells tolerate moderate shear but suffer at high local velocities from impeller tips.
πND quantifies tip speed, guiding agitation adjustments as diameter (D) increases.
Scale-up formulas reduce rotational speed (N) proportional to D^{-1} to hold v_tip steady.Option Breakdown
Each option links to a distinct scale-up criterion—only one prioritizes shear:
Parameter Represents Suitability for Mammalian Cells Impact on Scale-Up πND Impeller tip speed Ideal: Limits max shear directly Reduces N as D grows; protects cells πN²D Power per volume (P/V) Poor: Increases shear excessively Boosts energy input; harms viability πND² Circulation/mixing time Unsuitable: Prolongs exposure Slows mixing; indirect shear control None N/A Incorrect All options have bioprocess roles Practical Implications
In practice, scale-up from lab to production (e.g., 2L to 2000L) caps tip speed at 1-3 m/s for CHO cells.
Higher P/V from πN²D suits microbial cultures, not fragile mammalian lines.
Engineers use πND to balance oxygen transfer with shear protection.
