A) The choice of an appropriate impeller design: Different impeller designs can affect the shear forces experienced by mammalian cells. It is important to select an impeller design that minimizes shear and turbulence in order to maintain cell viability and productivity during scale-up.

b) The speed of rotation (N) of the impeller: Higher rotational speeds can increase shear forces on the cells. It is important to optimize the rotational speed to minimize shear stress while ensuring proper mixing and oxygen transfer.

c) The diameter of the impeller (D): The size of the impeller can affect the shear forces experienced by the cells. Larger impeller diameters can result in higher shear stress. It is important to select an appropriate impeller diameter that balances mixing efficiency with shear sensitivity of the cells.

d) The choice of culture vessel: The choice of culture vessel can also impact shear forces. Bioreactors with different geometries and agitation systems can result in different shear stress profiles. It is important to select a culture vessel that minimizes shear stress while providing adequate mixing and oxygen transfer.

e) Process duration: Prolonged exposure to shear stress can be detrimental to mammalian cells. Therefore, the duration of the process should be considered to minimize cumulative shear stress exposure.

f) Monitoring and control systems: To ensure optimal cell culture conditions, it is important to have robust monitoring and control systems in place. These systems can help monitor and adjust key parameters such as impeller speed, temperature, pH, and dissolved oxygen levels to minimize shear stress and maintain cell viability during scale-up.

Overall, the goal is to optimize the scale-up process to minimize shear stress while ensuring efficient mixing, oxygen transfer, and cell growth. This requires careful consideration of impeller design, rotational speed, impeller diameter, culture vessel choice, process duration, and monitoring/control systems.