3.1 Mixing time characterisation
Mixing time is an important parameter for mammalian cell culture processes. Inadequate mixing results in cells being exposed to different environments within the reactor, which can have adverse consequences on cell growth kinetics and productivity (Gogate, Beenackers, & Pandit, 2000; Alvin W. Nienow, 2006). Hence mixing should be optimised to produce a homogenous cell culture environment whilst avoiding any deleterious effects caused by potential hydrodynamic forces and bubble bursting. Short mixing times (tm < 10s) should provide the necessary homogeneity as well as ensuring a fast response to any changes in operating conditions such as pH and temperature (Amanullah, Buckland, & Nienow, 2004; Langheinrich & Nienow, 1999; Silk, 2014). For fed-batch culture, efficient mixing is particularly important to avoid formation of local nutrient gradients (Enfors et al., 2001; Alvin W. Nienow, 2006).
Mixing times in the 5 L STR and 24-DSW were determined using the DISMT method as described in section 2.1.