(71c) Mixing Studies in Viscoelastic Fluids and Their Application to Cell Lysis for Plasmid DNA Production
Vicoelasticity gives rise to normal forces (traditionally measured by a Weissenberg rheogoniometer) under the action of shear and agitation. There is also a characteristic time associated with the phenomenon, usually determined by creep-compliance or oscillatory rheometry. The impact of viscoelasticity in model Boger and elastic, shear-thinning fluids, characterised as indicated above, on the power drawn by Rushton and pitched blade turbines and dual Intermig impellers is reported and compared to that in similar Newtonian and shear-thinning inelastic fluids. Mixing times are also compared. These results were then used to help in the design of alkaline cell lysis reactors for plasmid DNA production from 5 L up to 60 L by volume. It is shown that in such reactors, the power characteristics of dual Intermig and helical screw impellers are in good agreement with those obtained in the model fluids, even though the rheological properties change during the lysis process as more chromosomal DNA is released and denatured by the concentrated alkali. It is also shown that these reactors have been used to produce a range of plasmids for therapeutic purposes of a quality as good as or better than that obtained at the bench scale.