as in any conventional stainless steel reactor for viral vector production the perfusion process allows for an increase in the cell concentration and thereby the post infection virus titer for a secreted product perfusion in the bioreactor offers the user the opportunity to increase the productivity by simply increasing the size of the culture bag most importantly there is no need for sterilization validation or cleaning because the system experiences zero cross contamination during the production process fig2 provides a graph of data that was generated using a reactor system according to one embodiment of the present invention human embryonic kidney hek 293 cells in 200 liters of cdm4 culture medium were incubated in a 250 liter capacity reactor system among other parameters shown in the graph the viable cell density of the reactor system culture increased for about the first 14 days of the batch run fig3 34 illustrate data obtained from a single use bioreactor system for mammalian cell culture according to one embodiment of the present invention the scaleable mass transfer characteristics of the single use stirred tank bioreactor are described cell growth and metabolism antibody production and antibody characterization data from batch culture using a 250 liter prototype system are presented and compared to results from a traditional stainless steel bioreactor of similar scale materials and methods u2014 mixing studies mixing time in the bioreactor was estimated at various agitation rates by tracking the change in ph in the reactor over time in response to addition of a base solution the reactor was filled to working volume of 250 liters with typical cell culture media at time zero 500 ml of 1n naoh was added at the top of the reactor and a combined ph glass electrode was used to.