Impact of Dean Vortices on the Integrity Testing of a Continuous Viral Inactivation Reactor

We propose a standard protocol for integrity testing the residence-time distribution (RTD) in a "Jig in a Box" design (JIB)-a previously described tortuous-path, tubular, low-pH, continuous viral inactivation reactor, ensuring that biopharmaceutical products will be incubated for the required minimum residence time, t_min . t_min is the time by which just 0.001% of the total product containing virus has exited the incubation chamber (i.e., t_0.00001 ). This t_0.00001 is selected to ensure a >4-log reduction in viral load. As current tracers and in-line analytical technologies may not be able to detect tracers at the 0.001% level, an alternative approach is required. The authors describe a method for deriving t_min from t_0.005 (i.e., the time at which 0.5% of the product has emerged from the reactor outlet) and an experimentally confirmed offset value, t_offset = t_0.005 -t_0.00001 . The authors also evaluate tracer candidates-including 100-nm-diameter gold nanoparticles, dextrose, monoclonal antibody, and riboflavin-for pre-process acceptability and the effects of viscosity, molecular diffusion coefficient, and particle size. The authors show that a JIB will yield t_min and RTDs that are nearly identical for multiple tracers due to Dean vortex induced mixing. Results indicate that almost any small-molecule tracer that is generally recognized as safe can be used in pre-use integrity testing of a continuous viral inactivation reactor under the Deans values (De) of 119-595.