Improving viral filtration capacity in biomanufacturing processes using aggregate binding properties of polyamide-6,6

Size-based analysis of virus removal filter fouling using fractionated protein aggregates

Fouling by protein aggregates reduces virus removal filter performance. In the present study, we investigated the effects of different-sized protein aggregates on fouling and aggregate retention in order to better understand the fouling mechanisms. Human immunoglobulin G was denatured by heating to produce aggregates of various sizes and then fractionated by size exclusion chromatography into different-sized aggregates with a narrow size distribution. The fractionated aggregates were filtered on Planova 20N, a virus removal filter known for its stable filtration capability. Analysis of flux behavior demonstrated different flux decrease patterns for different-sized aggregates. Observation of aggregate retention by staining revealed that larger aggregates were captured closer to the inner surface of the membrane while smaller aggregates penetrated farther into the membrane. These findings demonstrate that Planova 20N has a gradient structure with decreasing pore size from the inner to the outer surface of the membrane. This structure minimizes fouling and enables stable filtration by protecting the smaller pores located closer to the outer surface from clogging by large aggregates. Applying the predominant clogging models to the present filtrations revealed that clogging behavior transitioned from complete blocking to cake filtration as filtration progressed. In this combination model, after a certain number of pores are blocked by complete blocking, newly arrived aggregates begin to accumulate on previously captured aggregates, generating cake between capture layers within the membrane. Application of the approaches described here will facilitate elucidation of membrane fouling and virus removal mechanisms.

Role of membrane structure on the filtrate flux during monoclonal antibody filtration through virus retentive membranes

Virus removal filtration is a critical step in the manufacture of monoclonal antibody products, providing a robust size-based removal of both enveloped and non-enveloped viruses. Many monoclonal antibodies show very large reductions in filtrate flux during virus filtration, with the mechanisms governing this behavior and its dependence on the properties of the virus filter and antibody remaining largely unknown. Experiments were performed using the highly asymmetric Viresolve® Pro and the relatively homogeneous Pegasus™ SV4 virus filters using a highly purified monoclonal antibody. The filtrate flux for a 4 g/L antibody solution through the Viresolve® Pro decreased by about 10-fold when the filter was oriented with the skin side down but by more than 1000-fold when the asymmetric filter orientation was reversed and used with the skin side up. The very large flux decline observed with the skin side up could be eliminated by placing a large pore size prefilter directly on top of the virus filter; this improvement in filtrate flux was not seen when the prefilter was used inline or as a batch prefiltration step. The increase in flux due to the prefilter was not related to the removal of large protein aggregates or to an alteration in the extent of concentration polarization. Instead, the prefilter appears to transiently disrupt reversible associations of the antibodies caused by strong intermolecular attractions. These results provide important insights into the role of membrane morphology and antibody properties on the filtrate flux during virus filtration.