# Visualizing the Effect of Process Pause on Virus Entrapment During Constant Flux Virus Filtration

## TL;DR

This paper uses fluorescent labeling and microscopy to study how pauses in virus filtration processes affect virus entrapment in membranes.

## Contribution

The study introduces a novel visualization method to observe virus entrapment dynamics during virus filtration.

## Key findings

- A 30-minute process pause caused the virus entrapment zone to broaden and move deeper into the membrane.
- Aggregates in the feed stream increased the broadening of the entrapment zone.
- These effects may reduce virus clearance efficiency in filtration processes.

## Abstract

Virus filtration is an essential unit operation used to validate clearance of adventitious virus during the manufacture of biopharmaceutical products such as monoclonal antibodies. Obtaining at least a 10,000-fold reduction in virus particles in the permeate is challenging as monoclonal antibodies are about half the size of the virus particles. Minute virus of mice, FDA-recommended model adventitious virus, was labeled with a fluorescent dye. Laser scanning confocal microscopy was used to determine the location of virus entrapment within the virus filtration membrane. Three different hollow fiber membranes made of regenerated cellulose and polyvinylidene fluoride were tested. Feed streams consisted of MVM spiked in buffer and MVM spiked in 5 g L−1 bovine serum albumin known to contain aggregates similar in size to the MVM. After filtering the feed, a buffer flush was used, with and without 30 min pause before the buffer flush. For all virus filters, a 30 min process pause led to broadening and movement of the virus entrapment zone deeper into the membrane. The presence of aggregates led to greater broadening of the entrapment zone. Both effects could lead to reduced virus clearance. Visualization of virus entrapment helps improve understanding of the behavior of virus filtration membranes.