Viruses present unique challenges for biopharmaceutical manufacturing due to their small size. However, their presence, even in trace amounts, can compromise therapeutic efficacy and pose safety risks to patients. Nanofiltration has emerged as a valuable tool for the effective clearance of viruses during bioprocessing. This article explores the technique of nanofiltration and its role in assuring the virus safety of biopharmaceutical products.

What is Virus Filtration?

Nanofiltration is a physical size-exclusion based method used to remove viruses from liquid samples such as bulk drug substances, buffers, media, and final drug products. It relies on pores within Virus Filtration filters that allow the passage of desired product molecules while retaining even the smallest viral contaminants. Filters with pore sizes ranging from 15-50 nm are commonly used to sieve out viruses, which are typically 20-400 nm in size. During filtration, the product stream is passed through the virus filter under differential pressure, trapping contaminating viruses on the surface of or within the filter matrix.

Mechanism of Virus Retention

There are two main mechanisms through which viruses are retained by nanofiltration membrane filters: sieving and adsorption. Sieving relies on the size difference between viral particles and product molecules to physically block the passage of viruses. Viruses can also be retained through adsorption, where they interact and bind directly to chemical or physical sites on the membrane surface. Both mechanisms play a role, but sieving is the primary mode of retention for most non-enveloped viruses, while adsorption better describes the retention of some enveloped viruses that may temporarily deform to pass through pores. Together, these mechanisms allow virus filters to reliably capture and clear even parvoviruses, one of the smallest common viral contaminants.

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