User:Ali mmbr

Virus Filtration In recent years, virus filtration has been introduced as a robust operation for the viral clearance of biological products. Virus filtration membranes remove viruses based on size exclusion. The larger virus particles are rejected by the membrane, while smaller protein molecules are allowed to permeate through the membrane with high efficiency. Virus filtration is believed to be a robust process since the virus removal is predictable and is not affected by normal variations in process parameters. As a result, most downstream purification processes include a virus filtration step. Virus filters are classified into two main categories: filters that are capable of removing viruses of 50 nm and larger (e.g. retroviruses) and filters that can clear smaller (~20 nm) viruses (e.g. parvoviruses). Important factors governing the selection of a virus filter are virus retention capabilities, protein transmission/ recovery, and product throughput requirements. Generally, virus filtration is performed in two different modes of operation: Normal flow filtration (NFF; also known as dead end filtration) and Tangential flow filtration (TFF; also known as cross flow filtration). In NFF, the solution flows perpendicular to the membrane surface. In contrast, in TFF the feed fluid passes in a direction parallel to the surface of the membrane with only the permeating fluid passing through the membrane. The availability of various membranes with pore sizes and surface areas makes the process scalability relatively straightforward. In contrast to viral inactivation treatments, the recovery of protein product in filtration systems is usually over 90–95% and the product characteristics are not altered. Unlike other purification tools, virus filtration membranes are specifically designed for virus removal. The operating conditions such as pressure, temperature and flow rate are defined and controlled to ensure efficient and reproducible virus removal. The sieving mechanism in virus filtration membranes is capable of removing high concentrations of both enveloped and non-enveloped viruses. For viruses with sizes on the order of the mean pore size of the membrane, various factors may influence the extent of removal, including: virus aggregation, formation of complexes with antibodies, protein content of the solution and possible mechanisms of viruses adsorption to the membrane surface caused by charge effects.