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Filtration refers to the process of separating components in a fluid stream, typically by exploiting differences in size. The technology is often applied to remove contaminants from a product or from test samples when those contaminants are significantly larger than those components that are being purified. Their retention capability ranges from centimeters in large scale industrial applications, through micrometers in fine particulates and bacterial controls to nanometers for the removal of small contaminants such as viruses and small molecules. In some specialized applications it may also be used to retain larger, wanted components and to transmit smaller contaminants or solutes to purify or concentrate a feedstock.

Filters can be found in many laboratory applications and throughout a range or drug product manufacturing workflows.

• QC: Many standard methods use filters to purify or capture analytes. These include microbiological testing, dissolution testing and a range of environmental test methods.
• Research: Commonly used to purify test samples to increase test accuracy and protect analytical equipment
• Drug manufacturing
• Clarification filters are common in cell harvest applications.
• Bioburden control filters are applied liberally through the process as part of a contamination control strategy.
• Virus filters are used to control virus contamination in the manufacture of biologic drugs.
• Air and liquid sterilizing grade filters can be found in critical applications such as cell culture and final filling.

Sterile filtration removes microorganisms from a fluid stream and, when specified correctly, does so without altering the product of interest. When combined with other contamination control strategies it can be used to support aseptic processing and the production of sterile final drug products. It’s typically used when heat based terminal sterilization isn’t an option, such as with biologics, but it is routinely used throughout the QC and drug development process to control critical contaminants in cell culture media and process buffers.

A 0.2 µm membrane rating is commonly applied to those filters with the ability to retain small bacteria. When the performance is suitably validated, these filters may also be classified as sterilizing-grade filters. For critical applications, care should be taken to investigate this performance and not rely upon a simple 0.22 µm rating alone. When properly selected, such filters should remove all microbial contaminants while allowing proteins, buffers, and cell culture media to pass unaffected. Most filters are not designed to remove viruses, which require dedicated viral filtration technologies however, in dry gas applications, some 0.2 µm rated filters do provide significant virus reduction.

Direct flow filtration processes fluid perpendicularly through a membrane until it reaches capacity, making it ideal for clarification or sterile filtration. Tangential flow filtration uses a combination of fluid flow including a higher proportion across the membrane surface to reduce fouling while retaining large particles or molecules and transmitting smaller species. This makes them ideal for the concentration of dilute biologics and buffer exchange (diafiltration) in higher‑demand workflows.

Microfiltration, ultrafiltration (UF) and nanofiltration, target the retention or removal of different contaminants based upon their size. They support the purification, clarification, concentration, desalting and diafiltration, of test samples and process fluids across lab and bioprocess applications. Choosing the right membrane depends on what you need to remove, your molecule, the feed characteristics, and your required retention performance.

Fouling or blockage is influenced by feed composition and the filter construction. Some filters are more able to cope with an increased level of solids and a wider range of contaminant sizes than others. The addition of prefiltration can reduce the burden of the final filter and for many filters can be integrated into the filter construction. The right filter selection and sizing, coupled with close process controls help reduce blockages and maintain throughput under real‑world conditions.

Single‑use filters, integrated into single-use flow paths are valuable when cleaning steps slow you down, product changeovers are frequent, or cross‑contamination risks need to be avoided. They provide a flexible way to handle variable workloads and can be integrated into automated systems for high levels of process control.