Designing for Extended Performance in Life Science Contaminant Removal

Filters have a finite lifetime, and their performance also changes over time. How do you get the most performance over the longest lifespan? 

Filter optimization is based on a variety of factors. An individual filter may have characteristics that lend themselves to a long lifespan, but overall system design can also play a role.

• Pore morphology is a characteristic that relates to individual filters. This term refers to the pathways within a filter membrane. Different pore morphologies can interact with contaminants in different ways, while also contributing to a filter’s overall lifespan.
• Pre-filtration is a form of system design that favors placing a filter with larger and less-complicated pore morphology upstream of a sterile filter. This filter is essentially sacrificial – catching larger contaminants over a shorter lifespan in order to preserve the functionality of the more expensive sterile filter.

When you choose the right pore morphology and the right system design, you can control a large variety of contaminants that differ in size, density, and behavior.

Pore Morphology

Pore morphology refers to the nature and structure of the pore within a membrane. It is a key factor in filter performance as it governs the way particles and membranes interact. Membrane pore morphology can be divided into two types: symmetric and asymmetric. Membranes with symmetric pores are more uniform, while asymmetric pores have a gradually reducing pore structure. 

The uniform pore diameter of a symmetric membrane allows the entire membrane to act as an equally selective barrier to the passage of particles. In a symmetric membrane, the pores are a uniform size throughout the entire channel and retain particles in an equally selective manner. However, the symmetric nature of this type of pore structure also indicates that when a pore is plugged, it is plugged on the surface of the membrane based on size exclusion. As a result, filtration using symmetric membranes can become progressively less efficient as the membrane becomes irreversibly blocked.

In an asymmetric membrane, each pore increases in retention throughout the membrane's depth. When a particle is captured in an asymmetric membrane, the pore channel is not blocked in the same way as a symmetric membrane. While the particle remains trapped, the pore’s asymmetric structure allows for gradual blocking to occur on the surface and throughput the pores. In this manner, asymmetric morphologies allow for high flow rates while maintaining retention ratings. 

Watch our video from Entegris expert Chris Rios to learn how life sciences filtration can help achieve your goals.

Use of a Pre-filter

Traditionally, increasing a filter’s retention rating (reducing pore size) will increase pressure drop and reduce filter lifetimes. This results in increased process downtime due to the need for more frequent replacements. Extending filter lifetime requires a careful balance between particle retention and filtration performance. One way to achieve this balance is via the use of a pre-filter.

Contaminants in a product stream have a particle size distribution that varies from large to small when compared to a membrane’s pore rating. A pre-filter is typically a filter that has a larger pore size rating than the sterilizing grade filter.

Pre-filters can improve and/or protect the sterilizing grade filter’s performance by capturing the largest contaminants upstream so that the sterilizing grade filter primarily captures the smallest contaminants. For example, a membrane with a slightly larger pore size (commonly 0.45 μm) can capture the largest yeast, particulates, and bacteria. This creates a reduction in bioburden when the fluid passes through the smaller pores of the sterilizing grade filter. The sterilizing grade filter does not clog as quickly, since it only needs to capture the smallest particles. This allows for higher throughput performance while protecting the performance of the downstream sterilizing grade filter during normal processing.

Work With Entegris to Find the Optimal Life Sciences Filtration Setup

Pore morphology and pre-filters can positively impact your life sciences production process, but there are many more variables to consider. To get a sense of the factors involved, read our accompanying blogs on holdup volume and hydrophobic vs. hydrophilic membranes. 

Entegris is your turnkey provider for high-quality filtration solutions that are tailored to your specific needs. Once we know what you’re trying to achieve, we can help you design a system that creates the outcomes you need, optimizing cost and performance.

To learn more about Entegris’ filtration portfolio, download our ebook or contact our team to evaluate your target contaminants and process conditions.