Filters have a finite lifetime, and their performance varies over time; optimizing this performance is dependent on a number of parameters.
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An individual filter may have qualities that lend themselves to a long lifespan, but overall system design might also have an impact.
- Pore morphology refers to the paths inside a filter membrane, relating to individual filters. Different pore shapes can interact with pollutants in various ways, extending the filter's lifespan.
- Pre-filtration involves installing a filter with larger, simpler pores upstream of a sterile filter. This filter is essentially sacrificial, capturing more pollutants over a shorter period to preserve the effectiveness of the more expensive sterile filter.
When correct pore morphology and system design are chosen, a wide range of pollutants with varying sizes, densities, and behaviors can be regulated.
Pore morphology
Pore morphology relates to the nature and structure of a membrane's pores. It is an important factor in filter performance because it controls how particles and membranes interact.
There are two types of membrane pore morphology: symmetric and asymmetric. Membranes with symmetric pores are more consistent, whereas asymmetric pores have a gradually decreasing pore structure.
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A symmetric membrane's uniform pore diameter enables it to serve as an equally selective barrier to particle passage.
In a symmetric membrane, the holes are the same size along the channel and retain particles with equal selectivity. However, this symmetry indicates that pores are plugged on the membrane's surface via size exclusion. As a result, filtering that uses symmetric membranes may become increasingly inefficient as the membrane gets irreversibly clogged.
In an asymmetric membrane, the retention of each pore increases with its depth. When a particle is caught in an asymmetric membrane, the pore channel is not blocked as it would be in a symmetric membrane.
While the particle is trapped, the pore's asymmetric structure enables gradual blockage on the surface and throughout the pores. In this way, asymmetric geometries enable large flow rates while preserving retention ratings.
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Use of a pre-filter
Traditionally, increasing a filter's retention rating (decreasing pore size) results in increased pressure drop and shorter filter lifetimes. This results in greater process downtime due to the need for more frequent replacements. Extending filter lifetime necessitates a careful balance between particle retention and filtration efficiency: using a pre-filter can help achieve this.
When compared to the membrane's pore rating, contaminants in a product stream vary in particle size. A pre-filter is often a filter with a higher pore size rating than the sterilization grade filter.
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Pre-filters can improve the sterilizing grade filter's effectiveness by catching larger contaminants upstream, allowing the sterilizing grade filter to focus on capturing the smallest contaminants.
A membrane with a larger pore size (about 0.45 μm) may effectively trap larger yeast cells, particles, and bacteria. When the fluid travels through the sterilizing grade filter's small pores, it reduces bioburden.
The sterilizing grade filter does not clog as quickly because it only needs to capture the smallest particles. The use of a pre-filter enables increased throughput while preserving the downstream sterilizing grade filter's performance during regular processing.
Working with Entegris
Pore morphology and pre-filters can improve life sciences production processes, but there are many more factors to consider.
Entegris is a comprehensive provider of high-quality filtering solutions adapted to individual requirements. The company can help design a system that achieves the desired results while optimizing cost and performance.
About Entegris, Inc.
As a legacy semiconductor leader, Entegris brings unmatched sensitivity to purity and particle contamination, backed by robust quality systems, advanced contamination control technologies, and proprietary particle detection and sizing platforms - delivering a comprehensive, validated approach to particle risk mitigation. This holistic expertise is increasingly vital in the Life Sciences industry, where controlling particulate contamination is critical to ensuring product safety, regulatory compliance, and process integrity.
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