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The use of 0.1-µm rated sterilizing grade filters has been increasing in cell culture media filtration due to mycoplasma contamination concerns. Currently, no standards exist for conducting mycoplasma retention testing on these 0.1-µm labeled filters. A task force has been established at PDA to publish a technical report to standardize testing. Until such guidelines are published, conducting side-by-side tests under identical conditions is the only fair way to compare different 0.1-µm rated filters. Sartorius Stedim Biotech has conducted such tests on its Sartopore® 2 0.2/0.1 PES 10” cartridge filters at a third party lab using a modified ASTM F838-05 method to show A. Laidlawii removal at LRV = 7/cm².

Such mycoplasma-retentive filters usually have tight final membrane layers, and a high-performance prefilter is usually required to optimize the filter train. SSB has recently launched a new line of PES prefilters: Sartoguard®. These Prefilters are available in double layer PES as well as triple layer configuration with depth filters such as GF upstream. a combination of Sartoguard® 0.1 nominal → Sartopore® 2 0.2/0.1 has been tested into two media applications: the most common soy-hydrolysate supplemented serum-free media and the strategically important fully chemically defined media. These tests were conducted on 47-mm disks with Pre → Final filters in series under 25 psig constant upstream pressure. Media were prepared from powder in accordance with manufacturer's instructions.

For the serum-free soy hydrolysate supplemented media, all Sartoguard® filters performed very well with v∞ values > 6,000 L/m². Sartoguard® GF was the best prefilter with v∞~18,000 L/m², indicating flow-rate driven filtration. The number of 10” elements needed was also calculated for each media assuming 5,000 l batch size and two-hour filtration time. Sartoguard® GF/PES → Sartopore 2 0.1 were the best combinations overall, with 1-30” filter needed for each stage. A leading competitive combination required 2-30” filters for each stage (Figure 1).

Figure 1: (Click to enlarge)

The second media tested was a fully chemically defined media with high lipid content. As expected, this media was more difficult to filter. All combinations except Sartoguard® PES exhibited v∞ values > 1,000 L/m² (~6× less than previous media), indicating throughput driven filtration. Sartoguard® GF was the lead prefilter candidate once again closely followed by Sartoguard® PP and the competitive combination with v8 ~1,000–1,400 L/m2. Number of 10” elements needed for 5,000 l batch size for Sartoguard® GF → Sartopore® 2 0.1 was 17 each followed by 18 each for Sartoguard® PP → Sartopore® 2 0.1, and 19 each for the leading competitive combination (Figure 2).

Figure 2: (Click to enlarge)

In conclusion, Sartoguard® 0.1-µm nominal prefilters showed outstanding performance in two different types of cell culture media filtration applications in upstream processing. An application-specific approach of employing different versions of Sartoguard® prefilters proved to be successful as well. We would like to acknowledge SAFC Biosciences for providing different catalogued formulations for this testing.