Laboratory Equipment: Membrane Filters Membranes – With the Perfect Pleats for Performance

Author / Editor: Dr Jens Meyer / Dominik Stephan

It is becoming increasingly important for the biopharmaceutical industry to reduce production costs. The development of the new sterilizing-grade filter, Sartopore Platinum, therefore focused on three main factors; filtration efficacy, process safety and cost effectiveness. The result was a filter cartridge featuring performance specifications that helped optimize processes and filter handling. This article describes the new technologies implemented in these filter cartridges and the added value users will experience when using it.

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Sartopore Platinum application
Sartopore Platinum application
(Picture: Sartorius Stedim Biotech)

The polyethersulfone (PES) membranes used in the Sartopore family are characterized by high total throughput and flow rate performance, reliable microbial retention and broad chemical resistance in a pH range of 1-14. Moreover, to further maximize throughput and flow rate performance, improve thermal resistance and wettability and to reduce protein binding, two new innovative technologies have been incorporated into the new filter cartridge.

Twin Pleat

The effective filtration area (EFA) per cartridge must be maximized to obtain the best possible performance. However, care must be taken not to compromise the hydrodynamics during filtration. If the individual pleats are too densely packed, the liquid undergoing filtration cannot access all parts of the membrane. Consequently, this will lower filtration performance. There is gradually less space as liquid approaches the inner diameter of a cartridge compared with the area next to the outer diameter (see Figure 1).

The intelligent TwinPleat geometry of the new filter cartridges addresses this issue by alternating a sequence of long and short pleats, which increases the membrane area, especially in the outer diameter region, whereas the membrane area near the inner diameter remains unchanged. In combination with the specific angle of the pleats, this geometry increases the membrane area by 66 per cent – 1 m² for Sartopore Platinum.

Surface Modification of the PES Membrane

PES is a naturally hydrophobic polymer. Therefore, to render this membrane surface hydrophilic and allow filtration of aqueous solutions, it is specially modified during membrane manufacture. For Sartopore platinum PES membranes, an exceptionally hydrophilic polymer with extremely high thermal resistance is covalently bonded to the membrane, covering its entire surface. The combination of these two new technologies in the new filter provides users with exciting new cost-saving and efficiency benefits.

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Advantages of the Filter

The effective filtration area of a filter cartridge has a direct impact on total throughput. Consequently, fewer cartridges are needed to reliably filter the same quantity of a solution. Reducing the number of filters additionally decreases the total cost of a complete filtration process.

Total accessibility

The characteristics of TwinPleat, a unique alternating sequence of long and short pleats, ensures optimized hydrodynamics during filtration and total accessibility of the membrane for filtration of the product This can be visualized by filtering a colored test solution through the filter with TwinPleat technology and a cartridge based on a different pleating geometry with an identical length of the overlapping pleats. The colored test solution tested stained the entire Sartopore Platinum membrane brown, including deeply into each pleat. The same test procedure for the competitor cartridge led to white patches between the pleats.