Whereas traditional membrane constructions have a homogeneous pore size distribution across the membrane, the asymmetric structure
with its large void volume is able to capture solids across the entire depth and pore gradient of the membrane, improving
total filter capacity. (Figures 2 and 3).
Table 4. Cartridge construction affects flowrates
Deep Pleat Design Maximizes Throughput
Minimizing system size while maintaining process flow and volume has required unique approaches. One of these is modifying
the traditional pleat pack design. In order to achieve greater filter surface area, while keeping the same cartridge configuration
the traditional fan pleat filter has been replaced with a deep pleat design (Figure 4). This deep pleating technology is used
to form a very robust filter pack that allows up to 50% greater filtration area than traditional fan pleat and improved flow
distribution in the membrane cartridge. Table 3 shows the benefits of deep pleat design in that there is more area in the
PES and hybrid filters compared to traditionally pleated nylon and PVDF filters.
Table 5. Test of filtering 100 L of vaccine
Another factor employed to increase pleat length is a reduction in the size of the core-collecting chamber. This allows the
flow path to extend into the space that would normally be reserved for the core, enabling much greater membrane flow and fluid
throughput (Figure 5).
The core chamber's materials of construction also influence the integrity and usability of the filter. The combination of
a narrow polypropylene core and deep pleat design enhance mechanical stability and robustness during operation and steam sterilization.
The strength of the design means that a higher differential pressure (1 bar vs. 300 mbar for most fan pleated filters) can
be safely reached during steam in place operation without damaging the filter. This means that a 10-in. filter can be used
to achieve the flow rates of a conventional 20-in. filter. For example, a sterilizing-grade deep-pleat filter with 1 m2 membrane can achieve flow rates of greater than 17 L/min. A traditional 10-in. filter with the same removal efficiency might
only provide flow rates of 3 to 7 L/min. Figure 6 shows results of a test. By increasing flowrate capability of single filter
elements, the deep pleat design also allows biopharmaceutical companies to reduce the number and size of filter assemblies.
Table 6. Test of 550 L MAb batch
Filterability studies were performed using model buffer solutions to determine the optimum membrane for large-scale buffer
filtration applications. For solutions with low solids levels such as clean buffer solutions, results are best described in
terms of flowrate per 10-in. cartridge per hour, at a given pressure, rather than volume processed to point of plugging. Table
4 shows that the high-flow PES membrane demonstrated flow rates 3 to 5 times greater than the nylon membrane and 3 to 4 times
greater than the PVDF membrane. Based on the results, PES membrane demonstrated superior flow characteristics during filtration.
This is our membrane choice for buffer filtration applications.
Figure 5. Two types of cores