In some cases, where low concentrations of proteins or preservatives are in the fluid, there may be a loss in product yield
if the filter membrane adsorbs significant amonts of product . At high component concentrations this is not a concern, but
this is especially critical where a desired component is present in very low concentration. The effluent should be tested
to ensure that the amount of loss is acceptable.
Table 2. IgG Transmission
Here is a test run example. IgG protein transmission was measured to demonstrate differences in protein adsorption among membrane
types. Each disc was challenged with 60 mL protein solution at 100 μg/mL concentration. Filtrate was collected in 1 mL aliquots
for the first 10 mL followed by 5 mL aliquots to a total throughput of 60 mL. Data in Table 2 indicate that protein binding
occurs within the first 10 mL passed through each membrane disc. After the first 10 mL, the effluent contains protein at the
same concentration as the influent solution. PES and PVDF are generally low adsorptive materials. However, nylon bound 20
times more protein than PES in the first 10 mL. Extrapolating to production scale; this may affect product yield.
Table 3. Area per 10-inch cartridge
Lifetime is a Function of Construction
New filter designs have faster flow rates, smaller filter systems, improved microorganism and particle retention, and longer
service life. These benefits translate into significant cost and time savings for drug manufacturers. Advances in the speed,
size, and performance of new generation membrane filters are perhaps most critical because membrane technology is used in
a broad range of applications. Lifetime (throughput) and flowrate at process scale are highly influenced by the structure
of the membrane.
When flowrate is the main driver, new high-flow sterilizing-grade filters feature a serial layer construction where the upstream
layer is an asymmetric, high porosity PES membrane over the final sterilizing-grade layer. This PES filter offers exceptionally
high flows at a processing rate of 17 L/min at 100-mbar differential pressure (916;P), and is compatible with fluids across
a wide pH range, from buffers to numerous biological fluids.
Figure 2. Cross section of high-area asymmetric filter cartridge showing retained contaminant
When lifetime is the main driver, a high-capacity sterilizing-grade filter offers users an innovative hybrid technology by
fitting a finer grade of asymmetric PES membrane over a PVDF membrane. This membrane combination enables high dirt-holding
capacities and the flexibility for either wet or dry steaming. Because autoclaving or steam-in-place procedures can take
place in either wet or dry conditions, this flexibility accommodates different manufacturing specifications. The high-capacity
hybrid filter offers competitive flow rates at 10 L/min at 100-mbar ΔP; in addition it offers the high throughput required
in the filtration of high protein biotech solutions.
Figure 3. Upstream side of prefilter final filter layers showing clean membrane due to effective prefiltration
Asymmetric Prefilter Construction Improves Capacity
A technology that has contributed significantly to the performance of new generation membrane filters is an asymmetric membrane
structure that offers a 3 to 1 average pore size gradient through the depth of the membrane, resulting in higher porosity
and dirt holding capacity. This pore size gradient (Figure 1) enables larger particles to be captured in the outer portion
of the filter, while the sterilizing layer provides high efficiency removal of smaller microorganisms.
Figure 4. A unique folding pattern in a new filter design increases filter area