With downstream processing consuming up to 60% of the costs associated with producing biotech products, every incremental improvement in protein recovery is welcome. Filtration media, in particular, can be a source of considerable protein loss due to sticking. Clariflow polyethersulfone (PES) membrane cartridges and capsules from PTI Technologies (Newbury Park, CA) have an extremely low affinity for protein, making makes these filters ideal for the cold sterilization of protein-laden solutions such as ascites fluid, fermentation broth, and diagnostic reagents. Since less protein is withheld by the filter, more winds up in the filtrate, giving a higher overall process yield. This is extremely important for fermentions used to make therapeutics, or where monoclonal antibodies are produced for the manufacture of diagnostic test kits.
One of PTI's customers recently switched to 0.2 µm Clariflow capsules for their process after discovering that the PTI products increased their antibody yield by about 20%. (They had been using competitive 0.2 µm capsules with a different PES membrane that was also marketed as low protein-binding). Testing has shown Clariflow PES to be much lower in protein binding than other polymeric membranes, including this other competitive PES product (see Fig. 1).
Figure 1: Protein Binding Comparison of Hydrophilic Membranes. The experiment involved flowing 20 mls of a protein (see below) solution through a 5.3 cm2 EFA disc of each membrane, and collecting the filtrate(s). Delivery of 0.95 mg/cm2 (HSA) or of 0.38 mg/cm2 (IgG and Insulin) was achieved. The membranes were washed with 7 ml of PBS and allowed to dry. The membranes were then hydrolyzed under standard conditions (6N HCL, 1% phenol for 22 hours at 110°C), and subjected to RP-HPLC. Hydrolysates of new membranes without protein were used as blanks. The bound protein was calculated by measuring the amount of recovered glutamic acid.
Combined with a low protein-binding nature, Clariflow membrane exhibits some of the fastest fluid flow rates available among hydrophilic membranes (Fig. 2). This is due to the unique, mirrored anisotropic morphology that minimizes restriction to flow (Fig. 3). In addition, Clariflow membrane has a built-in prefiltration layer upstream of the central region where the absolute cut-off pores exist. By being situated in the middle of the membrane, these smallest pores are protected from minor surface damage that might occur during pleating of the membrane, manufacture into cartridges, or sterilization of the filters during use. This lessens the likelihood of an integrity failure during actual use and the scrapped batches of product that would result.
Figure 2: Water flow rate comparison of medium sized 0.2 µm capsule filters made up with the noted membranes.
Figure 3: SEM of cross section of Clariflow Polyethersulfone Membrane.
For more information: PTI Technologies, 950 Rancho Conejo Blvd. Newbury Park, CA 91320. Tel: 805-499-2661. Fax: 805-375-2296.