How to size sterile filters and TFF membranes

Sterile filtration (0.2 um) is a critical unit operation in biopharmaceutical manufacturing used for bioburden reduction and final sterile filtration. Proper filter sizing ensures complete batch processing without filter blockage or excessive processing time.

Vmax method: The Vmax test is the industry-standard approach for filter sizing. A small-scale test is performed at constant pressure using a 47 mm disc. Plotting t/V versus V yields a linear relationship whose slope gives 1/Vmax. The required production filter area is: A = V_batch x SF / Vmax, where SF is typically 1.3-1.5.

Scale-up: When scaling from disc to cartridge format, maintain the same membrane chemistry, pore size, and operating pressure. Scale linearly based on area while preserving throughput (L/m²) or flux (LMH). Always verify with a small-scale cartridge test before full production.

TFF/UF-DF: Tangential flow filtration is used for concentration and buffer exchange of protein products. Processing time depends on membrane area, permeate flux, concentration factor, and number of diafiltration volumes. Typical loading is 5-10 L feed per m² membrane area, with permeate fluxes of 20-80 LMH depending on the product and membrane MWCO.