Tangential Flow Filtration Explores New Niches

By Paul Thomas, Senior Editor There are greater combinations of pore sizes, membrane-protein bonding capabilities, and the ability to positively or negatively charge the membrane, all of which allow companies to tweak their filtration characteristics to suit a given process step. GE alone offers 700 variations of its hollowfiber models, and 50 of its TFF cassettes, Gach notes. The most significant advancements in tangential flow in the past few years have to do with membranes and their chemistry, says Dr. Michael Meagher, director of the University of Nebraska-Lincoln’s Biological Process Development Facility. Like Kopf, Meagher marvels at the robustness, pore distributions and control of pore chemistry of today’s membranes. High-performance tangential flow filtration (HPTFF) lies at the cutting edge of these advances, as a means of enabling concentration, purification and formulation in a single unit operation. HPTFF uses a charged membrane that allows manufacturers to separate product based on both molecule size and charge. Interest in the technique has been spurred by Genentech researchers, who have run feedstreams of recombinant proteins expressed in E. coli and achieved a 10-fold removal of host cell proteins with an overall process yield of 98%. Compared to a more conventional purification scheme, the process eliminated one chromatography step and a 12% improvement in yield. Beyond HPTFF, the future will see further increases in membrane capabilities for all filtration processes, says Dussault of Millipore. Manufacturers will expect tighter specifications and greater consistency to match their increasingly specific processing needs. While technology advances have allowed reusable TFF systems to remain standard, single-use (i.e., disposable) components are gaining traction. Disposable filter cassettes, as well as bags, adaptors, tubing and other filtration system components, are now commonplace. Major filtration vendors are racing to offer entire off-the-shelf disposable tangential flow systems—Sartorius Stedim, for example, expects to have completely disposable tangential