(32a) High Performance Tangential Flow Filtration for Bioprocessing Separations
Ultrafiltration (UF) is used in almost every process for concentration and buffer exchange of proteins made by recombinant DNA methods. Limited selectivity and throughput have precluded the use of UF for protein purification. High Performance Tangential Flow Filtration (HPTFF) is an emerging technology that enables concentration, purification, and buffer exchange in a single unit operation. HPTFF provides separation of solutes based on differences in both size and charge. Protein purification is possible due to enhanced selectivity and throughput. Significant improvement in performance has been achieved by 1) operating in the pressure-dependent flux regime; 2) generating similar flux throughout the membrane module; 3) developing defect-free composite regenerated cellulose (CRC) membranes; 4) optimizing pH and conductivity; 5) developing charged CRC membranes; 6) optimizing feed flow rate, bulk concentration, and flux; and 7) using optimization diagrams to determine the best combination of selectivity and throughput for a specific process application.
HPTFF technology is being developed to leverage the large installed base of UF systems in the biotechnology industry. Feed flow rates, process fluxes, concentration during diafiltration and product yields are comparable to UF. The main differences are in the use of charged membranes (same polarity as retained product), larger pore sizes (300 kD instead of 10-30 kD for MAbs), and potentially two buffers instead of one (one for purification and one for formulation if desired). The number of diavolumes may differ depending on the application. Like ion exchange chromatography, HPTFF with charged membranes operates best within certain ranges of conductivity. Similar to flow through anion exchange chromatography, HPTFF may require batch or in-line dilution on the load. If formulation in a high conductivity buffer is required, HPTFF may be operated using the same buffer at a lower conductivity followed by final conditioning to a higher conductivity formulation.
While HPTFF is selective with regard to both size and charge it may be used to replace chromatographic steps based on other principles. For example, a Protein-A affinity chromatography step was removed from a mammalian cell culture MAb purification process (Protein-A, Cation Exchange, Anion Exchange, and UF) by using Cation Exchange, Anion Exchange, and HPTFF with the same final product purity. In another example a hydrophobic interaction chromatography (HIC) step was removed from an e.coli Fab'2 purification process (last two steps HIC + UF) by using HPTFF. Product purity was the same in both cases and the HPTFF process increased yields by 12%.
A comprehensive review of HPTFF will be provided with emphasis on technology development, process applications, and process optimization.