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Cynthia A. Challener, PhD, is a contributing editor to BioPharm International.
Single-use and single-pass TFF devices are facilitating advances in biopharma manufacturing.
Purification and concentration of bioprocess fluids are crucial steps in biopharmaceutical manufacturing. Normal-flow filtration (NFF), or dead-end filtration, involves passage of the fluid through a filter made of materials ranging from paper and glass fibers to membranes. These filters typically are used only for removal of undesired contaminants. Tangential-flow filtration (TFF), which involves gently sweeping the bioprocess fluid tangentially along the surface of a semi-permeable membrane, allows for collection and use of both the retentate and the permeate and can thus be used in more biomanufacturing operations. As a result, TFF is used today for both upstream and downstream processing of most biologic drugs.
The need to reduce costs and speed product development, combined with the shift in focus from blockbusters to orphan drugs; the rapid advancement of personalized medicines based on next-generation therapeutics; and growing interest in continuous processing have together driven membrane/equipment providers to introduce enhanced TFF devices that facilitate flexible, low-cost biomanufacturing.
There are many different unit operations for which TFF has been proven useful, including cell harvesting and clarification in upstream perfusion processes and concentration, diafiltration (buffer exchange), and purification (product fractionation) via removal of various types of contaminants based on molecular size, which are common downstream processes. Most biologic drug substances, including monoclonal antibodies, recombinant proteins, vaccines, antibody conjugates, and next-generation products such as cell and gene therapies and nanoparticles, can be processed using TFF.
All unit operations are relevant because, by using TFF, the efficiency of the overall manufacturing processes and purity/concentration of biologic drug substances are improved, according to David Serway, vice-president of business development with Spectrum Laboratories.
“These applications are critical for meeting the stringent requirements for efficacy and safety of biopharmaceuticals,” states Andrew Bulpin, head of process solutions at MilliporeSigma, Ultimately, according to Kevin Marino, global product manager for continuous filtration with Pall Life Sciences, TFF technology helps ensure that final drug product is at the appropriate concentration and formulation for patient delivery.
The purification of biomolecules generally involves several tangential and/or normal flow filtration steps combined with chromatographic separations. Both filtration technologies purify bioprocess solutions by removing contaminates with a fixed porous medium, yet each format has unique advantages, according to Amit Sharma, an application scientist with GE Healthcare Life Sciences.
There are, he adds, three main differences between TFF and NFF: TFF filters are exclusively membranes, while NFF filters can be constructed of a variety of materials; TFF supports recirculation of the retentate solution, while the feed in NFF typically passes through the filter only once; and in TFF, the retentate remains a solution, allowing for direct recovery, whereas in NFF, solids are typically collected on the filter and must be resuspended for further processing.
In the majority of TFF applications, the product stays upstream of the membrane and passes over it multiple times until the desired concentration or buffer composition is achieved. An optimal pressure, referred to as the transmembrane pressure, is determined and maintained, allowing a large volume to be processed using an optimal membrane surface area, according to Serway. “This process allows achievement of a high concentration of the product without plugging the membrane or diafiltration without loss of any product,” Bulpin notes. Serway further points out that the design enables linear scale up; processes at the lab that are scaled to production volumes can be operated under similar conditions without the need to reinvestigate the operating conditions as long as the process material has not changed.
“Given these differences, NFF is used when clarification and/or bio-burden reduction is desired in relatively low-solid streams, for protecting or enhancing downstream operations, or when final polishing is required to achieve sterility. TFF is best suited for higher-solids, more viscous feed solutions, and/or where concentration or purification of cells or target species is desired,” Sharma observes. Bulpin adds that the process and economic benefits of TFF make it a necessary step in the manufacture of virtually all biopharmaceuticals.
Evolution in the biopharmaceutical market today is evidenced by the increasing numbers of biosimilars under development and the shift toward novel, next-generation therapies as alternatives to conventional monoclonal antibodies. “As a result, today there is greater need for higher and more effective facility utilization due to relentless cost pressures and, simultaneously, a growing requirement for drugs to be released more quickly to the market with short turn-around times,” Sharma observes. Several advances in TFF technology have helped answer the industry need for speed to market, novel therapies, and faster and more economical processing, according to Bulpin.
Single-use TFF assemblies and systems are one notable development. With disposable flow paths, single-use systems help minimize the risk for cross-contamination and reduce the time spent on cleaning and sanitization, according to Sharma. “Turnaround time between batches or products is improved and uptime is maximized, facilitating multiproduct and flexible manufacturing,” he notes.
Single-use TFF systems also facilitate the adoption of continuous manufacturing, such as perfusion processes, for which TFF is employed in continuous cell harvesting and clarification. “Although perfusion technology has been around for decades, the need to find more effective ways to reach extremely high cell densities and enable more efficient and flexible manufacturing has led to a surge in interest in continuous processing. Single-use TFF systems are ideally suited for continuous cell culture,” Serway explains.
Single-pass TFF (SPTFF) has also emerged as a critical enabler of intensified (faster, smaller, less expensive) processing, according to Bulpin. “Conventional TFF requires the fluid to be recirculated, typically for several hours, and the concentrated product is recovered from the feed tank and system at the end of the process, often resulting in less-than-desirable product yield due to inadequate recovery from the system/tank or product loss due to foaming, denaturization, or aggregate formation,” Marino says. “SPTFF allows for concentration with one pump pass and a single pass through the system using 5-10X lower feed flow rates compared to conventional TFF, resulting in smaller line sizes, significantly reduced hold up volumes, and subsequently increased product yield,” he adds.
In addition, the retentate is collected at the desired concentration throughout the process, eliminating the need to accumulate a batch, making it ideal for continuous bioprocessing. For instance, SPTFF enables ultrafiltration/diafiltration (UF/DF) in a continuous processing mode, according to Marino. Pall has an exclusive license to this patented SPTFF technology.
Other noteworthy advances in TFF technology, according to Bulpin, include TFF devices that are specifically designed for high-viscosity processing, allowing the production of drug formulations suitable for injection. Improvements in TFF manufacturing processes have also made it possible to produce membranes with better-defined pore sizes, leading to improved process yields and filtration selectivity.
Given the constant evolution of the biopharmaceutical manufacturing industry and thus biomanufacturing, processing technologies must also constantly evolve. For TFF, the strong demand for single-use technologies and the emergence of novel therapeutic molecules requiring enclosed processing (e.g., antibody-drug conjugates) highlighted the limitations of the conventional open, flat-sheet cassette design, according to Bulpin. “We expect increased use of fully enclosed TFF devices that still offer the scalability and performance of cassettes,” he states.
For Bulpin, one exciting solution in development is an enclosed, high-performance TFF device format that does not require external holders for use, thus dramatically simplifying installation and removal. The new enclosed devices also come pre-sterilized, thus eliminating the need for flushing of storage solutions and sanitization, thereby significantly reducing cleaning time and buffer usage.
Serway would like to emphasize the advances in TFF devices using hollow fibers with the design needed to more effectively handle bioprocess fluids containing nanoparticles and cells, such as Spectrum’s 3D TFF (TFDF) device for cell-perfusion applications. “In addition to being pre-sterilized, hollow fibers perform under lower pressures and are easier to set up/use compared to cassette technology. They also outperform other TFF technologies due to their flow dynamics,” he explains.
Both Sharma and Marino are interested in developments that further facilitate continuous processing. “With bioreactor output increasing 5-10X in terms of volumetric productivity and titers, the same cell culture capacity is now being reached in a fraction of the floor space and is acting as a constraint for further processing. Current TFF technology can be improved upon to be used in perfusion mode so that high product quality/quantity can be achieved by maintaining homogeneity, providing for complete glycosylation, avoiding aggregate formation and deterioration, and enabling the use of low expression systems during development,” he explains.
Sharma further asserts that “continuous manufacturing is the new vision in biomanufacturing, so molding TFF to adapt to the continuous scenario is the new challenge.” To address this need, GE introduced AKTA readyflux, a single-use, automated TFF system that reduces operator dependency and adds consistency to the process.
Diafiltration is one important gap in the technology portfolio for a truly continuous bioprocess, according to Marino. Pall is currently developing a product to address this need. “The Cadence Inline Diafiltration device addresses this gap for the biopharmaceutical industry by completing the product/technology offering for the realization of continuous final formulation and brings manufacturers another step closer to the realization of an end-to-end integrated continuous bioprocessing platform,” he says.
In fact, one of the biggest applications for TFF in the future will be in continuous processes. “I expect the use of SPTFF to become more widespread as the shift to continuous processing takes place,” Marino states. “Single-use TFF will be the future for clarification and concentration as an alternative to centrifugation in continuous bioprocessing, reducing capex expenses and improving process economies, as well as conserving water and reducing cleaning and validation costs,” agrees Sharma.
Bulpin adds that “fully enclosed, single-use TFF assemblies have the potential to dramatically change the way the technology is used in clinical and small manufacturing scale.” He also expects continued strong interest in using TFF for high viscosity formulations. There will also be a need for smaller-scale TFF devices than what is currently available in a truly scalable format for the processing of drugs for smaller population diseases and cell therapies, where the volume of product available for process development is too small for the existing TFF devices, according to Marino.
Volume 30, Number 9
When referring to this article, please cite it as C. Challener, “Singular Developments Advance TFF Technology," BioPharm International 30 (9) 2017.