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Tangential flow filtration is advantageous for bioreactor clarification as the permeate stream could be introduced directly to the subsequent product capture step. However, membrane fouling coupled with high product rejection has limited its use. Here, the performance of a reverse asymmetric hollow fiber membrane where the more open pore structure faces the feed stream and the barrier layer faces the permeate stream has been investigated. The open surface contains pores up to 40 μm in diameter while the tighter barrier layer has an average pore size of 0.4 μm. Filtration of Chinese hamster ovary cell feed streams has been investigated under conditions that could be expected in fed batch operations. The performance of the reverse asymmetric membrane is compared to that of symmetric hollow fiber membranes with nominal pore sizes of 0.2 and 0.65 μm. Laser scanning confocal microscopy was used to observe the locations of particle entrapment. The throughput of the reverse asymmetric membrane is significantly greater than the symmetric membranes. The membrane stabilizes an internal high permeability cake that acts like a depth filter. This stabilized cake can remove particulate matter that would foul the barrier layer if it faced the feed stream. An empirical model has been developed to describe the variation of flux and transmembrane pressure drop during filtration using reverse asymmetric membranes. Our results suggest that using a reverse asymmetric membrane could avoid severe flux decline associated with fouling of the barrier layer during bioreactor clarification.

 

Tangential flow filtration (TFF) has many advantages for bioreactor harvesting, as the permeate could be introduced directly to the subsequent capture step. However, membrane fouling has limited its widespread use. This is particularly problematic given the high cell densities encountered today. Here, a reverse asymmetric membrane, where the more open surface faces the feed stream and the tighter barrier layer faces the permeate stream, has been investigated. The open surface contains pores up to 40 μm in diameter while the tighter barrier layer has an average pore size of 0.4 μm. Filtration of yeast suspensions has been conducted under a range of conditions. The yeast cells are trapped in the open pore structure. The membrane stabilizes an internal porous cake that acts like a depth filter. This stabilized cake layer can remove particulate matter that would foul the barrier layer if it faced the feed stream. As filtration continues, a surface cake layer forms on the membrane surface. A resistance in series model has been developed to describe the permeate flux during TFF. The model contains three fitted parameters which can easily be determined from constant pressure normal flow filtration experiments and total recycle constant flux TFF experiments. The model can be used to estimate the capacity of the filter for a given feed stream. Our results suggest that using a reverse asymmetric membrane could avoid severe flux decline associated with fouling of the barrier layer during bioreactor harvesting.

 

Regulatory authorities place stringent guidelines on the removal of contaminants during the manufacture of biopharmaceutical products. Monoclonal antibodies, Fc-fusion proteins, and other mammalian cell-derived biotherapeutics are heterogeneous molecules that are validated based on the production process and not on molecular homogeneity. Validation of clearance of potential contamination by viruses is a major challenge during the downstream purification of these therapeutics. Virus filtration is a single-use, size-based separation process in which the contaminating virus particles are retained while the therapeutic molecules pass through the membrane pores. Virus filtration is routinely used as part of the overall virus clearance strategy. Compromised performance of virus filters due to membrane fouling, low throughput and reduced viral clearance, is of considerable industrial significance and is frequently a major challenge. This review shows how components generated during cell culture, contaminants, and product variants can affect virus filtration of mammalian cell-derived biologics. Cell culture-derived foulants include host cell proteins, proteases, and endotoxins. We also provide mitigation measures for each potential foulant. 

One major challenge in the development of nanoparticle-based therapeutics, including viral vectors for the delivery of gene therapies, is the development of cost-effective purification technologies. The objective of this study was to examine fouling and retention behaviors during the filtration of model nanoparticles through membranes of different pore sizes and the effect of solution conditions. Data were obtained with 30 nm fluorescently labeled polystyrene latex nanoparticles using both cellulosic and polyethersulfone membranes at a constant filtrate flux, and both pressure and nanoparticle transmission were evaluated as a function of cumulative filtrate volume. The addition of NaCl caused a delay in nanoparticle transmission and an increase in fouling. Nanoparticle transmission was also a function of particle hydrophobicity. These results provide important insights into the factors controlling transmission and fouling during nanoparticle filtration as well as a framework for the development of membrane processes for the purification of nanoparticle-based therapeutics. 

Mixed-matrix electrospun membranes were developed to investigate ammonium removal from low ammonium concentration wastewaters for the first time. Particles derived from the inexpensive zeolite 13X were successfully incorporated into polyethersulfone (PES) matrices. The fabricated mixed-matrix electrospun membranes demonstrate high ammonium removal capacity reaching over 55 mg/gzeolite, more than 2.5 times higher than the previously fabricated mixed-matrix membranes via non-solvent induced phase inversion. Moreover, the membranes fabricated exhibit high permeability and ease of regeneration. Over 90% of total ammonium nitrogen (TAN) can be removed from low TAN wastewaters such as aquaculture wastewaters. In addition to zeolite 13X, other zeolite particles including zeolite Y, zeolite 3A and 4A were also incorporated into the membrane matrix. The inexpensive zeolite 13X show the highest ammonium exchange capacity. Particle type, loading and the level of its dispersion all affect TAN removal capacity.