Ralf Kuriyel

High performance tangential flow filtration

Conventional tangential flow filtration (TFF) has traditionally been limited to separation of solutes that differ by about ten-fold in size. Wide pore-size distributions, membrane fouling, and concentration polarization phenomena have commonly been cited as reasons for this limitation. The use of TFF in the biotechnology industry has therefore been restricted to cell-protein, virus-protein, and protein-buffer separations. A multi-disciplinary team with industrial and academic members was formed to overcome these limitations and enable protein-protein separations using High Performance TFF (HPTFF) systems. Pore-size distributions have been improved with the development of new membrane formulation and casting techniques. Membrane fouling has been controlled by operating in the transmembrane pressure-dependent regime of the filtrate flux curve and by carefully controlling fluid dynamic start-up conditions. Concentration polarization was exploited to enhance, rather than limit, the resolution of solutes. Concentration polarization has also been controlled by operating a co-current filtrate stream that maintains transmembrane pressure constant along the length of the TFF module. High yields and purification factors were obtained even with small differences in protein sieving. IgG-BSA and BSA monomer-oligomer mixtures have successfully been separated with these systems. HPTFF technology provides a competitive purification tool to complement chromatographic processing of proteins.

A new coiled hollow-fiber module design for enhanced microfiltration performance in biotechnology

The microfiltration performance of a novel membrane module design with helically wound hollow fibers is compared with that obtained with a standard commercial-type crossflow module containing linear hollow fibers. Cell suspensions (yeast, E. coli, and mammalian cell cultures) commonly clarified in the biotechnology industry are used for this comparison. The effect of variables such as transmembrane pressure, particle suspension concentration, and feed flow rate on membrane performance is evaluated. Normalized permeation fluxes versus flow rate or Dean number behave according to a heat transfer correlation obtained with centrifugal instabilities of the Taylor type. The microfiltration performance of this new module design, which uses secondary flows in helical tubes, is significantly better than an equivalent current commercial crossflow module when filtering suspensions relevant to the biotechnology industry. Flux and capacity improvements of up to 3.2-fold (constant transmembrane pressure operation) and 3.9-fold (constant flux operation), respectively, were obtained with the helical module over those for the linear module.

High-performance tangential flow filtration: a highly selective membrane separation process☆

Abstract High-performance tangential flow filtration (HPTFF) is a new technology for protein and nucleotide purification. Conventional ultrafiltration (UF) is limited to separation of solutes that differ by tenfold in size. HPTFF is a two-dimensional purification method that exploits differences in both size and charge characteristics of biomolecules. It is hence possible to separate biomolecules with the same molecular weight. It is even possible to retain one biomolecule while passing a larger molecular weight species through the membrane. Current processes often use ion-exchange chromatography, UF and size exclusion chromatography (SEC) in three separate steps for purification, concentration and buffer exchange. HPTFF makes it possible to perform all of these steps in a single-unit operation, thereby reducing production costs. HPTFF uses the same linear scale-up principles already established for UF. Since HPTFF builds on existing UF technology, there is already a well-established industrial infrastructure in place for implementation of HPTFF processes. HPTFF can provide high-resolution purification while maintaining the inherent high throughput and high yield characteristics of conventional UF. HPTFF can therefore be used in initial, intermediate, and final purification stages. This presentation overviews the key aspects of this technology in terms of operation and optimization and reviews several real-world separations in biotechapplications such as IgG and monoclonal antibodies.

Internal virus polarization model for virus retention by the Ultipor® VF Grade DV20 membrane

Several recent studies have reported a decline in virus retention during virus challenge filtration experiments, although the mechanism(s) governing this phenomenon for different filters remains uncertain. Experiments were performed to evaluate the retention of PP7 and PR772 bacteriophage through Ultipor VF Grade DV20 virus filters during constant pressure filtration. While the larger PR772 phage was fully retained under all conditions, a 2‐log decline in retention of the small PP7 phage was observed at high throughputs, even under conditions where there was no decline in filtrate flux. In addition, prefouling the membrane with an immunoglobulin G solution had no effect on phage retention. An internal polarization model was developed to describe the decline in phage retention arising from the accumulation of phage in the upper (reservoir) layer within the filter which increases the challenge to the lower (rejection) layer. Independent support for this internal polarization phenomenon was provided by confocal microscopy of fluorescently labeled phage within the membrane. The model was in good agreement with phage retention data over a wide range of phage titers, confirming that virus retention is throughput dependent and supporting current recommendations for virus retention validation studies. These results provide important insights into the factors governing virus retention by membrane filters and their dependence on the underlying structure of the virus filter membrane.

A liquid porosimetry technique for correlating intrinsic protein sieving: Applications in ultrafiltration processes

Abstract The understanding of variation in sieving properties of membranes is of great importance for the successful development of ultrafiltration applications. A liquid porosimetry technique is presented to quantify the sieving variation among several polyethersulfone ultrafiltration membranes. Observed sieving coefficients were measured with proper precautions taken to control and minimize fouling. These data were translated to intrinsic sieving coefficients using a stagnant film model. The intrinsic membrane sieving coefficient correlated well with the liquid porosimetry data. This liquid porosimetry technique can distinguish between membranes of different molecular weight cut-off and is sensitive enough to capture slight changes in the sieving coefficient of variants of the same cut-off membrane. This technique has several attractive features: it is non-destructive, independent of the module configuration and relatively simple to perform. Two potential applications of this technique are also examined: (1) quantification of the effect of membrane variation on high performance tangential flow filtration (HPTFF) for protein separations and (2) development of a membrane integrity test to ensure batch-to-batch consistency. This technique has the potential for use in membrane quality control, membrane selection, and validation of industrial ultrafiltration processes.