Tangential flow filtration cell separations

Filtration can be used to separate cells or cell debris, concentrate cells or protein solution, and remove or exchange salts. Two broad categories of filtration are conventional dead-end filtration, where fluid flow is normal to the plane of the membrane, and cross-flow filtration (or tangential flow filtration), where the fluid flows parallel to the membrane surface. 

Tietjen, K. G. Hunkier, D. Matem, U. "Differential Response of Cultured Parsley Cells to Elicitors from Two Non-pathogenic Strains of Fungi, 1. Identification of Induced Products as Coumarin Derivatives" Eur. ]. Biochem. 1983,131, pp 401-407. Devereux, N. Hoare, M. Duimill, P. "Membrane Separation of Protein Precipitates Unstirred Batch Studies" Biotech, and Bioeng. 1986, 28, pp 88-96. Mateus, M. Cabral, J. M. S. "Recovery of 6-a-methylprednisolone from biotransformation medium by tangential flow filtration" In Bioprocess Engineering. 1989, Springer Verlag, (in press). 

Practical Aspects of Tangential Flow Filtration in Cell Separations... 

Figure 3. Simplified cell separation schematic of tangential flow filtration system.

Applications Of Tangential Flow Filtration In Cell Separation... 

Currently, there are many examples of cell processing in the industrial environment using tangential flow filtration. To illustrate the breadth of microbial types which may be processed by this technology, we will discuss three applications which have been in routine operation under production conditions. The applications include cell/growth medium separations directly from fermentors (Escherichia coli and Mycoplasma species) and the concentration/washing of influenza virus used in the production of flu vaccines. 

It was the object of this presentation to outline some of the key parameters which are evaluated during the application of tangential flow filtration for cell separations. A throrough understanding of what is required from the separation is an essential first step. 

Quirk AV, Woodrow JR (1983) Tangential flow filtration - a new method for the separation of bacterial enzymes from cell debris. Biotechnol Lett 5(4) 277-282 Raghavarao KSM, Ranganathan. STV, Srinivas ND et al. (2(X)3) Aqueous two phase extraction-an environmentally benign technique. J Qetm Technol Environ Pol 5(2) 136-141 Raimbault M (1998) General and microbiologictil aspects of solid substrate fetmentation. Electron J Biotechnol 1(3) 174-188... 

Filtration systems used for sterilization (membrane filters) can be used to separate cells from the supernatant but only for relatively small volumes as they do rapidly become clogged, and for this sort of volume centrifi ation is usually easier but not as efficient at removing small cell debris. Tangential flow filtration is used to reduce problems of filter blockage by continuous recirculation of the suspension across the membrane, and is recommended for larger volumes (several litres). Low volume systems are available from recognized filtration suppliers (e.g. Millipore, Sarstadt, Pall). Filtration systems have been reviewed (43). 

Microfiltration. Microfiltration, the use of tangential flow anisotropic membranes to permeate the product of choice while retaining solids, can be an attractive cell separation technique because it does not require the use of flocculants or filter aids. It is, in principle, a more technically sophisticated version of classic dead-end filtration processes. Microfiltration yields can be low due to progressive fouling of membranes. Advanced engineering has overcome many of the early... 

The concentration of viruses in water is much lower than that of bacteria therefore their preconcentration and separation from other suspended matter is important in virological analysis. Viruses may be enriched by UF by use of tangential-flow or hollow-fiber filtration units most suitable for preconcentration from large-volume water samples. Another possibility consists in adsorption of the viruses on the microfilter matrix followed by elution with diluents containing cell extracts, serum, or surfactants. 

Consider a typical antibiotic production process, as illustrated in Figure 11.1.1. The antibiotic is present in a fermentation broth as a very dilute solution in the presence of considerable soluble impurities, as well as a significant concentration of whole cells and cellular debris. The particulate materials, such as whole cells, cell debris, etc., are removed first by filtration or centrifugation. The filtration method is described under rotary vacuum filtration (Section 7.2.1.5) or microfiltration (Section 7.2.1.4) of the tangential-flow type (TFF). Centrifugation is illustrated in Sections 7.3.2.1 and 7.S.2.2 via different types of centrifuges. This step has heen characterized as removal of insolubles (Belter et al, 1988) - it is essentially separation of cellular particles from a liquid solution of the product. 

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