Tangential Flow Filtration: A Complete Guide for Bioprocessing Professionals

Tangential Flow Filtration (TFF) is a method of separating, purifying, and concentrating therapeutic biomolecules. This method is applied by the feed solution flowing parallel (or tangentially) across the membrane surface instead of directly through it. This tangential flow generates a sweeping or lifting force at the membrane surface that picks the retained material up and allows it to flow out of the retentate end of the filter device rather than leaving it deposited as a fouling layer. This effective method of filtration allows large and small volumes to be processed with less membrane surface area and lower risk of filter fouling than normal flow filtration (or dead-end filtration). It enables recovery of both the retentate and permeate as well as the possibility of rinsing and reusing membranes.

Flat Sheet Cassettes

Constructed by several layers of membrane stacked on top of one another with a woven mesh screen in-between the layers, flat sheet cassettes are ideal for processes that demand higher flux. As product flows through each of the mesh layers, the feed is forced into a turbulent flow. The advantage of turbulent flow is that it enhances the sweeping of the membrane surface and prevents material from building up and fouling the filter. Non-enveloped viruses such as AAV (Adeno-associated virus) are less sensitive to shear forces and benefit from the higher flux of a flat sheet cassette within TFF.

Hollow Fiber Modules

Made up of a simpler flow geometry than the flat sheet cassette. Hollow fiber modules are cylindrical structures that house a bundle of tubular self-supporting fibers. With this format, the feed travels through the hollow fiber lumen in a very laminar flow, resulting in lower shear and gentler processing. This makes hollow fiber modules an ideal option for enveloped viruses like lentivirus that are more shear sensitive.

The efficiency of TFF performance is a balancing act of finding the correct membrane chemistry and format, and the right combination of transmembrane pressure (TMP) and cross flow flux (CFF) rates. How accurately the pressure and flow rates can be measured and controlled has a direct impact on the performance and efficiency of your TFF process. If the TMP is too high then the gel layer formed on the membrane becomes too dense, severely restricting the flow to the permeate. If CFF is too high, more molecules will pass through the retentate reducing permeate flow, resulting in extended processing times that could jeopardize the end product. Additionally, an improper pairing of the pump’s flow rates with the tubing inner diameter (ID) and strength can cause cavitation or fluid velocities which can damage product. For these reasons and more, selecting the right TFF system and membrane are key to optimizing microfiltration, ultrafiltration, and diafiltration (UF/DF) performance.

The typical manual or semi-automated TFF set-up consists of pumps, scales, pressure gauges, manual valves, sensors, tubing, and vessels. Usually sourced across various suppliers, manual TFF also requires the integration and, perhaps, validation of these components prior to engaging in any unit operations.

Beyond set-up, the biggest challenge with manual TFF processing is the burden it places on the operator. Continuously monitoring to maintain the set-up, ensure consistency across all process parameters, intervene when needed, and manually document all data points puts a strain on the user. Moreover, all of these manual steps present opportunities for operational errors and compromised data integrity, which can result in extended process development, batch inconsistencies, or scale-up challenges.