Alternating Tangential Flow (ATF)-modules
allows biomass and/or product to be restrained by alternating tangential flow technology (a special filtration technology developed by the company Repligen, formerly Refine) after being coupled to a bioreactor. The ATF-module uses a diaphragm pump to suck the cell containing culture broth from the bioreactor through a hollow fiber module and back to the bioreactor using the same route. This leads to a varying direction of medium flow through the filter membrane, causing cells settled on the hollow fiber module to be washed off as cell-free medium passes through. The alternating tangential flow is responsible for a reduced deposition of material on the membrane (fouling) and blocking (clogging) of the membrane 11. In recent years, ATF-modules have been applied with stirred or wave-mixed bag bioreactors when realizing concentrated fed-batch processes or perfusion. A single-use model of an AFT-module is commercially available. See crossflow filtration.