Perfusion

means cell or biomass retention, generally performed in continuous cultivation mode (see continuous processes). It is possible to work with dilution rates higher than the maximal specific growth rate. Thereby, up to 10-fold higher cell concentrations with higher product concentrations can be reached in a reduced working volume compared to feeding processes ^{42, 43}. Perfusion processes, however, are more complex in both implementation and admission.

Perfusion can be implemented externally with single-use systems (centrifuges, hollow-fiber modules, TFF cassettes, ATF-modules) in combination with single-use stirred bioreactors and wave-mixed bioreactors. In addition, an internal perfusion with hollow-fiber bioreactors, wave-mixed bioreactors with special perfusion bags (with integrated membranes), fixed-bed bioreactors with macrocarriers as well as single-use bioreactors with microcarriers can be run. See crossflow filtration.