Figure 4 Concept of stepping co-current TFF (scTFF) by schematic representation of pressure gradient along filter length (A). Co-current flow ramping at 650 mL/min crossflow (B). Vertical dashed lines represent operating conditions for HPTFF (black), scTFF phase 1 with -10 mbar pressure difference (blue) and scTFF phase 2 with +10 mbar pressure difference (red) on filter inlet. Pressure measurements according to their position along the filter length are provided for all three dashed lines (C), grey areas represent absolute fiber length. Operation of scTFF with two alternating phases (±10 mbar pressure difference) is demonstrated by time resolved pressure distribution plots (D). Alternative operating mode of HPTFF with alternating membrane sweeps by scPTFF phases of ± 10 mbar in between HPTFF phases (E). Red areas represent flux of filtrate back into the retentate, blue areas represent flux from retentate to filtrate.