Co-current filtrate flow in TFF perfusion processes: Decoupling transmembrane pressure from crossflow to improve product sieving Patrick Romann1,2, Philip Giller1, Antony Sibilia3, Christoph Herwig2, Andrew L. Zydney4, Arnaud Perilleux5, Jonathan Souquet5, Jean-Marc Bielser5, and Thomas K. Villiger1*1Institute for Pharma Technology, School of Life Science, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland2Research Division Biochemical Engineering, Institute of Chemical Environmental and Bioscience Engineering, Vienna University of Technology, Austria3Levitronix GmbH, Zürich, Switzerland4Department of Chemical Engineering, The Pennsylvania State University, University Park, 16802 Pennsylvania, USA5Biotech Process Science, Merck Serono SA (an affiliate of Merck KGaA, Darmstadt, Germany), Corsier-sur-Vevey, Switzerland *To whom correspondence should be addressed: Email: thomas.villiger@fhnw.ch