Conclusion

This study evaluated the impact of co-current filtrate flow on product retention during steady-state perfusion processes using hollow fiber modules as cell retention devices. Whereas Starling recirculation in TFF and alternating crossflow TFF is dependent on crossflow velocity and filter module characteristics, co-current filtrate flow enabled independent control of Starling recirculation. Pressure characterization studies performed by inserting additional pressure sensors along the filter module length revealed detailed insights into the filtrate pressure gradient and confirmed the theoretical concept of altering TMP by co-current filtrate flow. Further, control of Starling flow was not only demonstrated at lab-scale, but also successfully applied to a manufacturing scale filtration module. The benefits of HPTFF operation or precisely controlling the direction and intensity of Starling recirculation in scTFF operation was further demonstrated in steady-state perfusion cell culture processes which showed much higher product sieving compared to standard TFF operation. Starling flow control enabled by co-current filtrate flow operation represents an effective tool not only to study filter fouling, but also to reduce product retention in steady-perfusion cell culture processes as well as other operations such as dynamic perfusion or N-1 perfusion.