Transmembrane pressure evolution during constant flux SPTFF – a comparison of two proteins

Single-pass tangential flow filtration (SPTFF) is an enabling technology for continuous bioprocessing, but its performance can be limited by membrane fouling at high protein concentrations. In this work, we investigate fouling mechanisms and critical flux using whey protein isolate (WPI) as a model protein and compare the results to a monoclonal antibody (mAb). Batch tangential flow filtration (TFF) experiments were performed under flux-stepping and pressure-stepping conditions to determine the critical flux of both protein systems over a range of concentrations. The critical flux declined significantly with increasing feed concentration for both WPI and mAb solutions, in agreement with the concentration polarisation model. Despite structural and molecular size differences between WPI and the mAb, their critical flux behaviour and gel concentration were remarkably similar, supporting the use of WPI as a surrogate in early-stage studies. The translation of batch TFF findings to SPTFF was also assessed. At low fluxes, fouling was dominated by a pore blocking mechanism. At higher fluxes, fouling severity increased beyond the critical flux, as concentration polarisation and cake layer formation became dominant. The data could be fitted to Hermia’s blocking laws, but more sophisticated models are needed to account for the changes in protein concentrations over both time and membrane length during the initial periods of operation. Overall, this study highlights both the strengths and limitations of WPI as a model protein and provides guidance for optimizing filtration strategies in therapeutic antibody manufacturing. • Concentration polarisation model shows similar results for whey proteins and a monoclonal antibody • Batch critical flux data predicts fouling onset in constant flux SPTFF • Changes in transmembrane pressure predicted by pore blockage and cake filtration models • Whey protein is validated as a low-cost surrogate in early SPTFF fouling studies