Clogging model analysis for aggregate-spiked mAb
Evaluation of the filtration behavior for the reference, control, mixed-mode AEX1 output and normal AEX output for aggregate-spiked mAb solutions in Figure 1 with each of the four clogging models is shown in Figure 4. The reference solution (no aggregate spike) and the output from mixed-mode AEX1 (complete removal of larger aggregate species) showed good agreement between experimental and calculated values, with plots for all four models being almost entirely identical and overlapping with the plot of experimental results (Figure 4a and 4c). In contrast, the control (aggregate-spiked mAb) and output from normal AEX (minimal aggregate removal) had different plots for each clogging model, and in both of these cases, the standard blocking model plot overlapped the most with experimental values (Figure 4b and 4d).
The calculated k for output from mixed-mode AEX1 and mixed-mode AEX2 was smallest, at around 0.001, followed by reference (no aggregate spike) at around 0.002 (Figure 5a). For these solutions with low proportions of aggregate, k was almost the same for all four clogging models, and all of the clogging models show good agreement with experimental values. On the other hand, the control, output from normal AEX and output from nylon prefilter (all three solutions having relatively high proportions of larger aggregate content) had markedly higher k than column output from mixed-mode AEX (low proportion of aggregate), and the higher the aggregate content, the larger the k. Further, for all three solutions with larger aggregates, the k decreased in the order of cake filtration, intermediate blocking, standard blocking and complete blocking models.
The differences between experimental and calculated values for each solution with all four clogging models in Figure 5b show that for solutions with high aggregate content and high k filtered on a virus filter at constant pressure, the standard blocking model is the best fit. On the other hand, for solutions with low aggregate proportion and small k, there was practically no difference between experimental and calculated values for all four clogging models, and it is suggested that the clogging model results are indistinguishable from each other for solutions with stable filtration behavior without clear clogging for the throughput tested.