An automated microscale bioprocessing platform for membrane filtration processes was
established to identify key process issues early and aid the rapid design of robust and
scaleable filtration processes. To demonstrate the utility of this platform, it was used to
investigate the impact of upstream operations on microfiltration performance. The
primary recovery of humanised antibody Fab’ fragments from Escherichia coli
(supplied courtesy of UCB Celltech) were used as a case study to evaluate the
microfiltration methodologies and devices created in this work.
Initially, the methodology associated with the microscale dead-end filtration device
previously created and investigated by Jackson et al. (2006) has been improved by
reducing the required volume by 50% (~500 \mu L). This improved method demonstrated
reproducibility and sensitivity to changes in feed preparation. The method was then
applied in the study of the influence of various cell disruption operations on subsequent
solid-liquid separation and hence, Fab’ product recovery. Results showed that the heat
extracted cells showed better dead-end microfiltration performance in terms of
permeate flux and specific cake resistance. In contrast, the cell suspensions prepared by
homogenisation and sonication showed more efficient product release but with lower
product purity and poorer microfiltration performance. Having established the various
microscale methods, the linked sequence was automated on the deck of the Tecan™
robotic platform and used to illustrate how different conditions during thermo-chemical
extraction impacted on the optimal performance of the linked unit operations of product
release by extraction and subsequent recovery by microfiltration.
The microscale approach was then extended for crossflow operations. A microscale
crossflow filtration device was designed to enable integration also within the Tecan™
platform for automated processing. The device has an effective membrane area of
0.001 m2, which is a hundred-fold smaller than the larger scale Pellicon-2™ membrane
module used for scale translation studies, and has two independent membrane channels
for parallel analysis. The device was first characterised by determining the normalised
water permeability (NWP) of a Poly(vinylidene fluoride) membrane and compared this
with the NWP of the membrane by dead-end filtration. NWP is an inherent membrane
property and as expected, the NWP values derived from crossflow filtration
experiments match the values derived from dead-end filtration to within 90%. For scale
translation studies, two types of feeds were used: a model feed, which is resuspended
active dry yeast and Bovine Serum Albumen in phosphate buffer, and the antibody
fragment expressing E. coli strain. Results showed, that at matched optimal shear rates
and transmembrane pressure, the percentage differences between microscale and large
scale values were up to ± 25% for the permeate flux, ± 10% for Fab’ and total protein
yields. These scale-up predictions were achieved with a ten-fold reduction in feed
material requirement for crossflow operation.
Overall, the results illustrate the power of microscale techniques to identify and enable
the understanding of key process performance attributes in a bioprocess sequence. The
broader implications derived from using these microscale membrane devices, further
applications and recommendations for future research are also discussed
