Optical Coherence Tomography Velocimetry for In-Line Processing of Biologics: Concentrated and Gelling Monoclonal Antibody Solutions

Optical coherence tomography velocimetry (OCTV) was demonstrated
with in-line processing of biologics for the first time. OCTV allowed
the velocity of concentrated monoclonal antibodies (mAbs at 39.5–84.7
mg mL–1) to be probed in 3.4 pL volumes over distances
0–5 mm from the pipe walls. The large penetration depth is
facilitated by the relatively low turbidity of mAbs at near-infrared
wavelengths (1300 nm). The mAb solutions could be concentrated in
situ and the changes to the viscoelasticity measured. Higher concentration
mAb solutions became shear thinning (following the power law fluid
model) and the amplitude of their velocity fluctuations decreased.
Furthermore, dropping the pH of the mAb solutions induced a gelation
phase transition and complex changes to the mAb rheology could be
observed with OCTV e.g. thixotropy and the formation of a stationary
boundary layer. Thus, in situ formulation of mAbs could be explored
with OCTV under industrially relevant conditions.