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.
Lewis et al. (Tue,) studied this question.