Measuring bioprocess shear stress

Researchers from University College London, UK and Cambridge Antibody Technology (CAT) have developed a device to study the stability of monoclonal antibodies when exposed to the shear forces that occur throughout the bioprocess. The latest research published in an early view article in the journal Biotechnology Progress​​ details the development of the device and its use to determine the effects of high shear strain on monoclonal antibodies and other therapeutic proteins. Shear strain forces occur throughout the bioprocess, including during the cell lysis step where cells are disrupted to release the therapeutic proteins they have produced. This step can occur under a variety of conditions, with manufacturers commonly varying the pH, shear stress and residence time to find optimal conditions. "Exposure to high shear during bioprocessing can cause losses in protein stability and lead to aggregation, rendering a product unfit for use,"​ write the authors. According to the authors, the two main aims of the study were to design the rotating-disk shear device to allow them to assess the impact of the high shear strain rates on proteins in the absence of an air-liquid interface and then to study the effects of high shear at the solid-liquid interface. The researchers studied the effects of shear stresses on two IgG4 human monoclonal antibodies provided by CAT and found that exposing the antibodies to high shear stresses over a period of 7 hours led to a reduction of 90 per cent in the amount of monomer. This high level of sample degradation highlights how important it is to minimise the amount of time biological drugs are exposed to shear stress during bioprocessing. Monomer loss was mirrored by an increase in the turbidity of the solution, with the formation of large protein aggregates causing the solution to turn from clear to milky white. Interestingly, the authors note that: "the presence of increasing numbers of large aggregates did no serve to increase the rate of aggregation, which might be expected if a classical orthokinetic aggregation process were occurring."​ They also note that no increase in soluble intermediate aggregates was observed during the study. One possible mechanism suggested by the authors is that the large aggregates form at the solid-liquid interface rather than in the bulk fluid before breaking away from the solid surface and returning to the fluid in suspension.