Electrorheoimaging Helps Manage Droplet Viscosity in Real-Time

A new technique combined with changes in material design is making reversible viscosity modulations possible, according to researchers from the University of Guelph in Ontario, Canada.

By connecting electrorheological properties to microscopic behaviors, biopharmaceutical manufacturers can simultaneously view real-time changes in emulsion microstructures and measure viscosity. Seeing droplet clustering, alignment, chaining, or breakup under electrorheological stress isn’t possible with traditional rheology. In practical terms, this still-experimental technique enables microfluidic droplets and droplet atomization, for example, to be controlled using electric fields.

Potential applications in biopharmaceutical manufacturing include mixing and blending, pumping and filtration, ultrafiltration, and filling. It may also improve injectable administration without harming stability.

Electrorheoimaging (ERI) builds on traditional rheology, which deals with the deformation and flow of liquids and other forms of matter. This new technique combines electrical forcing, rheological response, and imaging, co-authors Majid Bahraminasr, PhD, post-doctoral scholar, and Anand Yethiraj, PhD, professor, University of Guelph, explain in a recent paper.

In investigating the effects of direct currents on emulsions, Bahraminasr and Yethiraj found a “striking rheological response, previously unreported.” They noted “shear thinning and decreased intrinsic viscosity on one hand, and the emergence of field-induced bands in the spatial structure of the sheared emulsion, on the other.”

For alternating current, “Electrohydrodynamics is strongly frequency dependent,” they point out, adding that viscosity weakened as the electrical frequency increased.

When combined with a continuous phase that lowers electrohydrodynamic thresholds—an emulsion of castor oil dispersed in motor oil, in this research—the scientists were able to use an electric field to cause the emulsion to change viscosities instantly within a 30-fold range. Notably, viscosity could increase as well as decrease, and even “reduce viscosity below its quiescent, field-off state,” they report.

This suggests that this technique may be used to create a reversible viscosity switch that may be activated simply by tuning the frequency of the applied electrical field.

Unusual, but valuable

Although electrical field modulation is not a typical feature of biomanufacturing, it may help biopharmaceutical developers gain insights into energy dissipation, pattern formation, and nonequilibrium steady states in driven fluids.

For mAb manufacturing, therefore, applying ERI could help biopharmaceutical manufacturers:

• Optimize processes for scale-up
• Predict process behavior
• Link bulk viscosity increases to specific microstructural events
• Temporarily reduce viscosity during manufacturing
• Restore stability post-processing
• Inform excipient strategies

This work appears to be relevant to protein-based therapeutics, including mAbs, which often exhibit non-Newtonian rheology properties such as formation of submicrometer aggregates that complicate mixing, pumping, filtration, filling, and syringe usage, or that compromise product stability and ease of administration. “It also helps detect artifacts, such as bubbles, that could distort measurements,” the authors point out.

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