Researchers know that interfacial stress at the air-liquid interface contributes to protein particle formation and release into bulk product during the manufacturing of monoclonal antibodies and other biologics. What’s new is that the order in which biologic drug products experienced hydrodynamic shear and interfacial dilation—both at the interface and in the bulk solution—significantly affects protein concentrations.

“Our work shows that interfacial dilational stress plays a more dominant role [than expected], and that protein solutions subjected to interfacial dilational stress followed by pumping resulted in more protein particles [than] protein formulations that were first pumped and then subjected to [such] stress,” Prajnaparamita Dhar, PhD, director of graduate studies at the University of Kansas, tells GEN.

During manufacturing operations for therapeutics, “Reordering the sequences is not always feasible,” she notes. “However, limiting the exposure time to the air-liquid interface and/or removing the air-liquid headspace could, potentially, decrease protein adsorption and subsequent protein particle formation.

“On the other hand, our results also suggest that for unit operations such as ultrafiltration or diafiltration processes, multiple passes would lead to more protein particle formation. Therefore, biologics manufacturers may consider single-pass purification steps.”

Interface particle formation

In this study, most of the protein particle formation occurred at the air/liquid interface. These surface-mediated particles are more likely than others to become nucleation sites later, when the solution is stressed again. Increasing the pH of the buffer formulation still led to interface-induced particle formation.

The possibility of rupturing the viscoelastic film at the interface, where protein particle networks form, risks causing these particles to shed back into the bulk solution where they may either remain as smaller particles or form potential nucleation sites. Modifying the sequences of steps can significantly reduce protein formation.

In terms of take-home messages, Dhar says, “For protein-only formulations during drug substance manufacturing:

  • “Exposure to, and the subsequent protein adsorption to, the air-liquid interface is the predominant factor leading to increased protein particle formation.”
  • “Exposure to interfacial dilational stress followed by pumping (hydrodynamic shear stress) results in a magnitude-higher increase in protein particle formation than pumping followed by interfacial dilational stress.”
  • Adding surfactant “mitigates protein adsorption to interfaces, greatly decreasing particle formation in the presence of multiple stresses.”

Clearly, Dhar notes, “Avoiding or reducing interfacial dilation stresses is ideal.”

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