Protein aggregation in self-lubricating piston pumps: The impact of sustained shear stress.

Inherent protein particles (IPP) in injectable biopharmaceutical products can compromise product stability and safety. Hydrodynamic forces during low‑volume aseptic filling have been suggested as a contributor to IPP formation, but the mechanisms, particularly in self‑lubricating piston pumps, are not well defined. We have systematically analyzed the working principle of these pumps and used an insulin analogue formulation to understand the root cause for protein aggregation cases reported in this type of system, focusing on the role of high shear forces as a main driving mechanism. Our work suggests that sustained exposure to mechanical forces in confined pump clearances can contribute to IPP formation for susceptible protein formulations. While routine single‑pass filling is unlikely to reproduce the extreme recirculation conditions tested here, the results highlight the importance of early screening for sensitivity to prolonged low‑to‑moderate shear, attention to pump design and operating modes, and targeted process controls to mitigate localized aggregation risk. Further targeted studies are needed to quantify clearance gap residence times, isolate interfacial versus shear effects, and define practical engineering and formulation strategies to prevent IPP formation.