Visible and Sub-visible Particle Formation for a Model Bioconjugate

The time-course and extent of visible particle (VP) and sub-visible particle (SVP) formation was monitored as a function of interfacial area (IA) for a model bioconjugate. To facilitate particle formation, the bioconjugate was agitated in a glass vial and exposed to IAs up to 478 mm 2 . Since vials had equal fill and headspace volumes, the area of the air-water interface was varied by placing vials on angled blocks at 0°, 30°, 60°, or 90° from the horizontal. A significant increase in visible and sub-visible particle formation was observed with increasing air-water IA. Exposure to IAs below ∼305 mm 2 resulted in the formation of very few particles, while IAs > ∼305 mm 2 resulted in substantial particle formation. Visible and sub-visible particle morphology varied with interfacial area and time. The sub-visible particles initially increased with time but did not reach steady state; instead the initial increase was followed by complete depletion. These phenomena indicate that visible particle formation likely increased at the expense of the sub-visible particle population and demonstrate a potential link between the two particle populations for this model bioconjugate. Initiation of particle formation did not result in corresponding decreases in protein concentration or increases in soluble aggregates. However, extended agitation time resulted in a significant decrease in protein concentration.