The presence of subvisible particles is a stability and safety indicator for biologic therapeutics. Formulation developers routinely use excipients like polysorbate 20 (Tween-20) and polysorbate 80 (Tween-80) to minimize protein aggregation and improve product stability. However, polysorbate can degrade into free fatty acid (FFA) particles when formulations are stored at low temperatures for > 6 months or when they are hydrolyzed by host cell esterase and lipase enzymes. However, determining which particles in the formulation are due to polysorbate degradation versus other sources of protein aggregation is challenging using traditional methods like light obscuration and flow imaging, making it difficult to implement mitigation plans. Polysorbate concentrations are also much lower (<<0.5%) than biologic concentrations (>100 – 200 mg/mL), adding another level of difficulty when it comes to monitoring polysorbate degradation.
Aura+™ and Aura PTx™ systems use Backgrounded Membrane Imaging (BMI) and Fluorescence Membrane Microscopy (FMM) to specifically and quantitatively identify FFA particles in a sample. The assay analyzes 96 samples using 5 µL to 10 mL of sample in less than 2 hours.