Silicone oil droplets vs. protein aggregates: Qualitative and quantitative analysis of silicone oil in presence of proteinaceous subvisible particles
Silicone oil droplets are often found in therapeutic protein products, especially in pre-filled syringes or double-chamber cartridges, deriving from the lubrication process of the packaging material. Silicone oil droplets are not considered harmful by themselves, but might induce protein adsorption and aggregation leading to enhanced immunogenicity.
In routine methods for subvisible particle analysis such as light obscuration, silicone oil droplets are also detected as particles and cannot be differentiated from proteinaceous particles.
To avoid misinterpretation of the product stability due to high particle numbers caused by silicone oil droplets and to investigate the root cause of particle contamination, a differentiation of silicone oil droplets from protein particles is crucial.
On the one hand, this can be performed by optical discrimination of particle images captured by flow imaging microscopy (e.g. Micro-Flow Imaging) for particles larger than 5 µm. This differentiation is based on particle shape and transparency and allows a control of the result by optical evaluation of the sorted images. On the other hand, droplets can be differentiated from particles by the frequency shift they cause in resonant mass measurement (Archimedes). This differentiation of positively buoyant particles (silicone oil droplets) from negatively buoyant particles (protein particles) is based on the distinct physical parameter of particle density and enables an unbiased differentiation for particles between 0.5 and 5 µm (see also our publication “Micro-flow imaging and resonant mass measurement (archimedes) - complementary methods to quantitatively differentiate protein particles and silicone oil droplets”).
Further methods suitable for the discrimination are fluorescence microscopy, flow cytometry (if used with fluorescent dyes), and partially by asymmetrical flow-field-flow fractionation.
Coriolis has extensive experience in qualitative and quantitative differentiation of silicone oil from proteinaceous particles, including product-specific validation to GMP and batch release support.