Quantification and Characterization of Micrometer and Submicrometer Subvisible Particles in Protein Therapeutics by Use of a Suspended Microchannel Resonator

The ability to characterize micrometer and submicrometer particles in solution is of fundamental importance to understanding the relationship between protein particles in biotherapeutics and concerns raised regarding immunogenicity. While a number of characterization methods are available for analyzing subvisible particle content in protein pharmaceuticals, counting and characterizing particles within the entire subvisible size range remains a significant challenge due to the properties of the proteinaceous particles themselves and to the limitations of the available techniques. Additionally, as silicone oil-lubricated prefilled syringes become a favored primary packaging for biotherapeutic products, proteinaceous subvisible particle characterization is further complicated by the presence of silicone oil droplets in solution. Here, we critically evaluate and apply a novel method for particle characterization that relies on differences in particle buoyant mass to characterize particle content in the range of ca. 0.5-5 mu m. A model particle system was specifically designed to evaluate the ability of the suspended microchannel resonator (SMR) to distinguish between buoyant particles (e.g., silicone oil) and dense particles (e.g., protein particles) in aqueous solution. In addition, this emerging technique was successfully applied to high-concentration monoclonal antibody solutions stored in prefilled syringes in stressed stability studies. It is shown that the SMR system can potentially distinguish between silicone oil droplets and protein particles in a size range that is challenging for many subvisible particle characterization methods. Limitations of the SMR method are also discussed.