[Toward the Proper Biophysical Characterization of Aggregates in Biopharmaceuticals]

Biopharmaceuticals are often formulated as liquid dosage forms. During manufacturing and storage, protein molecules and active pharmaceutical ingredients form aggregates due to various stresses, including shaking and agitation, as well as by contact with silicone oils coated on pre-fillable syringes. The diameter of protein aggregates ranges from 15-20 nm, and that of dimers comprising a large number of antibody molecules can be up to 100 μm. Among these aggregates, those with a diameter of <100 nm are called nanometer aggregates, while those ranging between 100 nm and 1 μm are called sub-micron aggregates, and those ranging between 1 and 100 μm are called micron aggregates. In the last ten years, aggregates have been studied to determine their physical characteristics and their impact on immunogenicity. As a result, novel analytical methods and instruments for such characterizations have been established for a majority of aggregates, including those that are difficult to evaluate. Here, the biophysical features of protein aggregates are explained, followed by an introduction to the different methods for aggregate characterization, including their advantages and actual results. Finally, future perspectives and expectations regarding the characterization of protein aggregates are proposed.