Experimental Evaluation and xDLVO Modeling of Excipient Effects on Protein–Protein Interactions for High-Concentration Formulations

The rational design of high-concentration protein formulations remains a significant challenge in biopharmaceutical development, which requires the screening of effective excipients to suppress aggregation. This study presents a combined experimental and modeling approach to systematically evaluate the effects of key excipients (salts, sugars, polyols, and amino acids) on protein interactions through the measurements of the osmotic second virial coefficient (B₂₂) of bovine serum albumin (BSA) using static light scattering. The results demonstrate that the type and concentration of excipient significantly modulate intermolecular interactions, with repulsive interactions generally enhanced by sugars, polyols, and amino acids, while electrostatic shielding by salts reduces B₂₂. The exclusion volume (dominant)-water competition (secondary) mechanism was proposed to explain the distinct stabilizing behaviors of the sugars and polyols. In addition, the xDLVO model accurately captures the trends in B₂₂ as a function of excipient type and concentration. This framework provides a powerful predictive method for the early stage screening of excipients, facilitating the development of a stable high-concentration protein formulation.