The Effect of Low Ionic Strength on Diffusion and Viscosity of Monoclonal Antibodies

Purpose: To determine the effect of solution conditions, especially low ionic strength, on the dynamics of molecular diffusion and protein-protein interactions in monoclonal antibody solutions. Methods: The interaction parameter, k(D), was calculated from diffusion data obtained from dynamic light scattering (DLS) measurements performed using a Zetasizer. Theoretical considerations were utilized to evaluate the hard sphere and electrostatic contribution to molecular interactions. Results: At low ionic strengths, repulsions were the dominant forces governing the behavior of both mAbs. As ionic strength increased, attractions contributed to the behavior of mAb1, while repulsions remained the dominant factor affecting mAb3 behavior. Repulsions alone were not sufficient to affect mAb3 viscosity in water, while the presence of repulsions as well as specific attractions was suggested to cause an increase in the viscosity of mAb1 in water compared to 15 mM ionic strength. Conclusions: Solution physical properties varied for the mAbs investigated. Our findings highlighted the importance of developing a fundamental understanding of interplay of forces governing solution properties of each individual mAb under low ionic strength conditions. Such understanding is critical in enabling successful development of self-buffered formulations.