Competitive Adsorption of Monoclonal Antibodies and Nonionic Surfactants at the Air-Water Interface

Monoclonal antibodies (mAbs), due to their amphiphilicity, adsorb strongly at the air-water (a/w) interface, such that interfacial stresses can lead to the formation of visible and subvisible particles in solution that adversely affect the therapeutic efficacy and immunogenicity of protein formulations. Furthermore, prior work in our group shows that the interfacial shear elastic modulus of mAbs adsorbed at the a/w interface correlates strongly with the long-term (3 year) stability in solution, providing a possible means to accelerate the testing of formulations. To mitigate interface-induced instability in formulation and delivery, the biopharmaceutical industry employs excipients, such as nonionic surfactants, to rapidly adsorb to and protect against mAb adsorption at interfaces. However, the molecular interactions at the a/w interface during mechanical deformation are not established despite their technological importance. To address this need, the adsorption of a mAb (studied previously) at the a/w interface in the presence and absence of the nonionic surfactant Poloxamer 188 (P188) is examined through measurements of interfacial pressure and rheology, Brewster angle microscopy (BAM), and neutron reflectometry (NR). We find that mAb adsorbs rapidly to the air-water interface, but the evolution of the surface pressure and interfacial shear moduli continues long after the surface excess has reached a plateau. NR measurements quantify changes in the molecular layer when undergoing dilatational stresses, which may occur during the storage and transport of mAbs. The injection of P188 into the subphase below an established mAb interface increases the surface pressure and decreases interfacial shear moduli, but mAbs remain at the interface with a modified surface topology. Comparisons to adsorption from a premixed mAb-P188 solution highlight the importance of the order of addition in therapeutic formulations, and the results in totality provide molecular evidence for the effect of the a/w interface on mAb interactions and stability.