ZL and FP made equal contributions
AbstractDuring the formulation of therapeutic monoclonal antibodies (mAbs), nonionic surfactants are commonly added to attenuate structural rearrangement caused by adsorption/desorption at interfaces during processing, shipping and storage. We examined the adsorption of a mAb (COE-3) at the SiO 2 /water interface in the presence of pentaethylene glycol monododecyl ether (C 12 E 5 ), polysorbate 80 (PS80-20EO) and a polysorbate 80 analogue with 7 ethoxylates (PS80-7EO). Spectroscopic ellipsometry (SE) was used to follow COE-3 dynamic adsorption and neutron reflection (NR) was used to determine interfacial structure and composition.Neither PS80-20EO nor C 12 E 5 had a notable affinity for COE-3 or the interface under the conditions studied, and thus did not prevent COE-3 adsorption. In contrast, PS80-7EO did coadsorb but did not influence the dynamic process or the equilibrated amount of absorbed COE-3. Near equilibration, COE-3 underwent structural rearrangement and PS80-7EO started to bind the COE-3 interfacial layer and subsequently formed a well-defined surfactant bilayer via self-assembly. The resultant interfacial layer was comprised of an inner mAb layer of some 70 Å thick and an outer surfactant layer of a further 70 Å, with distinct transitional regions across the mAb-surfactant and surfactant-bulk water boundaries. Once formed, such interfacial layers were very robust and worked to prevent further mAb adsorption, desorption and structural rearrangement. Such robust interfacial layers could be anticipated to exist for formulated mAbs stored in type II glass vials; further research is required to understand the behaviour of these layers for siliconized glass syringes.