Importance of the dynamics of adsorption and of a transient interfacial stress on the formation of aggregates of IgG antibodiesElectronic supplementary information (ESI) available: DLS size distribution of IgGp solution as a function of the time of rotation with the needle (Fig. S1); dropwise flow of solutions inducing antibodies aggregation (Fig. S2); AFM evidence of the presence of the IgG monolayer at the mica surface (Fig. S3); dynamic surface tension of 1.5 g L1 antibodies (Fig. S4); fluore

It is common knowledge that aggregation of proteins may occur in aqueous solutions under mechanical stress (shaking or high shear), even in solutions that are stable at rest. Addition of surfactants is a practical generic means to prevent this stress-induced aggregation ( e.g. in formulations of therapeutic proteins), which suggests that interfaces contribute to destabilization. We studied here the role of interfacial stress by applying brief mechanical impacts on the airwater interface, in the presence or absence of surfactants, in solutions of immunoglobulin G (IgG), a class of proteins of high importance to the developments of new therapeutics. A variety of surfactants was tested including the neutral ones Tween80, C10C14 fos-cholines, alkylaminoxide, surfactin, and two ionic ones, TTAB and lauroylsarcosine sodium salt. We determined the presence of aggregates in solution by light scattering. Irrespective of the type of antibody, either human polyclonal or a monoclonal one, we show that the amount of aggregated IgG increases in proportion to the number of impacts on the interface. In the absence of stress, we recorded images of oblate aggregates of IgG ( ca. 12 nm height and 2001200 nm diameter) present at the airwater interface (fluorescence microscopy using anti-Fab or anti-Fc markers, and AFM scans after transfer on freshly cleaved mica). Our results evidence that aggregates are formed at the airwater interface, and are brought in solution by transient stresses applied on the water surface. Rupture of interfacial films is an important source of aggregates in solution. Finally, the role of surface dynamics in the protection brought by surfactants is discussed based on the comparison of protective efficiencies with dynamic surface tension properties (measured by the maximum bubble pressure method). Our work indicates that better protection is conferred by surfactants showing the faster interfacial dynamics, which corresponds also to conditions of faster lowering of the interfacial energy at a short time scale. The protection against stresses of therapeutic antibodies prone to interfacial aggregation is achieved by surfactants decreasing the surface tension at the shortest time scale as possible, which effectively reduces the release in solution of adsorbed aggregates upon mechanical rupture of the interface.