Interfacial tensions of protein solutions using axisymmetric drop shape analysis. Proteins at Liquid Interfaces. Elsevier; 1998. pp. 303-39. [DOI: 10.1016/s1383-7303(98)80055-0]

Armoring the Interface with Surfactants to Prevent the Adsorption of Monoclonal Antibodies

The pharmaceutical industry uses surface-active agents (excipients) in protein drug formulations to prevent the aggregation, denaturation, and unwanted immunological response of therapeutic drugs in solution as well as at the air/water interface. However, the mechanism of adsorption, desorption, and aggregation of proteins at the interface in the presence of excipients remains poorly understood. The objective of this work is to explore the molecular-scale competitive adsorption process between surfactant-based excipients and two monoclonal antibody (mAb) proteins, mAb-1 and mAb-2. We use pendant bubble tensiometry to measure the ensemble average adsorption dynamics of mAbs with and without the excipient. The surface tension measurements allow us to quantify the rate at which the molecules "race" to the interface in single-component and mixed systems. These results define the phase space, where coadsorption of both mAbs and excipients occurs onto the air/water interface. In parallel, we use X-ray reflectivity (XR) measurements to understand the molecular-scale dynamics of competitive adsorption, revealing the surface-adsorbed amounts of the antibody and excipient. XR has revealed that at a sufficiently high surface concentration of the excipient, mAb adsorption to the surface and subsurface domains was inhibited. In addition, despite the fact that both mAbs adsorb via a similar mechanistic pathway and with similar dynamics, a key finding is that the competition for the interface directly correlates with the surface activity of the two mAbs, resulting in a fivefold difference in the concentration of the excipient needed to displace the antibody.

Different surface corrugations occurring during drainage of axisymmetric thin liquid films

This paper deals with the different surface corrugations observable during the thinning of axisymmetric thin and large aqueous films, stabilized by saponin. The films are observed using a thin film balance under a constant driving pressure. This device allows measurement of the thicknesses of the film surface shapes arising all along the drainage, as well as the following-up of their evolution before equilibrium is attained. Depending on the electrolyte (NaCl) concentration, three different sorts of corrugation were originally observed in such suspended thin liquid films. At the lowest NaCl concentrations, corresponding to repulsive potential between film walls, only the hydrodynamic corrugations deformed the film surfaces. Regarding the higher NaCl concentrations, when van der Waals forces become predominant, and following the thickness of the first-established thin film, the experiments disclose either that the thinner films are broken up by spinodal decomposition, or that the thicker ones are broken by nucleation and growth of black film. In addition, an original aspect of these works appears in the fact that these observations of the spontaneous decomposition of suspended thin films are relatively similar to those usually described for dewetting experiments on solid substrates, and are well fitted by the existing theoretical models.

Electrostatic effects on the yield stress of whey protein isolate foams

The mechanisms responsible for foam structure are of practical interest within the food industry. The yield stress (tau) of whey protein isolate (WPI) foams as affected by electrostatic forces was investigated by whipping 10% (w/v) protein solutions prepared over a range of pH levels and salt concentrations. Measurements of foam overrun and model WPI interfaces, i.e. adsorption kinetics as determined via dynamic surface tension and dilatational rheological characterization, aided data interpretation. Interfacial measurements were also made with the primary whey proteins, beta-lactoglobulin (beta-lg) and alpha-lactalbumin (alpha-la). Yield stress of WPI foams was dependent on pH, salt type and salt concentration. In the absence of salt, tau was highest at pH 5.0 and lowest at pH 3.0. The addition of NaCl and CaCl2 up to 400 mM significantly increased tau at pH 7.0 but not at pH 3.0. Furthermore, at pH 7.0, equivalent molar concentrations of CaCl2 as compared to NaCl increased tau to greater extents. Salts had minimal effects on tau at pH 5.0. Comparisons with interfacial rheological data suggested the protein's capacity to contribute towards tau was related to the protein's potential at forming strong, elastic interfaces throughout the structure. The dynamic surface tension data for beta-lg and alpha-la were similar to WPI, while the interfacial rheological data displayed several noticeable differences.