(440b) Instrument for Measurement of Interfacial Structure-Property Relationships with Decoupled Interfacial Shear and Dilatational Flow: “Quadrotrough”

Understanding the interfacial structure-property relationship of complex fluid-fluid interfaces is increasingly important for guiding the formulation of systems with targeted interfacial properties, such as found in multiphase complex fluids, biological systems, biopharmaceuticals formulations and many consumer products. Mixed interfacial flow fields, typical of classical Langmuir trough experiments, introduce a complex interfacial flow history that complicates the study of interfacial properties of complex fluid interfaces. In this manuscript, we describe the design, implementation, and validation of a new instrument capable of independent application of controlled interfacial dilation and shear kinematics on fluid interfaces. Combining the Quadrotrough with both in situ Brewster angle microscopy and neutron reflectometry provides detailed structural measurements of the interface at the mesoscale and nanoscale in relationship to interfacial material properties under controlled interfacial deformation histories.

Monoclonal antibodies (mAbs) are important biotherapeutics to treat numerous human ailments, but the proteins have a natural tendency to aggregate in solution, which reduces drug formulation stability. One concerning source of instability for mAbs occurs at the air-water interface as mAbs are amphiphilic. In this work we study a well-defined NIST reference mAb (RM #8671, pI = 9.3, an IgG1 protein) with and without surfactant poloxamer P188 (Kolliphor ®, Sigma-Aldrich) in histidine buffer, and with added electrolyte (NaCl), including competitive adsorption. Surface tension, neutron reflectometry, and interfacial shear rheology are used to characterize the adsorbed mAb interfacial layer with and without P188. Further, we study the effects of a controlled deformation history of the air-water interface using a novel interfacial rheometer which enables both pure dilatation/compression and pure shear deformations at air-water interfaces. Using this technique, we first gain insight on isolated interfacial strain-induced behavior of NISTmAb at the air-water interface often attributed to aggregate formation in solution. Primary conclusions are made concerning the individual species and their competitive properties as follows: NISTmAb interface exhibits a strong gel-like network that adsorbs irreversibly as aggregated particles on the air-water interface. Dilatational strains cause interfacial aging as detected by surface pressure measurements, but do not show significant mesoscale differences under compression/expansion by Brewster angle microscopy. This observation suggests that the aging due to structural rearrangement or partial unfolding of mAbs at the interface. NISTmAb exhibits high shear elasticity but is not perturbed by shear straining the interface as detected by surface pressure measurements. Overall, NISTmAb forms a highly stable network at the air-water interface with no signs of unstable desorption under the imposed interfacial dilatational and shear strain conditions. P188 is a non-ionic surfactant used to stabilize protein formulations and forms an inviscid interface with negligible shear viscosity and low dilatational modulus due to its high solubility in aqueous solutions. This surfactant’s ability to prevent NISTmAb from reaching the air-water interface depends on the order of addition. P188 is observed to competitively adsorb to the air-water interface and fully prevent NISTmAb adsorption as determined both by rheological and structural measurements. However, P188 only slowly displaces some of the pre-adsorbed NISTmAb at the air-water interface under quiescent state. Instead, it can co-adsorb to the air-water interface and fluidize the NISTmAb network. Dilatational straining is shown to primarily weaken the gel-like NISTmAb network into densified aggregates. Using the unique capabilities of the Quadrotrough, shear and dilation experiments combined with Brewster angle microscopy and neutron reflectivity measurements enable the development of structure-property relationships of protein-surfactant pairings to identify the origin of interfacial formulation instability and provide guidance in designing stabilized formulations through excipient addition.

This work was performed under cooperative agreement # 370NANB17H302 from NIST, U.S. Department of Commerce. We acknowledge the support of the National Institute of Standards and Technology, U.S. Department of Commerce, in providing the neutron research facilities used in this work. This work utilized facilities supported in part by the National Science Foundation under Agreement No. DMR-0944772. The statements, findings, conclusions and recommendations are those of the authors and do not necessarily reflect the view of NIST or the U.S. Department of Commerce.