Effect of excipient addition on the extensional flow of protein solutions

With global sales of over $288 billion in 2016, solution-based protein medications represent a sizable portion of the pharmaceutical industry.¹ When protein solutions are injected however, strong shear and extensional forces can cause conformational changes such as protein denaturation and aggregation, leading to loss of function.² We developed a dripping-onto-substrate (DoS) instrument³ optimized for small-volume measurements on proteins, to link the spatiotemporal decay of a liquid bridge radius to extensional rheological properties. Despite the relatively fast timescales of DoS protein experiments (order of 10 ms), measurements expose protein solutions to air-liquid interfaces, where aggregation can occur.^4,5 Here, we compare DoS experiments with model albumin proteins alone to measurements with added excipients, such as poloxamers and polysorbates, that preferentially diffuse to interfaces and protect proteins structure.⁵ While these excipients have been found to be stabilizing to protein solutions in shear,⁵ in extensional flows and at higher concentrations, excipients can lengthen the total time or magnitude of extensional deformation, which can ultimately be destabilizing. This work quantifies the effect of extensional flows on protein behavior both with and without excipients, and identifies optimal ranges of excipients that prevent interface aggregation without introducing additional extensional destabilization.