Non-Newtonian Interfacial Modeling of Protein Drops Sheared in Microgravity

The presence of proteins at an air-liquid interface significantly alters fluid motion, making it a unique boundary for hydrodynamic studies. Its role is further accentuated in microgravity due to the prominence of surface tension without gravity. Results will be presented showing velocity measurements along with hydrodynamic simulations of human insulin solutions in microgravity and on Earth. The ring-sheared drop, RSD, operating aboard the ISS consists of a one inch diameter liquid drop contained by surface tension alone and pinned between two contact rings. One ring rotates to impart interfacial shear that is transmitted via surface shear viscosity to produce enhanced mixing of the bulk fluid. For native monomeric insulin, the RSD was modeled using COMSOL simulations with a non-Newtonian surface model two-way coupled to a Newtonian bulk. Insulin's interfacial gelation through shear-induced fibrillization is also explored using the knife-edge (surface) viscometer, KEV, that acts as an Earth analog.