MEAM Master’s Thesis Defense: “The Rheology and Microphysics of Monodisperse Synthetic Mucin”

Mucus, a complex fluid produced by every living organism, has multiple essential functions including acting as an effective barrier layer in various bodily processes, many of which involve important rheological (flow) and tribological (adhesive, lubricative) functions. The primary component of mucuses are mucins – highly glycosylated, linear polypeptides. Understanding how the structure and properties of mucins control the overall behavior of mucus is thus of substantial interest. However, natural mucus is often contaminated with non-mucin constituents that affect the rheological response, and purifying mucus without damaging the mucins themselves is difficult. Here, fully synthetic, monodisperse mucins have been prepared by a collaborator. Aqueous solutions of these mucins have been studied for comparison to the rheological response shown by natural mucin solutions. The purity and structural control of these synthetic mucins provide a model system where the mechanistic sources of the mucus’ rheological response can be isolated and identified. Experimental bulk rheometry demonstrates a shear-thinning behavior with a yield-stress fluid response. This behavior is attributed to associations between mucin molecules localized to the liquid-air interface, which contradicts previous literature on natural mucins. This conclusion is supported by interfacial rheology measurements and by a mathematical model encapsulating the dynamics of a thin mucin layer under shear. This work furthers the understanding of the dynamics of mucin solutions and the qualitative microphysics surrounding their dynamics.