(715g) Rheological and Microstructural Characterization of Native Lung Mucus

Mucus is a heterogeneous, gel-like material critical to life that coats different organs, including the respiratory, GI, and reproductive tracts, and performs multiple tasks including protection from bacteria, virus, toxins, and foreign particles. The major components of mucus are water and mucin o-linked glycoproteins with different monomer/oligomer configurations. Mucin glycoproteins and other mucus components contribute significantly to the viscoelastic properties of mucus.  In terms of modeling the viscoelastic behavior of mucus for application to simulations or production of a mucus substitute, there are relatively few studies in the literature conducted on native mucus samples. We established an experimental protocol to harvest pulmonary mucus from different mammals and here we report the mechanical properties of native lung mucus from a postmorterm horse. Rheological characterization were performed using oscillatory shear (small- and large- amplitude) and steady shear experiments.  The native mucus displayed nonlinear characteristics with a strain-stiffening behavior followed by a strain-softening behavior. Using optical microscopy and atomic force microscopy, linkages were examined between the microstructure behavior of mucus and the observed rheological data.  These results provide new insights for describing the viscoelastic behavior of mammalian lung mucus.  Especially important is developing a model to accurately describe both the viscoelastic behavior over a range of strain rates, as key physiological processes occur at both ends of the range from ciliary clearance to coughing and sneezing.  These processes are of key to understanding and modeling the clearance of mucus and particulates, and impacts occupational and environmental regulations of particulates, drug delivery methods and uptake, and changes in lung mechanisms in lung diseases.