Intellectual Merit
Work from Ribbeck, McKinley and Rubinstein (UNC Chapel Hill) provides new insight and methodology for studying the structure of complex biological gels with numerous length scales, using mucins, the gel-forming polymers in mucus, as a model system. A combination of macrorheology and single-particle tracking was used to investigate the bulk and microscopic mechanical properties of reconstituted MUC5AC mucin gels. In particular, it was shown that macroscopic stiffening of MUC5AC gels can be brought about in different ways by targeting specific associations within the network using environmental triggers such as modifications to the pH, surfactant, and salt concentration. This work is important for understanding how environmental factors alter the mechanical properties of mucus, and likely other natural hydrogels with similar association mechanisms as mucins. Insight from this work also suggest strategies for polymer and crosslink chemistries to generate highly responsive hydrogels.

The stiffness of mucus can be modified by targeting different associative groups on the mucin molecules. By performing both micro- and macro-rheological measurements on these gels, additional insight into the structural rearrangements leading to the observed differences in the bulk mechanical properties (such as heterogeneity) can be inferred.

Broader Impact
Mucus is one essential biological gel that coats all the wet surfaces in the human body, providing a selective barrier that allows nutrients and information in while keeping pathogens out. Despite its importance for health, there is the general lack of publically available scientific information on crucial facets of mucus functions. Together with STAT (Boston Globe Media) the Ribbeck group produced an educational video that outlines the functions of mucus in the context of health and disease. It also shows the Ribbeck group in action at a hands-on workshop on polymer science for children organized by the the group at the Boston Museum of Science in August 2017.