It is critical to understand the flow pattern of mucus to understand the affects of rheological properties and the propulsion mechanisms of cilia and air. To understand why mucus moves, we need to study how the primary generators of force, cilia and air (cough), couple to mucus flow. One of the key questions concerns the presence of mixing within the mucus layer. This would have important implications for the entrainment and isolation of bacteria in mucus, and hence one of the mechanisms of preventing colonization and plaque formation. Further, the transport of inhaled therapeutic agents from the airway to the epithelial cell surface would be dramatically increased by significant mixing, or compromised in the case of mucus stasis. While in project 4 we study the role of PCL in mucus adhesion and slippage, it is clear that the hydrodynamics of the mucus will exert forces on the mucus/PCL/cell surface interfaces and promote slippage. Traditionally, studies of mucus transport have been concerned with particulate motion on the airway surface of the mucus layer. There is a great need to understand the cross sectional profile of this hydrodynamics, including interfacial flows down through the PCL, the nature of the flow (stratified or plug flow) and the presence of mixing. The detailed imaging and modeling of this hydrodynamics is the object of this project.