Collections > Electronic Theses and Dissertations > Engineering Systems to Study the Mechanics of Cilia- and Airflow-mediated Mucus Clearance

The pulmonary airway surface liquid layer is comprised of two components: 1) inhaled pathogens that are stuck to a mucus layer and 2) a periciliary layer (PCL) that provides an environment for mucociliary clearance (MCC) out of the lungs. The mechanisms of how the beating of cilia from adjacent ciliated cells is coordinated are poorly understood. In Chapter 2, the perfusion of fluid flow along the apical surface of airway cells was hypothesized to yield airway cultures that transported mucus uni-directionally. To test this hypothesis, perfusion protocols were performed during ciliogenesis and post-ciliation phase of in vitro human bronchial epithelial (HBE) airway models. The length of exposure of fluid shear stress on the apical surface of airway epithelial cultures yielded transient or permanent unidirectional mucus transport in the direction of fluid flow cue. These characteristics matched in vivo biology and remained unseen in standard tissue culturing protocols. In addition to MCC, two other modes of mucus clearance have been studied namely cough clearance (CC) and proposed here, a third mechanism: cilia-independent "gas-liquid transport" (GLT). In Chapter 3, a system was engineered to deliver laminar, humidified airflow across the surface of HBE cultures, which emulated peak expiratory flow rates associated with exhalation. In the GLT models, three conditions of mucosal hydration were tested to represent a variety of clearance models between health and disease: from well-hydrated, normal-like mucus, in situ mucus, to dehydrated mucus, which represented severe Cystic Fibrosis (CF) mucus. At healthy mucus concentrations (2-4%), GLT rate was much faster at clearing mucus than MCC. In contrast, under conditions of severe dehydration, CF-like, GLT failed to produce significant mucus transport, as observed with MCC. In Chapter 4, the effect of mucus clearance with air velocities associated with cough was investigated and captured using high-speed photography. CC was also observed to decrease as mucus concentration increased. Together, the methods developed in this dissertation will help researchers to culture HBE cells with transport characteristics similar to in vivo behavior and help clinicians to better evaluate drug therapeutics on airway clearance for treating muco-obstructive diseases like CF.