(337db) In situ Magnetic Microrheology of Mucus on Live Cell Cultures

Mucus covers every wet epithelial surface of the body, from the eyes to the lungs to the gastrointestinal tract. As the first barrier to our inner organs, mucus must be viscous enough to protect the epithelium against shear forces but also elastic enough to be a selective physiochemical barrier against foreign or harmful molecules. Mucus viscoelasticity is determined by the underlying microstructure formed by the mucin polymer network, which is regulated by several factors including polymer concentration, density of covalent and physical bonds, and hydration. In airway diseases such as asthma and cystic fibrosis, mucus hypersecretion and dehydration results in thick, solid-like mucus that impairs transport, leading to mucus accumulation and blockage of the airway. Understanding the changes in mucus rheology with disease is key to elucidating the mechanism of pathologic mucus secretion and developing treatments to restore healthy flow properties. Prior approaches to the characterization of mucus have relied on the collection and pooling of mucus or sputum samples from humans, animals, or human epithelial cell cultures. Such methods have been limited by difficulty of collection, small volumes of available samples, and changes in material properties due to collection and handling procedures. To address these limitations, I have developed a custom rheological device, the Magnetic Microwire Rheometer (MMWR), to characterize the viscoelasticity of human epithelial cell culture mucus in situ for the first time, thus minimizing disturbance to the mucus structure prior to characterization and enabling direct mechanistic studies of disease models and treatment methods. Briefly, the MMWR consists of a micron-scale magnetic wire (microwire) probe that sits on the sample surface between two electromagnetic coils. When current is supplied to the electromagnets, a constant magnetic field gradient is produced between the coils, resulting in a translational force on the microwire along its axis. The apparatus is mounted on a microscope, allowing imaging of the probe motion and the live sample during the experiment. The relationship between the applied force and the measured microwire displacement is used to determine the rheological properties of the material. I have implemented the MMWR to characterize human airway and intestinal mucus on the respective live epithelial cell cultures in health and disease. With this device, we demonstrate the ability to interrogate the role of the physiological environment in determining mucus rheology by characterizing changes in mucus viscoelasticity with disease and quantifying the response to mucoactive drugs designed to restore healthy mucus flow properties.