BME MS Defense: Paul Narr

Magnetic Manipulators: An Alternative Approach for Investigating Mechanical Properties of the Cochlear Tissues

Supervised by Professor Jong-Hoon Nam

Abstract

Frequency tuning is the primary function of the cochlea. The underlying principle for this tuning is the mechanical resonance of cochlear micro-structures. Therefore, understanding cochlear mechanics correctly has implications in the entire field of hearing science. Almost all existing methods for cochlear mechanical property measurement involve micro-probes. Due to physical limitations of this method, there is large uncertainty in cochlear mechanics which thus delays the advance of hearing science. Here a new approach to overcome these limitations in cochlear mechanics experiments is introduced: the magnetic tweezers. The use of magnetic tweezers has become more common in molecular and cellular applications due to their ability to apply torque as well as translational forces to the magnetic micro-bead probe. First, an analytical model will be described and utilized to provide a basis for design of a magnetic tweezers system and a validation tool for the built system.

This model will be introduced with magnetic theory and executed with custom software to estimate the force output of the magnetic tweezers system. Following this, two experiments will be described which display the ability of magnetic tweezers for applying static and dynamic forces to magnetic micro-beads. Static forces will be analyzed by observing the change in velocity of magnetic micro-beads in a viscous fluid with and without a magnetic field applied. Dynamic force will be analyzed using magnetic beads adhered to cantilevers of known stiffness. The vibration response of the micro-bead and the cantilever to an oscillating field will be measured using laser vibrometry. Finally, the application of magnetic force to biological tissue will be discussed. The surgical procedure for isolating cochlear tissue will be introduced, and the placement of a single magnetic bead to a target location on the cochlea will be displayed.