Experimental Measurement of the Utricle's Dynamic Response and the Mechanoelectrical Characterization of a Micron-Sized DIB

Within the vestibular system are otolith organs, both the utricle and saccule. The primary function of these organs is to transduce linear head accelerations and static head tilts into afferent signals that are sent to the central nervous system for the utilization of image fixation, muscle posture control, and the coordination of musculoskeletal movement in dynamic body motion. The utricle of the red ear slider turtle was studied in this dissertation. The turtle's utricle is composed of several layers. The base layer contains a set of neural receptor cells, called hair cells, and supporting cells. The three layers above the base layer compose the utricle's otoconial membrane (OM) and are: 1.) a saccharide gelatinous layer, 2.) a column filament layer, and 3.) a calcite and aragonite otoconial crystal layer.

The primary goal of this research was to study the dynamic response of the turtle's OM to a variety of natural inertial stimuli in order to characterize its inherent mechanical properties of natural frequency ("n), damping ("), and shear modulus (G). The medial-lateral (ML) and anterior-posterior (AP) anatomical axes parameters were measured for the utricle. The ML axis median with 95% confidence intervals was found to be "n = 374 (353, 396) Hz, " = 0.50 (0.47, 0.53), and G = 9.42 (8.36, 10.49) Pa. The AP axis median with 95% confidence intervals was found to be "n = 409 (390, 430) Hz, " = 0.53 (0.48, 0.57), and G = 11.31 (10.21, 12.41). Nonlinearites were not found to occur in the OM for the tested inertial stimuli and no significant difference was found between the mechanical properties for the ML and AP axes.

Additionally, this research presents the initial steps to form a novel bio-inspired accelerometer based on the morphology of the utricle. The primary transducer element for this possible otolith organ inspired accelerometer design is a droplet interface bilayer (DIB). A DIB is a lipid bilayer that is formed when the interface of two aqueous droplets, that contain free-floating lipids, are joined. The aqueous droplets are suspended in a nonpolar environment (oil) and the oil/water interface forms a lipid monolayer. This research developed and used an experimental test setup to characterize the mechanoelectrical characteristics of a micron-sized DIB. This information, along with examples in the text, could be used to further design the aforementioned accelerometer.