A fiber optic interferometer for measuring sub-micrometer displacements of ciliary bundles
Barrett, Matthew Donald
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The inner ear contains cells with ciliary bundles that have been identified as sites of mechanoelectrical transduction; they take a mechanical stimuli and convert it to an electrical response. The ciliary bundles vary structurally within the organs of the inner ear; this structural difference may play a role in the mechanical properties of each bundle. A relationship between the structure and the mechanics of the ciliary bundle can be found by studying structurally diverse bundles. To explore this relationship, a system was designed to mechanically stimulate the ciliary bundles in normal physiological range and measure their displacement. An extrinsic Fabry-Perot interferometer (EFPI) was developed to measure the response of a ciliary bundle that is subjected to a force applied by a glass whisker. 'Imitation bundles', similar in stiffness to living ciliary bundles, were made to test the system. The stiffness of an 'imitation bundle' was first determined by suspending styrene beads from its tip and optically measuring the resultant displacement. Then the EFPI was also used to determine the stiffness. The EFPI compared well to the stiffness found using the styrene beads; the largest difference between the two methods was 130/0. The EFPI was also tested in water to ensure its operation in the tissue environment; this test was successful in that it was able to measure displacements in a bundle's normal physiological range. With both of the tests showing good results, we conclude that our system can be used to measure the stiffness of the ciliary bundles located in the inner ear.
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