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Section on Auditory Mechanics
Richard Chadwick, Ph.D., Chief
The aim of the section on Auditory Mechanics is to increase knowledge of the hearing process via an interweaving of mathematical, physical, and biological approaches and techniques. Advanced modeling techniques are used interactively with biophysical and structural data obtained from tissues in the organ of Corti to study cochlear physical phenomena related to the transduction of sound to auditory nerve impulses. Special emphasis is directed toward developing techniques to integrate subcellular, cellular, and macroscopic interactions.
Our efforts to study the multiscale nature of the hearing process run parallel to the multidisciplinary theme. Modeling wave propagation in a spiral shape cochlea begins as macroscopic phenomena, which cascades down to the molecular scale and ultimately affects how well mammals hear low frequencies. Nature has found a way to improve on the whispering gallery effect, where sound clings to a concave wall in architectural acoustics. In a spiral cochlea, with ever changing curvature, wave energy is focused at the apex, where low frequencies are processed, affecting the excitatory displacements of hair cell bundles. In a comparative study of morphology and audiometry across mammalian species, we have robustly validated our theory. We suggest the spiral form offers a selective advantage for hearing low frequencies, thus aligning the ideas of Darwin with “form follows function,” which can be traced back to Aristotle.
At the nanometer scale our lab specializes in probing cochlear tissues using the Atomic Force Microscope (AFM). We modified ours to impress controlled indentations in all three directions. We have coupled this capability with optical tracking of fluorescent microspheres at a resolution of tens of nanometers (Fig. 1) This technology, combined with our mathematical modeling ability, poises us to be highly competitive with the best labs in nanoscale measurement and analysis of cochlear tissue. While we have focused primarily on determining the elastic moduli of normal tectorial membrane fibers and matrix (Fig. 2), we also study the disrupted tectorial membranes of mutant mice.
Figure 1. Our experimental approach to study the mechanical properties of a biological material combines Atomic Force Microscopy (AFM) to exert point-like forces and optical tracking of microspheres to measure surface displacements. View Larger Image
Figure 2. A set of measurements on the tectorial membrane consists of several indentation measurements performed at increasing tip-bead distances in directions parallel or perpendicular to the collagen bundle. View Larger Image
- Cartagena-Rivera AX, Le Gal S, Richards K, Verpy E, Chadwick RS. Cochlear outer hair cell horizontal top connectors mediate mature stereocilia bundle mechanics. Science Advances 20 Feb 2019: Vol. 5, no. 2, eaat9934 DOI: 10.1126/sciadv.aat9934
- Logue JS, Cartagena-Rivera AX, Chadwick RS. c-Src activity is differentially required by cancer cell motility modes. Oncogene. 2018 Apr;37(16):2104-2121. Epub 2018 Jan 30.
- Van Itallie CM, Tietgens AJ, Aponte A, Gucek M, Cartagena-Rivera AX, Chadwick RS, Anderson JM. MARCKS-related protein regulates cytoskeletal organization at cell-cell and cell-substrate contacts in epithelial cells. J Cell Sci. 2018 Feb 2;131(3).
- Cartagena-Rivera AX, Van Itallie CM, Anderson JM, Chadwick RS. Apical surface supracellular mechanical properties in polarized epithelium using noninvasive acoustic force spectroscopy. Nat Commun. 2017 Oct 18;8(1):1030.
- Chadwick, RS. A dual probe and two tones reveal dual waves in the cochlea (commentary). Biophys J 110(11), 2528-39, 2016.
- Cartagena-Rivera AX, Logue JS, Waterman CM, Chadwick RS. Actomyosin cortical mechanical properties in nonadherent cells determined by atomic force microscopy. Biophys J. 2016 Jun 7;110(11):2528-2539.
- Gavara N, Chadwick RS. Relationship between cell stiffness and stress fiber amount, assessed by simultaneous atomic force microscopy and live-cell fluorescence imaging. Biomech Model Mechanobiol. 2016 Jun;15(3):511-23. Epub 2015 Jul 24.
- Logue JS, Cartagena-Rivera AX, Baird MA, Davidson MW, Chadwick RS, Waterman CM. Erk regulation of actin capping and bundling by Eps8 promotes cortex tension and leader bleb-based migration. eLife 4, e08314, 2015.
- Manoussaki D, Shin WD, Waterman CM, Chadwick RS. Cytosolic pressure provides a propulsive force comparable to actin polymerization during lamellipod protrusion. Sci. Rep. 5, 12314, 2015.
- Lamb JS, Chadwick RS. Phase of shear vibrations within cochlear partition leads to activation of the cochlear amplifier. PLoS One 14;9(2):e85969, 2014.
- Gavara N, Chadwick RS. Determination of the elastic moduli of thin samples and adherent cells using conical atomic force microscope tips. Nature Nanotechnology 7, 733-736, 2012.
- Petrie RJ, Gavara N, Chadwick RS, Yamada KM. Nonpolarized signaling reveals two distinct modes of 3D cell migration. J Cell Biol. 30;197(3):439-55, 2012.
- Lamb JS, Chadwick RS. Dual traveling waves in an inner ear model with two degrees of freedom. Physical Reviews Letters 107, 088101, 2011.
- Smith ST, Chadwick RS. Simulation of the response of the inner hair cell stereocilia bundle to an acoustical stimulus. PLoS One 6(3):e18161, 2011.