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In Review

The Inner Ear: A Beautiful Sensor A Rochester engineer explores the biomechanics of a remarkable biological structure.
earHEAR, HEAR: Ibrahim Mohammad ’17—a Xerox Engineering Research Fellow in the lab of Douglas Kelley, assistant professor of mechanical engineering—built and tested a laboratory model to simulate the movements of the inner ear’s hair cells in support of Jong-Hoon Nam’s project. (Photo: Adam Fenster)

Nearly four decades ago, English researcher David Kemp discovered that the human inner ear not only receives but also generates sounds as part of its normal functioning.

The finding led to the standard method now used to screen hearing in newborns. But even now, scientists are not sure how or why these “otoacoustic emissions” occur.

Jong-Hoon Nam, assistant professor of mechanical engineering and of biomedical engineering, hopes to provide answers to that and other mysteries of the incredibly complex sense of hearing. His lab is combining computer simulations with a novel microfluidic chamber to focus specifically on the organ of Corti. The organ—a complex, truss-like strip consisting of inner and outer hair cells, a basilar membrane and supporting cells—plays a key role in converting sound-generated oscillations in the cochlea’s fluid-filled chambers into electrical signals that go to the brain.

“The biomechanics of the organ of Corti have been underinvestigated,” he says. “We would like to know how the complicated structure of the organ of Corti contributes to the overall function of the cochlea.”

With support from an NIH grant that could total $1.8 million over the next five years, Nam hopes to lay groundwork that could eventually lead to better hearing aids or more finely customizable implants. Because the inner ear can process a wide range of both frequencies and loudness, understanding its processes might lead to more sensitive pressure transducers and other engineering applications. “Engineers continually obtain ideas from biological systems,” Nam says. “And the inner ear is a beautiful sensor, operating over a remarkably wide range.”

Nam and his lab will employ novel experimental and computational approaches, including the development of a microfluidic chamber that imitates the physiological conditions of the cochlea. That’s designed to help “address the pivotal question in cochlear research—how outer hair cells, the cochlear amplifier, work within the organ of Corti.”

Nam’s team is also developing a computational model that incorporates the physical, electrical, and fluid mechanical properties of the organ of Corti and the entire cochlea. Members of the group are developing the computer codes themselves because no commercial program provides an easier way to solve such problems.

Nam notes that much of the historical research on the inner ear has occurred at two extremes of scale: the macro biophysics of the cochlea as a whole, and the physiology of individual cells and molecules. By focusing on the multicellular physics of the organ of Corti, and the electromechanical interaction between outer hair cells and the microstructures around them, Nam hopes to “bridge” previous findings and provide a “new integrative paradigm of hearing research.”

—Bob Marcotte