BME MS Defense: Alex Ringo

Design of a Micro-Chamber to Mimic the Mammalian Cochlea

Co-Supervised by Professor Jong-Hoon Nam

Abstract

The mammalian cochlea is a biological frequency analyzer with an incredible frequency selectivity and operating range. Acoustic pressure waves travel through the outer and middle ears reach the cochlea and propagate through fluid filled compartments changing the pressure in the cochlear duct. This causes vibrations in the organ of Corti, the auditory sensory epithelium. The organ of Corti contains sensory receptor cells called the inner and outer hair cells. The outer hair cells are known as amplifiers that amplify small sounds. How the cochlear amplifier operates is the critical key to understanding the function of mammalian hearing.

Various experimental approaches have advanced auditory science by investigating the biophysics within the organ of Corti. However, how the cochlear amplifies and tunes sound are still illusive partially because of fundamental limitations of existing experimental methods. For example, current in vivo techniques have very limited access to the organ of Corti and limited means to control its physiology. In vitro methods can experiment on individual hair cells at the sacrifice of crucial physiological conditions such as electrical and chemical gradients across the organ of Corti. The present research is an effort to develop a new in vitro experimental method to avoid such limitations.

We designed and validated a new micro-chamber that overcomes the limitations of existing experiments. Our micro-chamber is designed to house a section of the sensory epithelium such that both the electrical and ionic gradients were kept physiologically accurate while allowing us access to stimulate the tissue mechanically and record its response. By using the mammalian cochlea as a natural model to design our chamber from, we believe this micro-chamber will be able to produce meaningful mechano-electrical response data from mid to low frequency locations of the cochlea where existing data is rare. The functionality of the micro-chamber was tested with both artificial membrane and the organ of Corti from the rat cochlea.