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京都大学 / 新制・課程博士 / 博士(医学) / 甲第24091号 / 医博第4867号 / 新制||医||1059(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 林 康紀, 教授 髙橋 良輔, 教授 渡邉 大 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Arrays of fully hydrogel-supported, artificial hair cell (AHC) sensors based on bilayer membrane mechanotransduction are designed and characterized to determine sensitivity to multiple stimuli. The work draws upon key engineering design principles inspired by the characteristics of biological hair cells, primarily the use of slender hair-like structures as flow measurement elements. Many hair cell microelectromechanical (MEMS) devices to sense fluid flow have already been built based on this principle. However, recent developments in lipid bilayer applications, namely physically encapsulated bilayers and hydrogel interface bilayers, have facilitated the development of AHCs made primarily from biomolecular materials. The most current research in this field of "membrane based AHCs," shows promise, yet still lacks the modularity to create large sensor arrays similar to those in nature. This paper presents a novel bilayer based AHC platform, developed for array implementation by applying some of the core design principles of biological hair cells. These principles are translated into key design, fabrication and material considerations toward improved sensor sensitivity and modularity. Single hair cell responses to base excitation and short air pulses are to investigate the dynamic coupling between hair and bilayer membrane transducer. In addition, a spectral analysis of the AHC system under varying voltages and air flow velocities helps to build simple, predictive models for the sensitivity properties of the AHC. And finally, based on these results, we implement a spatial sensing strategy that involves mapping frequency content to stimulus location by "tuning" linear, three-unit arrays of AHCs. Individual AHC sensors characterization results demonstrate peak current outputs in the nanoamp range and measure flow velocities as high as 72 m/s. Characterization of the AHC response to base excitation and air pulses show that membrane current oscillates with the first three bending modes of the hair. Output magnitudes reflect of vibrations near the base of the hair. A 2 degree-of-freedom Rayleigh-Ritz approximation of the system dynamics yields estimates of 19 N/m and 0.0011 Nm/rad for the equivalent linear and torsional stiffness of the hair's hydrogel base, although double modes suggest non-symmetry in the gel's linear stiffness. The sensor output scales linearly with applied voltage (1.79 pA/V), avoiding a higher-order dependence on electrowetting effects. The free vibration amplitude of the sensor also increases in a linear fashion with applied airflow pressure (3.39 pA/m s??). Array sensing tests show that the bilayers' consistent spectral responses allow for an accurate localization of the airflow source. However, temporal variations in bilayer size affect sensitivity properties and make airflow magnitude estimation difficult. The overall successful implementation of the array sensing method validates the sensory capability of the bilayer based AHC. / Master of Science

The cochlea is known to exhibit a nonlinear, mechanical amplification which allows the ear to detect faint sounds, improves frequency discrimination, and broadens the range of sound pressure levels that can be detected. In this work, active artificial hair cells (AHC) are proposed and developed which mimic the nonlinear cochlear amplifier. Active AHCs can be used to transduce sound pressures, fluid flow, accelerations, or another form of dynamic input. These nonlinear sensors consist of piezoelectric cantilever beams which utilize various feedback control laws inspired by the living cochlea. A phenomenological control law is first examined which exhibits similar behavior as the living cochlea. Two sets of physiological models are also examined: one set based on outer hair cell somatic motility and the other set inspired by active hair bundle motility. Compared to passive AHCs, simulation and experimental results for active AHCs show an amplified response due to small stimuli, a sharpened resonance peak, and a compressive nonlinearity between response amplitude and input level. These bio-inspired devices could lead to new sensors with lower thresholds of sound or vibration detection, improved frequency sensitivities, and the ability to detect a wider range of input levels. These bio-inspired, active sensors lay the foundation for a new generation of sensors for acoustic, fluid flow, or vibration sensing. / Ph. D.

This research documents the creation and use of an open-loop feed forward control scheme designed to manipulate the DC potential across lipid bilayer membranes in artificial hair cell sensors. Inspired by the human cochlea's non-linear gain phenomenon, whereby the cochlea can increase or decrease the effective gain of the auditory system, this controller is the first step in developing more sophisticated signal processing schemes for use with future bio-inspired artificial hair cell development. This open-loop controller allows for three preset gain mappings to tailor the DC offset in response to an external stimulus. Linear, nonlinear and sigmoidal mappings were created to observe the differences in system response during constant frequency and variable frequency excitation. In constant frequency testing, artificial hair cell sensors were excited at 100 Hz across a range of input intensities to observer current output response during increasing or decreasing excitation levels. Results showed average coherence values above 0.98 for the relationship between current output and fluid velocity, indicating a strong correlation between excitation and measured output. In the bilayer with stereocilia test case, RMS power increased with higher excitation levels but the various control laws did not appear to have any discernible impact on output power. In variable frequency testing, sensors were excited from 0-300 Hz to observe the real time effects of our control law on amplification or attenuation of output current with varying input intensity. Results of the variable frequency excitation could not definitively prove that the varied DC potential had an effect on current output due to excessive capacitive noise, but the controller did provide some encouraging results from its behavior during testing. We observed three distinct DC potential response curves for each mapping, indicating, that with some refinement, we should be able to manipulate output current with user defined gain tunings. / Master of Science

Hair cell structures are one of the most common forms of sensing elements found in nature. In humans, approximately 16,000 auditory hair cells can be found in the cochlea of the ear. Each hair cell contains a stereocilia, which is the primary structure for sound transduction. This study looks to develop and characterize a bilayer lipid membrane (BLM) operated artificial hair cell sensor that resembles the stereocilia of the human ear. To develop this sensor, a flexible substrate with internal compartments for hosting the biomolecules and mating cap are constructed and experimentally characterized. The regulated attachment method (RAM) is used to form bilayers within the sealed device. Capacitance measurements of the encapsulated bilayer show that the sealing cap slightly compresses the bottom insert and reduces the size of the enclosed bilayer. Single channel measurements of alamethicin peptides further verify that the encapsulated device can be used to detect the gating activity of transmembrane proteins in the membrane. The flexible substrate was incorporated into a low-noise, portable test fixture. The response of the sensor and tip velocity of the hair were measured with respect to an impulse input on the test fixture and several frequency response functions (FRFs) were created. The FRF between the sensor and the tip velocity was used to show that the hair vibration was transmitted to the bilayer for certain hair lengths. The transfer function between the sensor and the input was used to show the effect of membrane potential on sensor response. / Master of Science

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