Airflow Sensing With Arrays of Hydrogel Supported Artificial Hair Cells

The hair cell is a biological sensor that uses microscopic hair-like structures to detect delicate motions of surrounding fluid. Inspired by this principle, we have created an artificial hair cell (AHC) sensory method based on biomolecular transduction for sensing spatial variations in air flow. The key feature of this method is the use of one-dimensional arrays built from modular AHC units which measure local velocity at different points in a flow profile. Each of the AHC units uses thinly extruded glass fibers as mechanical receptors of air velocity. Hair vibrations are converted to current via hydrogel-supported lipid bilayer membranes through their mechanocapacitive properties. Preliminary tests with linear arrays of three AHC units attempt to measure the air source profile with varying position and intensity. Each unit was fabricated with a hair of different length, giving it a unique vibrational response. This technique was inspired by how organisms use hair cells with tuned responses to mechanically process flow stimuli. A significant challenge in processing the sensors’ output was the limitation of one input channel on the current measurement unit, thus each sensor output had to be sent over the same channel. When several AHC units are excited simultaneously by an airflow, the resulting signal is a superposition of each sensor’s individual response. To separate the signals back into their individual measurements, the Hair Frequency Response Decomposition method is developed, which maps the spectral content of a combined output to the location of excitation in the array. This method takes advantage of the AHC’s high signal-to-noise ratio (compared to other membrane-based AHCs) and linear output response to flow velocity. Results show that the bilayers’ consistent spectral responses allow for an accurate localization of sensor excitation within the array. However, temporal variations in bilayer size affect sensitivity properties and make accurate flow velocity estimation difficult. Nevertheless, under stable bilayer conditions the measured velocity profiles matched closely with theoretical predictions. The implementation of the array sensing method demonstrates the sensory capability of bilayer-based AHC arrays, but highlights the difficulties of achieving consistent performance with bio-molecular materials.