Evaluation of micro-epidermal actuators on flexible substrate for noninvasive, pediatric-friendly conductive hearing aid

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SUMMARY Hearing loss during infancy and early childhood has detrimental effects on language and speech development. Hearing loss must be identified and corrected as early as possible to avoid life-long consequences. One major type of pediatric hearing impairment is conductive, in which the auditory pathway in the ear is obstructed or damaged, preventing sounds from properly conducting to the inner ear. Temporary conductive hearing loss (CHL), including otitis media and tympanic membrane perforation, is addressed by medication or a minor surgery. Anatomical conditions such as aural atresia, canal stenosis and ossicular malformation result in permanent CHL and are more difficult to address. Prevalent practice calls for surgical procedures to correct the damage in the pathway or implant hearing aids into the skull to bypass the obstruction in the ear. However, these procedures are invasive and present challenges for newborns and infants. Because of the risks, FDA guidelines prevent children younger than 5 from receiving bone-anchored hearing aids that are standard devices for adults. The long-term goal of this research is to find new strategies to non-invasively transfer sounds into the inner ear and address CHL in pediatric patients. The central hypothesis is that the sounds can be transferred into the inner ear via the skin-bone route with soft hearing aids. The innovation in this project is to integrate chip-scale, ultrathin, micromechanical transducers on flexible substrates to achieve micro-epidermal actuators (MEAs), generating sounds in direct contact with the skin to vibrate the bone and bypass the CHL in a truly non-invasive manner. Our proposed aid will generate 120 dB SPL with ultrathin, low mass, flexible electronics, which have showed promise by robustly sticking to infants' skin. This will eliminate the need for invasive procedures required for corrective surgeries and auditory osseointegrated implants (AOI) as well as the risks and discomfort associated with mechanical actuators and rigid components in the existing aids. The objective of this application is to evaluate the efficacy of the flexible substrate on acoustic coupling, adhesion strength and motion-related noises in soft hearing aids. To that end, we defined three major aims for this project. In aim 1 the acoustic coupling between the epidermis and MEAs will be evaluated and characterized. The hypothesis is that the flexible substrate will reduce the acoustic mismatch with the skin and improve the acoustic coupling into the ear. The noises associated with facial and body motion as well as rubbing noises are characterized in aim 2. The hypothesis is that the soft, conformal, lightweight MEAs will move with facial and body motion, reducing overall noises. The adhesive strength between the skin and MEAs will be evaluated in aim 3. Because of the small size (1.5 cm × 2.5 cm × 300 µm), low mass (120 milligram), and low elastic modulus, the substrates gently bond to the epidermis with adhesion strength 1-2 kPa. The successful implementation of these aims will identify the important features tied to pediatric-friendly conductive hearing aids.