PROJECT SUMMARY Severe to profound sensorineural hearing loss (SNHL), caused by disease, aging, ototoxicity, head trauma and heredity, affects about 60 million worldwide, and is expected to reach around 100 million by 2050. This disability leads to a significantly lowered quality of life and a large economic burden, estimated to be around $750 billion worldwide, coming from health sector costs, educational support, and loss of workplace productivity. For this population, amplification with even the most sophisticated hearing aids is usually ineffective, and restorative biological therapies are years away. A cochlear implant is currently the only available route for restoring ‘adequate’ functionality. Only 600,000 implants have been done worldwide till 2019, and about 50,000 devices are being sold annually. This large discrepancy between those that can benefit and those that actually get the implant is driven partly by their cost, availability and the lack of trained surgeons and facilities. However, there are several limitations in the current devices that contribute to very low adoption: (a) The highly visible unit attached to the skull outside the mastoid bone, connected by a cable to the sound processor and rechargeable battery placed behind the ears, makes the disability very obvious, and creates an unacceptable social stigma for many patients, causing them to refuse this option; (b) Sound filtering by the auricle and auditory canal is bypassed because of the external microphone, introducing unnatural cues; (c) The device typically must be taken off during showering or swimming (although a few water- resistant versions are now available), and during sleeping, increasing the likelihood of damage, misplacement, or the ability to hear in these situations; (d) Having an external magnet that couples and aligns the internal and external components can lead to skin breakdown and implant extrusion; (e) The large footprint and placement leaves open the risk for device migration requiring revision surgery. A fully internal cochlear implant (FICI), that does not have any behind the ear components, would address this large unmet medical need. There are no FICIs currently approved by the FDA. The lack of a self-contained power supply is a key roadblock preventing realization of all FICIs. Through innovations in circuit design and signal processing, collaborating groups at Massachusetts Eye and Ear and Massachusetts Institute of Technology have developed, tested and patented a low power (1 mW) system-on-a- chip (SoC) for a FICI, a critical advance. Current rechargeable batteries have organic liquid electrolytes making them unsafe for this application. With SBIR Phase I funding, Audiance, Inc. has shown proof of concept of an all-solid single-stack cell that is the building block for a battery that meets the electrochemical, safety and footprint requirements for a FICI. The focus of this SBIR Phase II project is to build a multi-stack wirelessly rechargeabl...