The aim of this research project is to examine the feasibility of developing an implantable acoustic sensor that picks up speech and sounds from under the skin. This would be incorporated in the proposed TIKI system to replace the externally placed conventional microphone used in the BTE processor.

An elegant approach is to implant a miniature acoustic sensor in the middle or inner ears to directly pick up the vibrations of the ossicular chain or the pressure waves in the cochlea, respectively. The advantage of such an implantable sensor design is that it utilises the natural filtering function of the outer ear and the acoustic amplification of the middle ear, which are normal in a majority of the cochlear implant users but are totally bypassed in current cochlear implant systems.

The project currently focuses on the development of an intra-cochlear pressure sensor for the TIKI system application, with the main research activities being conducted in the following three areas:

Sensor Prototype Development
The intra-cochlear pressure sensor has a structure similar to that of the cochlear implant electrode array, and uses a piezoelectric polymer to pick up hydrodynamic pressure changes in the cochlea. The fabrication process employs advanced technologies such as thin film deposition, micro inject moulding, thermal and Corona poling techniques. Signal conditioning circuitry designs will be optimised to minimise the noise floor and power consumption. The research objective is to verify the important design parameters and demonstrate the concept in a working prototype.

Biomechanical and Physiological Studies
The aim is to verify the hydrodynamic characteristics of the middle ear after cochlear implantation, since the inner ear mechanics and physiology are changed due to the placement of the electrode array and the sensor in the cochlear scalae. Clinical results from cochlear implant recipients for whom some hearing has been preserved so far imply a normal transfer function of the middle ear, due to the use of a soft insertion technique with the current electrode array such as the Nucleus® system. Our research will further investigate the effects of the changes in the inner ear on the impedance and pressure in the scalae vestibuli and tympani.

Surgical and Biological Investigations
A surgical study will be carried out in temporal bones to verify the implant surgical procedure and dimensions of the sensor. It is important to investigate the impact of the mechanical properties of sensor on the delicate structure of the cochlea. Further in-vitro and in-vivo studies will be conducted to test the performance of the sensor prototypes.