Master thesis presentation: Expected lifetime and short-term mechanical vulnerability of the Bone Conduction Implant

Welcome to a master thesis presented by Helga Jona Hardardottir, MPBME, on Wednesday, June 10th at 15.15 in Landahlsrummet, Hörsalsvägen 9, 7th floor.
Supervisor: Karl-Johan Fredén Jansson and Bo Håkansson
Examiner: Sabine Reinfeldt

The bone conduction implant (BCI) is an active transcutaneous bone conduction device for rehabilitation of patients suffering from conductive or mixed hearing loss. Today, the device is used by 8 patients in an ongoing clinical trial, and it has been shown to provide sufficient rehabilitation for indicated patients. However, the expected lifetime and short term mechanical vulnerability of the BCI have not yet been investigated and remain unknown. The objective of this project was to estimate the lifetime of the BCI through an accelerated test under continuous high input sound stimuli, and to investigate vulnerability to mechanical stress that can occur during surgery and normal conditions.
wo types of investigations were used. (1) A long-term sound exposure investigation was performed on one full BCI system in order to estimate the total lifetime of the implant. (2) The robustness of the implanted transducer was thoroughly investigated by performing a series of mechanical investigations comprising: mechanical shock, random vibration, drop, and impact tests. The performance after each of these tests was evaluated by measuring the frequency response and the total harmonic distortion of the device on a skull simulator.
No change was detected in the performance after 5 weeks of the continuously ongoing accelerated sound exposure, except from a temporary variation in frequency response, which was due to a short-term temperature drop in the test chamber. In the mechanical shock and vibration tests, the change in the transducer’s frequency response was minor and assumed to be clinically insignificant.
The accelerated sound exposure indicates that the lifetime is at least 7.5 months based on the follow-up time until end of Master thesis project (assumed scaling factor of 6 times was used), but this test will continue until a major change in performance occurs to find out the actual life time of this particular transducer.
All mechanical tests imply that the transducer is safe with respect to mechanical stress and that there is no systematic failure in its design. However, a larger study on greater number of transducers needs to be performed to get more statistically reliable results.