Corrosion of active implant materials for cochlear hearing aids and cardiac pacemakers

摘要

Active implant materials are used in the electrical stimulation of nerves in the human body for information transfer from electronics to human tissue. Examples of applications are cochlear implants supporting hearing aids and cardiac pacemakers stimulating the periodic contraction of the heart muscle. In order to allow for a sufficient stimulation rather high potentials must be used that bring the electrode material far beyond the limits of the electrochemical window of water as described in Pourbaix diagrams. Corrosion under these conditions is extremely small and for a long time it was thought to be unmeasurable and thus negligible. Only the coupling of microelectrochemical tools such as scanning droplet cell microscopy with ultrasensitive chemical trace analysis enables one to explore the limits of stability. Given the impact of the ultimate consequences in case of failure of such devices namely total loss of hearing or even cardiac death motivates this challenging attempt. Corrosion products in the concentration range of ppb or even ppt may cause deterioration of endolymphatic proteins and finally human nerve cells. This study demonstrates not only the possibility for a quantitative determination of released metal ions but also the influence of the chosen electrical parameters on the amount of released metal. In this sense this work does not only demonstrate the possibility to prove and describe the problembut also shows the way for a solution.