Longterm Stability of TiN

Metallic materials which are used in orthopaedics, heart valves and pacemaker electrodes have to be biocompatible; i.e. they have to avoid the reaction with the surrounding tissue. Especially for long-term stability it is essential to inhibit chemical reactions. Titanium and its compounds like oxides and nitrides are well known to behave biocompatible. Therefore, electrodes with a porous surface were produced by sintering titanium alloy powder or PVD of TiN. The electron conductivity can be further increased by Boron doping. To differentiate between threshold changes resulting from surface oxidation or from fibrotic layer, secondary ion mass spectroscopy (SIMS) was performed. Depth profiles of the oxygen concentration allow the evaluation of the electrode interface characteristics with regard to time dependent on the formation of oxide layers. The results indicate that the high long-term efficiency of titanium compound pacing electrodes is a result of the interface structure, the high dielectric constants of the thin surface oxide layer determines the potential and charge distribution resulting in an improved biocompatibility. Therefore the low stimulation threshold is a good indicator of an improved tissue compatibility inhibiting the protein activation.