Influence of fibrous encapsulation on electro-chemical properties of TiN electrodes

• Influence of encapsulation on electrochemical properties of TiN neural electrodes.
• Healing and encapsulation occurred during the first 3–4 weeks.
• Electrode polarization during stimulation increased and charge storage decreased.
• Electrode polarization was at the pre-implantation level after the implanted period.
• Changing electrochemical properties in vivo seem related to tissue responses.

The aim of this study was to investigate how the electrochemical properties of porous titanium nitride stimulation electrode are affected by fibrous encapsulation in vivo. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry and voltage transient (VT) measurements were performed in vivo and in phosphate buffered saline, where the encapsulation process is absent. EIS was used as a non-invasive measurement to follow the inflammation, healing and encapsulation process. EIS showed that the healing and encapsulation process lasted 3–4 weeks. The VTs increased during the first 3–4 weeks, after which they stabilized. The charge storage capacity (CSC) decreased most during the first 3–4 weeks. The increasing VTs and decreasing CSC during the first 3–4 weeks after implantation of the in vivo electrodes seem related to healing and fibrous encapsulation. It is suggested that the charge injection pathway during the encapsulation process changes, which implies that charge injection limits are underestimated with conventional methods.

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