A comparative study of electrochemical stability and biocompatibility of TiN nanowires and thin films for neural-electrode application

Neural-electrode devices with adequate charge injection capacity, long operating lifetime and excellent biocompatibility with interfaced tissues are essential to treat chronic neurological disorders. The device's efficiency hinges on the electrochemical properties of the electrode material, prompting extensive research on diverse material surfaces. Here, we investigate the electrochemical stability and biocompatibility of titanium nitride (TiN) nanowires (NWs) synthesized previously through the novel plasma enhanced chemical vapor deposition (PECVD) utilizing lower temperature as compared to conventional methods. These TiN-NWs were compared with TiN thin films, shedding light on their respective performances. TiN-NWs electrode revealed far superior electrochemical stability over 1000 cycles, achieving a capacitance retention of 93 % as compared to 68 % to that of TiN film electrode, under ambient conditions with dissolved oxygen. Additionally, impedance of TiN-NWs showed almost no change with cycling as compared to the film electrode. Moreover, our in-vitro cell culture spanning 20 days exhibited excellent biocompatibility for both substrates. Interestingly, cell distribution on the NWs appeared more dispersed with fewer clusters, potentially facilitating controlled electrical stimulation. These findings not only highlights the potential use of TiN-NWs for chronic stimulation of neurons, but also shows that surface morphology has a potential effect in minimising surface oxidation and improving electrochemial performance of the material.