2D-ice templated titanium oxide films as advanced conducting platforms for electrical stimulation

Abstract

Directional freezing has been widely employed to prepare highly ordered three-dimensional (3D) porous assemblies. However, in this scenario, there is one concept that has not been extensively explored: by applying directional freezing to a nanoparticle (NP) dispersion supported on a substrate, two-dimensionally (2D) patterned films may be produced. In this study, tunable 2D-patterning of TiO₂-NP dispersions on alumina substrates is demonstrated. By imposing different temperature gradients throughout the ceramic dispersion coatings, both homogeneous (non-patterned) and highly aligned patterned topologies (consisting of parallel grooves) were produced. In the case of patterned films, the orientation of the grooves was modulated from those oriented along the freezing direction to those perpendicularly oriented to the temperature gradient. Thermally induced reduction of the prepared films led to electrically conducting titanium oxide Magnéli phases. The measured resistances were strongly dependent on the orientation of the aligned patterns. To demonstrate the possibility of employing these structured films as platforms for electrical stimulation-related applications, a stimulating electronic circuit was developed and connected to the prepared films. Charge-balanced biphasic stimulus pulses with tunable current amplitudes and frequencies were successfully delivered through the conducting 2D-patterned assemblies.