Residual rubber shielded multi walled carbon nanotube electrodes for neural interfacing in active medical implants

Advanced neuroprostheses need high density, mechanically flexible contacts with superior electrophysiological performance. Carbon nanotubes have shown interweaving with neurites are well suited but are opposed by ongoing nanoparticle biocompatibility discussions. We present a route circumventing those issues by immersing multiwalled carbon nanotubes (MWCNT) in silicone rubber and re-etch the surface yielding a MWCNT-lawn electrically contacted towards the percolative bulk. The use of tetra-n-butylammonium fluoride (TBAF) and sodium hydroxide solution (NaOH) leads to desired freestanding CNT strands still covered by residual rubber of approximately 13 nm thickness. The biocompatibility of such interfaces has been proven by WST-1-Assays for cell metabolism of 3T3NIH fibroblasts and SH-SY5Y neuroblastoma cells in terms of growth and morphology. Neural cell adhesion is proven with biomolecular markers. The electrical performance reaches percolation conductivities of up to 1.6 × 10² S/m. The lowest impedance was 1.3 × 10² Ωcm² at 1 kHz, which is similar to gold reference electrodes whilst their capacitive roll off is lowered in electrophysiological arrangements. When compared to pure MWCNTs the performance is decreased due to the insulating residual rubber encasement. However, this is seen to be a reasonable loss in the light of the increased biosafety of rubber shielded MWCNT neural interfaces.