Nanoporous Gold As An Implantable Electrode Coating

Covering an implantable neural electrode with nanoporous gold could eliminate the risk of scar tissue forming over the electrode’s surface, researchers from Lawrence Livermore National Laboratory and University of Califonia Davis have found.

The team showed that the nanostructure of nanoporous gold achieves close physical coupling of neurons by maintaining a high neuron-to-astrocyte surface coverage ratio. Close physical coupling between neurons and the electrode plays a crucial role in recording fidelity of neural electrical activity.

Neural interfaces, liike implantable electrodes or multiple-electrode arrays, have emerged as transformative tools to monitor and modify neural electrophysiology, both for fundamental studies of the nervous system, and to diagnose and treat neurological disorders.

These interfaces need minimal electrical impedance to reduce background noise and close electrode-neuron coupling for enhanced recording fidelity.

Scar Tissue Issues

Engineering neural interfaces that maintain close physical coupling of neurons to an electrode surface remains a major challenge for both implantable and in vitro neural recording electrode arrays.

An important obstacle in maintaining robust neuron-electrode coupling is the encapsulation of the electrode by scar tissue.

Typically, low-impedance nanostructured electrode coatings rely on chemical cues from pharmaceuticals or surface-immobilized peptides to suppress glial scar tissue formation over the electrode surface, which is an obstacle to reliable neuron−electrode coupling.

But the research team found that nanoporous gold, produced by an alloy corrosion process, is a promising candidate to reduce scar tissue formation on the electrode surface solely through topography by taking advantage of its tunable length scale.

Nanoporous Gold

Monika Biener, one of the LLNL authors of the paper, said:

“Our results show that nanoporous gold topography, not surface chemistry, reduces astrocyte surface coverage.”

Nanoporous gold has attracted significant interest for its use in electrochemical sensors, catalytic platforms, fundamental structure, property studies at the nanoscale and tunable drug release.

It also features high effective surface area, tunable pore size, well-defined conjugate chemistry, high electrical conductivity and compatibility with traditional fabrication techniques.

“We found that nanoporous gold reduces scar coverage but also maintains high neuronal coverage in an in vitro neuron-glia co-culture model,” said Juergen Biener, the other LLNL author of the paper. “More broadly, the study demonstrates a novel surface for supporting neuronal cultures without the use of culture medium supplements to reduce scar overgrowth.”

Reference:

Christopher A. R. Chapman, Hao Chen, Marianna Stamou, Juergen Biener, Monika M. Biener, Pamela J. Lein, and Erkin Seker
Nanoporous Gold as a Neural Interface Coating: Effects of Topography, Surface Chemistry, and Feature Size
ACS Appl. Mater. Interfaces, 2015, 7 (13), pp 7093–7100 DOI: 10.1021/acsami.5b00410

Illustration depicts a neuronal network growing on a novel nanotextured gold electrode coating. The topographical cues presented by the coating preferentially favor spreading of neurons as opposed to scar tissue. This feature has the potential to enhance the performance of neural interfaces. Credit: Ryan Chen/LLNL