A new coating boosts the performance of implantable electrodes

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cross-section of a coated carbon-fibre electrode

This scanning electron microscopy image shows a cross-section of a carbon-fibre electrode coated with carbon ‘nanowalls’, which increase its surface area. The coating is less than 30 microns thick.

By increasing the surface area of electrodes, a newly developed carbon-fibre coating improves their electrochemical properties.


Read the abstract


A new type of carbon-based coating increases the ability of carbon-fibre electrodes to stimulate single cells without affecting neighbouring cells. It also enables electrodes to record activity from target cells without interference from distant neural activity.

The coating was developed by researchers from the University of Melbourne, National Vision Research Institute and RMIT University.

Implantable electrodes are used to study how the body works and to develop new therapies for neurological diseases. But current technology is limited in its design and application. Most implantable electrodes can communicate with a nerve cell in only one way: they either record the cell’s activity or stimulate it. And, because inserting electrodes into the body can lead to inflammation and scarring, the devices have limited lifespans.

The new coating addresses these limitations. The research team included groups led by Professor Steven Prawer, Professor Michael Ibbotson and Dr David Garrett.

The coating is made from two-dimensional plates of carbon-based material, which are stacked vertically to create ‘nanowalls’. Adding a coating of nanowalls increases the surface area of electrodes. This in turn increases the electrical charge that the electrode can deliver safely to the cell. It also decreases the electrochemical impedance, thus leading to more sensitive recording. This combination of improved electrochemical properties allows the electrodes both to record and to stimulate brain activity.

The researchers demonstrated the improved performance of coated electrodes by stimulating cells in retinal tissue. They also recorded activity from single brain cells with a high signal-to-noise ratio.

The new coating is flexible and does not peel or crack when the electrodes are bent. Coated electrodes are still ultrathin, so they cause minimal damage to the body during insertion. And because the nanowalls are made from a carbon-based material, the immune system does not treat them like a foreign substance. This reduces the likelihood of scarring and enables long-term use of the coated electrodes.

Next steps

The researchers plan to test the safety and function of the coated electrodes in rodents over extended periods, such as 6 months or more.

Funding

ARC Linkage Project (LP160101515)

NHMRC Project Grant (1101717)

The CASS Foundation Medical/Science Grant to Dr Wei Tong

Melbourne Centre for Nanofabrication Technology Ambassador Fellowship to Dr David Garrett

Publication

Hejazi MA et al (2020) High fidelity bidirectional neural interfacing with carbon fiber microelectrodes coated with boron-doped carbon nanowalls: An acute study. Advanced Functional Materials 30: 2006101. doi: 10.1002/adfm.202006101

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