What’s the first thing you did when you woke up this morning? Maybe you swung your legs over the side of your bed, placed your feet on the floor and stood up. Simple, right?

Walking around on your own two feet is something most of us don’t even think about. But for the thousands of Australians with spinal cord injuries, this ‘simple’ act feels a world away.

A close-up photo comparing the size of electrodes, which are 10 microns, and a human hair, which is 70 microns — The carbon fibre electrodes are just a fraction of the size of a human hair. Picture: Supplied

The frustrating part is that for many of these people, the rest of their body is healthy, but the brain can’t get its messages through the spine where the damage is – like a phone line that’s been cut.

So, what if we could reconnect that signal? What if we could relay the messages and bridge the gap caused by spinal injuries, reconnecting the communication between the brain and the rest of the body?

For the last six years I've been developing ultra-tiny carbon fibre electrodes for the brain. And now, in collaboration with Canadian researchers through the RE-MOVE initiative, we’re exploring adapting them for the spinal cord.

The idea is to implant these electrodes into the spinal cord, enabling them to ‘talk’ directly to individual neurons using the body’s own electrical and chemical languages.

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Not only can these electrodes speak the language of our nervous system, but we’ve coated them in an ultra-thin layer of diamond, so they are tougher and more durable than ever before.

The smaller the electrode, the louder the conversation

Many of the current electrodes used for the brain are either too bulky, too stiff or too floppy to work safely in the spine. The spinal cord is a hard place to work – the areas we want to target are deep, they’re delicate, and the spine is constantly moving.

This is where carbon fibre comes in.

A large system of neurons connected via pathways with bursts of light passing through them — Walking is a complex movement that requires a two-way conversation between single neurons, so larger electrodes are not suited for treatment. Picture: Getty Images

You might recognise carbon fibre from its use in lightweight car panels or in aeroplanes. Well, that same material is made up of countless individual carbon fibre strands, about one-fifth the width of a human hair.

These strands can conduct electricity and are perfect as biomaterials. They’re flexible enough to move with the body, stiff enough to enter tissue and gentle enough that the body doesn’t reject them.

It’s basically the Goldilocks of conductive materials for the body.

Because carbon fibre electrodes are so small, they can communicate with the tissue right down to a single neuron.

Larger electrodes, like those used for the treatment of Parkinson’s disease through deep brain stimulation, converse with larger groups of neurons from farther away, which is like trying to talk to your friend at the other end of a crowded restaurant.

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While very effective for Parkinson’s disease, these large electrodes aren’t useful for understanding fine movement.

Walking is a complex movement that requires a lot of control and feedback from your body, so to relay this information, you need to hear every word the neuron is saying (and not what the person is ordering on the table next to you).

Obviously, this comes with difficulty, as the more information you want, the more electrodes you need. This is where the small size of the carbon fibres is so useful – you can implant several of them and still not cause any damage.

A close up of multiple ultra tiny carbon fibre electrodes being inserted into a brain mimic — Initial tests have shown the carbon fibres can be inserted deep enough into tissue to talk to neurons in the spinal cord. Picture: Supplied

Why diamond?

Carbon fibre is already one of the best materials for the job, but this hasn’t stopped us from trying to make it even better.

Our lab in the School of Physics specialises in diamond growth, and diamond is one of the toughest materials on earth. So, it makes sense that this might help us create the toughest electrode – one that can last a lifetime.

Through a collaboration with the Mayo Clinic led by Dr Wei Tong, we coated our electrodes in an ultra-thin layer of diamond, providing the toughness needed for the carbon fibre to withstand the harsh conditions of sending electrical signals back to the neurons.

With conventional treatments, carbon fibres can both talk and listen to single neurons, but the jury is still out on how long they will last – especially for the talking.

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With the help of the diamond coating, our electrodes can support the two-way conversation required for restoring movement, without wearing out like traditional carbon fibres.

So, this coating could provide a surface with lifelong capabilities while retaining all the best parts of carbon fibre.

The coated electrodes can also still retain their sensitivity to effectively measure neurochemicals like dopamine, which could be a big factor in improving potential therapies.

Small steps

Our initial tests have shown that we can insert our carbon fibres deep enough to talk to neurons in the spinal cord – that’s a big tick for step number one.

Back of person sitting in wheelchair in park with a glowing spring sky in front of them — While further testing is needed, these diamond-coated electrodes may help people with spinal cord injuries walk again. Picture: Getty Images

The next step is to test these electrodes to prove that we can have meaningful conversations with the neurons in the spinal cord to both understand and control movement.

If we can demonstrate this, we will have the ability to bridge the gaps caused by spinal injury and restore communication between the brain and the body – offering new hope for people living with paralysis.

These electrodes may be small, but their impact is almighty. And because of them, one day, someone who previously couldn’t imagine the joy of being able to swing their legs out of bed and walk again, may be able to do so.

This article was first published on Pursuit. Read the original article.

Dr

Simon Higham

Device Development Research Fellow

School of Physics

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Simon Higham

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