A ‘Holy Grail’ for bionics?

stentrode

This image shows a ‘stentrode’ developed by Australian scientists. Image used with permission from Dr Thomas Oxley, from the University of Melbourne’s website Pursuit.

Australian scientists have created a tiny device that may eventually change the lives of people with paralysis. This device could allow people with spinal cord injuries to control bionic limbs via signals – with the power of thought. Think this is too good to be true? Read on! 

This device was designed in collaboration with the University of Melbourne’s Florey Institute and the Royal Melbourne Hospital. The first human trials for the new device are set to occur in 2017 in Melbourne.  The devices will be implanted into three patients at the Royal Melbourne hospital. These participants for the trial will be selected from the Austin Health spinal cord unit.

Why is this such a breakthrough?

There have been devices created before with the potential to help paralysed people move bionic limbs. However these required invasive surgeries. Such surgeries included a craniotomy, wherein a piece of the skull is removed to access the brain; this carries the risk of infection and other complications. “The step we’ve taken is in avoiding the open brain surgery step and delivering our technology without having to conduct any open brain surgery,” – so explains Dr Thomas Oxley from the University of Melbourne. Professor Terry O’Brien adds “it’s the first time that we’ve been able to demonstrate and develop a device that can be implanted without the need for a big operation, to chronically record brain activity”.

The new device is small – around three centimetres long and just a few millimetres thick. It is minimally invasive compared to other technologies. Professor Clive May of the Florey Institute has said that the device will be inserted into a blood vessel via a catheter (a commonly used technique in medicine) – it will rest above the motor cortex, which is the brain region responsible for sending nerve impulses that control voluntary body movement. This technique is similar to that used to removing blood clots, so surgeons from the Royal Melbourne Hospital can rely on experience and techniques from previous surgeries to insert the device.  

Why is this ‘stentrode’ special?

The device is structured as a stent; it’s flexible enough to move around in blood vessels yet is strong enough to hold its shape as it is pushed out of the catheter during insertion. Dr Nick Opie, a biomedical engineer from the Florey Institute, explains that the device is made of nitinol, a nickel titanium composite. This gives it greater resilience when compressed,so it retains its shape when it flexes open to form a stent in the blood vessel. The benefit of this stent-based device is that it should not impede blood flow – if it did, this would cause a (potentially fatal) blood clot.  

Typically, inserting a foreign object into the human body carries a high risk of immune rejection*. If this occurs then scar tissue may form over the  electrode, reducing signal quality. The additional benefit of this device being designed as a stent, is that it is protected inside the blood vessel so the body won’t try to reject it.  But what does it do once inside?

The stent-based device is referred to as a ‘stentrode’ as it contains 12 electrodes, which are pressed up against the walls of a blood vessel close to the motor cortex. Electrical signals sent from the neurons in the motor cortex are received by the electrodes and then converted into commands. These commands would then in theory be sent via wires to a transmitter which can be implanted under the skin on the chest. The transmitter could then send the commands to bionic limbs, thereby bypassing the damaged area of the spinal cord. In practice, a paralysed patient might be able to move once more via communication between this device and an exoskeleton.

However just having the transmitters in place would not be enough to automatically give the patient fine-tuned control over their bionic limbs. Prof Terry O’Brien, head of the Royal Melbourne Hospital neurology department, explained that the patients would initially require some help with training their bionic limbs using thoughts. Patients would have to be taught what to think about in order to move their bionic limb. However it is hoped that over time the thought process could become subconscious.  

How does it compare to surgically implanted electrodes?

Research conducted on sheep was outlined in a study published in Nature Biotechnology. The stentrode was implanted in sheep and left there for 190 days. The device was implanted in a vein above the motor cortex using the same catheter procedure described above. The sheep were then free to move around and neural recordings of their movement were collected from the nerve impulses that were generated by the motor cortex.  The researchers found that the signals from the stentrode matched those of electrodes surgically implanted into the sheep’s brain – possibly indicating this could be a comparable alternative to brain implants. Essentially this pilot study indicated the stentrode is safe and tolerated by a large-animal model, hence showing the promise of strategies that do not require invasive craniotomy. As it could effectively record brain activity, this is a step in the right direction with regards to engineering an interface between a damaged nervous system and a bionic device.

The stentrode could be termed ‘the holy grail of bionics’

The stentrode has been designed to do what no other electrode has done before. By avoiding the shortcomings of traditional open brain surgery implantation methods it is the most biocompatible bionic brain interface currently available.  However the use of the stentrode is just not limited to the operation of bionic limbs – it has potential for wide-ranging applications in other areas of bionics. If the electrode is placed in an area of the brain that is responsible for receiving and transmitting nerve impulses from the eye, this might help scientists continue to develop technology for a bionic eye. Because of the stentrode, scientists and doctors can now sit back and brainstorm… “what would happen if we put the stentrode in a region of the brain responsible for…?”. Time will tell!

Zach Holmes.

Zach recently graduated from the Shell Questacon Science Circus where he performed science shows to schools – these involved setting his hands on fire and blowing up balloons with liquid nitrogen, so he fits in well at Bio Detectives. Before the circus he was a high school maths and science teacher; he studied plant science at the University of Tasmania, investigating flammability of Eucalypts.

When Zach isn’t getting on with strongman training and pulling 10-tonne trucks (!). he likes to make science YouTube videos.

* This is why people who receive organ transplants must take so many immunosuppressant drugs – otherwise the new ‘foreign’ organ will be rejected by their immune system.

** A video from the University of Melbourne about this stentrode is available here.

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One Comment
  1. Um, white cells travel in the blood stream as much as they do in the rest of the body. They are the main immune response in the body. Why wouldn’t they attack something on the INSIDE of a blood vessel?

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