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Cochlear implants have restored hearing to hundreds of thousands of people living with sensorineural hearing loss worldwide. It’s perhaps the best-known of the neuroprosthetics – devices that interact with the body’s nervous system to replace a lost biological function.

Sensorineural hearing loss is commonly due to damaged sensory hair cells in the inner ear. This may be present from birth, or be the result of ageing or exposure to loud noise. The cochlear implant essentially does the work of the damaged hair cells, stimulating sensory cells to provide sound signals to the brain. 

The device has been life-changing for individuals, but despite more than four decades of development there are still real challenges. 

The platinum used in the array of 22 tiny electrodes placed in the cochlea, for example, can dissipate within the body over time, affecting the device’s performance. There is also the issue of fibrosis, the body’s natural response that ‘walls off’ foreign objects by building thicker tissue around a device, making it harder to pass through electrical signals to stimulate sensory cells.

, a biomaterials expert and co-director of the Sir William Tyree Foundation Institute of Health Engineering (Tyree IHealthE), is leading a multidisciplinary team of researchers, partly funded with a grant from implant manufacturer Cochlear Limited, to find solutions to these issues. 

“There’s a real buzz about doing research because you’re basically trying to answer questions which nobody knows the answer to,” she says. “It’s very open ended, but it’s also quite exciting. You can think it’s going to go one way, and then it’ll go in a different direction. That’s really quite fun, but challenging.”

New coatings and new materials 

Some of the researchers are focusing on how materials such as platinum interact with cells and tissues in the body. The first step on the project, says Laura, will be designing and testing new coatings that better protect the platinum electrodes, allowing them to be further miniaturised. 

“Instead of having 22 electrodes, you could have 44 or, you might get 100 or 1,000 on an array,” says Laura, explaining that the increase in electrodes could produce a better auditory performance. 

The next step could be changing the material used in the device, such as replacing the platinum electrodes with ones made with a conductive polymer. Dr Dorna Esrafilzadeh is one of those exploring the options.

“My research is looking at synthesising and fabricating a wide range of electromaterials that are flexible, non-toxic, and better suited to be replaced in the body,” she says. “It will provide patients and clinicians with safer, more comfortable devices.”

Even further into the future, there is the potential for tissue-engineered solutions, according to Laura.

“Instead of putting in a device, can you actually deliver drugs or genes that might actually fix the situation? Or could you design something, a device that might be made up of cells that are functional and replace the cells that are there?,” she questions. “That’s far in the future, but we’re working on the initial building blocks to those now.” 

Avoiding the fibrosis response is another complexity.

“Nobody’s really worked out how to switch off the body’s response, so you have to think, how can I decrease that response to the device? How can I stop that walling off or slow it down or make it smaller?” says Laura. 

To explore all of these possibilities, it is essential to develop new tissue models that can recreate human cochlea in the lab. This challenge is one of the research goals of Dr. Ulises Aregueta Robles. 

“My research focuses on creating customised cochlea models using biomaterials combined with state-of-the-art stem cell technologies” says Ulises. “A humanised model can enable high throughput testing of emerging materials while reducing unnecessary animal use. These models can also serve as training tools for surgeons who need to develop ultra-fine motor skills to implant these devices without damaging inner ear structures.”

Change is incremental 

Since the cochlear implant was approved by the there have been more than one million cochlear devices put into use. Cochlear Limited is the market leader, supplying more than 750,000 devices to assist 650,000 people globally. In the , it helped more than 44,000 people regain their hearing.  

The work the �ʹڲ�Ʊ team is doing will feed into the next generation of cochlear implants, but it may be some time before their innovations are seen in clinics. The testing and regulatory processes required to ensure device safety can take years to complete.  

“When you look at medical devices that are used in the clinic, the change is very incremental. You can’t suddenly just pull this one off the market and go in with something that's completely different,” Laura says.

“Then there’s the manufacturing side. Can it actually be slotted into a manufacturing process that a company might use? If you think of a company like Cochlear, they’ve been making a very simple 22-electrode array for 40 years, and there’s a really huge bar to get over to actually change that.”

Connecting industry and university researchers to get the best results for end-users of therapies and devices is at the core of IHealthE’s approach, Laura adds.

“The exciting thing with our work is, you know, there is that end game – you look at doing things that are going to improve people’s lives.”