The silk road to recovery – solving the problem of burst eardrums

Dr Ben Allardyce is working on a silk skin for burst eardrums. Photo: Simon O’DwyerGeelong researchers are testing a silk membrane to fix badly perforated eardrums. Traditional materials used to repair eardrums have either provided good acoustic properties or mechanical strength that resists further tearing. It appears that the silk drum skin provides both.
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While most eardrum perforations heal themselves, chronic middle-ear infections or trauma leads to larger permanent holes. Untreated, they lead to further infection and hearing loss.

“Repairing these perforations usually means grafting material from somewhere else on the body,” says Dr Ben Allardyce, postdoctoral research fellow at Deakin University’s Institute for Frontier Materials.

The long-time go-to material was the temporalis fascia, the fibrous covering of the chewing muscle, just above the ear. “It gives good hearing outcome because it’s thin and flexible,” says Allardyce. “The downside is it is relatively weak.”

Certain infections, such as that of the eustachian tubes that lead from the ear to the nasal cavity, can cause negative pressure – leading the grafted material to collapse. In such cases a surgeon will opt for ear cartilage as the grafting material. “It’s mechanically very strong but causes a dampening of the sound waves,” says Allardyce.

“It’s also completely opaque, which makes follow-up observation of the middle ear very difficult.”

In 2009, while attending a conference on silk powders, one of Allardyce’s colleagues, Dr Rangam Rajkhowa​, met with representatives of the Ear Science Institute  , a research and advocacy group based in Western . The institute was keen to see a fibre-based solution to the problem. Silk is particularly useful in bio-medical applications because it’s a protein that the human body can well tolerate. Issues of rejection are minimal.

“There’s a very low immune response to silk protein,” says Allardyce. “And it appears that a silk membrane offers both mechanical strength and good acoustic properties.”

The production of the basic membrane is fairly straightforward. The silkworm cocoons are boiled in an alkaline solution to get rid of gummy protein.

They’re then dissolved in a concentrated lithium bromide solution at 60 degrees. This leaves a honey-coloured solution of liquid protein, which is transparent.

Dialysis is then deployed to get rid of the salt. The remaining silk protein waster is poured into a dish to dry out. What remains is a clear membrane.

So far the membrane has been tested on guinea pigs and rats. Cell culture work shows the cells of the eardrum can attach to the membrane and grow across it. Testing of the membrane’s acoustic properties is being done using a laser doppler vibrometer – a laser that measure the vibration of an object – an audiology ear phone, a microphone and plastic ear canal tube.

All of this is looking good. “But we still don’t know how the membrane will behave in the environment of the middle ear,” says Allardyce.

Next up are human clinical trials. But given there are intellectual property and patent issues at play, it’s not clear when these will begin.

The silk skin innovation has profound implications for ‘s Indigenous children, who have the highest rates of middle-ear disease in the developed world, with around one-third suffering moderate to severe hearing loss, according to a Medical Journal of report from 2010, and a World Health Organisation red flag in 2004.

“Indigenous ns are more prone to large perforations because they have less access to antibiotics when suffering infections,” says Allardyce. “For children the outcomes include developmental problems … because their speech is significantly impacted.”

Tympanic membrane perforation, or hole in the ear drum, reportedly affects around 100,000 ns and more than 80 million people worldwide.

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