Professor Martin Ptok; © private
A small, new device that is worn in the ear canal and that emphasizes the latest technology is meant to provide relief in the future. COMPAMED.de talked about this with one of the developers of the ring-shaped osteophone for the hard of hearing, Professor Martin Ptok of the Medical University of Hannover, Germany.
COMPAMED.de: Professor Ptok, you are currently developing a novel, ring-shaped hearing aid for people hard of hearing, which can be worn in the ear canal. What is the difference compared to conventional hearing devices that we have known thus far?
Martin Ptok: We are presently developing a device that is based on the technology from well-established hearing aids. We considered the following: Normally aside from the microphone and the amplifier, a hearing device consists of a loudspeaker. It carries the airborne sound signal to the eardrum. Usually, conventional hearing aids are supposed to be very small – which is why the loudspeaker that sits in or on the ear is also very tiny. Especially music lovers know though that larger loudspeakers typically are better than small ones. Of course this is also true for the loudspeaker in the ear. If we have very small loudspeakers, we nowhere near reach the frequency response – including the high-frequency range – which we would actually want. To achieve good speech comprehension though, the high-frequency rate is mostly responsible.
As a result of these characteristics, we considered presenting the acoustic signal to the inner ear through another way, namely through the so-called bone conduction. We are currently developing a virtually vibrating ring for this, which acts as a loudspeaker and which is able to deliver signals via the bone conduction and with a significantly better frequency response to the inner ear. This would particularly benefit patients with a hearing deficiency in the high-frequency range. Typically these are patients, who for instance hear more poorly when surrounded by ambient noise, but are able to still understand a lot in a quieter environment. You also talk about the so-called cocktail party effect in this case.
COMPAMED.de: There are already headphones available that are placed behind the ear and conduct the acoustic noise via the bone. Is this a similar principle?
Ptok: The principle is similar, although these headphones are more like bars that can be placed on the petrous bone. However, these are vibrating pieces that due to their size of course cannot be inserted in the auditory canal. Since size plays an important role in our design, our approach is a different one.
COMPAMED.de: How large is your concept device going to be?
Ptok: The hearing aid we are developing is meant to nestle in the ear canal and has a hole in the middle through which low frequency can still reach the eardrum in a natural way. That’s why there is a ring structure. We are talking about a size of about 5 to 8 millimeters in cross section diameter here, since the size of the ear canal varies somewhat from person to person. For this reason, the device will also have to be individually manufactured for each patient.
COMPAMED.de: Is there a risk for the hearing aid to get out of place in the auditory canal due to its small size?
Ptok: Theoretically speaking, anything is possible, but after all the normal shells of a hearing aid don’t shift either. Our designed ring is meant to sit tightly in the ear canal, although of course it is not supposed to press on anything. Yet it is not supposed to have to be bonded or surgically attached. The goal is that it stays in because of the natural grip in the ear. But that’s our smallest issue. There are other challenges in the design which we have in part already solved and in other parts we still need to solve. Because even though this it just a small ring, this is after all a true high tech device.
Otoplasty = a form-fitted piece, customized to the auditory canal; © Medizinischen Hochschule Hannover
COMPAMED.de: What material is the ring meant to be made of?
Ptok: It is a relatively complicated piezo actuator, which is manufactured in a multi-layer production process. We are collaborating with a company here, which has special experience in this area.
COMPAMED.de: What kind of life cycle do you expect from this hearing aid? And could it also for instance be reduced by earwax, which corrodes the device?
Ptok: Ear wax can be removed fairly easily, especially by a professional ear specialist. In addition, the ring can be taken out and cleaned just like a normal hearing aid. There are always patients that have to regularly check in for a professional ear cleaning, regardless of them having a hearing aid or not. I think the life cycle will fall into a similar realm to present hearing devices.
COMPAMED.de: Have there already been early experiments with test listeners?
Ptok: I personally have already acted as a test listener, albeit with a still very preliminary prototype. I was amazed how high the frequency response really is. It goes beyond 10 kilohertz, while the conventional hearing aids have a frequency response that generally maybe ends at 5 to 6 kilohertz. So this was very impressive.
COMPAMED.de: Where are you currently in the development? What are the next steps that you still need to take?
Ptok: There are still many steps. One next step, which is also a very exciting one will be the answer to the question of where the optimal coupling with the ear canal is. Another step raises questions of a more technical nature: How do we manage to create a complex, individual form? What process steps do we need? Does manual production make sense? Is it a block from which we can mill out the form? Piezo actuators are made of very brittle, hard material. The question of energy supply also needs to still be resolved. In addition, we of course have to also still perform an audiological characterization. And you have to self-critically keep asking yourself: What benefit will the patient have from this design? Can we really reach patients with a high-frequency hearing loss with this amazing frequency response?
COMPAMED.de: You brought up the still open issue of energy supply: How long does the hearing aid currently run?
Ptok: Among other things this depends on how much amplification you need. But it is not uncommon that the device needs a new battery approximately once a week.
COMPAMED.de: When do you anticipate the first test runs with patients?
Ptok: At the moment we are primarily interested in developing this “loudspeaker“, the hearing aid receiver so to speak. I think we will have a first model designed in about six to nine months. However, it will still have a decoupled electronic circuit. With an electronic circuit, that is to say that a complete system is available, will still take about one to two years.
The interview was conducted by Simone Ernst and translated by Elena O'Meara.