Micro-LEDs for optogenetic stimulus transmission

The OSRAM Podcast: Episode #8 with Prof. Dr. Ulrich Schwarz

Welcome to the Photonstudio, the podcast from OSRAM. My name is Karin Steinmetzer. Today’s topic is can you hear light? I would like to welcome Prof. Dr. Ulrich Schwarz. He is a professor for experimental sensor technology and optoelectronics at the Chemnitz University of Technology. He is co-founder of the start-up company OptoGenTech and has been connected with OSRAM for many years through research projects. I have already got to know many applications of LEDs.

For example, we carry many of them around in our cell phones. Increasingly also on the body as displays and sensors, for example in the form of fitness trackers. Ulrich Schwarz has made it his business to go one step further. His field of research is implantable LEDs. I would like to talk to him about this today in Munich.

Karin: Welcome Ulrich!

Ulrich: Hello, I am very pleased that you are interested in this topic!

Karin: The most exciting question first: can we hear light?

Ulrich: Humans cannot yet hear light. We have already taught mice that they react to light like an acoustic stimulus.

Karin: What can you use it for? What is the field of application you have in mind?

Ulrich: Our vision is to develop a new type of hearing aid for people with severe hearing loss, which replaces the previous technology and allows a hearing impression that is much more real than what can be achieved with a conventional cochlear implant.

Karin: How are severely hearing-impaired people currently being helped and what would you like to do differently?

Ulrich: It is mostly about the fact that the hair cells in the inner ear have been destroyed, but the nerve cells are still intact and the lines from the inner ear to the brain are also intact. The question is, how do you now stimulate these nerve cells in the inner ear? The very successful conventional cochlear implant does this with electronic impulses. It electrically stimulates the nerve cells in the inner ear in certain areas of the cochlea.

Karin: What is the cochlea?

Ulrich: This is a spiral in the ear, along which the nerve cells sit. And when they are stimulated, they reach the brain as if it were an acoustic stimulus. Even if the hair cells no longer exist.

Karin: About how many people are we talking here?

Ulrich: Currently, 700,000 people worldwide already have a cochlear implant. They have this button on their head in addition to a hearing aid that sits on their ear. There, sound from the environment is picked up, divided into frequency channels, inductively transmitted to the implanted electronics and from there to the inner ear, to the cochlea, where nerve cells are stimulated.

Karin: And what can light do better than electricity?

Ulrich: The electric cochlear implant can stimulate approximately eight to ten frequency channels. This is due to the fact that these electrical impulses spread relatively widely in the ear. Light can be concentrated much better. This means we can then stimulate up to 100 frequency channels or more in the ear.

Karin: Can you illustrate this a bit? How does that sound?

Ulrich: With a conventional cochlear implant, you can understand speech as if you were speaking through a narrow oven tube. Music is actually not heard at all. Speech understanding is possible, but you cannot distinguish between male and female voices. You cannot hear if it is a question or an answer. You cannot distinguish speakers. And especially when several people are speaking or there is background noise, the speech is very quickly unintelligible with a conventional cochlear implant because we lack frequency resolution.

Karin: This means that with an optical cochlear implant, music enjoyment would also be possible again?

Ulrich: Exactly, that is our hope. A much better understanding of speech and also of music.

Karin: And how is this fine frequency resolution achieved? Do I need a lot of colors for this? So a rainbow in the ear along the cochlea or how can I imagine that?

Ulrich: The translation of spectral colors into pitches is a nice idea, but it is not like that. In the inner ear, these pitches are coded along the cochlea. The high tones are at the entrance of the cochlea and the low tones are at the tip of the cochlea. And depending on where you now stimulate, you can experience different pitches. This is called tonotopic, meaning that the pitch is determined at the nerve location. And you always start with one color, there are different approaches, blue or red. The pitch and the frequency resolution come from how many different places you can excite separately. And with light, the resolution is much finer, because the light does not spread so far in the cochlea.

Karin: But the nerve cells in the ear are not naturally sensitive to light, you need a light switch, so to say. For that you have to help...

Ulrich: Exactly, for this purpose we build ion channels into the membranes of the nerve cells, which react to light and create a flow of ions between the inner and outer cell, thus switching the nerve cells. In other words: then they react to light, with a nerve pulse.

Karin: Do I have to repeat this several times or will it last a lifetime?

Ulrich: This whole area is called optogenetics. By the way, the sound cells come from algae, which use them to recognize above and below. And the advantage of nerve cells is that they do not renew themselves. Nerve cells remain for a whole life. This is of course also the disadvantage, if nerve cells are damaged, they remain damaged. For us here it is an advantage. If these proteins are built into the cell membrane of the nerves, then they will remain intact.

Karin: So it is also clear that it is not only about the semiconductor side, the topic also has a very strong biomedical component. Who covers this area? You are the expert for semiconductors, but who covers the medical part?

Ulrich: Medicine was the first impulse. Our colleague Professor Tobias Moser from the Auditory Neurosciences at the University Hospital Göttingen did the essential preliminary work. He first proved that optogenetics works in the ear and that it is possible to make these nerve cells sensitive to light. All the preclinical studies are also being carried out in his group. This really is an interdisciplinary project in the best sense of the word. Not only do physicians and optoelectronics physicists work together here, but also within the disciplines. On the medical side, it's molecular biology and the neurosciences. On our side it is optoelectronics, i.e. the light sources and microsystems technology we need to create these implants. So it is a very broad field.

Karin: I would still focus a little bit on semiconductors, because this is the area we are particularly interested in. As I said at the beginning, LEDs are used in many ways, even on the human body, but not yet in the body. Which requirements have to be met in order for LEDs to be implanted?

Ulrich: First of all they have to be tiny. We are now talking about light-emitting diodes with an approximate surface area of 50 x 50 micrometers square, which are then built into a flexible strip. 100 or more of these light-emitting diodes are built into a very small plastic band, which is then inserted into the inner ear. It was absolutely clear that such LEDs do not exist, so an in-house development is necessary. This is derived from thin-film light-emitting diode technology, which also led to OSRAM's Future Prize. We have been working together with OSRAM for a long time in various projects and our first big task was to transfer this thin-film process so that the luminaire can not only be made even smaller, but can also be integrated with this polymer.

Karin: So, on flexible substrates?

Ulrich: Flexible substrates are polymers and of course they can only tolerate much lower process temperatures than conventional substrates made of semiconductors. That was a lot of process technology behind it...

Karin: If I may interrupt here: on the one hand, they have to be tiny, flexible and last quite long. Right?

Ulrich: Exactly, this is the next, very big challenge. Ideally, an implant is implanted in a young child in the first year of life so that all the structures we need to hear can develop in the brain as well. And that means that the implant must last at least 80 years in the body. That is a great challenge.

Karin: And what is the next step in Professor Moser's field of research? What is the next milestone on the way to marketability?

Ulrich: The next big step is the preparation of a clinical study. We are preparing for a clinical study of an implant in humans. This requires tolerability and longevity. The requirements for a medical device are correspondingly high here. And of course, this has to be prepared accordingly from the biomedical side as well as from the optoelectronic side.

Karin: As far as I know, you have also taken a third side into focus: the economic side! You and a few more have founded a start-up, the OptoGenTech. Who is working with you in the team and what is your goal?

Ulrich: The founders are Tobias Moser, Daniel Keppeler, Christian Goßler and myself. We are sure that the conventional implant can no longer be further developed in terms of frequency channels. These are simply physical limits. We now have a product that is better. The market is correspondingly large; we expect a market of several billion euros per year.

Karin: I think you may also have other applications beyond the optical cochlear implant just discussed.

Ulrich: Exactly, there are several medical applications where nerves in the body can be stimulated with light.

Karin: There is already work in progress on pacemakers based on optics. In fact, in the eye as well, especially there is no other solution. That is why the activities here are already relatively extensive. For the optical cochlear implant, access to the nerves in the inner ear has already been successfully demonstrated, so we hope that our optical cochlear implant will be the first medical product on the market in which optogenetics is successfully used.

Ulrich: Can you give a short forecast, when something like this might be available on the market?

Karin: This should be through the clinical study in a few years.

Ulrich: Then I say thank you very much for the interview. Good luck to you and the team! We are really excited about how optogenetic methods will change the medical market.

Karin: Many thanks to you and to all OSRAM colleagues for your interest in the topic.

As always, you can listen to the latest episode of our Photonstudio on Soundcloud, iTunes, Spotify and Google Podcast. If you want to know more about how light can sound, I recommend the online version of our innovation magazine ON. At www.osram-group.com/innovation you will also find many other exciting articles from the world of photonics. Until the next episode in the Photonstudio!

Photonics is THE key technology in every OSRAM solution