Fraunhofer IPMS improves cochlear implants with OLED-on-silicon probes

25 Sep 2024

Tiny locally controllable pixels on a chip allow light stimulation to be precisely directed.

Researchers from the Fraunhofer Institute for Photonic Microsystems (Fraunhofer IPMS) and the Max Planck Institute for Multidisciplinary Natural Sciences (MPI-NAT) have designed novel optical stimulators for future cochlear implants.

Designed as part of the NeurOpto project, a collaboration between the two institutions, the new emitters are being presented at the W3+ event in Jena.

The breakthrough is based on OLED-on-silicon technology, a research field that Fraunhofer has been studying for displays and other purposes for some years. Placing OLED emitters onto silicon substrates can allow smaller light-emitting pixels to be created, and more of them fitted onto a given display area.

Fraunhofer IPMS has now used an OLED-on-silicon approach to create a CMOS-integrated pixelated OLED microsensor, able to individually control spatially distributed light channels with high pixel density and brightness along with low power consumption.

According to the project, this could be particularly valuable for novel cochlear implants, as an improvement over conventional electrical implants which attempt to convert sounds into electric impulses and deliver them to the auditory neurons of a patient, to restore some degree of hearing that is otherwise lost.

Photonics is known to offer a promising alternative approach. The auditory neurons involved are not naturally light sensitive, but developments in optogenetics make it possible to induce the neurons into expressing light-sensitive proteins, which can then be stimulated by light pulses.

In 2020 the University of Göttingen demonstrated an optical cochlear implant (oCI) for auditory treatment featuring a linear array of 10 LED chips, each 270 by 220 microns and emitting at 457 nanometers. The new Fraunhofer research sought to leverage OLED-on-silicon technology to produce improved emitters for a similar purpose.

Precisely controlled optical stimulation

"With OLED-on-silicon technology, we can bring tiny, locally controllable light pixels onto a chip," said Uwe Vogel from Fraunhofer IPMS. "This chip can be flexibly designed to reach the desired locations even in curved structures like the cochlea. This allows light to be used precisely where electrical stimulation alone is insufficient."

In electrical cochlear implants, each electrode contact can lead to stimulation not just of the cells of interest but also more distant nerve cells that code different frequencies, severely limiting speech recognition in background noise and enjoyment of music. Since light can be controlled much more precisely, an oCI could overcome this problem.

According to Fraunhofer IPMS the new design should also increase the number of independent frequency bands being utilized, through dozens of microscale light emitters along the frequency axis of the cochlea, ideally individually controllable. MPI-NAT have been working for many years with academic and industrial partners on the development of the oCI and gene therapy, commented the team.

"Although Fraunhofer IPMS has already introduced unique features with its OLED-on-silicon technology for microdisplays that are also important for optogenetics, there are still some challenges," noted the project.

"The necessary brightness and degree of integration have been successfully demonstrated; however flexibility and biocompatibility are not yet verified. The silicon microtechnology used has shown that these properties are generally achievable."