Researchers at EPFL (École Polytechnique Fédérale de Lausanne) have developed a soft auditory brainstem implant (ABI) that could significantly improve hearing restoration for individuals who are not candidates for cochlear implants. Unlike traditional rigid ABIs, this new flexible device is designed to conform to the natural contours of the brainstem, reducing side effects and improving sound perception.
Cochlear implants have helped many people regain hearing by transmitting sound signals from the inner ear to the brain. However, these implants require an intact cochlear nerve to function. For individuals with damaged or missing cochlear nerves, auditory brainstem implants offer an alternative by directly stimulating the brainstem. Existing ABIs, made of rigid materials, do not fit the curved surface of the brainstem well, often resulting in unintended stimulation of surrounding nerves. This can cause side effects such as dizziness, facial twitching, and discomfort, leading to the deactivation of several electrodes and limiting the implant’s effectiveness.
The new ABI developed at EPFL addresses these challenges using ultra-thin, flexible materials. The implant consists of micrometer-scale platinum electrodes embedded in a soft silicone substrate, forming a highly pliable array less than a millimeter thick. This design improves contact between the electrodes and brain tissue, reduces unintended nerve stimulation, and enhances the precision of auditory signals.
The device was tested in macaques with normal hearing through a series of behavioral experiments. The animals were trained to perform auditory discrimination tasks, such as recognizing whether two tones were the same or different. Over time, electrical stimulation from the soft ABI was gradually introduced and blended with natural acoustic tones, allowing the animals to associate the prosthetic signals with real sounds. The macaques ultimately responded to stimulation from the ABI alone, demonstrating that they could distinguish different electrode activation patterns with a level of precision similar to their perception of natural sound.
The implant’s soft, conformable design offers several advantages. By naturally adapting to the brainstem’s shape, the device maintains better contact, lowers stimulation thresholds, and allows more electrodes to remain active. Conventional ABIs often leave air gaps between the device and brain tissue, leading to current spread and reduced signal accuracy. The flexible EPFL device eliminates these gaps and offers improved spatial targeting.
Additionally, the implant’s design is customizable thanks to advanced microfabrication techniques. While the current prototype includes 11 electrodes, future versions could support higher electrode counts and customized layouts to better match the frequency mapping of human hearing.
In the macaque study, the implant did not cause any observable discomfort or off-target effects, such as facial muscle twitching. The animals voluntarily initiated stimulation multiple times, suggesting that the prosthetic input was tolerable and not aversive. The implant also remained stable in position over several months, a critical improvement over traditional ABIs, which are prone to migration over time.
Though the device is still in preclinical stages, researchers are planning further studies to prepare for human trials. One proposed approach is to test the flexible implant during existing ABI surgeries to compare its performance in real-time with standard devices. All materials used will need to meet medical-grade standards and demonstrate long-term reliability in human tissue.
The development of this soft ABI represents a significant advance in auditory prosthetics, offering new possibilities for patients with severe hearing loss who cannot benefit from cochlear implants. With continued research and clinical validation, this technology could lead to more effective, comfortable, and precise hearing restoration solutions.
By Impact Lab
