*The authors are in alphabetical order – both authors are first authors on this publication
A groundbreaking fully implantable cochlear implant marks the start of a new era in hearing restoration – discreet, continuous and free from external hardware.
The cochlear implant is the first prosthesis to replace a human sense: hearing. Designed for people with unilateral or bilateral severe-to-profound sensorineural hearing loss, cochlear implant development is evolving at an unprecedented speed.
A significant leap forward has recently been made with the publication of the first-in-human feasibility study of a totally implantable cochlear implant (TICI). The TICI marks a pivotal step in cochlear implant development, making hearing restoration effective and discreet, and hearing available without limitations in various everyday scenarios and at all times.
Image courtesy of MED-EL.
Audio processor drawbacks
Conventional cochlear implants (CI) consist of an internal implant and an external audio processor. Although they have become considerably smaller in the past 25 years, from body-worn models to behind-the-ear and single-unit models, external processors still come with drawbacks. They still mean restrictions for users in some everyday situations where they may impede engagement in routine activities, such as personal hygiene (e.g. shower), recreational pursuits like sailing, or professional responsibilities requiring availability during nocturnal hours. They require regular maintenance and can potentially be lost. External audio processors are vulnerable to damage, leaving users without hearing until repaired. Furthermore, they are a visible marker of disability, thus being a potential for stigmatisation and self-esteem issues. In fact, the visibility of audio processors has been identified as one reason for the low cochlear implant uptake rate.
"A fully implantable device must function independently of external power sources, ensuring safe and uninterrupted operation for periods exceeding 24 hours without the need for recharging"
Challenges on the way to a new era
To address these issues, a totally implantable cochlear implant has been developed by the Austrian cochlear implant manufacturer MED-EL in close cooperation with leading universities and cochlear implant centres. It integrates all components of a conventional CI into a single, fully implantable device, thus eliminating the need for an external audio processor with all its drawbacks.
Developing the TICI required overcoming numerous technical challenges, most notably concerning power supply, the subdermal microphone and the wireless data link for programming and diagnostics without transcutaneous physical connectors.
A fully implantable device must function independently of external power sources, ensuring safe and uninterrupted operation for periods exceeding 24 hours without the need for recharging, and needs to overcome a variety of associated technical challenges.
"From a surgical perspective, the TICI is safe to implant and comparable to that of a conventional CI"
An implantable microphone needs to address the acoustic attenuation through the skin and soft tissue, the placement issue in the skull and constrained directional sensitivity. Body-generated sounds that the internal microphone may pick up may lead to a degraded signal-to-noise ratio.
First in-human feasibility study
Solutions for these challenges were found with contributions, developmental efforts and input for over a decade. Finally, the first six TICI implantations were performed at the CI centres in Liège (Belgium) in September 2020 and Munich University LMU (Germany) in November 2020, after the necessary formal regulations were approved by the local notified bodies. Thus, the first in-human feasibility study with this novel, fully implantable device was initiated.
The study’s primary aim was to assess the safety of the TICI by describing the occurrence of adverse events over a 52-week observation period. Its secondary objectives included evaluating speech perception in quiet and noise, subjective user experiences and device usage time.
Six postlingually deafened participants aged between 20 and 80 years who all met the stringent inclusion criteria for cochlear implantation were enrolled in the study.
To allow within-subject comparisons of performance between the TICI and a conventional CI, all participants received an external MED-EL SONNET audio processor.
TICI surgery
The TICI can be implanted safely, using a slightly modified and adapted surgical approach, similar to what is accepted as standard procedure for conventional cochlear implants, including double layer flaps, implant bed and securing the implant housing with sutures. Preoperatively, the most suitable electrodes for the patients’ individual cochlear duct lengths and hearing loss were chosen. Postoperative recoveries were uneventful in all cases. From a surgical perspective, the TICI is safe to implant and comparable to that of a conventional CI.
Hearing performance with the TICI
The TICI was activated four weeks after implantation. Standard speech tests in quiet and in noise, performed several times during the 52-week study period, showed that the hearing performance with the MED-EL TICI was comparable to that of a conventional cochlear implant with an external audio processor. The results remained stable with a slight tendency to improve over more than four years follow-up.
This is a critical finding, as it demonstrates that the internal microphone and signal processing capabilities of the MED-EL TICI are on par with established external systems.
Patient insights
To understand how the TICI impacted daily life, we used four standard validated tools to measure patient-reported outcomes, capturing both quality of life and the personal impression of hearing improvement. Across all measures, participants reported significant improvements from the preoperative baseline to the 52-week follow-up. These gains reflect enhanced hearing performance, improved self-esteem and greater social engagement.
Participants also maintained daily satisfaction diaries. Usage logs are integrated in modern cochlear implants, including the TICI, granting the CI team at the clinic a detailed insight into daily usage with and without the external processor. Most patients reported increasing satisfaction over time, with six using the TICI without the external processor for most of the day, up to 18.5 hours daily in some cases.
The pioneering TICI surgeons’ conclusion
The development of the TICI required research and development teams to overcome several engineering hurdles while observing rigorous standards for biocompatibility, durability and performance.
In our study, the TICI’s safety, hearing performance and user satisfaction equalled or outperformed conventional cochlear implants. We are eagerly awaiting the results of larger multicentre trials to confirm the TICI’s long-term outcomes and efficacy.
"The results remained stable with a slight tendency to improve over more than four years follow-up"
As the cochlear implant field moves toward more personalised and patient-centred care, totally implantable solutions like the MED-EL TICI can potentially help advance the field of auditory prosthetics. For now, the TICI stands as a testament to what is possible when clinical insight, patient needs and technological innovation converge. The TICI will offer a chance to better quality of life for many patients, and will help to reduce the stigma.
Since the technological challenges are considerably greater than the medical and surgical contributions, we want to congratulate MED-EL for the realisation of this highly innovative technology.
Read the Open Access paper in full at:
https://www.nature.com/articles/s43856-024-00719-0
Declaration of competing interests: Departments of both authors have received funds for research. Funds have been provided by multiple organisations.
