Smart cochlear implants could monitor inner ear health, deliver drugs and adapt in real time, merging biosensing, microfluidics and personalised hearing care.
From passive hearing aids to smart implants
Hearing technology has advanced dramatically over the last few decades, yet today’s cochlear implants still face an important limitation: they are not well integrated with the body’s natural biological signals. While clinicians can assess impedance measures and record neural responses such as electrically evoked compound action potentials (ECAPs) to evaluate device integrity and auditory nerve activity, these metrics offer limited information about the broader physiological state of the inner ear [1].
Imagine if an implant could not only stimulate cochlear neurons but also go further, monitoring the inner ear’s activity and delicate internal processes – including changes in electrochemical activity, diffused gases and tissue responses such as inflammation.
This can be the future potential of biosensor-integrated cochlear implants: a new generation of ‘smart’ auditory prostheses designed to combine stimulation, electrochemical measurements, biosensing, and/or precision drug delivery within one closed-loop system [2,3].
Why biosensing matters
The inner ear is an extraordinarily sensitive yet fragile sensory organ, protected deep within the temporal bone and filled with ionic fluids (i.e. perilymph and endolymph) that make hearing possible. Even minor perturbations in ion concentration, oxygen level or tissue inflammation can drastically affect cochlear sensitivity.
Traditional cochlear implants deliver electrical signals but provide no real-time biological feedback, meaning that clinical adjustments are largely based on screening tests rather than real-time information from the inner ear. By integrating miniaturised biosensors with stimulating electrode arrays, it becomes possible to measure electrochemical changes in real time, such as potassium or oxygen levels, to monitor cochlear health and assist diagnosis and guide therapies [4].
This represents a shift from open-loop systems (only stimulate) to closed-loop auditory prosthetics, where sensor feedback can adapt stimulation patterns or use drug delivery based on biomarker detection.
Mimicking the natural cochlea
Biosensors draw inspiration from the ear itself. In nature, the cochlea’s mechanosensory hair cells and basilar membrane perform exquisite frequency discrimination, converting sound waves into frequency-dependent patterns or electrical signals. We have developed biomimetic (i.e. imitating the structure and function of biological systems) artificial basilar membranes (ABMs) using piezoelectric materials like polyvinylidene fluoride (PVDF), which convert sound waves directly into electrical signals inspired by the functional operation of the cochlea [5].
Figure 1: Schematic illustration of frequency-selective acoustic sensing using a PVDF-based circular artificial basilar membrane (CABM), demonstrating bioinspired frequency discrimination (Licensed under CC BY 4.0) [5].
These thin, flexible membranes respond to different sound frequencies depending on their geometry, somewhat mimicking the cochlea’s tonotopic organisation and passive mechanics (Figure 1). When integrated with microelectronics, they form multichannel acoustic sensors capable of detecting sound without external power. This self-powered behaviour comes from the piezoelectric material itself: when the artificial basilar membrane vibrates in response to sound, mechanical deformation of the piezoelectric film generates an electrical charge, meaning the sensor produces its own signal without needing a battery. Such biomimetic sensors may one day replace or enhance traditional microphones in cochlear implants or even be used in robotic hearing, providing more natural sound perception while reducing background noise.
Microfluidics: a miniaturised inner ear
Beyond sound detection, researchers are now mimicking the cochlea’s microenvironment using microfluidic platforms, essentially ‘lab-on-a-chip’ systems that simulate the movement of perilymph and endolymph. These have the potential to allow drugs, cells and even stem-cell-derived organoids (which means miniature 3D tissue models that reproduce key features of the inner ear) to be tested under controlled near-physiological conditions.
"Such integrated systems could also monitor biomarkers…to enable early intervention before hearing performance declines. Ultimately, biosensor-guided implants could lead to truly self-regulating auditory devices"
Microfluidic systems (devices that integrate channels with micro-scale diameter to allow analysing fluids in micro- or even nano-scale volume) have been incorporated into a cochlear device in recent in vitro experimental studies – laboratory experiments performed outside the body – demonstrating the feasibility of targeted intracochlear drug delivery [6,7]. Such integration allows precise administration of anti-inflammatory or neuroprotective agents through the implant array, addressing local inflammation or fibrosis that can compromise long-term device performance. By enabling flow control at the microlitre scale, these systems provide a pathway toward highly localised and programmable therapeutic delivery within the cochlea [8].
Recent studies have demonstrated pumpless microfluidic drug delivery systems powered by capillary action or tiny on-chip micropumps. These may offer long-term, programmable release of therapeutic agents within the cochlea that could be game-changing for chronic inner ear disease management [9].
Integrating biosensors, drug delivery and electronics
The real innovation lies at the intersection of these technologies. By integrating biosensors and microfluidic systems onto flexible electrode arrays, a future cochlear implant could simultaneously:
- Detect ionic or metabolic changes via electrochemical sensors
- Deliver drugs in response to detected inflammation or hypoxia
- Adjust stimulation parameters automatically based on biosensor feedback
Such integrated systems could also monitor biomarkers (molecules that indicate cellular stress or neural damage) to enable early intervention before hearing performance declines. Ultimately, biosensor-guided implants could lead to truly self-regulating auditory devices capable of long-term inner ear health monitoring.
Bridging diagnostics and therapy: theragnostics
This convergence of diagnostics and treatment, known as theragnostics, is already transforming other areas of medicine. In otology, it could enable precision diagnostics and therapies for conditions such as Ménière’s disease, hearing loss, or post-implantation trauma.
For example, electrochemical sensors built into implant electrodes to measure oxygen within the cochlea of animal models provide a direct indicator of metabolic stress. Similarly, ion-selective microelectrodes can monitor potassium fluctuations linked to inner ear fluid imbalance, which may contribute to acute attacks of vertigo and fluctuating hearing loss in Ménière’s disease [10].
Towards regenerative hearing devices
The next frontier involves combining biosensors with regenerative medicine. Tissue-engineered cochlear ‘organoids’ are already being used to model human hearing development and diseases. When coupled with microfluidic systems and biosensors that present next-generation organ-on-a-chip systems, these living models can provide real-time data on drug responses and neural regeneration [11].
In the long term, such hybrid bioelectronic systems may help regenerate damaged inner ear structures, merging prosthetic function with regenerative therapy (Figure 2).
Figure 2: Future perspective of biosensors, microfluidics, drug delivery, regenerative medicine and AI converge to enable personalised inner ear diagnostics and therapy (Licensed under CC BY 4.0) [12].
Challenges ahead
Translating these laboratory breakthroughs into clinical reality remains challenging. Devices must be miniaturised, biocompatible and stable within the inner ear’s complex yet delicate microenvironment. Preventing biofouling (i.e. the accumulation of biological material on device surfaces that can impair function), ensuring long-term power supply and maintaining safe electrode–tissue interfaces are critical engineering hurdles.
Equally important is interdisciplinary collaboration for bridging otolaryngology, neuroscience, materials science and microengineering. Clinical trials will also need to establish safety and performance benchmarks for biosensor-enabled implants. Yet, the pace of innovation suggests that the first ‘smart cochlear implants’ capable of biosensing may not be far away.
Figure 3: A futuristic conceptual illustration of a bionic artificial inner ear.
A new era of personalised hearing care
The evolution of cochlear implants from electrical stimulators to active, self-monitoring systems represents a major step forward in personalised hearing care. By integrating biosensing, microfluidics and adaptive control, future implants have the potential to continuously monitor and adapt their function to each patient’s unique inner ear microenvironment.
These developments may ultimately transform the way clinicians diagnose, treat and manage inner ear dysfunction, shifting the focus to preserving and monitoring cochlear health.
References
1. Brown CJ, Abbas PJ, Borland J, Bertschy MR. Electrically evoked whole nerve action potentials in Ineraid cochlear implant users: responses to different stimulating electrode configurations and comparison to psychophysical responses. J Speech Hear Res 1996;39(3):453–67.
2. Lee HJ, Son Y, Kim J, et al. A multichannel neural probe with embedded microfluidic channels for simultaneous in vivo neural recording and drug delivery. Lab Chip 2015;15(6):1590–7.
3. Lei IM, Jiang C, Lei CL, et al. 3D printed biomimetic cochleae and machine learning co-modelling provides clinical informatics for cochlear implant patients. Nat Commun 2021;12(1):6260.
4. Weltin A, Kieninger J, Urban GA, et al. Standard cochlear implants as electrochemical sensors: Intracochlear oxygen measurements in vivo. Biosens Bioelectron 2022;199:113859.
5. Aghajanloo B, Moshizi SA, Asadnia M, Pastras C. Frequency-selective acoustic sensing using circular PVDF-based artificial basilar membranes. Sens Actuators A Phys 2025;391:116633.
6. Peppi M, Marie A, Belline C, Borenstein J. Intracochlear drug delivery systems: a novel approach whose time has come. Expert Opin Drug Deliv 2018;15(4):319–24.
7. Lehner E, Menzel M, Gündel D, et al. Microimaging of a novel intracochlear drug delivery device in combination with cochlear implants in the human inner ear. Drug Deliv Transl Res 2022;12(1):257–66.
8. Alharbi A, Abdelazim MH, Alshammari AS. A microfluidic reciprocating intracochlear drug delivery system with reservoir and active dose control. Lab Chip 2014;14(4):710–21.
9. Yu H, Xing J, Zhang H, Pang X. Electroacoustic responsive cochlea‐on‐a‐chip. Adv Mater 2024;36(4):2309002.
10. Ivandini TA, Einaga Y. Electrochemical sensing applications using diamond microelectrodes. Bull Chem Soc Jpn 2021;94(12):2838–47.
11. Holloway EM, Capeling MM, Spence JR. Generation of inner ear organoids containing functional hair cells from human pluripotent stem cells. Nat Biotechnol 2017;35(6):583–9.
12. Aghajanloo B, Nazarnezhad S, Arshadi F, et al. Emerging trends in biosensor and microfluidics integration for inner ear theragnostics. Biosens Bioelectron 2025;286:117588.
Declaration of competing interests: None declared.
