Models of Cochlea Used in Cochlear Implant Research: A Review

Emerging trends in biosensor and microfluidics integration for inner ear theragnostics

Advancements in inner ear theragnostics are critical for addressing the pervasive challenges of diagnosing and treating hearing and balance disorders, which significantly impact quality of life. This paper reviews biosensors and devices that leverage advanced functional nanomaterials, microfabrication techniques, and nano-biotechnology to enhance theragnostic applications for the inner ear. The paper highlights the development of diverse electromechanical, electrochemical, and biomarker sensors for inner ear theragnostics. Electromechanical sensors replicate the cochlear and vestibular sensory structures through bioinspired designs, while electrochemical sensors are used to measure the level of ions and chemicals in the inner ear fluid, providing insights into the health and disease of the hearing and balance organs. Biomarker sensors focus on screening of inner ear diseases through early detection of correlated biomarkers based on point of care diagnostics. This study also examines the use of microfluidic devices with sensory elements to provide a compact and integrated model of the fluid-filled cochlea. In addition, advanced delivery strategies, including targeted drug delivery systems and nanocarriers are explored for their ability to improve the penetration and distribution of therapeutics within the inner ear. The study also highlights the importance of pharmacokinetics and post-treatment monitoring as critical indicators for assessing the efficacy of micro/nanotechnology-based theragnostic approaches. By consolidating these innovations, this work offers a comprehensive framework for advancing otology, paving the way for novel diagnostic tools, effective treatments, and future clinical applications.

Thermally Drawn Shape and Stiffness Programmable Fibers for Medical Devices

Despite the significant advantages of Shape Memory Polymers (SMPs), material processing and production challenges have limited their applications. Recent advances in fiber manufacturing offer a novel approach to processing polymers, broadening the functions of fibers beyond optical applications. In this study, a thermal drawing technique for SMPs to fabricate Shape Memory Polymer Fibers (SMPFs) tailored for medical applications, featuring programmable stiffness and shape control is developed. Rheological and differential scanning calorimetry analyses are conducted to assess SMP's compatibility with the proposed thermal drawing process and applications, leading to the production of multilumen, multimaterial SMPFs activated at body temperature. Different properties of SMPFs are investigated in three medical devices: stiffness-adjustable catheters, softening neural interface, and shape-programmable cochlear implants. Comprehensive characterization of these devices demonstrates the potential of thermally drawn SMPs to be employed in a wide range of applications demanding programmable mechanical properties.

A full-head model to investigate intra and extracochlear electric fields in cochlear implant stimulation

Objective.Despite the widespread use and technical improvement of cochlear implant (CI) devices over past decades, further research into the bioelectric bases of CI stimulation is still needed. Various stimulation modes implemented by different CI manufacturers coexist, but their true clinical benefit remains unclear, probably due to the high inter-subject variability reported, which makes the prediction of CI outcomes and the optimal fitting of stimulation parameters challenging. A highly detailed full-head model that includes a cochlea and an electrode array is developed in this study to emulate intracochlear voltages and extracochlear current pathways through the head in CI stimulation.Approach.Simulations based on the finite element method were conducted under monopolar, bipolar, tripolar (TP), and partial TP modes, as well as for apical, medial, and basal electrodes. Variables simulated included: intracochlear voltages, electric field (EF) decay, electric potentials at the scalp and extracochlear currents through the head. To better understand CI side effects such as facial nerve stimulation, caused by spurious current leakage out from the cochlea, special emphasis is given to the analysis of the EF over the facial nerve.Main results.The model reasonably predicts EF magnitudes and trends previously reported in CI users. New relevant extracochlear current pathways through the head and brain tissues have been identified. Simulated results also show differences in the magnitude and distribution of the EF through different segments of the facial nerve upon different stimulation modes and electrodes, dependent on nerve and bone tissue conductivities.Significance.Full-head models prove useful tools to model intra and extracochlear EFs in CI stimulation. Our findings could prove useful in the design of future experimental studies to contrast FNS mechanisms upon stimulation of different electrodes and CI modes. The full-head model developed is freely available for the CI community for further research and use.

Impact of Insertion Speed, Depth, and Robotic Assistance on Cochlear Implant Insertion Forces and Intracochlear Pressure: A Scoping Review

Cochlear implants are crucial for addressing severe-to-profound hearing loss, with the success of the procedure requiring careful electrode placement. This scoping review synthesizes the findings from 125 studies examining the factors influencing insertion forces (IFs) and intracochlear pressure (IP), which are crucial for optimizing implantation techniques and enhancing patient outcomes. The review highlights the impact of variables, including insertion depth, speed, and the use of robotic assistance on IFs and IP. Results indicate that higher insertion speeds generally increase IFs and IP in artificial models, a pattern not consistently observed in cadaveric studies due to variations in methodology and sample size. The study also explores the observed minimal impact of robotic assistance on reducing IFs compared to manual methods. Importantly, this review underscores the need for a standardized approach in cochlear implant research to address inconsistencies and improve clinical practices aimed at preserving hearing during implantation.

Robotic assistance during cochlear implantation: the rationale for consistent, controlled speed of electrode array insertion

Cochlear implants (CI) have revolutionized the treatment of patients with severe to profound sensory hearing loss by providing a method of bypassing normal hearing to directly stimulate the auditory nerve. A further advance in the field has been the introduction of "hearing preservation" surgery, whereby the CI electrode array (EA) is carefully inserted to spare damage to the delicate anatomy and function of the cochlea. Preserving residual function of the inner ear allows patients to receive maximal benefit from the CI and to combine CI electric stimulation with acoustic hearing, offering improved postoperative speech, hearing, and quality of life outcomes. However, under the current paradigm of implant surgery, where EAs are inserted by hand, the cochlea cannot be reliably spared from damage. Robotics-assisted EA insertion is an emerging technology that may overcome fundamental human kinetic limitations that prevent consistency in achieving steady and slow EA insertion. This review begins by describing the relationship between EA insertion speed and generation of intracochlear forces and pressures. The various mechanisms by which these intracochlear forces can damage the cochlea and lead to worsened postoperative outcomes are discussed. The constraints of manual insertion technique are compared to robotics-assisted methods, followed by an overview of the current and future state of robotics-assisted EA insertion.