Audio Overview
Listen to a professional acoustic narrative providing a summary of this simulation's mechanics, clinical background, and functional architecture.
Overview
This interactive simulator models the mechanical and biophysical parameters governing the insertion of a flexible electrode array into the human cochlea—specifically the scala tympani. The cochlea is a delicate spiral structure embedded in the temporal bone of the skull. It is responsible for translating acoustic vibrations into neural signals. The primary mechanism of modern cochlear implants is the electrical stimulation of the spiral ganglion cells located inside the modiolus, the central conical axis of the cochlea.
In patients suffering from severe-to-profound sensorineural hearing loss, the delicate hair cells within the organ of Corti are either damaged or entirely absent, terminating the pathway of mechanoreception. Cochlear implants bypass these dysfunctional hair cells by surgically placing an array of metallic electrode rings along the spiral path of the scala tympani. The spatial coordinates of these electrodes map to a tonotopic hierarchy governed by the Greenwood frequency function:
$$f = A \left( 10^{a \cdot x} - k \right)$$
where $f$ represents the mapped acoustic frequency (Hz), $x$ denotes the normalized distance from the cochlea apex, and $A$, $a$, and $k$ are empirical constants specific to the human ear ($A \approx 165.4$, $a \approx 2.1$, $k \approx 0.85$). High-frequency signals are processed near the basal entry of the cochlea, while low-frequency acoustic signals map to the deeper, apical regions.
Maintaining structural integrity during insertion is critical. If the surgeon applies excessive force, the array may translocate from the scala tympani into the adjacent scala vestibuli, rupturing the delicate basilar membrane. Such mechanical trauma permanently destroys any residual natural hearing and compromises the sensory outcomes of the implant. This model simulates the interaction forces, speed limits, and insertion depths to illustrate these clinical thresholds in a real-time, interactive environment.
How to Use
Interactive 3D Workspace: You can directly rotate, orbit, and zoom the 3D model. Left-click and drag on the background region to orbit around the spiral structures. Right-click and drag (or use a two-finger drag on mobile devices) to pan the viewpoint. Use the scroll wheel or pinch gestures to zoom into specific sections of the scala tympani.
Direct Array Grabbing: Click and hold any of the 30 metallic electrode rings or the semi-transparent blue silicone carrier directly within the 3D canvas, and drag vertically to push the implant inward or pull it back out. Dragging downward moves the array deeper; dragging upward retracts it.
Control Side-Panel Interface: Use the Insertion Depth range slider on the side panel to dynamically push the array. The Wall Friction range slider adjusts the coefficient of friction ($\mu$) between the outer walls of the cochlear lumen and the dynamic silicone carrier. Increasing friction causes the resultant mechanical resistance forces to rise as the array negotiates the logarithmic spiral turns.
Autonomous Simulation Sequence: Click Start Demo to trigger an automated, multi-stage educational looping demonstration. This sequence walks through various insertion scenarios, automatically adjusting camera framing, insertion depth, and friction coefficients to simulate different real-world clinical events:
- Stage 1 - Safe Insertion ($\mu = 0.12$): The array is slowly inserted under low friction. Resistive force stays in the safe green zone.
- Stage 2 - Safe Retraction: The array is smoothly withdrawn to prepare for alternative trials.
- Stage 3 - High Friction Trauma ($\mu = 0.38$): Demonstrates insertion into a calcified or narrow canal. Wall forces spike exponentially, triggering red visual trauma warnings.
- Stage 4 - High Friction Retraction: The array is withdrawn to reset variables.
- Stage 5 - Rapid "Yank" Insertion: Rapid insertion generates severe visco-fluid resistance due to shear rates, illustrating why slow insertion is clinically mandatory.
- Stage 6 - Rapid Extraction & Reset: Retracts quickly and loops back to Stage 1.
If you interact with the viewport, sliders, or touch targets during the demo, the manual override system instantly captures the physical interrupt, ceases automated movement, restores your original pre-demo parameters, and returns total control back to you. Click Reset Baseline at any time to instantly restore the model to default settings.
Analytical Monitor: The collapsible diagnostics panel plots live surgical parameters. This high-contrast oscilloscope charts three distinct metrics over a continuous time-series rolling window:
- Insertion Depth (Blue): Evaluated in millimeters ($0.0 \text{ mm}$ to $25.0 \text{ mm}$).
- Dynamic Resistive Force (Red): Calculated in millinewtons ($\text{mN}$). Pushing too rapidly or forcing the array beyond its physical limits will exceed the tissue safety threshold ($\tau_{\text{critical}} = 10.0 \text{ mN}$), flashing a crimson warning.
- Insertion Velocity (Green): Measured in millimeters per second ($\text{mm/s}$). High velocity induces viscous drag forces.
Technical Details
The mechanical framework is simulated using a logarithmic spiral equation representing the anatomical geometry of the human cochlear lumen:
$$\vec{r}(\theta) = R_0 \cdot e^{-a \cdot \theta} \cdot \hat{u}_r(\theta) - b \cdot \theta \cdot \hat{k}$$
where $R_0$ is the initial basal radius, $a$ is the angular contraction parameter, and $b$ represents the pitch rate of the helical descent. This spatial path is interpolated using a cubic Catmull-Rom spline formulation. The renderer heavily leverages native WebGL components to ensure high-performance 60 FPS graphics.
To simulate real-world catheter dynamics, the electrode array transitions smoothly from a rigid, straight insertion guide into the spiral canal. This is governed by evaluating path tangents: if the calculated coordinate of an electrode ring falls outside the spiral path ($s < 0$), its position is derived by projecting backward linearly along the entrance tangent vector:
$$\vec{x}(s) = \vec{p}_{\text{entry}} + s \cdot \vec{t}_{\text{entry}}$$
A dynamic, highly optimized geometric tube is reconstructed every frame along the computed spatial locations of the 30 electrode rings, mapping the physical behavior of a flexible medical-grade silicone carrier.
The friction forces modeled within the simulation are derived from a modified version of the Capstan Friction Model for flexible catheters traveling through tight anatomical lumens:
$$F_{\text{friction}}(d) = F_0 \cdot \left( e^{\mu \cdot \theta(d)} - 1 \right)$$
where $d$ represents the current insertion depth, $\theta(d)$ is the cumulative angular wrap of the array around the modiolus, and $\mu$ is the adjustable wall friction coefficient. Viscous resistance from the displaced perilymph fluid is modeled as:
$$F_{\text{viscous}} = \eta \cdot v = \eta \cdot \frac{dd}{dt}$$
The cumulative dynamic force ($F_{\text{total}} = F_{\text{friction}} + F_{\text{viscous}}$) is plotted in real-time. The real-time metric chart operates on a relative simulation time ticker ($t$), preventing timeline compression or timeline squashing bugs during pause states.
Future Directions
Planned features include:
- Perimodiolar Stylet Retraction: Simulating the insertion of pre-curved electrode arrays that wrap tightly around the modiolus upon the gradual retraction of an internal wire stylet.
- Local Stress FEA Mapping: Integrating an on-canvas Finite Element Method (FEM) solver to visually highlight localized shear points along the basilar membrane using heat-map shaders.
- Patient-Specific CT Importing: Enabling medical personnel to upload DICOM slice files or raw 3D mesh files of patient-specific cochleae to pre-plan optimal arrays and minimize translocation risks.
- Haptic Device Integration: Expanding the controller bindings to support external haptic feedback styluses, translating the calculated real-time resistive forces into physical resistance for surgical trainees.
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