How It Works

The valve-in-stent device consists of a flexure-based PDMS valve system secured within an hourglass-shaped, Nitinol stent. The gold coating on the valve diaphragm center absorbs sound when the valve is sealed closed against the polypropylene rigid body. The valve opens after deflection of the PDMS arms and allows for pressure equalization. The device maintains functionality over the long term and is delivered in a minimally invasive procedure.

Sound Reduction

Sound is produced by vibrating air molecules in the eustachian tube due to breathing, talking, and pulsatile blood flow in the external carotid artery. The sound can be reflected, transmitted, or absorbed. Therefore, the material and geometry of the diaphragm center should yield a high sound transmission loss (STL). STL is the standard measurement for understanding the transmission of sound between mediums and is displayed in equation below for a plate at most frequencies including those in the human speech range (0.1-17 kHz roughly).

Key parameter for design: Mass surface density of the plate (m_s )

Must be large enough to absorb ≥13.1 dB
m_s = mass / surface area
Increase m_s by increasing material thickness, using a denser material, or shrinking the radius of the diaphragm.

Other parameters in equation:

Frequency (ω): 1 kHz
Incident angle of sound constant (θ): 0°
Density of air constant (ρ): 1.18 kg/m³
Speed of sound in air constant (c₀ ): 344 m/s

Pressure Equalization

If the ET was completely blocked, an uncomfortable pressure gradient (> 1000 Pa) would build-up for patients. Therefore, the valve opens to allow for air movement (indicated by the red arrows) and furthermore pressure equalization. The diaphragm can also open in the opposite direction given a reverse pressure gradient.

The valve functions as a flexure-based system because the arms begin to deflect at a cracking pressure (300 Pa). Pressure continues to build-up until 500 Pa is reached. At 500 Pa, the arms will experience the maximum deflection and allow for pressure equalization. The calculation for maximum deflection (δ) at the tip of each ‘arm’ (point A) can be modeled as a simple cantilever with 2 loads.

Key parameter for design: Length, width, thickness of 'arm' (L, w, t)

Deflection must be large enough to allow for quick equalization from 500 Pa.
Small enough deflection so that large stress concentrations do not occur at point of attachment between 'arm' and rigid body.
Have 'arm' as long as is feasible, and maintain integrity of 'arm' by having appropriate width and thickness.

Other parameters in equation:

Distributed load from pressure (q): (500 Pa * wt) / L
Point load from rigid diaphragm coating (P): (500 Pa*π *r²)/5
Young's Modulus for 10:1 PDMS (E): 2 MP

Long Term Integrity of Rigid Body/Valve

The following items have the potential to decrease the device integrity over the long term. Therefore, mitigations are incorporated into the device design.

Accumulation of mucus on device
- Anti-fouling Teflon coating on all rigid body and valve surfaces.
Device undergoes 48 cycles /day for the 10 year device life.
- Yield Stress of PDMS: ~4 MPa
- Stress concentrations limited by fillets on valve 'arms' and diaphragm.
Large pressure changes (during sneezing / altitude changes)
- Ultimate Tensile Strength of PDMS: 5.13 ± 0.55 MPa
Reduction in diameter of ET if Ostmann's fat pad returns to normal size and applies pressure to ET
- Stent and rigid body hold the ET open so that the valve can still operate.

Minimally Invasive Delivery Method

The rigid body/valve glued to the commercial stent will attach to the end of the altered ACCLARENT AERA® delivery system via a latching mechanism. The device is delivered to the isthmus in the eustachian tube through the nasal cavity. After the ideal device location is achieved below the isthmus +/- 2mm, the device is deployed. The Nitinol shape-memory alloy returns to its original dimensions. The stent maintains its hourglass shape because the ET also has an hourglass shape.

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