Flexible Sheath With Independent Liner And Outer Layer
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Solution Overview
Problem
Tubular medical devices often kink when traversing tortuous pathways, leading to reduced effectiveness and increased trauma due to insufficient flexibility and kink resistance, especially in smaller vessels, limiting access to complex anatomy.
Innovation Solution
A sheath design featuring an inner liner, a coil with closely spaced windings, and an outer layer with a lower melt temperature, where the inner liner and outer layer are attached independently, allowing for coaxial movement, and a filler material in the voids between coil windings to inhibit bonding and enhance flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the sheath uses thin-wall construction to enter narrow vessels, then the ability to enter narrow vessels is improved, but the trackability and kink resistance deteriorate
Solution Approach 1:
The sheath combines multiple materials with different properties: an inner liner (PTFE or similar low-friction material) for smooth tracking, a reinforcement layer (braid or mesh) for structural support and kink resistance, and an outer cover for flexibility. This composite structure enables the sheath to navigate narrow vessels while maintaining trackability and resisting kinking.
Solution Approach 2:
The reinforcement layer is applied selectively at specific locations along the sheath, particularly at the tip and along the shaft where kink resistance is most needed, while maintaining thin walls in other areas to preserve flexibility for entering narrow vessels.
2Reliability
If the sheath increases wall thickness to improve kink resistance, then the kink resistance is improved, but the ability to enter narrow vessels and lumen diameter deteriorate
Solution Approach 1:
Instead of increasing overall wall thickness, the sheath uses a composite structure with a thin inner liner and a reinforcement layer that provides kink resistance through its braided or mesh configuration, maintaining flexibility while preventing collapse.
Solution Approach 2:
The sheath wall is segmented into functional layers: an inner liner for flexibility and low friction, a reinforcement layer for kink resistance, and an outer cover for protection. This segmentation allows each layer to optimize its specific function without compromising overall performance.
3Reliability
If the sheath includes both coil and braid reinforcement, then the kink resistance and pushability are improved, but the device complexity increases
Solution Approach 1:
The sheath integrates coil and braid reinforcements as composite structural elements within the wall layers, where the coil provides radial support and the braid provides longitudinal strength, achieving enhanced mechanical properties through material composition rather than complex assembly.
Solution Approach 2:
The reinforcement features (coil and braid) are merged into the sheath wall structure itself rather than being separate components, simplifying the overall device architecture while maintaining the mechanical benefits of both reinforcement types.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design significantly reduces kinking and improves bending flexibility, enabling better access to tortuous anatomy without collapsing, thus enhancing the utility of tubular medical devices in minimally invasive procedures.
Implementation Method 1
the outer layer having a lower melt temperature than the inner liner
Implementation Method 2
a filler material in the voids between coil windings to inhibit bonding and enhance flexibility
Data Source
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AI summary
A medical device including a sheath (20) having an inner liner (50) and an outer layer (40) attachable to a coil (34) independent from each other to allow the inner liner and the outer layer the freedom to move coaxially independent from each other. The coil can be closely wound at a predetermined coil spacing sufficient to inhibit portions of the outer layer from entering into voids between the adjacent coil windings. Intermediate layers (52) for bonding between the coil and the inner liner and/or the outer layer may also be provided. A filler material (60) can be disposed within the voids between the adjacent windings of the coil. The filler material has a dimension sized to bridge the void between adjacent coil windings in order to inhibit portions of the outer layer from bonding to the inner liner. The filler material can be in the form of a ribbon (62).