Expandable Sheath Structure for Constant-Length Radial Expansion
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Solution Overview
Problem
Existing expandable introducer sheaths for prosthetic devices suffer from axial elongation and increased force requirements due to longitudinal forces during device insertion, leading to reduced diameter and difficulty in delivery.
Innovation Solution
The sheath design includes a braided layer surrounded by resilient elastic and polymeric layers, allowing radial expansion without significant axial elongation, with polymeric layers resisting axial forces and an elastic layer applying radial force for return to original diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a radially expandable sheath is used to deliver prosthetic devices, then the sheath can expand to accommodate larger diameter devices, but the sheath undergoes axial elongation which reduces its diameter and increases insertion force
Solution Approach 1:
The sheath is divided into multiple functional layers: a braided layer for radial expansion, an elastic layer for radial force application, and polymeric layers for axial constraint. Each layer performs a specific function, and together they resolve the contradiction by allowing radial expansion while preventing axial elongation.
Solution Approach 2:
The sheath uses a composite structure combining braided materials (for expandability), elastic materials (for radial force), and polymeric materials (for axial constraint). This composite design enables simultaneous radial expansion capability and axial dimension stability, preventing the diameter reduction that would increase insertion force.
2Adaptability or versatility
If the sheath expands radially to pass a larger diameter device, then device delivery is enabled, but the sheath length increases due to axial elongation
Solution Approach 1:
The sheath is segmented into distinct layers with specific functions: the braided layer handles radial expansion, the elastic layer provides radial force, and the polymeric layers constrain axial movement. This segmentation ensures that radial expansion occurs without corresponding axial elongation, maintaining constant sheath length.
Solution Approach 2:
Different regions of the sheath have different mechanical properties tailored to specific functions. The polymeric layers are designed to resist axial elongation specifically, while the braided and elastic layers are optimized for radial expansion. This local differentiation of material properties resolves the contradiction between device size accommodation and length stability.
3Adaptability or versatility
If existing expandable sheath mechanisms are used, then radial expansion is achieved, but complex ratcheting mechanisms are required to maintain expanded configuration
Solution Approach 1:
The invention extracts and eliminates the complex ratcheting mechanism from the sheath design. Instead of using mechanical ratchets to maintain expansion, the patent uses the inherent elastic properties of the elastic layer and the structural design of the braided layer to automatically maintain the expanded configuration through material science rather than mechanical complexity.
Solution Approach 2:
The sheath structure is designed to be self-maintaining through its material properties. The elastic layer naturally applies radial force to maintain expansion, and the braided layer's structure inherently resists collapse, eliminating the need for external ratcheting mechanisms. The system serves itself through the intrinsic properties of its components.
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 ensures consistent sheath length during prosthetic device delivery, reducing insertion force and maintaining lumen diameter, facilitating safe and efficient implantation of prosthetic devices.
Implementation Method 1
The elastic layer is configured to apply radial force to the braided layer and the first polymeric layer... The sheath resiliently returns to the first diameter by radial force applied by the elastic layer
Implementation Method 2
the first and second polymeric layers resist axial elongation of the sheath such that a length of the sheath remains substantially constant
Data Source
AI summary
An expandable sheath is disclosed herein, which has a first polymeric layer and a braided layer positioned radially outward of the first polymeric layer. The braided layer includes a plurality of filaments braided together. The expandable sheaths further include a resilient elastic layer positioned radially outward of the braided layer. The elastic layer is configured to apply radial force to the braided layer and the first polymeric layer. The expandable sheath further includes a second polymeric layer positioned radially outward of the elastic layer and bonded to the first polymeric layer such that the braided layer and the elastic layer are encapsulated between the first and second polymeric layers. Methods of making and using the devices disclosed herein are also disclosed, as are crimping devices that may be used in methods of making the devices disclosed herein.