Self-Expanding Stent Delivery via Flared Bend Geometry
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Solution Overview
Problem
Delivery systems for self-expanding stents face high frictional forces between the stent and the restraining sheath, leading to difficulties in reliable delivery and accurate positioning, as well as potential damage to the system components due to excessive forces required to overcome friction.
Innovation Solution
The method involves compressing the self-expanding stent using a stent crimper to create flared and unflared bends, where the stent is loaded into a restraining sheath with the proximal end pushed first, allowing the unflared bends to lead during delivery, reducing friction and minimizing the forces needed for stent release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the stent is compressed and loaded into the restraining sheath for delivery, then the stent can be delivered through minimally invasive procedures, but high frictional forces occur between the stent and the restraining sheath
Solution Approach 1:
The stent bends are pre-formed during the crimping process before loading into the sheath. The distal bends are configured to flare outward in advance, so that when the stent is pushed into the restraining sheath, the flared distal bends lead the way and reduce contact friction with the sheath inner surface during delivery
Solution Approach 2:
Different bends of the stent are given different geometric configurations - distal bends are made to flare outward while proximal bends remain relatively straight. This local differentiation in bend geometry allows the distal portion to interact differently with the sheath, reducing friction where the stent enters the sheath
2Reliability
If sufficient axial force is applied to overcome frictional forces during stent release, then the stent can be delivered from the sheath, but the restraining sheath may stretch, tear or fail
Solution Approach 1:
The stent distal bends are pre-flared during crimping so that when loading into the sheath, the frictional resistance is reduced from the beginning of the loading process. This preliminary geometric configuration prevents the buildup of excessive forces that would otherwise require the sheath to withstand high tensile loads during release
3Manufacturing precision
If the inner catheter is designed to prevent the stent from moving proximally with the restraining sheath, then the stent remains axially in place during delivery, but the inner catheter may compress in length or buckle
Solution Approach 1:
The frictional force between the stent and sheath, which was previously a harmful force causing excessive loads, is converted into a beneficial stabilizing force. The flared distal bends create controlled friction that prevents the stent from moving proximally with the sheath during delivery, eliminating the need for the inner catheter to resist stent movement and preventing catheter compression or buckling
4Strength
If relatively stiff materials are used for the restraining sheath and inner catheter to withstand delivery forces, then the components can handle the expected forces, but the delivery system diameter increases and kinking may occur
Solution Approach 1:
The stent bend geometry is pre-configured during crimping to reduce frictional forces before delivery begins. This preliminary action reduces the peak forces that the delivery system must withstand, allowing the use of more flexible, smaller-diameter materials for the restraining sheath and inner catheter without sacrificing strength or risking kinking
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
This approach reduces frictional forces between the stent and the sheath, minimizing damage to the delivery system and enabling smoother stent deployment with lower required forces, thus enhancing the reliability and accuracy of stent placement.
Implementation Method 1
self-expanding stents are made from an elastic material. A self-expanding stent is typically designed with an expanded diameter that is slightly greater in size than the body passageway that the stent will be implanted within. In the expanded diameter, the elastic material of the stent is unstressed, or relaxed.
Implementation Method 2
Because the stent is elastically compressed inside of the restraining sheath as it is pushed out of the sheath during delivery, friction occurs between the outer surface of the stent and the inner surface of the restraining sheath.
Data Source
AI summary
A method is provided for loading and delivering a self-expanding stent. The stent is compressed from its expanded diameter to a smaller delivery diameter. While compressed, the stent is pushed from the proximal end through the proximal end opening of a restraining sheath. The restraining sheath retains the stent in the delivery diameter. In order to deliver the stent, the proximal end of the stent is pushed and the restraining sheath is withdrawn proximally from the stent. As a result, the stent is released from the distal end opening of the restraining sheath.