Flexible Stent Hinge Design for Expansion Control
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Solution Overview
Problem
Existing stent designs face challenges such as instability, non-uniform expansion, high recoil, and difficulty in accurate placement due to thin-walled materials, leading to issues like buckling, thrombosis, and inadequate lumen support, as well as inconsistent drug delivery in drug-eluting stents.
Innovation Solution
A flexible stent design featuring a helical section with longitudinally oriented strut members and circumferentially oriented hinge members, along with a unique connector geometry that includes ductile hinges with a crown design to distribute plastic strains and maintain structural integrity, allowing for consistent expansion and drug delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If thin-walled materials are used to reduce expansion forces to acceptable levels, then expansion force is reduced, but visibility on fluoroscopic and x-ray equipment deteriorates
Solution Approach 1:
The stent is divided into multiple struts that are interconnected by hinges, creating a segmented structure. This segmentation allows the stent to achieve the desired expansion force characteristics while maintaining sufficient material thickness for visibility, as the segmented design distributes mechanical loads more effectively than a solid thin-walled structure.
Solution Approach 2:
The stent employs a composite structure combining rigid strut members with flexible hinge connections. This composite approach allows optimization of each component: struts can be thick enough for visibility while hinges provide the necessary flexibility and force characteristics, resolving the contradiction between expansion force and radiopacity.
2Stability of the object's composition
If long slender struts with width two or more times greater than thickness are used, then structural continuity is improved, but stability deteriorates due to buckling
Solution Approach 1:
The struts are pre-formed with specific geometric configurations and cross-sectional shapes that provide inherent resistance to buckling before deployment. The preliminary shaping includes optimizing the width-to-thickness ratio and incorporating reinforcement features that prevent twisting and buckling during expansion and in the deployed state.
Solution Approach 2:
The strut cross-sections incorporate curved or rounded geometries rather than sharp corners, and the overall strut shapes follow optimized curves that distribute stresses more evenly. This curvature-based design reduces stress concentration points that would initiate buckling and twisting.
3Manufacturing precision
If uniform strut width is used for simplicity of manufacture, then manufacturing ease is improved, but expansion uniformity deteriorates
Solution Approach 1:
The strut width is varied locally along the length of each strut and at different positions around the stent circumference. This local variation in geometry is strategically designed to compensate for non-uniform stresses and strains during expansion, ensuring uniform overall expansion while maintaining compatibility with standard manufacturing processes like laser cutting or forming.
4Ease of operation
If large elastic recovery is present to compensate for crimping, then delivery flexibility is improved, but recoil increases causing over-expansion
Solution Approach 1:
The elastic properties of the stent material and structure are carefully optimized to achieve an optimal balance of recoil. By adjusting parameters such as material composition, strut thickness, hinge geometry, and overall stent configuration, the recoil is controlled to provide sufficient flexibility for crimping and delivery while preventing excessive expansion that would damage the vessel wall.
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 flexible stent provides improved radial strength, reduced recoil, and consistent drug delivery while maintaining vessel patency, with enhanced structural integrity and flexibility for easier placement, addressing the limitations of existing stent designs.
Implementation Method 1
ductile hinges with a crown design to distribute plastic strains and maintain structural integrity
Implementation Method 2
the tubular members are mechanically expanded beyond their elastic limit and thus permanently fixed within the body
Data Source
AI summary
The present invention relates to tissue-supporting medical devices and drug delivery systems, and more particularly to tubular flexible stents that are implanted within a body lumen of a living animal or human to support the organ, maintain patency and/or deliver drugs or agents. The tubular flexible stent has a cylindrical shape defining a longitudinal axis and includes a helical section having of a plurality of longitudinally oriented strut members and a plurality of circumferentially oriented hinge members connecting circumferentially adjacent strut members to form a band. The band is wrapped about the longitudinal axis in a substantially helical manner to form a plurality of helical windings. At least one connector member extends between adjacent windings.