Polygon Transition Zone Stent Uniform Expansion
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Solution Overview
Problem
Self-expanding stents with helical designs face issues of differential expansion due to uneven termination of windings, leading to non-uniform stress and bending moments across the transition zone, which complicates insertion into convoluted vessels and affects expansion uniformity.
Innovation Solution
A self-expanding stent design featuring a transition zone with a plurality of polygons, such as hexagons, where the surface area increases circumferentially, connected by struts, ensuring a constant bending moment across the transition zone for uniform expansion and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a helical design with main body and end zones is used, then the stent can be inserted into vessels, but differential expansion occurs due to uneven termination of windings
Solution Approach 1:
The stent is divided into three distinct zones: a main body zone with helical windings, transition zones with polygons having equal surface areas, and end zones. This segmentation allows each zone to have optimized characteristics - the main body provides structural support while the transition zones ensure uniform expansion by distributing stress evenly through equal-area polygons.
Solution Approach 2:
Different zones of the stent are given different geometric properties tailored to their specific functions. The main body has continuous helical windings for overall support, while the transition zones use polygons with equal surface areas specifically to achieve uniform expansion and reduce stress concentration at the junction between zones.
2Stability of the object's composition
If a transition zone joins different structural segments, then connection between zones is achieved, but strut lengths vary causing non-uniform stress and bending moments
Solution Approach 1:
The transition zone uses polygons with equal surface areas to create a stress-distributing structure. This equipotential approach ensures that bending moments and stresses are uniformly distributed across the transition zone, eliminating the stress concentration that would occur with varying strut lengths in conventional designs.
3Stability of the object's composition
If conventional transition zones are used, then zone connection is achieved, but expansion uniformity is affected due to varying strut lengths
Solution Approach 1:
The transition zone is segmented into multiple polygons with equal surface areas, creating a structured approach to connecting the main body and end zones. This segmentation ensures that each polygon contributes equally to the transition, maintaining uniform expansion characteristics while providing stable structural connection.
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 allows for uniform expansion and high radial strength, enabling the stent to be inserted into small diameter vessels with complex geometry and dynamically respond to blood pressure changes, ensuring secure fixation within the vessel.
Implementation Method 1
Stents formed from NiTi alloys are highly resilient, even when compressed because of the superelastic properties of the alloy. When cooled below the transformation temperature such as by liquid nitrogen, the NiTi alloy transforms to a martensite phase, holding a new shape until it warms back-up. This transformation can be referred to as a change between a martensite phase (stable at low temperatures) and an austenite phase (stable at high temperatures).
Implementation Method 2
Self-expanding stents may be formed from super-elastic or shape memory metal. Stents formed from NiTi alloys are highly resilient, even when compressed because of the superelastic properties of the alloy.
Data Source
Figure 1
Figure 2
Figure 3~4b
AI summary
The self-expanding stent of the present invention provides for a transition zone between the main body of the stent and the end zone, comprising a plurality of n-sided polygons where the surface area of the adjacent polygons in the transition zone is unequal. In one embodiment, the surface area of the polygons in the transition zone increases circumferentially across the transition zone in a clockwise or counterclockwise manner. The polygons are formed from two pairs of undulations which are connected by segments. The bending moment of the undulations is equal within each polygon and constant across the transition zone.