Stent With Undulating Struts For Fatigue Resistance
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Solution Overview
Problem
Stents implanted in certain body locations, such as the superficial femoral artery, often fracture due to high mechanical forces from patient activity and heart pulsation, leading to issues like intimal hyperplasia, pain, and vessel occlusion, with existing stents lacking sufficient resistance to fracture under non-pulsatile loading conditions like elongation, torsion, and flexion.
Innovation Solution
A stent design featuring a tubular structure with apertures and struts of varying widths and lengths, forming undulating patterns, where apices are circumferentially offset, enhancing axial, bending, and torsional flexibility, and reducing tensile strains during elongation, thereby improving fatigue life and fracture resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stent designs are used, then the stent can maintain luminal patency, but the stent fractures under high mechanical forces from patient activity and heart pulsation
Solution Approach 1:
The stent is divided into multiple struts of varying widths and lengths that form undulating patterns, allowing each segment to independently absorb and distribute mechanical stresses, thereby preventing fracture under high mechanical forces
Solution Approach 2:
Different portions of the stent structure have different strut widths and lengths optimized for local stress distribution, with wider struts in high-stress areas and narrower struts in lower-stress areas, providing non-uniform strength distribution matched to local mechanical demands
2Reliability
If the stent structure is made more rigid to resist fracture, then fracture resistance improves, but the stent loses flexibility to accommodate axial, bending, and torsional deformations
Solution Approach 1:
The stent incorporates undulating patterns with circumferentially offset apices that allow the structure to dynamically adapt its configuration under axial, bending, and torsional loads, maintaining both flexibility and fracture resistance through motion rather than rigid resistance
Solution Approach 2:
The stent features asymmetric strut configurations with varying widths and lengths arranged in undulating patterns, providing different mechanical properties in different directions and enabling the structure to accommodate multi-axial deformations while maintaining overall integrity
3Ease of manufacture
If the stent uses uniform strut design, then manufacturing is simplified, but tensile strains are concentrated at specific points during elongation, reducing fatigue life
Solution Approach 1:
The stent employs struts with non-uniform widths and lengths distributed throughout the structure, creating local variations in strain distribution that prevent stress concentration at any single point, thereby extending fatigue life under cyclic loading conditions
Solution Approach 2:
The design converts the potential harm of structural complexity into a benefit by using varied strut configurations to distribute and reduce peak tensile strains, transforming what would be manufacturing complexity into a fatigue-life-extending feature
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 stent design significantly enhances fatigue life and resistance to fracture, maintaining structural integrity under complex loading conditions, such as those encountered in the superficial femoral artery, by distributing strain more evenly and reducing peak tensile strains, leading to improved performance and reduced risk of stent failure.
Implementation Method 1
a tubular structure having a central axis defining a longitudinal direction and a circumferential sidewall having a wall thickness
Implementation Method 2
the stent is preprogrammed to remember a reduced diameter or shape at one temperature and an expanded diameter or shape at a higher temperature
Implementation Method 3
a phase change of the shape memory material results in expansion of the stent from a collapsed state to an expanded state
Implementation Method 4
made of an elastically deformable material (e.g., a superelastic material such a nitinol)
Data Source
Figure 1~1A
Figure 2
Figure 2A
AI summary
The present invention relates to a stent for implant in a mammalian body comprising a tubular structure having a central axis defining a longitudinal direction and a circumferential sidewall having a wall thickness, and apertures extending through the sidewall, said apertures separating longitudinal struts having different widths and joined at apices, with a plurality of the struts grouped to define a cell, and adjacent cells being joined by connectors on opposed sides of the cell in the longitudinal direction, the struts, apices and connectors forming undulating row patterns, wherein in the circumferential direction of the stent, each cell comprises a first group of struts having a first width and a second group of struts having a second width different from the first width, and wherein at least one of the struts in the first group of struts extends from a connector and has a smaller width dimension than the struts in the second group of struts.