Self-expanding Stent Radiopaque Marker Stress Distribution
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Solution Overview
Problem
Self-expansible stents face stress concentration on radiopaque markers during release from the delivery system, which can lead to physical damage and reduced visibility under radiation, especially when using a co-axial catheter delivery system.
Innovation Solution
A radially self-expansible stent design with radiopaque markers attached to selected inflection zones, where the compressive stress during release is shared between markers and non-marker inflection zones, minimizing strain on marker/inflection zone joints and allowing for larger marker sizes for improved visibility while maintaining mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If radiopaque markers are attached to inflection zones of a self-expansible stent, then visibility under radiation is improved, but stress concentration on markers during release causes physical damage and reduced reliability
Solution Approach 1:
The end annulus is segmented into multiple inflection zones distributed around its circumference. Only selected inflection zones carry radiopaque markers, while others remain marker-free to bear the brunt of release stresses. This segmentation distributes the mechanical load across multiple locations while maintaining adequate radiation visibility through the spaced markers.
Solution Approach 2:
Different inflection zones are assigned different functions: some zones are optimized for radiation visibility by carrying markers, while others are optimized for mechanical stability by remaining marker-free. This local differentiation allows each zone to excel at its specific function without compromising the other.
2Difficulty of detecting and measuring
If larger markers are attached to improve visibility, then radiation contrast is enhanced, but stress concentration on marker joints increases leading to breakage risk
Solution Approach 1:
The population of markers is segmented into a sparse distribution around the circumference rather than a dense arrangement. This allows each individual marker to be larger in size for better radiation contrast while reducing the total number of marker joints that could fail under stress.
3Measurement precision
If markers are placed at both ends of the stent for precise position determination, then placement accuracy is improved, but stress concentration on markers during release increases
Solution Approach 1:
Each end annulus is segmented into multiple inflection zones with only selected zones carrying markers. This segmentation allows the stent to maintain precise position determination capability through markers at both ends while distributing release stresses across multiple unmarked inflection zones at each end.
Data Source
AI summary
Pushing a self-expanding stent from one of its ends, during release of the stent at a stenting site in a bodily lumen, by proximal withdrawal of a surrounding sheath, can impose unacceptably high stresses on parts of the strut network of the stent. For location of stents in a bodily lumen, it is customary to equip the end annulus of a stent with radiopaque markers. The present invention involves arranging the markers so that they share with non-marker portions of the end annulus the stresses imposed in the stent by the end pushing, whereby the high stresses are shared more equally by all the struts of the stent in the end annulus.