Helical Stent End Orientation via Variable Pitch
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Solution Overview
Problem
Helical stents often exhibit non-uniform behavior during crimping and expansion due to their ends not being perpendicular to the longitudinal axis, leading to a 'dog bone' effect.
Innovation Solution
A method of manufacturing a helical stent with a wave form comprising struts and crowns, where the wave form is wrapped around a longitudinal axis with varying pitch angles, including an end turn oriented substantially perpendicular to the axis, and additional turns with gradually transitioning pitch angles to achieve uniform contraction and expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the last turn of a helical stent includes a wave form with varying amplitudes to square off the ends, then the ends become perpendicular to the longitudinal axis, but the stent exhibits non-uniform behavior during crimping and expansion
Solution Approach 1:
The patent applies local quality by differentiating the wave form characteristics between end portions and central portion of the stent. The end portions include wave forms with varying amplitudes to achieve perpendicular ends, while the central portion maintains a different pitch angle for uniform expansion. This localized differentiation allows each region to have optimized properties for its specific function.
Solution Approach 2:
The stent is segmented into distinct regions with different pitch angles. The end portions are separated from the central portion, with each having unique wave form characteristics. This segmentation allows the end turns to be squared off independently while the central portion maintains its helical structure for uniform expansion behavior.
2Ease of manufacture
If a helical stent is manufactured with a single pitch angle, then the manufacturing process is simple, but the ends are not perpendicular to the longitudinal axis
Solution Approach 1:
The patent implements local quality by assigning different pitch angles to different regions of the stent. The end portions have wave forms with varying amplitudes that create perpendicular ends, while the central portion has a different pitch angle. This allows the stent to achieve the desired end orientation without requiring complete redesign of the entire structure.
Solution Approach 2:
The wave form with varying amplitudes is incorporated into the stent structure during manufacturing as a preliminary design feature. By pre-configuring the end portions with appropriate pitch angles and wave characteristics, the perpendicular end orientation is achieved without requiring additional post-manufacturing operations.
3Ease of manufacture
If the wave form has uniform strut lengths, then the structure is simpler to manufacture, but the stent cannot achieve both perpendicular ends and uniform expansion behavior
Solution Approach 1:
The patent applies local quality by allowing different strut length characteristics in different regions. The end portions may have varying strut lengths to achieve perpendicular orientation, while the central portion maintains more uniform strut characteristics for consistent expansion. This regional differentiation enables both orientation precision and expansion uniformity.
Solution Approach 2:
The patent utilizes parameter changes by varying the pitch angle and wave amplitude parameters along the length of the stent. The end portions have different pitch angles and wave characteristics compared to the central portion. This gradual parameter transition allows the stent to achieve perpendicular ends while maintaining uniform expansion behavior through controlled variation of geometric parameters.
Data Source
AI summary
A method of manufacturing a stent includes forming a wave form having a plurality of struts and a plurality of crowns. Each crown connects two adjacent struts. The wave form has a central portion and two end portions located on opposite sides the central portion. Some of the struts located in the end portions have lengths longer and/or shorter than an average length of all of the struts of the wave form. The method includes wrapping the wave form about a longitudinal axis to define a plurality of turns so that an end turn is oriented at an angle relative to the longitudinal axis, a second turn is at a first pitch angle that is less than the angle that the end turn is disposed relative to the longitudinal axis, a third turn is at a second pitch angle that is less than the first pitch angle, and a fourth turn is at a third pitch angle that is less than the second pitch angle.