Tapering Stent With Varying Wall Thickness for Venous Patency
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Solution Overview
Problem
Current stents for treating May-Thurner syndrome and deep venous thrombosis face issues such as severe foreshortening, lack of flexibility, vessel wear, and potential impedance of flow, leading to early fatigue failure and complications like peripheral arterial disease.
Innovation Solution
A stent with a firm region, transition region, and flexible region, designed to have varying radial stiffness and flexibility along its length, featuring a thicker wall structure in the firm region for increased radial stiffness and a more flexible structure distally to accommodate tortuous venous passageways, while maintaining radial strength through strut density and interconnection adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the stent has high radial stiffness to treat May-Thurner syndrome, then the stent can effectively counteract venous compression, but the stent lacks flexibility to accommodate tortuous venous passageways
Solution Approach 1:
The stent is divided into multiple segments with different wall thicknesses along its length. The proximal portion has greater wall thickness for higher radial stiffness to counteract compression at the iliac vein, while the distal portion has reduced wall thickness for increased flexibility to navigate tortuous venous anatomy. This segmentation allows each portion to be optimized for its specific functional requirements.
Solution Approach 2:
Different portions of the stent are given different local properties through varying wall thickness. The firm region near the compression site has thicker walls for strength, while the flexible region in the distal portion has thinner walls for adaptability. This local differentiation of material distribution resolves the contradiction between needing strength in one location and flexibility in another.
2Adaptability or versatility
If the stent wall thickness is reduced to increase flexibility, then the stent can better accommodate venous anatomy, but the radial stiffness is compromised
Solution Approach 1:
The stent employs non-uniform wall thickness distribution where the firm region has greater thickness for radial stiffness while the flexible region has reduced thickness for flexibility. This local quality variation allows the stent to have different mechanical properties in different segments, resolving the contradiction between overall flexibility and localized strength requirements.
Solution Approach 2:
The stent structure is segmented into distinct firm and flexible regions with intermediate transition zones. This segmentation allows the thin-walled flexible portion to provide adaptability without compromising the radial stiffness of the thick-walled firm portion, as each segment independently contributes its optimized property to the overall stent performance.
3Ease of manufacture
If the stent has uniform structure throughout, then the manufacturing is simpler, but the stent cannot provide both high radial stiffness and flexibility in different regions
Solution Approach 1:
The stent is manufactured with varying wall thickness through processes such as selective material deposition, differential forming, or staged manufacturing. The firm region receives greater material thickness while the flexible region receives less, creating the desired gradient of mechanical properties. This approach balances manufacturing feasibility with the need for spatially varying performance characteristics.
Solution Approach 2:
The manufacturing process is segmented into stages that create different wall thickness regions. For example, the stent may be formed with a base thickness and then selectively reinforced in the firm region, or manufactured in sections that are subsequently joined. This segmented manufacturing approach enables variable mechanical properties while maintaining reasonable manufacturing complexity.
4Adaptability or versatility
If the stent is made highly flexible to navigate tortuous vessels, then the stent can be delivered more easily, but the stent suffers from early fatigue failure
Solution Approach 1:
The stent is segmented into flexible and firm regions, with the flexible portion handling the bending and navigation stresses during delivery while the firm portion remains structurally robust. This segmentation protects the overall stent from fatigue failure by concentrating flexural stresses in the thinner-walled flexible region that is designed to accommodate such stresses, while the thicker-walled firm region maintains structural integrity and fatigue resistance.
Solution Approach 2:
The stent has locally optimized wall thickness where the flexible region has reduced thickness to accommodate repeated bending without fatigue failure, while the firm region has increased thickness for structural strength. This local quality differentiation allows the stent to withstand delivery maneuvers and long-term implantation stresses without premature failure.
Data Source
AI summary
A stent includes a high radial force segment and a highly flexible segment, where the diameters of the high radial force segment and the highly flexible segment are different. For example, the stent may be formed from a tube having varying diameters as it extends distally combined with increased strut density to achieve increased flexibility distally while reducing loss of radial stiffness. The stent may further be placed with an additional stent segment, where the additional stent segment has a radial force similar to the radial force of the highly flexible force segment.