Helical Stent-Graft With Zig-Zag Struts For Fatigue Resistance
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Solution Overview
Problem
Current stent-grafts face challenges in balancing flexibility and strength, especially under high stress and fatigue environments, as they are often deployed in vessels of varying sizes and tortuosity, requiring enhanced material properties and configurations to maintain performance.
Innovation Solution
A stent-graft design featuring a continuous shape memory member with zig-zag struts and a graft member made of ultra-high molecular weight polyethylene fibers, which are woven or knitted into a tubular shape, providing flexibility and strength through a combination of shape memory properties and high-strength materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a stent-graft uses a continuous helically wrapped member or braid configuration, then flexibility is improved, but strength and fatigue resistance deteriorate
Solution Approach 1:
The stent is segmented into multiple discrete struts rather than using a continuous helical wrap or braid. The struts are arranged in a pattern with longitudinal spacing and radial orientation, creating a lattice structure that provides both flexibility through the pattern configuration and strength through the discrete strut elements and their junctions.
Solution Approach 2:
The stent combines different materials with complementary properties: a shape memory alloy (such as Nitinol) providing superelasticity and fatigue resistance, and a polymer coating (such as ePTFE) providing biocompatibility and flexibility. This composite approach allows the stent to achieve both flexibility and strength simultaneously.
2Strength
If stent struts are spaced closer together, then strength is improved, but flexibility and adaptability to varying vessel sizes deteriorate
Solution Approach 1:
The stent employs shape memory alloy material with superelastic properties that allow the structure to dynamically adapt to different vessel sizes and shapes. The struts can bend and deform elastically under compression during delivery, then recover their original configuration upon deployment, accommodating varying vessel dimensions while maintaining structural integrity.
Solution Approach 2:
The stent design utilizes the phase transition properties of shape memory alloy, changing from a compressed low-strength state during delivery to an expanded high-strength state upon deployment. This parameter change allows the same structure to adapt to different vessel sizes while providing adequate strength support.
3Strength
If the stent is made more rigid to withstand circumferential forces, then strength is improved, but flexibility and ability to navigate tortuous vessels deteriorate
Solution Approach 1:
The stent design provides different mechanical properties at different locations and orientations: struts oriented radially provide circumferential strength to resist vessel wall forces, while the longitudinal spacing and helical arrangement of struts provide flexibility for navigation. The junction design also provides localized reinforcement where struts connect, distributing stresses to maintain overall strength without requiring increased rigidity throughout the entire structure.
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 improved flexibility and strength, enabling the stent-graft to maintain structural integrity and deploy effectively in varying vessel conditions without shortening, while also allowing for the controlled release of bio-active agents.
Implementation Method 1
a continuous shape memory member disposed over the outer surface of the substrate
Data Source
AI summary
An implantable prosthesis, including a generally tubular substrate and a continuous shape memory member disposed over the outer surface of the substrate. The shape memory member may include a series of zig-zag struts alternating between a first strut with a first length and a second strut with a second length different from the first length. A graft member may be positioned over the substrate and shape memory member.