Nitinol Stent Fatigue Resistance via Phase Control
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Solution Overview
Problem
Stents implanted in locations experiencing high mechanical forces from patient activity often fracture due to inadequate design and material properties, leading to issues like pain, bleeding, vessel occlusion, and high restenosis rates.
Innovation Solution
A self-expanding stent made from a nickel-titanium alloy with a specific Austenite finish temperature and kink radius, configured to self-expand and withstand high mechanical forces, with a bend-rotate fatigue life of at least 1 million cycles, is developed for improved resistance to fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional stent materials and designs are used, then the stent can be manufactured and deployed, but the stent fractures under high mechanical forces from patient activity
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Austenite finish temperature (Af) of the nickel-titanium alloy to be between -50°C and +50°C, and setting the kink radius to no greater than 4.953mm. These specific parameter ranges transform the material's mechanical properties to achieve superior fatigue resistance and fracture protection under cyclic loading conditions while maintaining self-expanding functionality.
Solution Approach 2:
The patent utilizes a nickel-titanium alloy composite material with specific compositional ratios and heat treatment characteristics. This composite material combines the superelasticity and shape memory effects of nitinol with controlled microstructure through heat treatment, creating a material that resists fracture under high mechanical forces while maintaining flexibility for delivery through body lumens.
2Strength
If the stent is made more rigid to resist fracture, then fracture resistance improves, but the stent cannot be delivered through body lumens in a collapsed state
Solution Approach 1:
The patent applies dynamics by utilizing the time-dependent phase transformation characteristics of the nickel-titanium alloy. The stent exhibits dynamic mechanical properties that change with temperature and loading rate: it remains flexible and compressible during delivery, then transforms to a rigid, fracture-resistant state upon deployment at body temperature through martensite-austenite phase transformation.
Solution Approach 2:
The patent exploits phase transitions of the nickel-titanium alloy between martensite and austenite phases. During delivery at lower temperatures, the alloy remains in the flexible martensitic phase, allowing compression. Upon deployment at body temperature (37°C), the phase transition to austenite occurs, providing the rigid, fracture-resistant structure needed to withstand mechanical forces while maintaining the ability to be delivered in a collapsed state.
3Duration of action of stationary object
If the stent uses a larger kink radius to improve fatigue life, then bend-rotate fatigue resistance improves, but the stent cannot achieve adequate radial support and expandability
Solution Approach 1:
The patent resolves this contradiction by optimizing the kink radius parameter to a specific range (no greater than 4.953mm) and controlling the Austenite finish temperature within -50°C to +50°C. This parameter optimization creates a balance where the smaller kink radius enables adequate radial support and expandability, while the controlled Af ensures the material has sufficient fatigue life through its superelastic properties and phase transformation characteristics.
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 effectively resists fracture under cyclic loading conditions, reducing the need for re-intervention and improving vessel patency by maintaining structural integrity over extended periods.
Implementation Method 1
the implant is shape set to a first substantially longitudinal configuration... the implant is configured to self-expand from a collapsed condition to an expanded condition
Implementation Method 2
An implant is disclosed that has a nickel titanium alloy and has a bend-rotate fatigue life of at least 1 million cycles to failure
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
According to one aspect of the present invention, a fatigue resistant stent comprises a flexible tubular structure having an inside diameter, an outside diameter, and a sidewall therebetween and having apertures extending through the sidewall. According to other aspects of the invention, processes for making a fatigue resistant stent are disclosed. According to further aspects of the invention, delivery systems for a fatigue resistant stent and methods of use are provided.