Ni-Ti Ternary Alloy Stent for Controlled Deployment
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Solution Overview
Problem
Current medical stents face challenges in achieving high flexibility for navigation through tortuous passageways while maintaining the mechanical strength to hold open body lumens, and they often require high deployment forces and can cause vessel trauma due to rapid expansion and chronic outward forces.
Innovation Solution
A Ni—Ti ternary alloy with strain-induced austenite properties is developed, allowing for controlled deformation to shift the austenite start temperature above body temperature, enabling the alloy to be flexible during insertion and stiffening upon deployment, reducing the need for external constraints and minimizing deployment forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional alloys (stainless steel, cobalt chrome) are used with high yield strength, then mechanical strength is improved, but the alloy cannot sustain strains greater than 0.2% without permanent set and requires high deployment forces
Solution Approach 1:
The patent applies parameter changes by utilizing stress-induced martensite transformation in Ni-Ti alloys. The material transitions from austenite to martensite under stress, enabling large reversible strains (up to 10%) without permanent deformation. This phase transformation fundamentally changes the mechanical behavior from elastic-plastic (conventional alloys) to pseudoelastic, resolving the contradiction between strength and deployability.
Solution Approach 2:
The invention directly exploits phase transitions between austenite and martensite in Ni-Ti shape memory alloys. During deployment, the material undergoes stress-induced martensite formation that accommodates large deformations reversibly. This phase transition mechanism enables the alloy to sustain strains much greater than conventional alloys while maintaining high strength, eliminating the need for high deployment forces.
2Ease of operation
If superelastic NITINOL is used to achieve complete elastic recovery of strains up to 10%, then flexibility and ease of insertion are improved, but the temperature range for superelasticity is limited to about 60°C
Solution Approach 1:
The patent modifies the transformation temperature parameters through alloy composition adjustment (ternary Ni-Ti alloys with additional elements) and thermal-mechanical processing. By controlling the austenite finish temperature (Af) and martensite start temperature (Ms), the superelastic temperature range is expanded to cover the desired medical application range of +10°C to +40°C, resolving the temperature limitation while maintaining flexibility.
3Productivity
If stents are deployed with rapid expansion to fulfill medical needs, then functionality is improved, but vessel trauma is caused due to high expansion forces
Solution Approach 1:
The patent utilizes the stress-induced martensite phase transition to enable controlled, progressive expansion. As the stent expands, the material transforms from austenite to martensite, absorbing deployment energy and reducing peak expansion forces. This phase transition acts as a mechanical buffer that slows down the expansion process, reducing vessel trauma while maintaining deployment effectiveness.
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 alloy allows for easy insertion and deployment of stents with reduced trauma and vessel expansion forces, maintaining shape until expanded, and providing superior mechanical properties post-deployment, enhancing the delivery and functionality of medical devices.
Implementation Method 1
the strain is accommodated by austenite to martensite crystalline transformation, rather than by the mechanisms that prevail in other alloys such as slip, grain boundary sliding and dislocation motion
Implementation Method 2
thermoelastic shape memory alloys can change from martensite to austenite and back again on heating and cooling over a very small temperature range
Data Source
AI summary
This invention relates to medical devices comprising shape memory alloys which have been subjected to a thermal and mechanical treatment to increase the austenite start temperature As to As′ such that the shape memory alloy is martensitic at body temperature and when subsequently subjected to a controlled deformation, the shape memory alloy preferentially reverts to the parent phase. The shape memory alloy comprises nickel, titanium and a ternary element, preferably 3 at. % to about 20 at. %. The ternary element is insoluble in a Ni—Ti matrix. In a preferred embodiment, the element is selected from the group consisting of niobium, tantalum and zirconium.