Ni-Ti-Nb Guide Wire Torque Response
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Solution Overview
Problem
Guide wires used in intravascular procedures face challenges with torqueability due to the low stiffness of linear pseudo-elastic Ni—Ti alloys, which results in poor torque transmission and steerability compared to austenitic stainless steel.
Innovation Solution
A guide wire device is fabricated using a cold-worked Ni—Ti—Nb alloy with niobium content ranging from 3 to 30 atomic percent, which stabilizes the martensitic phase and imparts a higher elastic modulus, enhancing torque response and steerability by forming a dual phase microstructure with martensitic Ni—Ti and Nb-rich phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If linear pseudo-elastic Ni-Ti alloy is used for guide wire core member, then flexibility and pushability are improved, but torqueability deteriorates due to low elastic modulus
Solution Approach 1:
The patent applies parameter changes by modifying the Ni-Ti alloy composition through cold working processes. Specifically, the alloy is cold worked to achieve a linear pseudo-elastic state with stabilized martensitic structure, which increases the elastic modulus from the typical 5 Msi to higher values while maintaining flexibility. This parameter modification resolves the contradiction between flexibility and torqueability.
Solution Approach 2:
The patent employs composite materials by creating a dual-phase microstructure in the Ni-Ti alloy through controlled cold working. The resulting composite structure consists of martensitic phases with enhanced stiffness properties, combining the flexibility of pseudo-elastic materials with the higher elastic modulus needed for torque transmission, thereby resolving the technical contradiction.
2Reliability
If cold working is applied to Ni-Ti alloy to achieve linear pseudo-elasticity, then durability is improved, but elastic modulus remains low
Solution Approach 1:
The patent uses parameter changes by optimizing the cold working parameters and alloy composition. The cold working process is controlled to achieve a specific level of martensitic transformation that simultaneously maximizes durability through stabilized microstructure and increases elastic modulus. This resolves the contradiction between durability and stiffness.
Solution Approach 2:
The patent applies local quality by creating regions with different microstructural characteristics within the guide wire. The cold working process produces localized martensitic phases with enhanced mechanical properties in specific regions, providing both durability and improved elastic modulus where needed while maintaining overall flexibility.
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 cold-worked Ni—Ti—Nb alloy provides improved torqueability and steerability while maintaining durability and shapeability, allowing for effective navigation through tortuous anatomy and minimizing kinking risks.
Implementation Method 1
Non-linear pseudo-elasticity is known to occur due to a reversible phase transformation from austenite to martensite, the latter more precisely called 'stress-induced martensite' (SIM).
Implementation Method 2
Linear pseudo-elasticity is processed by cold working the material (e.g., by permanently deforming the material such as by wire-drawing) without subsequent heat treatment
Data Source
AI summary
Guide wire devices fabricated from a linear pseudo-elastic Ni—Ti alloy and methods for their manufacture. The Ni—Ti alloy that includes nickel, titanium, and about 3 atomic % (at %) to about 30 at % niobium (Nb). Cold working the Ni—Ti alloy stabilizes the alloy's martensitic phase and yields a linear pseudo-elastic microstructure where reversion to the austenite phase is retarded or altogether blocked. The martensitic phase of cold worked, linear pseudo-elastic Ni—Ti—Nb alloy has an elastic modulus that is considerably higher than the comparable cold worked, linear pseudoelastic binary Ni—Ti alloy. This yields a guide wire device that has better torque response and steerability as compared to cold worked, linear pseudoelastic binary Ni—Ti alloy or superelastic binary Ni—Ti alloy.