Nitinol Stent Forming via Composite Wire Etching
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Solution Overview
Problem
Forming stents from nitinol wires is challenging due to the difficulty in achieving accurate geometry and the need for complex custom fixtures, which complicates the heat treatment process and increases costs, especially for hollow wire stents.
Innovation Solution
A method using a composite wire with a core member, an intermediate nitinol member, and an outer member, where the outer member holds the nitinol in shape during heat treatment and is subsequently removed by chemical etching, allowing the nitinol to retain the stent pattern, and optionally filling the lumen with a biologically active substance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nitinol wire is formed into stent shape using traditional fixtures and heat treatment, then the stent can achieve shape memory properties, but the process becomes complex and costly requiring custom fixtures for each design
Solution Approach 1:
A polymer coating is applied to the nitinol wire to serve as an intermediary that holds the wire in the desired stent configuration during heat treatment. This coating acts as a temporary mold or fixture, eliminating the need for complex custom mechanical fixtures while maintaining shape accuracy during the heat setting process.
Solution Approach 2:
The patent utilizes changes in the polymer coating's properties through heat treatment. The coating is applied in a state that allows it to conform to and hold the wire shape, then during heat treatment the coating's properties change to maintain the shape, and finally the coating is removed to leave the permanently set nitinol stent shape.
2Ease of manufacture
If nitinol wire is laser cut from tube to form stent, then manufacturing is simplified, but the stent loses the ability to be compressed to small diameter for insertion
Solution Approach 1:
The patent exploits the phase transition properties of nitinol material, which transitions between martensite and austenite phases at different temperatures. This allows the stent to be formed in a soft, compressible state, delivered in a compressed configuration, and then transition to its expanded functional shape upon heating to body temperature, combining manufacturing simplicity with compressibility.
3Manufacturing precision
If complex fixtures are used to hold nitinol wire during heat treatment, then accurate stent geometry can be achieved, but production time and cost increase
Solution Approach 1:
The polymer coating serves as a simple intermediary that can be applied uniformly to the wire before shaping, eliminating the need for complex custom fixtures for each stent design. This approach maintains geometric accuracy while significantly simplifying the manufacturing process and improving production efficiency.
Solution Approach 2:
The polymer coating process is a universal method that can be applied to different nitinol wire configurations and stent designs without requiring custom fixtures for each design. This multi-functional approach improves productivity by using the same basic process for various stent geometries.
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
This method simplifies the stent formation process by eliminating the need for complex fixtures and allows for the creation of both hollow and solid nitinol stents with precise geometry and the ability to incorporate pharmacologically active substances for controlled release.
Implementation Method 1
The composite wire is heat treated to set the stent pattern into the intermediate nitinol member of the composite wire
Implementation Method 2
Nitinol possesses shape memory, i.e., the metal 'remembers' a specific shape fixed during a particular heat treatment and can resort to that shape under proper conditions
Implementation Method 3
Nitinol, under certain conditions, is also superelastic, which allows it to withstand extensive deformation and still resume its original shape
Implementation Method 4
The outer member of the composite wire holds the intermediate nitinol member in the stent pattern until a heat treatment step is applied
Implementation Method 5
The composite wire is then processed such that the outer member is removed from around the intermediate member without adversely affecting the intermediate member, such as by chemical etching
Data Source
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AI summary
A method of a forming a hollow, drug-eluting nitinol stent includes shaping a composite wire (170) into a stent pattern, wherein the composite wire comprises an inner member (120), a nitinol intermediate member (102), and an outer member (130). After the composite wire is shaped into the stent pattern, the composite wire is heat treated to set the nitinol intermediate member in the stent pattern. After heat treatment, the composite wire is processed to remove the outer member and the inner member without adversely affecting the intermediate member. Openings may be provided through the intermediate member and the lumen of the intermediate member may be filled with a substance to be eluted through the openings.