Ni-Ti Stent Wire Over-Bending for Precise Bend Pattern Forming
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Solution Overview
Problem
The existing methods for fabricating self-expanding stents from nickel-titanium alloy wire are laborious and prone to wire fracture, requiring careful wrapping around pins and tension to maintain the desired geometry, which limits efficiency and increases the risk of errors.
Innovation Solution
A method involving over-bending nickel-titanium alloy wire by 85% to 105% to create predetermined bends, which are then heat-set on a mandrel without wrapping around pins, allowing for efficient formation of self-expanding stents with improved elasticity and reduced risk of fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the wire is carefully wrapped around pins and restrained during positioning, then the desired geometry can be maintained, but the process becomes laborious and time-consuming
Solution Approach 1:
The wire is pre-formed into the desired stent geometry and bend patterns before being positioned on the mandrel. This preliminary shaping eliminates the need for time-consuming wrapping and restraining operations during the main fabrication process, thereby maintaining geometric accuracy while significantly improving productivity
Solution Approach 2:
The manual mechanical process of wrapping wire around pins and restraining it is replaced by a forming process that creates the geometry directly. The over-bending technique with controlled stress application substitutes the labor-intensive mechanical manipulation with a more efficient forming mechanism
2Manufacturing precision
If the wire is bent around pins with tension to maintain geometry, then the stent shape can be achieved, but the risk of wire fracture increases
Solution Approach 1:
The wire is subjected to controlled over-bending with stress parameters optimized to remain within the elastic range of the nickel-titanium alloy. By carefully controlling the bend stress and using the wire's superelastic properties, the desired geometry is achieved without exceeding the fracture threshold, thus maintaining both shape accuracy and wire integrity
Solution Approach 2:
The forming process is designed to distribute bending stresses uniformly and avoid stress concentrations that could lead to fracture. The over-bending technique with subsequent stress release acts as a cushioning mechanism, allowing the wire to settle into the desired geometry without experiencing damaging peak stresses
3Productivity
If multiple stents are formed on a single mandrel, then productivity increases, but the complexity of positioning and maintaining geometry increases
Solution Approach 1:
Each wire is pre-formed with the complete stent geometry and bend patterns before being placed on the mandrel. This preliminary preparation simplifies the positioning process for multiple stents, as each unit is self-contained and requires minimal adjustment, thereby enabling higher productivity without proportionally increasing positioning complexity
Solution Approach 2:
The fabrication process is segmented into independent wire forming operations that can be performed separately before assembly on the mandrel. This segmentation allows multiple stents to be prepared in parallel and then efficiently positioned on a single mandrel, reducing the overall complexity of the multi-stent fabrication process
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 enables rapid, cost-effective fabrication of self-expanding stents with precise bend patterns, enhancing efficiency and reducing the risk of wire fracture, while allowing for multiple stents to be formed on a single mandrel, suitable for various endovascular applications.
Implementation Method 1
the source of the shape recovery is a phase transformation between a lower temperature phase (martensite) and a higher temperature phase (austenite) that may be driven by an increase in temperature (shape memory effect)
Implementation Method 2
the source of the shape recovery is a phase transformation between a lower temperature phase (martensite) and a higher temperature phase (austenite) that may be driven by the removal of an applied stress (superelastic effect)
Implementation Method 3
the wire may be formed into the desired expanded geometry for heat setting by a time-consuming process of bending the wire around pins projecting from a mandrel
Data Source
AI summary
A method of making a self-expanding stent entails applying a bend stress sufficient to over-bend a portion of a wire by an amount in a range from about 85% to about 105%, where the wire comprises a Ni—Ti alloy and includes from about 40% to about 46% cold work. The bend stress is then released, thereby forming a bend having a predetermined bend angle in the wire. The application and release of the bend stress are repeated on successive portions of the wire in order to create a series of bends along a length of the wire in a predetermined bend pattern. The wire comprising the predetermined bend pattern is then positioned about a mandrel in an expanded stent geometry and heat set. Thus, a self-expanding stent is formed.