Polyimide-Coated Composite Wire for Fatigue-Resistant Pacing Leads
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Solution Overview
Problem
Existing biostimulation leads, such as those used in cardiac pacemakers and neurostimulators, face challenges with fatigue resistance due to the high number of flexural cycles they undergo, necessitating materials with improved durability and strain-fatigue properties.
Innovation Solution
A composite wire is developed using a superelastic nickel-titanium alloy core coated with polyimide, which is then wound and thermomechanically treated to maintain a desired shape, enhancing fatigue resistance by withstanding at least 10^8 cycles at 0.5% alternating strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional materials (35N LT, MP35N) are used in biostimulation leads, then the leads can function for decades with hundreds of millions to billions of flexural cycles, but fatigue resistance is insufficient and service life is limited
Solution Approach 1:
The patent employs a composite wire structure consisting of a nickel-titanium alloy shell (providing superelasticity and fatigue resistance) surrounding a conductive metal core (silver or copper, providing electrical conductivity). This composite construction allows the lead to withstand hundreds of millions to billions of flexural cycles while maintaining electrical functionality, thereby resolving the contradiction between fatigue resistance and service life extension
Solution Approach 2:
The patent utilizes phase transformation characteristics of nickel-titanium alloy, where the material transitions between austenite and martensite phases during cyclic deformation. This parameter change mechanism enables the alloy to absorb mechanical energy and resist fatigue damage, allowing the lead to maintain reliability over extended service periods of decades
2Reliability
If the wire is wound into a helical or stranded configuration to reduce maximum strain on individual wires, then fatigue resistance improves, but the wire structure becomes more complex
Solution Approach 1:
The patent divides the wire into multiple fine filaments (typically 7-19 strands) wound into a helical configuration around a central core. This segmentation reduces the maximum strain experienced by any individual filament during flexural cycling, thereby improving fatigue resistance while maintaining a manageable overall structure that can be implanted in medical leads
3Reliability
If a polymer coating is applied to the wire to provide electrical isolation and biocompatibility, then the wire can function safely in medical applications, but the coating may degrade during thermomechanical shape-setting processes
Solution Approach 1:
The patent applies a polyimide coating to the nickel-titanium alloy wire before performing thermomechanical shape-setting operations. The polyimide coating is specifically selected for its high thermal stability, allowing it to withstand the elevated temperatures (typically 400-500°C) required for shape-setting without degrading. This preliminary coating application ensures that electrical isolation and biocompatibility are maintained throughout subsequent manufacturing processes
Solution Approach 2:
The patent utilizes the thermal stability parameter of polyimide coating, which maintains its structural integrity at temperatures up to 500°C. This parameter change capability allows the coating to survive the thermomechanical shape-setting process without degradation, preserving electrical isolation properties while enabling the wire to be formed into its final helical or stranded configuration
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 composite wire exhibits improved fatigue endurance and maintains electrical isolation properties, enabling extended service life and new design possibilities for medical leads.
Implementation Method 1
a shell made of superelastic or shape memory alloy
Implementation Method 2
The wire is coated with polyimide and subsequently wound into a strand, cable, coil, or helically stranded tube. This wound structure is thermomechanically treated to shape-set the wire construct and retain a desired wound and shaped configuration
Data Source
AI summary
A composite wire suitable for use as a pacing or biostimulation lead has improved durability when compared to currently available materials. Specifically, a lead includes a superelastic wire including, e.g., nitinol. The wire is coated with polyimide and subsequently wound into a strand, cable, coil, or helically stranded tube. This wound structure is thermomechanically treated to shape-set the wire construct and retain a desired wound and shaped configuration, without adversely affecting the integrity of the polyimide coating.